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  • 1.
    Chung, Sunjae
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Department of Physics, University of Gothenburg.
    Jiang, Sheng
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Eklund, Anders
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektronik, Integrerade komponenter och kretsar.
    Iacocca, Ezio
    Department of Applied Mathematics, University of Colorado.
    Le, Quang Tuan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Mazraati, Hamid
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Mohseni, Seyed Majid
    Department of Physics, Shahid Beheshti University, Tehran 19839, Iran.
    Sani, Sohrab Redjai
    Department of Physics and Astronomy, Uppsala University,.
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Effect of canted magnetic field on magnetic droplet nucleation boundariesManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The influence on magnetic droplet nucleation boundaries by canted magnetic elds are investigated and reported. The nucleation boundary condition, In = αAH + BH + C, is determined at different canted angles (0°< θH<20°) using magnetoresistance (MR) and microwave measurements in nanocontact spintorque oscillators (NC-STOs). As θH increased, the nucleation boundary shifts gradually towards higher In and H. The coefficient B of the nucleation boundary equation also nearly doubled as θH increases. On theother hand, the coefficient αA remained constant for all values of θH. These observations can be explained by considering the drift instability of magnetic droplets and the different tilt behaviour of the Co fixed layer induced by different θH.

  • 2.
    Chung, Sunjae
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Le, Quang Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Ahlberg, Martina
    Department of Physics, University of Gothenburg.
    Awad, Ahmad A.
    Department of Physics, University of Gothenburg.
    Mazraati, Hamid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. NanOsc AB.
    Houshang, Afshin
    Department of Physics, University of Gothenburg.
    Jiang, Sheng
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Nguyen, Thi Ngoc Anh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Institute of Materials Science, Vietnam Academy of Science and Technology.
    Dumas, Randy K.
    Department of Physics, University of Gothenburg.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden; NanOsc AB, Sweden.
    Magnetic droplet solitons in all-perpendicular nano-contact spin torque oscillatorsManuskript (preprint) (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    Spin-torque-generated magnetic droplets are nontopological solitons that have both dynamic and static characteristics. Although   theoretical studies of these droplets originally dealt with  an all-perpendicular magnetic system, all experimental demonstrations have so far relied on orthogonal spin valve structures that require a rather strong magnetic field to nucleate the droplet. Here, for the first time, we show the nucleation and sustained operation of magnetic droplets under a low magnetic field using nanocontact spin-torque oscillators (NC-STO),  both the free Co/Ni and fixed Co/Pd multilayers of which have strong perpendicular magnetic anisotropy. Droplet nucleation is observed as a change in the NC-STO resistance and the appearance of significant broadband microwave signal generation below 1 GHz. We also observe another important phenomenon in which the nucleated magnetic droplet can transform into a skyrmionic nanobubble in the low-field regime. Both magnetic droplet solitons and skyrmionic nanobubbles have been studied in detail using micromagnetic simulation.

  • 3.
    Jiang, Sheng
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. NanOsc AB, S-16440 Kista, Sweden..
    Chung, Sunjae
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Diez, Liza Herrera
    Univ Paris Saclay, Univ Paris Sud, CNRS, Inst Elect Fondamentale, F-91405 Orsay, France..
    Le, Quang Tuan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.
    Magnusson, Fredrik
    NanOsc AB, S-16440 Kista, Sweden..
    Ravelosona, Dafine
    Univ Paris Saclay, Univ Paris Sud, CNRS, Inst Elect Fondamentale, F-91405 Orsay, France.;Spin Ion Technol, 28 Rue Gen Leclerc, F-78000 Versailles, France..
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. NanOsc AB, S-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Tuning the magnetodynamic properties of all-perpendicular spin valves using He+ irradiation2018Inngår i: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 8, nr 6, artikkel-id 065309Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using He+ ion irradiation, we demonstrate how the magnetodynamic properties of both ferromagnetic layers in all-perpendicular [Co/Pd]/Cu/[Co/Ni] spin valves can be tuned by varying the He+ ion fluence. As the perpendicular magnetic anisotropy of both layers is gradually reduced by the irradiation, different magnetic configurations can be achieved from all-perpendicular (up arrow up arrow), through orthogonal (->up arrow), to all in-plane (paired right arrows). In addition, both the magnetic damping (alpha) and the inhomogeneous broadening (Delta H-0) of the Co/Ni layer improve substantially with increasing fluence. While the GMR of the spin valve is negatively affected, decreasing linearly from an original value of 1.14% to 0.4% at the maximum fluence of 50x10(14) He+/cm(2), most of the Co/Ni layer improvement is achieved already at a fluence of 10x10(14) He+/cm(2), for which GMR only reduces to 0.9%.

