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  • 1.
    Kravets, Anatolii
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Gomonay, O. V.
    Polishchuk, Dmytr
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Tykhonenko-Polishchuk, Yu.O.
    Polek, T. I.
    Tovstolytkin, A. I.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Effect of nanostructure layout on spin pumping phenomena in antiferromagnet/nonmagnetic metal/ferromagnet multilayered stacks2017In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 7, no 5, article id 056312Article in journal (Refereed)
    Abstract [en]

    In this work we focus on magnetic relaxation in Mn80Ir20(12 nm)/Cu(6 nm)/Py(dF) antiferromagnet/Cu/ferromagnet (AFM/Cu/FM) multilayers with different thickness of the ferromagnetic permalloy layer. An effective FM-AFM interaction mediated via the conduction electrons in the nonmagnetic Cu spacer - the spin-pumping effect - is detected as an increase in the linewidth of the ferromagnetic resonance (FMR) spectra and a shift of the resonant magnetic field. We further find experimentally that the spin-pumping-induced contribution to the linewidth is inversely proportional to the thickness of the Py layer. We show that this thickness dependence likely originates from the dissipative dynamics of the free and localized spins in the AFM layer. The results obtained could be used for tailoring the dissipative properties of spintronic devices incorporating antiferromagnetic layers.

  • 2. Pogorily, A. N.
    et al.
    Kravets, Anatolii
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Nevdacha, V. V.
    Podyalovskiy, D. Y.
    Ryabchenko, S. M.
    Kalita, V. M.
    Kulik, M. M.
    Lozenko, A. F.
    Vovk, A.Ya.
    Godinho, M.
    Maurel, L.
    Pardo, J. A.
    Magen, C.
    Korenivski, V.
    Magnetic anisotropy of epitaxial Co2Fe-Ge Heusler alloy films on MgO (100) substrates2017In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 7, no 5, article id 055831Article in journal (Refereed)
    Abstract [en]

    Films of Co2Fe-Ge Heusler alloy with variable Ge concentration deposited on monocrystalline MgO (100) substrates by magnetron co-sputtering are investigated using microstructural, morphological, magnetometric, and magnetic resonance methods. The films were found to grow epitaxially, with island-like or continuous-layer morphology depending the Ge-content. The ferromagnetic resonance data versus out-of-plane and in-plane angle indicate the presence of easy plane and 4-fold in-plane anisotropy. The magnetometry data indicate additional weak 2-fold in-plane anisotropy and pronounced at low fields rotatable anisotropy. The observed magnetic anisotropy properties discussed in correlation with the microstructure and morphology of the films.

  • 3.
    Polishchuk, Dmytr
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Tykhonenko-Polishchuk, Yu. O.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. National Academy of Sciences of Ukraine, Ukraine.
    Holmgren, Erik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Kravets, Anatolii
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. National Academy of Sciences of Ukraine, Ukraine.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Thermally induced antiferromagnetic exchange in magnetic multilayers2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 10, article id 104427Article in journal (Refereed)
    Abstract [en]

    We demonstrate sharp thermally induced switching between ferromagnetic and antiferromagnetic RKKY ( Ruderman-Kittel-Kasuya-Yosida) exchange in a spin-valve with the spacer incorporating a thin diluted ferromagnetic layer as the core. We illustrate the mechanism behind the effect as being due to a change in the effective thickness of the spacer induced by the Curie transition into its paramagnetic state. The ability to switch between ferromagnetic and antiferromagnetic states in a magnetic multilayer by a slight change in temperature may lead to new types of spin-thermoelectronic devices for use in such applications as memory or oscillators.

  • 4.
    Polishchuk, Dmytr
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. Inst Magnetism NAS & MES Ukraine.
    Tykhonenko-Polishchuk, Yu. O.
    Kravets, Anatolii
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Tovstolytkin, A. I.
    Dzhezherya, Yu. I.
    Pogorily, A. M.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Ferromagnetic resonance in nanostructures with temperature-controlled interlayer interaction2016In: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, E-ISSN 1090-6517, Vol. 42, no 9, p. 761-767Article in journal (Refereed)
    Abstract [en]

    This study is a comprehensive analysis of a multilayer F-1/f(d)/F-2pin structure's magnetic resonance properties, wherein F-1 and F-2pin are the free and exchange-coupled strong magnetic layers, and f is the weakly magnetic layer with a Curie point in the room temperature region. Depending on the magnetic state of the spacer f (ferromagnetic or paramagnetic) the exchange interaction between the F-2 and F-2pin layers becomes a function of the temperature, which opens up opportunities for practical applications. The obtained results show that the interlayer exchange coupling can be enhanced by decreasing the thickness of the spacer d, or by lowering the temperature. Strengthening the exchange coupling leads to a stronger manifestation of unidirectional anisotropy in the ferromagnetic resonance layer F-1, as well as to a broadening of the resonance line that is atypical for thin films. The observed features are analyzed in the context of comparing the effects of two different natures: the influence of the spacer d and the influence of the temperature. Thus, the behavior of changes to the unidirectional anisotropy remains the same given variation of both the thickness of the spacer and the temperature. However the broadening of the magnetic resonance line is more sensitive to changes in the interlayer interaction caused by variation of d, and is less susceptible to changes caused by temperature.

