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  • 1.
    Andersson, Sebastian
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Exchange coupling and magnetoresistance in CoFe/NiCu/CoFe spin valves near the Curie point of the spacer2010Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 107, nr 9, s. 09D711-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thermal control of exchange coupling between two strongly ferromagnetic layers through a weakly ferromagnetic Ni-Cu spacer and the associated magnetoresistance is investigated. The spacer, having a Curie point slightly above room temperature, can be cycled between its paramagnetic and ferromagnetic states by varying the temperature externally or using joule heating. It is shown that the giant magnetoresistance vanishes due to a strong reduction in the mean free path in the spacer at above similar to 30% Ni concentration-before the onset of ferromagnetism. Finally, a device is proposed which combines thermally controlled exchange coupling and large magnetoresistance by separating the switching and the readout elements.

  • 2.
    Andersson, Sebastian
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Thermoelectrically Controlled Spin-Switch2010Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 46, nr 6, s. 2140-2143Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The search for novel spintronic devices brings about new ways to control switching in magnetic thin-films. In this work we experimentally demonstrate a device based on thermoelectrically controlled exchange coupling. The read out signal from a giant magnetoresistance element is controlled by exchange coupling through a weakly ferromagnetic Ni-Cu alloy. This exchange coupling is shown to vary strongly with changes in temperature, and both internal Joule heating and external heating is used to demonstrate magnetic switching. The device shows no degradation upon thermal cycling. Ways to further optimize the device performance are discussed. Our experimental results show a new way to thermoelectrically control magnetic switching in multilayers.

  • 3. Balkashin, O. P.
    et al.
    Fisun, V. V.
    Korovkin, I. A.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Ferromagnetic resonance in copper-permalloy point contacts2014Inngår i: Fizika Nizkih Temperatur, ISSN 0132-6414, E-ISSN 1816-0328, Vol. 40, nr 10, s. 1187-1197Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The systematic investigations of the response signal of Copper-Permalloy (Ni80Fe20) point contacts to microwave irradiation (8-12 GHz) are performed. The influence of external magnetic field strength, transport current flowing through the contact, the intensity and frequency of the RF exposure on the measured signal is studied. The contributions to the contacts resistance from the effects of giant and anisotropic magnetoresistance are analyzed. It is established experimentally that the position of resonance features is in good agreement with the Kittel formula calculation for FMR in the film at a parallel H field. The resonance signal was observed on the background of an additional contribution due to the rectification of RF current on the nonlinear contact IV-curve. It is found that there are two mechanisms for the resonant response are revealed: a synchronous self-detection by means of mixing of RF current with temporal variations of resistance and a bolometric mechanism associated with a steady-state change of contact resistance under excitation of magnetization precession (a bolometric response). It is found that the resonance signal amplitude is linearly proportional to transport current through the contact and microwave irradiation intensity.

  • 4. Balkashin, O. P.
    et al.
    Fisun, V. V.
    Korovkin, I. A.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Ferromagnetic resonance in copper-permalloy point contacts2014Inngår i: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, E-ISSN 1090-6517, Vol. 40, nr 10, s. 929-936Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The response of copper-permalloy (Ni80Fe20) point microcontacts to microwave irradiation (8-12 GHz) is investigated systematically. The effects of the external magnetic field strength, transport current flowing through the contact, and microwave intensity and frequency on the measured signal are studied. The contributions to the contact electrical resistance owing to giant and anisotropic magnetoresistance are analyzed. The experimentally determined positions of the resonance features are in good agreement with Kittel's formula for FMR in films in parallel magnetic fields. The resonance signal is observed against the background of an additional contribution owing to rectification of the rf field on the nonlinear current-voltage characteristic of the contact. Two mechanisms for the resonance response are discovered: synchronous self-detection from mixing of the rf current with temporal variations in the resistance and a bolometric response associated with the steady-state variation in the contact resistance when magnetization precession is excited. The amplitude of the resonance signal is linearly proportional to the transport current through the contact and to the intensity of the microwave irradiation.

  • 5. Balkashin, O. P.
    et al.
    Fisun, V. V.
    Triputen, L. Yu
    Andersson, Sebastian
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Naidyuk, Yu G.
    Spin-valve effects in point contacts to exchange biased Co40Fe40B20 films2014Inngår i: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, E-ISSN 1090-6517, Vol. 40, nr 10, s. 915-918Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nonlinear current-voltage characteristics and magnetoresistance of point contacts between a normal metal (N) and films of amorphous ferromagnet (F) Co40Fe40B20 of different thickness, exchange-biased by antiferromagnetic Mn80Ir20 are studied. A surface spin valve effect in the conductance of such F-N contacts is observed. The effect of exchange bias is found to be inversely proportional to the Co40Fe40B20 film thickness. This behavior as well as other magneto-transport effects we observe on single exchange-pinned ferromagnetic films are similar in nature to those found in conventional three-layer spin-valves.

