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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) (Övrigt vetenskapligt)
    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) (Övrig (populärvetenskap, 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.
    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) (Övrigt vetenskapligt)
    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.

  • 4.
    Jiang, Sheng
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. NanOsc AB, S-16440 Kista, Sweden.
    Chung, Sunjae
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Le, Quang Tuan
    Mazraati, Hamid
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. NanOsc AB, S-16440 Kista, Sweden..
    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.
    Using Magnetic Droplet Nucleation to Determine the Spin Torque Efficiency and Asymmetry in Co-x(Ni,Fe)(1-x) Thin Films2018Ingår i: Physical Review Applied, E-ISSN 2331-7019, Vol. 10, nr 5, artikel-id 054014Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We demonstrate how to extract the material-dependent spin-torque efficiency (epsilon) and asymmetry (lambda) from the field-current nucleation boundaries of magnetic droplet solitons in orthogonal nano-contact spintorque oscillators with Co-x(Ni80Fe20)(1-x), (x = 0 -1), fixed layers. As the perpendicular component of the fixed-layer magnetization plays a central role in governing droplet nucleation, the nucleation boundaries exhibit monotonic shifts towards higher perpendicular magnetic fields when the fixed-layer magnetization mu M-0(s, p) is tuned from 1.04 to 1.7 T. We then extract epsilon and lambda from fits to the nucleation boundaries and find that while epsilon does not vary with composition,lambda increases from 1.5 to 3 with increasing Co content. The analysis of droplet nucleation boundaries is hence a useful tool for the systematic study of both epsilon and lambda as functions of material composition.

  • 5.
    Mazraati, Hamid
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Linear, Non-Linear, and Synchronizing Spin Wave Modes in Spin Hall Nano-Oscillators2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Spin Hall nano-oscillators (SHNOs) are nanoscale spintronic devices that generate microwave signals with highly tunable frequency. This thesis focuses on improving the signal quality of nanoconstriction-based SHNOs and also on developing a better understanding of their magnetization dynamics.

    In the first part of the thesis, we fabricate and characterize low-threshold current SHNOs using NiFe/β-W bilayers. Due to the high spin Hall angle of the β-phase W, the auto-oscillation threshold current is improved by 60% over SHNOs based on NiFe/Pt. We also demonstrate low operational current by utilizing W/Co20Fe60B20/MgO stacks on highly resistive silicon substrates. Thanks to the moderate perpendicular magnetic anisotropy (PMA) of Co20Fe60B20, these SHNOs show much wider frequency tunability than SHNOs based on NiFe with no PMA. Performance is further improved by using highly resistive silicon substrates with a high heat conductance, dissipating the generated excess heat much better than sapphire substrates. Moreover, it also means that the fabrication of SHNOs is now compatible with conventional CMOS fabrication, which is necessary if SHNOs are to be used in integrated circuits. In another approach, we attempt to decrease the threshold current of SHNOs based on an NiFe/Pt stack by inserting an ultra-thin Hf layer in the middle of the stack. This Hf dusting decreases the damping of the bilayer linearly but also degrades its spin Hall efficiency. These opposing trends determine the optimum Hf thickness to ≈0.4 nm, at which the auto-oscillation threshold current is minimum. Our achievements arising from these three approaches show a promising path towards the realization of low-current SHNO microwave devices with highly efficient spin-orbit torque.

    In the next chapter, we use both electrical experimentation and micromagnetic simulation to study the auto-oscillating spin wave modes in nanoconstriction-based SHNOs as a function of the drive current and the applied field. First, we investigate the modes under an in-plane low-range field of 40-80 mT, which is useful for developing low-field spintronic devices with applications in microwave signal generation. It is also essential for future studies on the synchronization of multiple SHNOs. Next, using an out-of-plane applied magnetic field, we observe three different modes and demonstrate switching between them under a fixed external field by tuning only the drive current. The flexibility of these nanopatterned spin Hall nano-oscillators is desirable for implementing oscillator-based neuromorphic computing devices.

    In the final part, we study the synchronization of multiple nanoconstriction-based SHNOs in weak in-plane fields. We electrically investigate the synchronization versus the angle of the field, observing synchronization for angles below a threshold angle. In agreement with the experimental results, the spatial profile of the spin waves from the simulations shows that the relative angle between the modes from the nanoconstrictions decreases with decreasing the field angle, thus facilitating synchronization. The synchronization observed at low in-plane fields improves the microwave signal quality and could also be useful for applications such as neuromorphic computing.

  • 6.
    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 bilayers2016Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 109, nr 24, artikel-id 242402Artikel i tidskrift (Refereegranskat)
    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.