  • 4.
    Jiang, Sheng
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Chung, Sunjae
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Department of Physics and Astronomy, Uppsala University.
    Le, Quang Tuan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Diez, Liza Herrera
    Institut d'Electronique Fondamentale, CNRS, Universite Paris-Sud, Universite Paris-Saclay.
    Houshang, Afshin
    Department of Physics, University of Gothenburg.
    Zahedinejad, Mohammad
    Department of Physics, University of Gothenburg.
    Ravelosona, Dafine
    Institut d'Electronique Fondamentale, CNRS, Universite Paris-Sud, Universite Paris-Saclay.
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. Department of Physics, University of Gothenburg.
    Experimental evidence of tunable nonlinearity in He+ irradiated spin-torque oscillatorsManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Spin-torque nano-oscillators (STNOs) are among the most promising candidates for nanoscale broadband microwave generators. Before this application can be realized, however, enormous efforts are required of researchers to meet the commercial requirements of high-frequency tunability, high power, and narrow linewidth. As the performance of STNOs is mainly attributed to the nonlinearity on the basis of nonlinear auto-oscillator theory, we here systematically study how this nonlinearity is affected by the free-layer's effective magnetization Meff (i.e., the perpendicular magnetic anisotropy, PMA) in STNOs. The PMA is gradually tuned by using different fluences of He+ irradiation. Consequently, the nonlinearity can be continuously tailored from positive to negative. In addition, due to the almost zero nonlinearity, the linewidth shows an improvement of more than two orders of magnitude. This experimental observation is in strong agreement with the theory of nonlinear auto-oscillators. Our study not only confirms the theoretical prediction of nonlinearity, but also indicates the route to be taken towards realizing commercial microwave generators.

  • 5.
    Jiang, Sheng
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Chung, Sunjae
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Le, Quang Tuan
    Mazraati, Hamid
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Houshang, Afshin
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Using magnetic droplet nucleation to determine the spin torque effciency and asymmetry in Cox(NiFe)1-x thin filmsManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    We demonstrate how to extract the material dependent spin torque efficiency (ε) and asymmetry(λ) from the eld{current nucleation boundaries of magnetic droplet solitons in orthogonal nanocontacts in-torque oscillators with Cox(Ni80Fe20)1-x, (x=0{1), fixed layers. As the perpendicular component of the xed layer magnetization plays a central role in governing droplet nucleation, the nucleation boundaries exhibit monotonic shifts towards higher perpendicular magnetic elds when the xed layer magnetization μ0Ms,p is tuned from 1.04 to 1.7 T. We then extract ε and λ from tsto the nucleation boundaries and nd that while ε does not vary with composition, λ increases from1.5 to 3 with increasing Co content. The analysis of droplet nucleation boundaries is hence a useful tool for the systematic study of both ε and λ as functions of material composition.

  • 6.
    Jiang, Sheng
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. NanOsc AB, S-16440 Kista, Sweden..
    Etesami, Seyyed Ruhollah
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Chung, Sunjae
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Le, Quang Tuan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Houshang, Afshin
    NanOsc AB, S-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Impact of the Oersted Field on Droplet Nucleation Boundaries2018Inngår i: IEEE Magnetics Letters, ISSN 1949-307X, E-ISSN 1949-3088, Vol. 9, artikkel-id 3104304Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate how the Oersted field affects the magnetic droplet nucleation boundary in spin-torque nano-oscillators based on orthogonal spin-valve stacks with a perpendicular magnetic anisotropy Co/Ni free layer and an easy-plane anisotropy Ni80Fe20 fixed layer. The current-field nucleation boundary is determined experimentally using both microwave signal and dc resistance measurements. The Oersted field can, in principle, have an impact on droplet nucleation. This effect is considered approximately using an analytical equation for the nucleation boundary, which is extended to cover fields larger than the fixed-layer saturation field. We test the accuracy of this approach by comparing with micromagnetic simulations. Finally, we carry out a numerical fit to experimental data and find good agreement.