  • 6. Balkashin, O. P.
    et al.
    Fisun, V. V.
    Yanson, I. K.
    Triputen, L. Yu
    Konovalenko, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Nonstationary magnetization dynamics of point contacts with a single ferromagnetic film2009Inngår i: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, E-ISSN 1090-6517, Vol. 35, nr 8-9, s. 693-701Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electric conductivity of point nanocontacts between 5, 10, and 100 nm thick ferromagnetic (F) cobalt films and a nonmagnetic (N) metal (copper or silver) needle is investigated. Two fundamentally different mechanisms for the formation of the response, signal to microwave irradiation have been observed for the first time. One mechanism is due to the effect of the rectification of high frequency ac current on the nonlinearity of the current-voltage characteristics due to the precession of the magnetization under the action of a constant transport current flowing through the contact. The second one is associated with the resonance excitation of the precession of the magnetization vector at the fundamental frequency and its harmonic by an external high-frequency field. The experimental results support a previous contention that a "surface spin valve" whose static and dynamic properties are similar to conventional F-1-N-F-2 spin valve [Nano Letters 7, 927 (2007)] is formed in the experimental F-N nanocontacts.

  • 7.
    Balkashin, O. P.
    et al.
    B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine.
    Fisun, V. V.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Yanson, I. K.
    B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine.
    Triputen, L. Yu.
    B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine.
    Konovalenko, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Spin dynamics in point contacts to single ferromagnetic films2009Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 9, s. 092419-1-092419-4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Excitation of magnons or spin waves driven by nominally unpolarized transport currents in point contacts of normal and ferromagnetic metals is probed by irradiating the contacts with microwaves. Two characteristic dynamic effects are observed: a suppression of spin-wave nonlinearities in the point contact conductance by off-resonance microwave irradiation and a resonant stimulation of spin-wave peaks in the differential resistance of the nanocontacts by the microwave field. These observations provide direct evidence that the magnetoresistance peaks observed are due to gigahertz spin dynamics at the ferromagnetic interface driven by the spin transfer torque effect of the transport current.

  • 8. Ban, S.
    et al.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Pattern storage and recognition using ferrofluids2006Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 99, nr 8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An implementation of an associative memory based on a ferromagnetic nanocolloid is proposed. The design contains inductive input and output units for training the ferrofluid as well as sensors incorporated into the output units for performing recall. Using Monte Carlo simulations of the system we demonstrate the possibility of creating nanoparticle configurations that can serve to associate input/output pattern pairs.

  • 9.
    Bondarenko, Artem
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Holmgren, Erik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Koop, Björn C.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Descamps, Thomas
    KTH.
    Ivanov, B. A.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Stochastic dynamics of strongly-bound magnetic vortex pairs2017Inngår i: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 7, nr 5, artikkel-id 056007Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate that strongly-bound spin-vortex pairs exhibit pronounced stochastic behaviour. Such dynamics is due to collective magnetization states originating from purely dipolar interactions between the vortices. The resulting thermal noise exhibits telegraph-like behaviour, with random switching between different oscillation regimes observable at room temperature. The noise in the system is further studied by varying the external field and observing the related changes in the frequency of switching and the probability for different magnetic states and regimes. Monte Carlo simulations are used to replicate and explain the experimental observations.

  • 10.
    Bondarenko, Artem
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Holmgren, Erik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Li, Zhong Wei
    Ivanov, B. A.
    Institute of Magnetism, National Academy of Science, 03142 Kiev, Ukraine; National University of Science and Technology “MISiS”, Moscow 119049, Russian Federation..
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Chaotic dynamics in spin-vortex pairs2019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, artikkel-id 054402Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on spin-vortex pair dynamics measured at temperatures low enough to suppress stochastic core motion, thereby uncovering the highly nonlinear intrinsic dynamics of the system. Our analysis shows that the decoupling of the two vortex cores is resonant and can be enhanced by dynamic chaos. We detail the regions of the relevant parameter space, in which the various mechanisms of the resonant core-core dynamics are activated. We show that the presence of chaos can reduce the thermally induced spread in the decoupling time by up to two orders of magnitude.

  • 11.
    Cherepov, Sergiy
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Dzhezherya, Yu. I.
    Worledge, D. C.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Resonant Activation of a Synthetic Antiferromagnet2011Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, nr 7, s. 077202-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The magnetic decay time of a synthetic antiferromagnet comprised of two closely spaced magnetic dipoles is measured in the presence of microwave excitation. The system is known to be highly stable with respect to switching between its two antiparallel ground states under quasistatic magnetic fields. We show that an order of magnitude lower field can switch the pair, provided the field is applied in resonance with the optical eigenmode of the collective spin dynamics in the system. We furthermore show that thermal agitation can play an essential role in spin-flop switching for resonant excitations of near-or subcritical amplitude.

  • 12.
    Cherepov, Sergiy
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Konovalenko, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Worledge, D. C.
    IBM T.J. Watson Researh Center.
    Micromagnetics of Spin-Flop Bilayers: S, C, and Vortex Spin States2010Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 46, nr 6, s. 2124-2127Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spin-flop tunnel junctions subjected to strong gigahertz excitations are found to exhibit highly stable resistance states, intermediate between the two spin-uniform ground states of high and low resistance. The associated spin distributions are necessarily nonuniform and differ significantly from the ground-state anti-parallel spin configuration in their static and dynamic properties. Detailed micromagnetic modeling reveals that inplane spin vortices in dipole-coupled thin-film bilayers are stable spin configurations, where the orientation of the vortex cores and the vortex chirality play an important role in the response of the system to external magnetic fields.