  • 5.
    Polishchuk, Dmytr
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Tykhonenko-Polishchuk, Yuliya
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Borynskyi, Vladyslav
    NAS Ukraine, Inst Magnetism, UA-03142 Kiev, Ukraine.;MES Ukraine, UA-03142 Kiev, Ukraine..
    Kravets, Anatolii
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Tovstolytkin, Alexandr
    NAS Ukraine, Inst Magnetism, UA-03142 Kiev, Ukraine.;MES Ukraine, UA-03142 Kiev, Ukraine..
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Magnetic Hysteresis in Nanostructures with Thermally Controlled RKKY Coupling2018In: Nanoscale Research Letters, ISSN 1931-7573, E-ISSN 1556-276X, Vol. 13, article id 245Article in journal (Refereed)
    Abstract [en]

    Mechanisms of the recently demonstrated ex-situ thermal control of the indirect exchange coupling in magnetic multilayer are discussed for different designs of the spacer layer. Temperature-induced changes in the hysteresis of magnetization are shown to be associated with different types of competing interlayer exchange interactions. Theoretical analysis indicates that the measured step-like shape and hysteresis of the magnetization loops is due to local in-plane magnetic anisotropy of nano-crystallites within the strongly ferromagnetic films. Comparison of the experiment and theory is used to contrast the mechanisms of the magnetization switching based on the competition of (i) indirect (RKKY) and direct (non-RKKY) interlayer exchange interactions as well as (ii) indirect ferromagnetic and indirect antiferromagnetic (both of RKKY type) interlayer exchange. These results, detailing the rich magnetic phase space of the system, should help enable the practical use of RKKY for thermally switching the magnetization in magnetic multilayers.

  • 6.
    Polishchuk, Dmytr
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Tykhonenko-Polishchuk, Yuliya
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Holmgren, Erik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Kravets, Anatolii
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Tovstolytkin, A. I.
    NAS Ukraine, Inst Magnetism, UA-03680 Kiev, Ukraine ; MES Ukraine, UA-03680 Kiev, Ukraine.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Giant magnetocaloric effect driven by indirect exchange in magnetic multilayers2018In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 2, no 11, article id 114402Article in journal (Refereed)
    Abstract [en]

    Indirect exchange coupling in magnetic multilayers, also known as the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, is highly effective in controlling the interlayer alignment of the magnetization. This coupling is typically fixed at the stage of the multilayer fabrication and does not allow ex situ control needed for device applications. In addition to the orientational control, it is highly desirable to also control the magnitude of the intralayer magnetization, ideally, being able to switch it on/off by switching the relevant RKKY coupling. Here we demonstrate a magnetic multilayer material incorporating thermally and field-controlled RKKY exchange, focused on a dilute ferromagnetic alloy layer and driving it though its Curie transition. Such on/off magnetization switching of a thin ferromagnet, performed repeatedly and fully reproducibly within a low-field sweep, results in a giant magnetocaloric effect, with an estimated isothermal entropy change of Delta S approximate to -10 mJ cm(-3) K(-1 )under an external field of similar to 10 mT, which greatly exceeds the performance of the best rare-earth based materials used in the adiabatic-demagnetization refrigeration systems.

  • 7.
    Polishchuk, Dmytr
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Tykhonenko-Polishchuk, Yu.O.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. National Academy of Sciences of Ukraine, Ukraine.
    Kravets, Anatolii
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. National Academy of Sciences of Ukraine, Ukraine.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Thermal switching of indirect interlayer exchange in magnetic multilayers2017In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 118, no 3, article id 37006Article in journal (Refereed)
    Abstract [en]

    We propose a magnetic multilayer layout, in which the indirect exchange coupling (IEC also known as RKKY) can be switched on and off by a slight change in temperature. We demonstrate such on/off IEC switching in a Fe/Cr/FeCr-based system and obtain thermal switching widths as small as 10-20 K, essentially in any desired temperature range, including at or just above room temperature. These results add a new dimension of tunable thermal control to IEC in magnetic nanostructures, highly technological in terms of available materials and operating physical regimes.

1 - 7 of 7
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