  • 7.
    Jiang, Sheng
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Khymyn, Roman
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Chung, Sunjae
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Korea Natl Univ Educ, Dept Phys Educ, Cheongju 28173, South Korea..
    Le, Quang Tuan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Diez, Liza Herrera
    Univ Paris Saclay, Ctr Nanosci & Nanotechnol, CNRS, F-91120 Palaiseau, France..
    Houshang, Afshin
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;NanOsc AB, S-16440 Kista, Sweden..
    Zahedinejad, Mohammad
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Ravelosona, Dafine
    Univ Paris Saclay, Ctr Nanosci & Nanotechnol, CNRS, F-91120 Palaiseau, France.;Spin Ion Technol, 10 Blvd Thomas Gobert, F-91120 Palaiseau, France..
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;NanOsc AB, S-16440 Kista, Sweden..
    Reduced spin torque nano-oscillator linewidth using He+ irradiation2020Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 116, nr 7, artikkel-id 072403Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate an approach for improving the spectral linewidth of a spin torque nano-oscillator (STNO). Using He + ion irradiation, we tune the perpendicular magnetic anisotropy (PMA) of the STNO free layer such that its easy axis is gradually varied from strongly out-of-plane to moderate in-plane. As the PMA impacts the non-linearity N of the STNO, we can, in this way, control the threshold current, the current tunability of the frequency, and, in particular, the STNO linewidth, which dramatically improves by two orders of magnitude. Our results are in good agreement with the theory for nonlinear auto-oscillators, confirm theoretical predictions of the role of the nonlinearity, and demonstrate a straightforward path toward improving the microwave properties of STNOs.

  • 8.
    Le, Quang Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Magnetodynamics in Spin Valves and Magnetic Tunnel Junctions with Perpendicular and Tilted Anisotropies2016Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Spin-torque transfer (STT) effects have brought spintronics ever closer to practical electronic applications, such as MRAM and active broadband microwave spin-torque oscillator (STO), and have emerged as an increasingly attractive field of research in spin dynamics. Utilizing materials with perpendicular magnetic anisotropy (PMA) in such applications offers several great advantages such as low-current, low-field operation combined with high thermal stability. The exchange coupling that a PMA thin film exerts on an adjacent in-plane magnetic anisotropy (IMA) layer can tilt the IMA magnetization direction out of plane, thus creating a stack with an effective tilted magnetic anisotropy. The tilt angle can be engineered via both intrinsic material parameters, such as the PMA and the saturation magnetization, and extrinsic parameters, such as the layer thicknesses.

          STOs can be fabricated in one of a number of forms—as a nanocontact opening on a mesa from a deposited pseudospin-valve (PSV) structure, or as a nanopillar etching from magnetic tunneling junction (MTJ)—composed of highly reproducible PMA or predetermined tilted magnetic anisotropy layers.

          All-perpendicular CoFeB MTJ STOs showed high-frequency microwave generation with extremely high current tunability, all achieved at low applied biases. Spin-torque ferromagnetic resonance (ST-FMR) measurements and analysis revealed the bias dependence of spin-torque components, thus promise great potential for direct gate-voltage controlled STOs.

          In all-perpendicular PSV STOs, magnetic droplets were observed underneath the nanocontact area at a low drive current and low applied field. Furthermore, preliminary results for microwave auto-oscillation and droplet solitons were obtained from tilted-polarizer PSV STOs. These are promising and would be worth investigating in further studies of STT driven spin dynamics.

  • 9.
    Le, Quang Tuan
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Eklund, Anders
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Banuazizi, Seyed Amir Hossein
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Fallahi, Vahid Fallahi
    Faculty of Physics, Amirkabir University of Technology.
    Nguyen, Thi Ngoc Anh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Yamanouchi, M.
    Laboratory for Nanoelectronics and Spintronics, RIEC, Tohoku University.
    Enobio, Eli C. I.
    Center for Spintronics Integrated Systems, Tohoku University.
    Ikeda, S.
    Laboratory for Nanoelectronics and Spintronics, RIEC, Tohoku University.
    Ohno, Hideo
    Laboratory for Nanoelectronics and Spintronics, RIEC, Tohoku University.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden; NanOsc AB, Sweden.
    Ultra-high frequency tunability in low-current and low-field spin-torque oscillators based on perpendicular magnetic tunnel junctionsManuskript (preprint) (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    We demonstrate ultra-high frequency tunability of up to 4.4 GHz/mA, and low threshold currents of about -21 $\mu$A, in spin-torque oscillators based on CoFeB/MgO/CoFeB magnetic tunnel junctions, in which both free and fixed layers have perpendicular magnetic anisotropy (PMA). By using different thicknesses of the two CoFeB layers, their individual PMA strengths can be tailored to achieve significant relative misalignment of their respective magnetizations in moderate in-plane fields. We observe a broad maximum in both the device resistance and the generated microwave power around maximum misalignment. Maximum frequency tunability is observed at low-to-moderate fields and decrease rapidly after maximum misalignment.