  • 13.
    Cherepov, Sergiy
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Koop, Björn
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Galkin, A. Yu.
    Khymyn, R.S.
    Institute of Magnetism, Ukrainian Academy of Science.
    Ivanov, B. A.
    Institute of Magnetism, Ukrainian Academy of Science.
    Worledge, D. C.
    IBM T.J. Watson Researh Center.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Core-Core Dynamics in Spin Vortex Pairs2012Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 109, nr 9, s. 097204-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate nanopillars in which two thin ferromagnetic particles are separated by a nanometer thin nonmagnetic spacer and can be set into stable spin vortex-pair configurations. We find that the previously unexplored limit of strong vortex core-core coupling can dominate the spin dynamics in the system. We observe experimentally and explain analytically and numerically how the 0.2 GHz gyrational resonance modes of the individual vortices are transformed into a 2 GHz collective rotational resonance mode in the configurations where the two cores form a bound pair.

  • 14.
    Cherepov, Sergiy
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    Worledge, D. C.
    IBM T.J. Watson Researh Center.
    Resonant activation of asynthetic antiferromagnetManuskript (preprint) (Annet vitenskapelig)
  • 15.
    Cherepov, Sergiy
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Worledge, D. C.
    IBM T.J. Watson Researh Center.
    Resonant Switching of Two Dipole-Coupled Nanomagnets2010Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 46, nr 6, s. 2112-2115Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The storage layer of recently developed spin-flop magnetic random-access memory consists of two closely spaced dipole-coupled nanomagnets and is highly stable in the ground state as well as in quasistatic fields applied off the easy axis. We show experimentally and confirm by using micromagnetic simulations that these spin-flop bilayers can be switched relatively easily by dynamic fields, applied at the frequency of the optical spin resonance of the bilayer. The field amplitude sufficient for this resonant switching can be an order of magnitude lower than the fields necessary for quasistatic reversal. Our data and micromagnetic analysis suggest that thermal agitation can play a role in the observed resonant switching behavior.

  • 16. Dzhezherya, Yu. I.
    et al.
    Demishev, K. O.
    Korenivskii, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Kapitza problem for the magnetic moments of synthetic antiferromagnetic systems2012Inngår i: Journal of Experimental and Theoretical Physics, ISSN 1063-7761, E-ISSN 1090-6509, Vol. 115, nr 2, s. 284-288Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dynamics of magnetization in synthetic antiferromagnetic systems with the magnetic dipole coupling in a rapidly oscillating field has been examined. It has been revealed that the system can behave similar to the Kapitza pendulum. It has been shown that an alternating magnetic field can be efficiently used to control the magnetic state of a cell of a synthetic antiferromagnet. Analytical relations have been obtained between the parameters of such an antiferromagnet and an external magnetic field at which certain quasistationary states are implemented.

  • 17. Dzhezherya, Yu I.
    et al.
    Yurchuk, V. P.
    Demishev, K. O.
    Korenivskii, Vladislav N.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Remagnetization of synthetic antiferromagnetic cells by a magnetic field pulse2013Inngår i: Journal of Experimental and Theoretical Physics, ISSN 1063-7761, E-ISSN 1090-6509, Vol. 117, nr 6, s. 1059-1065Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The theory of the dynamic remagnetization of a synthetic antiferromagnetic system and magnetic points located on a magnetic substrate in an external magnetic field has been considered. The energies of the equilibrium states of the system have been calculated. The conditions of switching between equilibrium states have been described. The conditions of applicability of this theory have been formulated. It has been shown that the process of remagnetization can be implemented in an inertialess regime, escaping the long-term relaxation of the system to a new equilibrium position with the use of a special shape of the field signal. The possibility of the reduction of the switching field amplitude by varying the pulse duration has been demonstrated.

  • 18. Fisun, V. V.
    et al.
    Balkashin, O. P.
    Najdyuk, Y. G.
    Bashlakov, D. L.
    Yanson, I. K.
    Korenivski, Vladislav
    KTH, Tidigare Institutioner, Fysik.
    Shekhter, R.
    Features in nonlinear electroconductivity of nanocontacts on the base of ferromagnetic metals (Co and Fe)2004Inngår i: Metallofizika i novejsie tehnologii, ISSN 1024-1809, Vol. 26, nr 11, s. 1439-1446Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    For normal metal-ferromagnet (N-F) point contacts, a step-like change of the resistance is observed at reaching of the current density similar to 10(9) A/cm(2). This is observed only for the case, when electron flow is directed from the normal metal to the ferromagnetic one, and is connected with magnetization reversal in the microconstriction at high transport-current density. Increasing of a magnetic field leads to the shift of observed peculiarity into the higher-current region that testifies its magnetic origin. As shown, the observed effect, which is widely studied in the recent time in N-F sandwiches, has more common character and requires the presence only N-F boundary and high-current density. The increasing of the amplitude of the resistance peculiarity is observed at electromagnetic radiation with a frequency of 3.10(9) Hz that testifies stimulating influence of the HF-radiation on the dynamics of precessing spins in the contacts at issue.

  • 19. Gromov, A.
    et al.
    Korenivski, Vladislav
    KTH, Tidigare Institutioner                               , Fysik.
    Electromagnetic analysis of layered magnetic/conductor structures2000Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 33, nr 7, s. 773-779Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A method is described for calculating the impedance of conductor structures comprised of ferromagnetic and non-magnetic layers of arbitrary cross sectional shape with transverse dimensions which are small compared to the conductors length. The method is exemplified on a conductor of axial symmetry enclosed in a high permeability film of uniaxial anisotropy along the conductor axis. To find the impedance the full boundary value problem for the vector potential is solved, allowing driving and eddy currents in both the conductor and the magnetic film, and taking into account the dynamics of the magnetization governed by the Landau-Lifshitz equations. The results obtained are used to model the giant magneto impedance effect in ferromagnetically coated wires.

