| 1. |
- Sheykhifard, Z., et al.
(författare)
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Magnetic graphene/Ni-nano-crystal hybrid for small field magnetoresistive effect synthesized via electrochemical exfoliation/deposition technique
- 2018
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Ingår i: Journal of Materials Science-Materials in Electronics. - : Springer Science and Business Media LLC. - 0957-4522 .- 1573-482X. ; 29:5, s. 4171-4178
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional heterostructures of graphene (Gr) and metal/semiconducting elements convey new direction in electronic devices. They can be useful for spintronics because of small spin orbit interaction of Gr as a non-magnetic metal host with promising electrochemical stability. In this paper, we demonstrate one-step fabrication of magnetic Ni-particles entrapped within Gr-flakes based on simultaneous electrochemical exfoliation/deposition procedure by two-electrode system using platinum as the cathode electrode and a graphite foil as the anode electrode. The final product is an air stable hybrid element including Gr flakes hosting magnetic Ni-nano-crystals showing superparamagnetic-like response and room temperature giant magnetoresistance (GMR) effect at small magnetic field range. The GMR effect is originated from spin scattering through ferromagnetic/non-magnetic nature of Ni/Gr heterostructure and interpreted based on a phenomenological spin transport model. Our work benefits from XRD, XPS, Raman, TEM, FTIR and VSM measurements We addressed that how our results can be used for rapid manufacturing of magnetic Gr for low field magneto resistive elements and potential printed spintronic devices.
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| 2. |
- Dürrenfeld, Philipp, et al.
(författare)
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Low-current, narrow-linewidth microwave signal generation in NiMnSb based single-layer nanocontact spin-torque oscillators
- 2016
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 109:22
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Tidskriftsartikel (refereegranskat)abstract
- We report on the fabrication of nano-contact spin-torque oscillators based on single layers of the epitaxially grown half-metal NiMnSb with ultralow spin wave damping. We demonstrate magnetization auto-oscillations at microwave frequencies in the 1-3 GHz range in out-of-plane magnetic fields. Threshold current densities as low as 3 x 10(11) A m(-2) are observed as well as minimum oscillation linewidths of 200 kHz, both of which are much lower than the values achieved in conventional metallic spin-valve-based devices of comparable dimensions. These results enable the fabrication of spin transfer torque driven magnonic devices with low current density requirements, improved signal linewidths, and in a simplified single-layer geometry. Published by AIP Publishing.
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| 3. |
- Gupta, S., et al.
(författare)
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Co/Ni multilayers with robust post-annealing performance for spintronics device applications
- 2018
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Ingår i: Journal of Physics D-Applied Physics. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 51:46
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Tidskriftsartikel (refereegranskat)abstract
- The effect of annealing on the diffusion induced changes in the magnetic and magnetodynamic properties of (Co/Ni) multilayers were investigated. Here, we report, all aspects of post annealing induced effect on perpendicular magnetic anisotropy (PMA), domain morphology, switching mechanism and high frequency magnetization dynamics to understand spin relaxation. (Co/Ni) multilayers of this study exhibited a loop squareness of 95%, a slight drop in saturation magnetization from 650 emu/cc to 620 emu/cc and high magnetic anisotropy (K-u similar to 3 x 10(5) J m(-3)) even after annealing at temperatures as high as 400 degrees C. Successive domain mapping by magnetic force microscopy revealed characteristics of multi-domains stripe that feature at all stages of annealing except at 500 degrees C, attributed to the loss of PMA, driven by interfacial diffusion. High frequency broadband ferromagnetic resonance measurements showed little effect of annealing on intrinsic damping parameter (alpha = 0.019-0.024) while inhomogeneous linewidth broadening varied without a clear trend. These results are discussed considering crystallographic modifications and it was found that fcc (111) texture was retained in the samples until 400 degrees C post annealing. The retention of a high anisotropy, high magnetization and low damping constant after high temperature annealing makes these Co/Ni multilayers suitable for designing spin torque based memory devices.
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| 4. |
- Balinsky, Michael, et al.
(författare)
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Spin Pumping and the Inverse Spin-Hall Effect via Magnetostatic Surface Spin-Wave Modes in Yttrium-Iron Garnet/Platinum Bilayers
- 2015
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Ingår i: Ieee Magnetics Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1949-307X .- 1949-3088. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Spin pumping at a boundary between a yttrium-iron garnet (YIG) film and a thin platinum (Pt) layer is studied under conditions in which a magnetostatic surface spin wave (MSSW, or Damon-Eshbach mode) is excited in YIG by a narrow strip-line antenna. It is shown that the voltage created by the inverse spin-Hall effect (ISHE) in Pt is strongly dependent on the wavevector of the excited MSSW. For YIG film thicknesses of 41 and 0.9 mu m, the maximum ISHE voltage corresponds to the maximum of efficiently excited MSSW wavevectors and does not coincide with the maximum of absorbed microwave power. For a thinner (0.175 mu m) YIG film, the maximum of the ISHE voltage moves closer to the ferromagnetic resonance and almost coincides with the region of the maximum microwave absorption. We show that the effect is related to the change in the thickness profile and the wavenumber spectrum of the excited MSSW taking place when the YIG film thickness is increased.
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| 5. |
- Chung, Sunjae, et al.