  • 10.
    Le, Quang Tuan
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Mazraati, Hamid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Nguyen, Thi Ngoc Anh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Institute of Materials Science, Vietnam Academy of Science and Technology.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden; NanOsc AB, Sweden.
    Bias dependence of parallel spin torque in all-perpendicular magnetic tunnel junction nanodevicesManuskript (preprint) (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    We performed spin-torque ferromagnetic resonance measurements on spin-torque oscillators based on CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs), with both free and fixed layers having perpendicular magnetic anisotropy, under the application of an in-plane field. A dc current between near-zero and -250 $\mu{A}$ was introduced to investigate the influence of spin-transfer torque effects on the asymmetric and symmetric components of the output voltage. Both components showed a minimum at a misalignment of about 30$^\circ$ between the magnetization of the two CoFeB layers, indicating a strong electric-field effect. We also found that the bias dependence of the spin-torque terms is in contrast to that of in-plane anisotropy CoFeB MTJs.

  • 11.
    Mazraati, Hamid
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Houshang, Afshin
    Dvornik, Mykola
    Piazza, Luca
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Qejvanaj, Fatjon
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Jiang, Sheng
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Le, Tuan Q.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Low operational current spin Hall nano-oscillators based on NiFe/W bilayers2016Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 109, nr 24, artikkel-id 242402Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate highly efficient spin Hall nano-oscillators (SHNOs) based on NiFe/beta-W bilayers. Thanks to the very high spin Hall angle of beta-W, we achieve more than a 60% reduction in the auto-oscillation threshold current compared to NiFe/Pt bilayers. The structural, electrical, and magnetic properties of the bilayers, as well as the microwave signal generation properties of the SHNOs, have been studied in detail. Our results provide a promising path for the realization of low-current SHNO microwave devices with highly efficient spin-orbit torque from beta-W. Published by AIP Publishing.

  • 12.
    Mazraati, Hamid
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. NanOsc AB.
    Le, Quang Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Awad, Ahmad A.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Hirayama, Eriko
    Ikeda, Shoji
    Matsukura, Fumihiro
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden; NanOsc AB, Sweden.
    Free- and reference-layer magnetization modes vs.~in-plane magnetic field in  a magnetic tunnel junction with perpendicular magnetic easy axis2016Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    We study the magnetodynamic modes of a magnetic tunnel junction with perpendicular magnetic easy axis (p-MTJ) in in-plane magnetic fields using device-level ferromagnetic resonance spectroscopy. We compare our experimental results to those of micromagnetic simulations of the entire p-MTJ. Using an iterative approach to determine the material parameters that best fit our experiment, we find excellent agreement between experiments and simulations in both the static magnetoresistance and magnetodynamics in the free and reference layers. From the micromagnetic simulations, we determine the spatial mode profiles, the localization of the modes and, as a consequence, their distribution in the frequency domain due to the inhomogeneous internal field distribution inside the p-MTJ under different applied field regimes. We also conclude that the excitation mechanism is a combination of the microwave voltage modulated perpendicular magnetic anisotropy, the microwave Oersted field, and the spin-transfer torque generated by the microwave current.

  • 13.
    Mazraati, Hamid
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. NanOsc AB, Sweden.
    Le, Tuan Q.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Awad, Ahmad A.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. University of Gothenburg, Sweden.
    Hirayama, Eriko
    Ikeda, Shoji
    Matsukura, Fumihiro
    Ohno, Hideo
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. NanOsc AB, Sweden; University of Gothenburg, Sweden.
    Free- and reference-layer magnetization modes versus in-plane magnetic field in a magnetic tunnel junction with perpendicular magnetic easy axis2016Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, nr 10, artikkel-id 104428Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the magnetodynamic modes of a magnetic tunnel junction with perpendicular magnetic easy axis (p-MTJ) in in-plane magnetic fields using device-level ferromagnetic resonance spectroscopy. We compare our experimental results to those of micromagnetic simulations of the entire p-MTJ. Using an iterative approach to determine the material parameters that best fit our experiment, we find excellent agreement between experiments and simulations in both the static magnetoresistance and magnetodynamics in the free and reference layers. From the micromagnetic simulations, we determine the spatial mode profiles, the localization of the modes and, as a consequence, their distribution in the frequency domain due to the inhomogeneous internal field distribution inside the p-MTJ under different applied field regimes. We also conclude that the excitation mechanism is a combination of the microwave voltage modulated perpendicular magnetic anisotropy, the microwave Oersted field, and the spin-transfer torque generated by the microwave current.