  • 20.
    Gromov, Andrey
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Gigahertz Sandwich Strip Inductors Based on Fe-N Films: The Effect of Flux Closure at the Flange2010Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 46, nr 6, s. 2097-2100Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Planar strip inductors consisting of soft Fe-N films enclosing a conductor made of Cu are fabricated on Si substrates and exhibit 70 to 100% inductance gain at 1 Ghz with quality factors of 3 to 5. The magnetic part of the inductance is less than predicted theoretically, which is attributed to hardening of the magnetic material at the edges of the strip, where the deposition is close to 60 degrees incidence. Test films were fabricated on tilted substrates and found to develop very high anisotropy for deposition angles larger than 30 degrees. Optimizing the flux closure at the strip edges is essential for further improving the performance of sandwich strip inductors.

  • 21.
    Holmgren, Erik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Bondarenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik. National Academy of Sciences of Ukraine, Ukraine.
    Ivanov, B. A.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Resonant pinning spectroscopy with spin-vortex pairs2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 9, artikkel-id 094406Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Vortex pairs in magnetic nanopillars with strongly coupled cores and pinning of one of the cores by a morphological defect, are used to perform resonant pinning spectroscopy, in which a microwave excitation applied to the nanopillar produces pinning or depinning of the cores only when the excitation is in resonance with the rotational or gyrational eigenmodes of the specific initial state of the core-core pair. The shift in the eigenmode frequencies between the pinned and depinned states is determined experimentally and explained theoretically, and illustrates the potential for multicore spin-vortex memory with resonant writing of information onto various stable vortex pair states. Further, it is shown how the same resonant spectroscopy techniques applied to a vortex pair can be used as a sensitive nanoscale probe for characterizing morphological defects in magnetic films.

  • 22.
    Holmgren, Erik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Bondarenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik. Institute of Magnetism, National Academy of Science, 03142 Kiev, Ukraine.
    Koop, Björn
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Ivanov, Boris
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Non-Degeneracy and Effects of Pinning in Strongly Coupled Vortex Pairs2017Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 53, nr 11, artikkel-id 4400505Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the effects of pinning on the quasi-static behavior of stacked, strongly coupled spin-vortex pairs in magnetic multilayered nanopillars, with vertical vortex separation small compared with the vortex-core size. The small separation causes the core-core interaction to be the dominant energy contribution for small applied fields and excitations, which results in highly non-linear dynamics. The properties of such a vortex pair are expected to only be dependent on the relative vortex core polarizations and relative chiralities, so that the individual configurations should be degenerated. We show how pinning can lift this degeneracy, which can be used to distinguish the individual chirality configurations.

  • 23.
    Holmgren, Erik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Bondarenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik. Natl Acad Sci, Kiev, Ukraine..
    Persson, M.
    KTH.
    Ivanov, B. A.
    Natl Acad Sci, Inst Magnetism, UA-03142 Kiev, Ukraine.;Natl Univ Sci & Technol MISiS, Moscow 119049, Russia..
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Transient dynamics of strongly coupled spin vortex pairs: Effects of anharmonicity and resonant excitation on inertial switching2018Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 112, nr 19, artikkel-id 192405Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spin vortices in magnetic nanopillars are used as GHz oscillators, with frequency however essentially fixed in fabrication. We demonstrate a model system of a two-vortex nanopillar, in which the resonance frequency can be changed by an order of magnitude, without using high dc magnetic fields. The effect is due to switching between the two stable states of the vortex pair, and we show that it can be done with low-amplitude fields of sub-ns duration. We detail the relevant vortex-core dynamics and explain how field anharmonicity and phase control can be used to enhance the performance.

  • 24.
    Holmgren, Erik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Persson, Marcus
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Effects of asymmetry in strongly coupled spin vortex pairs2019Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 52, nr 10, artikkel-id 105001Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Effects of magnetic asymmetry on strongly coupled spin-vortex pairs with parallel core polarization and antiparallel chirality in synthetic nanomagnets are investigated. This includes vortex-core length asymmetry, biasing field asymmetry, and pinning of one of the two vortex cores. Our experimental observations as well as analytical and micromagnetic modeling show how magnetic asymmetry can be used to differentiate magneto-resistively otherwise degenerate multiple stable states of a vortex pair. These results expand the knowledge base for spin vortex arrays in nanostructures and should be useful in light of the recent proposals on coding information into multiple topological spin states, such as single and multiple vortex core/chirality states.

  • 25. Iovan, A.
    et al.
    Haviland, David B.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Diode effect in asymmetric double-tunnel barriers with single-metal nanoclusters2006Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, nr 16Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Asymmetric double-tunnel barriers with the center electrode being a metal cluster in the quantum regime are studied. The zero dimensionality of the clusters used and the associated quantized energy spectra are manifest in well-defined steps in the current-voltage characteristic. Record high current rectification ratios of similar to 10(4) for tunneling through such clusters are demonstrated at room temperature. We are able to account for all of the experimentally observed features by modeling our double-barrier structures using a combination of discrete states and charging effects for tunneling through quantum dots.