  • 7.
    Mazraati, Hamid
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Etesami, Seyyed Ruhollah
    University of Gothenburg.
    Banuazizi, S. Amir Hossein
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Chung, Sunjae
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Houshang, Afshin
    University of Gothenburg.
    Awad, Ahmad A.
    University of Gothenburg.
    Dvornik, Mykola
    University of Gothenburg.
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. University of Gothenburg.
    Auto-oscillating spin-wave modes of constriction-based spin Hall nano-oscillators in weak in-plane fieldsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    We experimentally study the auto-oscillating spin-wave modes in Ni80Fe20/β-W constriction-based spin Hall nano-oscillators as a function of bias current, in-plane applied field strength, and azimuthal field angle, in the low-field range of 40-80 mT. We observe two different spin-wave modes: i) a linear-like mode confined to the minima of the internal field near the edges of the nanoconstriction, with weak frequency dependencies on the bias current and the applied field angle, and ii) a second, lower frequency mode that has significantly higher threshold current and stronger frequency dependencies on both bias current and the external eld angle. Our micromagnetic modeling qualitatively reproduces the experimental data and reveals that the second mode is a spin-wave bullet and that the SHNO mode hops between the two modes, resulting in a substantial increase in linewidths. In contrast to the linear-like mode, the bullet is localized in the middle of the constriction and shrinks with increasing bias current. Utilizing intrinsic frequency doubling at zero eld angle we can reach frequencies above 9 GHz in fields as low as 40 mT, which is important for the development of low-eld spintronic oscillators with applications in microwave signal generation and neuromorphic computing.

  • 8.
    Mazraati, Hamid
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. NanOsc AB, SE-16440 Kista, Sweden.
    Etesami, Seyyed Ruhollah
    Univ Gothenburg, Dept Phys, SE-41296 Gothenburg, Sweden..
    Banuazizi, Seyed Amir Hossein
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Chung, Sunjae
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Houshang, Afshin
    NanOsc AB, SE-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, SE-41296 Gothenburg, Sweden..
    Awad, Ahmad A.
    NanOsc AB, SE-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, SE-41296 Gothenburg, Sweden..
    Dvornik, Mykola
    NanOsc AB, SE-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, SE-41296 Gothenburg, Sweden..
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. NanOsc AB, SE-16440 Kista, Sweden.;;Univ Gothenburg, Dept Phys, SE-41296 Gothenburg, Sweden..
    Auto-oscillating Spin-Wave Modes of Constriction-Based Spin Hall Nano-oscillators in Weak In-Plane Fields2018Ingår i: Physical Review Applied, E-ISSN 2331-7019, Vol. 10, nr 5, artikel-id 054017Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We experimentally study the auto-oscillating spin-wave modes in Ni(80)Fc(20)/beta-W constriction-based spin Hall nano-oscillators as a function of bias current, strength of the in-plane applied field, and azimuthal field angle in the low-field range of 40-80 mT. We observe two different spin-wave modes: (i) a linearlike mode confined to the internal field minima near the edges of the nanoconstriction, and only weakly dependent on the bias current and the applied-field angle, and (ii) a second, lower-frequency mode with significantly higher threshold current and stronger dependence on both the bias current and the externalfield angle. Micromagnetic modeling qualitatively reproduces the experimental data and reveals that the second mode is a spin-wave bullet and that the spin Hall nano-oscillator mode hops between the two modes, resulting in a substantial increase in linewidths. In contrast to the linearlike mode, the bullet is localized in the middle of the constriction and shrinks with increasing bias current. Using intrinsic frequency doubling at zero field angle, we can reach frequencies above 9 GHz in fields as low as 40 mT, which is important for the development of low-field spintronic oscillators with applications in microwave-signal generation and neuromorphic computing.

  • 9.
    Mazraati, Hamid
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Etesami, Seyyed Ruhollah
    University of Gothenburg.
    Houshang, Afshin
    University of Gothenburg.
    Chung, Sunjae
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Dvornik, Mykola
    University of Gothenburg.
    Åkerman, Johan
    University of Gothenburg.
    Contracting vs. expanding spin wave bullets in spin Hall nano-oscillatorsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    We employ electrical measurements complemented by systematic micromagnetic simulations to reveal the complex dynamics of nanoconstriction-based spin Hall nano-oscillators. In particular, depending on the strength and out-of-plane angle of the applied magnetic field, we observe three distinct types of magnetization auto-oscillation: (a) a linear-like mode localized in the vicinity of the nanoconstriction by the demagnetizing field, (b) a further localized “regular” spin wave bullet, and(c) a “large” bullet that fills the entire area of the nanoconstriction. Although it has been assumed for some time that bullets only emerge if the nonlinearity of the system is negative (corresponding to the attraction of magnons), our results demonstrate that, in patterned films, they could be sustained even if the nonlinearity of the system is positive (corresponding to the repulsion of magnons). So, in contrast to the regular spin wave bullet, the auto-oscillation volume of its novel large counterpart enlarges, with the amplitude enhancing their drift stability and, correspondingly, reducing their linewidth. We demonstrate that tuning can be achieved between the observed modes at a fixed external field by changing only the drive current, thanks to the amplitude-dependent nonlinearity of the auto-oscillations. This flexibility of nanopatterned spin Hall nano-oscillators is desirable to achieve synaptic functionality in oscillator-based neuromorphic computing devices.