  • 14. Mukherjee, Sumanta
    et al.
    Knut, Ronny
    Mohseni, S. Majid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Shahid Beheshti Univ, Iran.
    Anh Nguyen, T. N.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. VNU HCM, Vietnam.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Le, Quang Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Persson, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sahoo, Anindita
    Hazarika, Abhijit
    Pal, Banabir
    Thiess, Sebastian
    Gorgoi, Mihaela
    Kumar, P. S. Anil
    Drube, Wolfgang
    Karis, Olof
    Sarma, D. D.
    Role of boron diffusion in CoFeB/MgO magnetic tunnel junctions2015Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, nr 8, artikkel-id 085311Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Several scientific issues concerning the latest generation read heads for magnetic storage devices, based on CoFeB/MgO/CoFeBmagnetic tunnel junctions (MTJs) are known to be controversial, including such fundamental questions as to the behavior and the role of B in optimizing the physical properties of these devices. Quantitatively establishing the internal structures of several such devices with different annealing conditions using hard x-ray photoelectron spectroscopy, we resolve these controversies and establish that the B diffusion is controlled by the capping Ta layer, though Ta is physically separated from the layer with B by several nanometers. While explaining this unusual phenomenon, we also provide insight into why the tunneling magnetoresistance (TMR) is optimized at an intermediate annealing temperature, relating it to B diffusion, coupled with our studies based on x-ray diffraction and magnetic studies.

  • 15.
    Nguyen, T. N. Anh
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Vietnam Natl Univ Ho Chi Minh City, Vietnam.
    Knut, R.
    Fallahi, V.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Le, Quang Tuan Le
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Mohseni, S. M.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Shahid Beheshti Univ, Iran.
    Karis, O.
    Peredkov, S.
    Dumas, R. K.
    Miller, Casey W.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden; NanOsc AB, Sweden.
    Depth-Dependent Magnetization Profiles of Hybrid Exchange Springs2014Inngår i: PHYS REV APPL, ISSN 2331-7019, Vol. 2, nr 4, s. 044014-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on the magnetization depth profile of a hybrid exchange-spring system in which a Co/Pd multilayer with perpendicular anisotropy is coupled to a CoFeB thin film with in-plane anisotropy. The competition between these two orthogonal anisotropies promotes a strong depth dependence of the magnetization orientation. The angle of the magnetization vector is sensitive both to the strength of the individual anisotropies and to the local exchange constant and is thus tunable by changing the thickness of the CoFeB layer and by substituting Ni for Pd in one layer of the Co/Pd stack. The resulting magnetic depth profiles are directly probed by element-specific x-ray magnetic circular dichroism of the Fe and Ni layers located at different average depths. The experimental results are corroborated by micromagnetic simulations.

  • 16.
    Nguyen, Thi Ngoc Anh
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Vietnam Natl Univ, Vietnam.
    Fallahi, Vahid
    Le, Quang Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Chung, Sunjea
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Mohseni, Seyed Majid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Shahid Beheshti Univ, Iran.
    Dumas, Randy K.
    Miller, Casey W.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Investigation of the Tunability of the Spin Configuration Inside Exchange Coupled Springs of Hard/Soft Magnets2014Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, nr 6, s. 2004906-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Magnetic multilayer (ML) structures comprising a perpendicular magnetic anisotropy (PMA) layer coupled to an in-plane magnetic anisotropy (IMA) layer are promising materials for zero/low field operating spin-torque oscillators and bit patterned recording media. The magnetization tilt angle can be easily tuned by varying the IMA layer thickness due to the competition between PMA and IMA layers. To explore the underlying magnetization reversal mechanism and to further understand the control of tilt angle and uniformity of the magnetization, the IMA (NiFe, Co, and CoFeB)/PMA (Co/Pd MLs) exchange spring systems are systematically studied. Experimental data obtained from magnetometry show good agreement with 1-D micromagnetic simulations, allowing us to design tunable exchange coupled spring as a function of IMA thickness.

  • 17. Qejvanaj, Fatjon
    et al.
    Zubair, M.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Persson, A.
    Mohseni, S. M.
    Fallahi, V.
    Sani, Sohrab Redjai
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Le, Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Magnusson, F.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Thick Double-Biased IrMn/NiFe/IrMn Planar Hall Effect Bridge Sensors2014Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, nr 11, artikkel-id 4006104Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we present a new material stack for planar Hall effect bridge (PHEB) sensors and a detailed investigation of the sensitivity and noise properties of PHEB sensors made from these. The sputter deposited material stack was based on a ferromagnetic (FM) NiFe sensing layer surrounded by two layers of anti-FM IrMn. This material stack enables implementation of a thick NiFe layer without loss of sensitivity. We present an improvement in detectivity in the PHEB by changing the shape and the materials of the corners between the sensors in a meander shape. A significant reduction of noise also comes from the thick NiFe layer, due to the reduced resistance of the sensor.

1 - 17 of 17
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