  • 26. Iovan, A.
    et al.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Haviland, David B.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Rectification of current for tunneling through metallic nano-particles2006Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 99, nr 8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Double tunnel barrier structures were obtained by using a scanning tunneling microscope and samples composed of metallic nanoparticles deposited onto an oxidized bottom electrode. The nanoparticles were formed by evaporating subpercolation thin metallic layers. Due to the small size of the particles their energy spectrum is discrete, which is evidenced by the measured quantized current-voltage characteristics. Current rectification ratios of 100-1000 for tunneling through such quantum dots are demonstrated at room temperature.

  • 27.
    Iovan, Adrian
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Andersson, Sebastian
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Naidyuk, Yu. G.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Vedyaev, A.
    Dieny, B.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Spin diode based on Fe/MgO double tunnel junction2008Inngår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 8, nr 3, s. 805-809Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate a spin diode consisting of a semiconductor-free nanoscale Fe/MgO-based double tunnel junction. The device exhibits a near perfect spin-valve effect combined with a strong diode effect. The mechanism consistent with our data is resonant tunneling through discrete states in the middle ferromagnetic layer sandwiched by tunnel barriers of different spin-dependent transparency. The observed magnetoresistance is a record high > 1000%, essentially making the structure an on/off spin switch. This, combined with the strong diode effect, similar to 100, demonstrates a new device principle, promising for memory and reprogrammable logic applications.

  • 28.
    Iovan, Adrian
    et al.
    KTH.
    Fischer, Marco
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Lo Conte, Roberto
    KTH.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Sub-10 nm colloidal lithography for circuit-integrated spin-photo-electronic devices2012Inngår i: Beilstein Journal of Nanotechnology, ISSN 2190-4286, Vol. 3, s. 884-892Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Patterning of materials at sub-10 nm dimensions is at the forefront of nanotechnology and employs techniques of various complexity, efficiency, areal scale, and cost. Colloid-based patterning is known to be capable of producing individual sub-10 nm objects. However, ordered, large-area nano-arrays, fully integrated into photonic or electronic devices have remained a challenging task. In this work, we extend the practice of colloidal lithography to producing large-area sub-10 nm point-contact arrays and demonstrate their circuit integration into spin-photo-electronic devices. The reported nanofabrication method should have broad application areas in nanotechnology as it allows ballistic-injection devices, even for metallic materials with relatively short characteristic relaxation lengths.

  • 29.
    Iovan, Adrian
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Lam, Kanber
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Andersson, Sebastian
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Cherepov, Sergiy
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Haviland, David B.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Tunneling spectroscopy of magnetic double barrier junctions2007Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 43, nr 6, s. 2818-2820Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Scanning tunneling microscopy (STM) is used to study transport in magnetic double tunnel junctions (DTJs) formed using a fixed transparency barrier of a patterned tunnel junction (TJ), and a variable tunnel barrier between the top electrode of the patterned junction and the STM tip. A sufficiently thin top electrode has been predicted to result in a rectification of charge current through a DTJ when the two barriers have different transparency. Our measurements indeed show a high current rectification ratio for 3-nm-thick, continuous film top electrodes, which is observed for junctions with asymmetric tunnel barriers.

  • 30.
    Johansson, Jan
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Korenivski, Vladislav
    KTH, Tidigare Institutioner, Fysik.
    Haviland, David B.
    KTH, Tidigare Institutioner, Fysik.
    Brataas, A.
    Giant fluctuations of superconducting order parameter in ferromagnet-superconductor single-electron transistors2004Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 93, nr 21Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spin dependent transport in a ferromagnet-superconductor single-electron transistor is studied theoretically taking into account spin accumulation, spin relaxation, gap suppression, and charging effects. A strong dependence of the gap on the magnetic state of the electrodes is found, which gives rise to a magnetoresistance of up to 100%. We predict that fluctuations of the spin accumulation can play such an important role as to cause the island to fluctuate between the superconducting and normal states. Furthermore, the device exhibits a nearly complete gate-controlled spin-valve effect.

  • 31.
    Johansson, Jan
    et al.
    KTH, Tidigare Institutioner                               , Fysik.
    Korenivski, Vladislav
    KTH, Tidigare Institutioner                               , Fysik.
    Urech, Mattias
    KTH, Tidigare Institutioner                               , Fysik.
    Haviland, David B.
    KTH, Tidigare Institutioner                               , Fysik.
    Suppression of superconductivity due to spin imbalance in Co/Al/Co single electron transistor2003Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 93, s. 8650-8652Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Transport properties of ferromagnetic/nonmagnetic/ferromagnetic single electron transistors are investigated as a function of external magnetic-field, temperature, bias, and gate voltage. By designing the magnetic electrodes to have different switching fields, a two-mode device is realized having two stable magnetization states, with the electrodes aligned in parallel and antiparallel. Magnetoresistance of approximately 100% is measured in Co/AlOX/Al/AlOX/Co double tunnel junction spin valves at low bias, with the Al spacer in the superconducting state. The effect is substantially reduced at high bias and temperatures above the T-C of the Al. The experimental results are interpreted as due to spin imbalance of charge carriers resulting in suppression of the superconducting gap of the Al island.

  • 32.
    Johansson, Jan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Urech, Mattias
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Haviland, David B.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Enhanced spin accumulation in superconductors2006Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 99, nr 8, s. 08M513-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A lateral array of ferromagnetic tunnel junctions is used to inject and detect nonequilibrium quasiparticle spin distribution in a superconducting strip made of Al. The strip width and thickness are kept below the quasiparticle spin diffusion length in Al. Nonlocal measurements in multiple parallel and antiparallel magnetic states of the detectors are used to in situ determine the quasiparticle spin diffusion length. A very large increase in the spin accumulation in the superconducting state compared to that in the normal state is observed and is attributed to a diminishing of the quasiparticle population by the opening of the gap below the transition temperature.