  • 10.
    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 axis2016Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795Artikel i tidskrift (Övrig (populärvetenskap, 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.

  • 11.
    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 axis2016Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, nr 10, artikel-id 104428Artikel i tidskrift (Refereegranskat)
    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.

  • 12.
    Mazraati, Hamid
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Zahedinejad, Mohammad
    University of Gothenburg.
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. University of Gothenburg.
    Improving the magnetodynamical properties of NiFe/Pt bilayers through Hf dusting2018Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 113, nr 9, s. 092401-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the effect of hafnium (Hf) dusting on the magnetodynamical properties of NiFe/Pt bilayers using spin-torque-induced ferromagnetic resonance measurements on 6 μm wide microstrips on high-resistive Si substrates. Based on two series of NiFe(tNiFe)/Hf(tHf)/Pt(5) stacks, we first demonstrate that the zero-current magnetodynamic properties of the devices benefit from Hf dusting: (i) the effective magnetization of the NiFe layer increases by 4%–8% with Hf present and (ii) the damping α decreases linearly with tHf by up to 40%. The weaker anisotropic magnetoresistance (AMR≈0.3%–0.4%) of the 3 nm NiFe series is largely unaffected by the Hf, while the stronger AMR of the 5 nm NiFe series drops from 0.7% to 0.43% with increasing tHf. We find that the spin Hall efficiency ξSH is independent of the NiFe thickness, remaining unaffected (ξSH = 0.115) up to tHf = 0.4 nm and then decreasing linearly for higher tHf. The different trends of α and ξSH suggest that there is an optimum Hf thickness (≈0.4 nm) for which the threshold current for auto-oscillation should have a minimum, while the much lower damping should improve mutual synchronization. Our results also indicate that the spin-orbit torque is entirely damping-like with no field-like torque component. Finally, the internal spin Hall angle of Pt is estimated to be θSH = 0.22 by calculating the transparency of the interface.

  • 13. Qejvanaj, Fatjon
    et al.
    Mazraati, Hamid
    Jiang, S.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Persson, A.
    Redjai Sani, Sohrab
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Magnusson, F.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik. NanOsc AB, Sweden.
    Planar Hall Effect Bridge sensor with NiFeX (X = Cu, Ag and Au) sensing layer.2015Konferensbidrag (Övrigt vetenskapligt)
  • 14.
    Qejvanaj, Fatjon
    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.
    Jiang, S.
    Persson, A.
    Sani, Sohrab Redjai
    Chung, S.
    Magnusson, F.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik. Göteborg univ.
    Planar Hall-Effect Bridge Sensor With NiFeX (X = Cu, Ag, and Au) Sensing Layer2015Ingår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 51, nr 11, artikel-id 4005404Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents a new material alloy for planar Hall-effect bridge (PHEB) sensors and the accurate analysis of the resistance and sensitivity of these materials. The sensing layer is based on NiFeX (X = Cu, Ag, and Au). These alloys have a lower resistance without a significant loss of sensitivity. The presented PHEB sensors with NiFeX sensing layer show a coercivity of 1.7 Oe, lower than that of PHEB sensors with NiFe sensing layers, which have coercivities of 2.2 Oe.

  • 15.
    Zahedinejad, M.
    et al.
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Mazraati, Hamid
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. NanOsc AB, S-16440 Kista, Sweden.
    Fulara, H.
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Yue, J.
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Jiang, Sheng
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Awad, A. A.
    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.;NanOsc AB, S-16440 Kista, Sweden.
    CMOS compatible W/CoFeB/MgO spin Hall nano-oscillators with wide frequency tunability2018Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 112, nr 13, artikel-id 132404Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We demonstrate low-operational-current W/Co20Fe60B20/MgO spin Hall nano-oscillators (SHNOs) on highly resistive silicon (HiR-Si) substrates. Thanks to a record high spin Hall angle of the beta-phase W (theta(SH) = -0.53), a very low threshold current density of 3.3 x 10(7) A/cm(2) can be achieved. Together with their very wide frequency tunability (7-28GHz), promoted by a moderate perpendicular magnetic anisotropy, HiR-Si/W/CoFeB based SHNOs are potential candidates for wide-band microwave signal generation. Their CMOS compatibility offers a promising route towards the integration of spintronic microwave devices with other on-chip semiconductor microwave components.

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