  • 33.
    Kadigrobov, A.
    et al.
    Department of Physics, University of Gothenburg.
    Andersson, Sebastian
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Park, Hee Chul
    Department of Physics, University of Gothenburg.
    Radic, D.
    Department of Physics, University of Gothenburg.
    Shekhter, R. I.
    Department of Physics, University of Gothenburg.
    Jonson, M.
    Department of Physics, University of Gothenburg.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Thermal-magnetic-electric oscillator based on spin-valve effect2012Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, s. 044315-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A thermal-magnetic-electric valve with the free layer of exchange-spring type and inverse magnetoresistance is investigated. The structure has S-shaped current-voltage characteristics and can exhibit spontaneous oscillations when integrated with a conventional capacitor within a resonator circuit. The frequency of the oscillations can be controlled from essentially dc to the GHz range by the circuit capacitance.

  • 34. Kadigrobov, A.
    et al.
    Kulinich, S. I.
    Shekhter, R. I.
    Jonson, M.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Joule heating and current-induced instabilities in magnetic nanocontacts2006Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, nr 19Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We consider the electrical current through a magnetic point contact in the limit of a strong inelastic scattering of electrons. In this limit local Joule heating of the contact region plays a decisive role in determining the transport properties of the point contact. We show that if an applied constant bias voltage exceeds a critical value, the stationary state of the system is unstable, and that periodic, nonharmonic oscillations in time of both the electrical current through the contact and the local temperature in the contact region develop spontaneously. Our estimations show that the necessary experimental conditions for observing such oscillations with characteristic frequencies in the range 10(8)-10(9) Hz can easily be met. We also show a possibility to manipulate upon the magnetization direction of a magnetic grain coupled through a point contact to a bulk ferromagnet by exciting the above-mentioned thermal-electric oscillations.

  • 35. Kadigrobov, A. M.
    et al.
    Andersson, Sebastian
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Radic, D.
    Shekhter, R. I.
    Jonson, M.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Thermoelectrical manipulation of nanomagnets2010Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 107, nr 12, s. 123706-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate the interplay between the thermodynamic properties and spin-dependent transport in a mesoscopic device based on a magnetic multilayer (F/f/F), in which two strongly ferromagnetic layers (F) are exchange-coupled through a weakly ferromagnetic spacer (f) with the Curie temperature in the vicinity of room temperature. We show theoretically that the Joule heating produced by the spin-dependent current allows a spin-thermoelectronic control of the ferromagnetic-to-paramagnetic (f/N) transition in the spacer and, thereby, of the relative orientation of the outer F-layers in the device (spin-thermoelectric manipulation of nanomagnets). Supporting experimental evidence of such thermally-controlled switching from parallel to antiparallel magnetization orientations in F/f(N)/F sandwiches is presented. Furthermore, we show theoretically that local Joule heating due to a high concentration of current in a magnetic point contact or a nanopillar can be used to reversibly drive the weakly ferromagnetic spacer through its Curie point and thereby exchange couple and decouple the two strongly ferromagnetic F-layers. For the devices designed to have an antiparallel ground state above the Curie point of the spacer, the associated spin-thermionic parallel to antiparallel switching causes magnetoresistance oscillations whose frequency can be controlled by proper biasing from essentially dc to GHz. We discuss in detail an experimental realization of a device that can operate as a thermomagnetoresistive switch or oscillator.

  • 36. Kadigrobov, A. M.
    et al.
    Andersson, Sebastian
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Radic, D.
    Shekhter, R. I.
    Jonson, M.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Thermoelectrical manipulation of nano-magnets: A spin-thermionic oscillator2010Inngår i: Proceedings of SPIE - The International Society for Optical Engineering, San Diego, CA, 2010, Vol. 7760, s. 77600R-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We investigate the interplay between the thermodynamic properties and spin-dependent transport in a mesoscopic magnetic multilayer, in which two strongly ferromagnetic layers are exchange-coupled through a weakly ferromagnetic spacer. We show theoretically that the system allows a spin-thermoelectronic control of the relative orientation of the outer layers. Supporting experimental evidence of thermally controlled switching from parallel to anti-parallel magnetization orientations in the sandwich is presented. We show magneto-resistance oscillations may take place with frequencies up to GHz. We discuss in detail an experimental realization of a device that can operate as a thermo-magneto-resistive switch or oscillator.

  • 37. Kadigrobov, A. M.
    et al.
    Shekhter, R. I.
    Kulinich, S. I.
    Jonson, M.
    Balkashin, O. P.
    Fisun, V. V.
    Naidyuk, Yu G.
    Yanson, I. K.
    Andersson, Sebastian
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Hot electrons in magnetic point contacts as a photon source2011Inngår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 13, s. 023007-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We propose to use a point contact between a ferromagnetic and a normal metal in the presence of a magnetic field for creating a large inverted spin population of hot electrons in the contact core. The key point of the proposal is that when these hot electrons relax by flipping their spin, microwave photons are emitted, with a frequency tunable by the applied magnetic field. While point contacts are an established technology, their use as a photon source is a new and potentially very useful application. We show that this photon emission process can be detected by means of transport spectroscopy and demonstrate stimulated emission of radiation in the 10-100 GHz range for a model point contact system using a minority-spin ferromagnetic injector. These results can potentially lead to new types of lasers based on spin injection in metals.

  • 38.
    Kamra, Akashdeep
    et al.
    Norwegian Univ Sci & Technol, Ctr Quantum Spintron, Dept Phys, Trondheim, Norway..
    Polishchuk, Dmytr
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Brataas, Arne
    Norwegian Univ Sci & Technol, Ctr Quantum Spintron, Dept Phys, Trondheim, Norway..
    Anisotropic and Controllable Gilbert-Bloch Dissipation in Spin Valves2019Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 122, nr 14, artikkel-id 147201Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spin valves form a key building block in a wide range of spintronic concepts and devices from magnetoresistive read heads to spin-transfer-torque oscillators. We elucidate the dependence of the magnetic damping in the free layer on the angle its equilibrium magnetization makes with that in the fixed layer. The spin pumping-mediated damping is anisotropic and tensorial, with Gilbert- and Bloch-like terms. Our investigation reveals a mechanism for tuning the free layer damping in situ from negligible to a large value via the orientation of fixed layer magnetization, especially when the magnets are electrically insulating. Furthermore, we expect the Bloch contribution that emerges from the longitudinal spin accumulation in the nonmagnetic spacer to play an important role in a wide range of other phenomena in spin valves.

  • 39.
    Konovalenko, Alexander
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Yanson, I. K.
    B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine.
    Naidyuk, Yu. G.
    B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine.
    Spin-torque driven excitations and hysteresis in magnetic point contacts2006Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 99, nr 8, s. 08G503-1-08G503-3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Magnetic multilayers are known to exhibit magnetization excitations, which are due to exchange fields produced by densely distributed spin-polarized electron currents. We report an observation of such excitations as well as hysteretic spin states produced by unpolarized currents in point contacts to single ferromagnetic layers. By measuring diffusive and ballistic contacts for various material combinations, we investigate the microscopic mechanism of the single interface spin-torque effect and discuss the possible origin of the observed hysteresis.

  • 40.
    Konovalenko, Alexander
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Yanson, I. K.
    B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine.
    Naidyuk, Yu. G.
    B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine.
    Fisun, V. V.
    B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine.
    Balkashin, O. P.
    B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine.
    Triputen, L. Yu.
    B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine.
    On the mechanism of hysteresis in conductance of point contacts to single ferromagnetic films2007Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, nr 9, s. 09A513-1-09A513-3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Single nonmagnetic/ferromagnetic interfaces can exhibit magnetic excitations and hysteretic switching, provided that the current density traversing the interface is sufficiently high (greater than or similar to 10(8) A/cm(2)) and the flow regime is diffusive. We measure hysteretic switching in conductance induced by nominally unpolarized electron currents in nanocontacts to thin Co films and successfully model the effect for similar to 20 nm scale point contacts using micromagnetic simulations, which take into account an out of plane stress-induced magnetic anisotropy in the point contact region.

  • 41.
    Konovalenko, Alexander
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Lindgren, Erik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Cherepov, Sergiy
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Worledge, D. C.
    IBM T. J. Watson Research Center, Yorktown Heights.
    Spin dynamics of two-coupled nanomagnets in spin-flop tunnel junctions2009Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, nr 14, s. 144425-1-144425-6Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Collective spin dynamics of two dipole-coupled nanomagnets in spin-flop tunnel junctions are studied experimentally and theoretically. The measured GHz magnetization oscillations reveal several collective spin-precessional modes. Analytical macrospin and numerical micromagnetic models of the spin-flop dynamics are developed, which provide a detailed explanation of the observed frequency spectra in terms of optical, acoustical, and micromagnetic modes in the antiparallel, parallel, and scissor magnetization states of the junctions.

  • 42.
    Koop, Björn C.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Dzhezherya, Y. I.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Quantitative magnetic characterization of synthetic ferrimagnets for predictive spin-dynamic behavior2014Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, nr 11, artikkel-id 6971569Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Geometric or magnetic asymmetries in synthetic antiferromagnetic particles give rise to ferrimagnetic-like magnetization behavior, both quasi-static and dynamic. Such asymmetries in synthetic ferrimagnets can originate from a thickness imbalance or a fringing field from the reference layer in a nanopillar stack. In this paper, we theoretically describe the effects of the corresponding magnetic asymmetry contribution on the structure's static and spin-dynamic behavior. The developed model is then used to experimentally determine the asymmetry parameters of typical nanoscale spin-flop junctions, as well as successfully describe their microwave resonant properties, such as the frequency splitting and the field dependence of the optical spin-resonance spectra.

  • 43.
    Koop, Björn C.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Dzhezherya, Yu. I.
    Demishev, K.
    Yurchuk, V.
    Worledge, D. C.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Demonstration of bi-directional microwave-assisted magnetic reversal in synthetic ferrimagnets2013Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, nr 14, s. 142408-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study spin dynamics in synthetic ferrimagnets, in which two dipole-coupled magnetic nanoparticles are different in thickness or biased asymmetrically with an external field. We observe a splitting of the optical spin-resonance for the two antiparallel ground states of the system and demonstrate how this splitting can be used to deterministically select a particular ground state. The demonstrated resonant switching is a fast and low-field way of controlling the magnetic state of nanodevices currently used in such large scale applications as magnetic random access memory.

  • 44.
    Koop, Björn C.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Gruschke, M.
    KTH.
    Descamps, Thomas
    KTH.
    Bondarenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Ivanov, B. A.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Static and dynamic properties of vortex pairs in asymmetric nanomagnets2016Inngår i: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 6, nr 5, artikkel-id 056406Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Stacked spin-vortex pairs in magnetic multilayered nanopillars, with vertical separation between the vortices small compared to the vortex core size and pure magnetostatic coupling, exhibit spin dynamics absent in individual vortices. This dynamics is nonlinear and is due to the strong direct core-core coupling in the system, dominating energetically for small-signal excitation. We observe and explain the appearance of spin resonance modes, forbidden within linear dynamics, and discuss how they depend on the magnetic and morphological asymmetries in the samples.

  • 45.
    Koop, Björn C.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Ivanov, B. A.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Nonlinear dynamics in spin vortex pairs with strong core-core coupling2014Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, nr 11, artikkel-id 6971321Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate the dynamics of spin vortex pairs in magnetic multilayer particles, with the vortices closely spaced vertically and therefore with strong core-core coupling. We focus on the spin-dynamic behavior of the system beyond the linear small-signal regime, and on the state with antiparallel vortex chiralities and parallel cores, in which the vortex cores are strongly dipole coupled. The data show a clear transition from the dominant single rotational resonance at 2-3 GHz for small excitation field amplitudes to a dominant gyrational resonance at high excitation fields. The concomitant changes in the microwave spectra, seen as satellite resonances near the rotational peak as well as a pronounced low-frequency resonance, are interpreted as arising from the nonlinearities of the main rotational mode, which also mediate microwave power transfer from the high- to the low-frequency mode.

  • 46.
    Koop, Björn
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Descamps, Thomas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Relaxation-free and inertial switching in synthetic antiferromagnets subject to super-resonant excitationManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Applications of magnetic memory devices greatly benefit from ultra-fast, low-power switching. Here we propose how this can be achieved efficiently in a nano-sized synthetic antiferromagnet by using perpendicular-to-the-plane picosecond-range magnetic field pulses. Our detailed micromagnetic simulations, supported by analytical results, yield the parameter space where inertial switching and relaxation-free switching can be achieved in the system. We furthermore discuss the advantages of dynamic switching in synthetic antiferromagnets and, specifically, their relatively low-power switching as compared to that in single ferromagnetic particles. Finally, we show how excitation of spin-waves in the system can be used to significantly reduce the post-switching spin oscillations for practical device geometries.

  • 47.
    Korenivski, V.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Leuschner, R.
    Thermally Activated Switching in Nanoscale Magnetic Tunnel Junctions2010Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 46, nr 6, s. 2101-2103Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Magnetic tunnel junctions 90 to 300 nm wide and of aspect ratio approximate to 2 are studied using high-speed pulse fields with regard to the soft-layer magnetization reversal under thermal agitation. It is found that the larger cells, 200-300 nm wide, reverse through nonuniform magnetization states with the energy barriers to thermal activation an order of magnitude smaller than those expected for single-domain magnets. The single-domain limit is reached for the smallest cells, having elliptical soft layers approximately 90 nm wide and 150-200 nm long. The magnetization decay in the small cell limit is well described by the Stoner-Wohlfarth single-domain model and the Arrhenius activation law. The results demonstrate that the penalty due to the smaller magnetic volume is compensated by a larger relative energy barrier to activation as the junction size is reduced to similar to 90 nm. This determines the important length scale for geometric scaling of such technologies as magnetic random access memory.

  • 48.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Associative memory device for particle pattern storage, has magnetically responsive layer with magnetic nanoparticles dispersed in solvent with variable viscosity2005Patent (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    The present invention provides an associative memory device based on a ferromagnetic nano-colloid, or ferrofiuid. The design comprises inductive input and output units for training the ferrofiuid as well as sensors incorporated into the output units for performing recall.

  • 49.
    Korenivski, Vladislav
    KTH, Tidigare Institutioner                               , Fysik.
    GHz magnetic film inductors2000Inngår i: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 215, s. 800-806Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Use of magnetic films for miniaturization of planar inductors operating at ultra-high frequencies is reviewed. Materials and design aspects determining the efficiency of the devices are analyzed. Mechanisms involved in magnetic dissipation and their role in limiting the device operation frequency range and quality factor are discussed. Typical inductor geometries are considered. A magnetically sandwiched strip inductor is argued to hold a promise for GHz applications.

  • 50.
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Magnetic junction device useful as, e.g. sensor of magnetic field in magnetic recording, comprises magnetic layers of different anisotropy and center layer of doped magnesium oxide with metal or combination of metals as dopant2006Patent (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    The present invention provides a low resistance high magnetoresistance (MR) device comprised of a junction of two magnetic elements separated by a magnesium oxide (MgO) layer doped with such metals as Al and Li. Such device can be used as a sensor of magnetic field in magnetic recording or as a storage element in magnetic random access memory (MRAM). The invention provides a high-MR device possessing a diode function, comprised of a double junction of two outer magnetic elements separated by two MgO insulating layer and a center MgO layer doped with such metals as Al and Li. Such device provides design advantages when used as a storage element in MRAM. The invention provides a three terminal logic device with MR wherein a gate electrode is placed in electrical or physical contact to the center layer of the double tunnel junction.

12 1 - 50 of 98
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