(författare)
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Magnetic droplet solitons in orthogonal spin valves
- 2015
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Ingår i: Fizika Nizkih Temperatur. - : American Institute of Physics (AIP). - 0132-6414 .- 1816-0328. ; 41:10, s. 833-837
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Tidskriftsartikel (refereegranskat)abstract
- We review the recent experimental advancements in the realization and understanding of magnetic droplet solitons generated by spin transfer torque in orthogonal nanocontact based spin torque nanooscillators (STNOs) fabricated on extended spin valves and spin valve nanowires. The magnetic droplets are detected and studied using the STNO microwave signal and its resistance, the latter both quasistatically and time-resolved. The droplet nucleation current is found to have a minimum at intermediate magnetic field strengths and the nature of the nucleation changes gradually from a single sharp step well above this field, mode-hopping around the minimum, and continuous at low fields. The mode-hopping and continuous transitions are ascribed to droplet drift instability and re-nucleation at different time scales, which is corroborated by time-resolved measurements. We argue that the use of tilted anisotropy fixed layers could reduce the nucleation current further, move the nucleation current minimum to lower fields, and potentially remove the need for an applied magnetic field altogether. Finally, evidence of an edge mode droplet in a nanowire is presented.
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| 6. |
- Ranjbar, Vanja, et al.
(författare)
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The Swedish Psychotrauma Society : Joining forces for a national psychotrauma platform from a multidisciplinary and holistic approach
- 2015
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Ingår i: European Journal of Psychotraumatology. - : CoAction Publishing. - 2000-8198 .- 2000-8066. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- Events such as the discotheque fire in Gothenburg, Sweden, in 1998 and the 2004 tsunami in Thailand, in which many Swedish citizens’ lives were lost, exemplify events of traumatic character with implications for different professions in Sweden (Arnberg, Hultman, Michel, & Lundin, 2013; Wahlström, Michélsen, Schulman, Backheden, & Keskinen-Rosenqvist, 2013). Such events highlight the need for Swedish research on psychotraumatology to meet needs arising in connection with such traumas. Also events in Sweden's immediate vicinity, such as the terrorist attacks in Oslo and in Utøya in 2011, can be considered to have impact on Swedish society and its emergency preparedness. The Swedish Psychotrauma Society was formed in 2013. Its objectives are to increase and disseminate knowledge on psychotraumatology by creating a network of professionals and individuals who are active and/or interested in the subject, promote research and training in the field, and collaborate nationally and internationally on issues relating to psychotraumatology. The society is open to researchers, students, practitioners, and others alike with an interest in psychotraumatology, thereby encouraging multidisciplinary and holistic work and collaboration as well as being one of its kind in Sweden within this field. Not least, the society strives to be a link between research and practice. To this effect, the society organised its first scientific conference in May 2015, with a grant from The Swedish Foundation for Humanities and Social Science. The conference aimed to offer internationally renowned psychotrauma researchers as keynote speakers (Litz, 2015; Newman & Drevo, 2015; Olff, Van Zuiden, & Bakker, 2015) and gather a nationwide audience consisting of professionals and researchers from various disciplines. By establishing a Swedish psychotrauma society and inspire and strengthen the field of psychotraumatology in Sweden, it is hoped that the Swedish Psychotrauma Society during the coming year can become affiliated to the ESTSS and commence collaborations with its European counterparts.
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| 7. |
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| 8. |
- Sbiaa, R., et al.
(författare)
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Ferromagnetic resonance measurements of (Co/Ni/Co/Pt) multilayers with perpendicular magnetic anisotropy
- 2016
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Ingår i: Journal of Physics D. - : Institute of Physics Publishing (IOPP). - 0022-3727 .- 1361-6463. ; 49:42
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Tidskriftsartikel (refereegranskat)abstract
- Multilayers of [Co/Ni(t)/Co/Pt]×8 with varying Ni thickness were investigated for possible use as a free layer in magnetic tunnel junctions and spintronics devices. The thickness t of the Ni sub-layer was varied from 0.3 nm to 0.9 nm and the resulting magnetic properties were compared with (Co/Ni) and (Co/Pt) multilayers. As determined from magnetic force microscopy, magnetometry and ferromagnetic resonance measurements, all multilayers exhibited perpendicular magnetic anisotropy. Compared with (Co/Pt) multilayers, the sample with t of 0.9 nm showed almost the same anisotropy field of μ 0 H k = 1.15 T but the damping constant was 40% lower. These characteristics make these multilayers attractive for spin torque based magnetoresistive devices with perpendicular anisotropy.
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| 9. |
- Sbiaa, R., et al.
(författare)
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Temperature effect on exchange coupling and magnetization reversal in antiferromagnetically coupled (Co/Pd) multilayers
- 2015
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 118:6
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Tidskriftsartikel (refereegranskat)abstract
- Magnetization reversal of antiferromagnetically coupled (AFC) soft and hard (Co/Pd) multilayers was studied as a function of temperature. While the hard [Co(0.3 nm)/Pd(0.8 nm)](x10) was kept unchanged, the softness of the [Co(t)/Pd(0.8 nm)](x3) was controlled by varying the thickness t of the Co sublayer. Clear two-step hysteresis loops were observed for all the investigated multilayers with t ranging between 0.4 and 1 nm. The spin reorientation of the soft layer magnetization from in-plane direction to out-of-plane direction was investigated from 50 to 300 K. The antiferromagnetic field H-AFC measured from the shift of the minor hysteresis loop reveals a good agreement to the quantum-well model. From the out-of-plane hysteresis loop of the uncoupled soft layer, its magnetization shows an in-plane orientation for t >= 0.6 nm. The strong H-AFC helps to induce an out-of plane orientation of the soft layer with a linear decrease of its coercivity with temperature. These investigated structures show the possibility to reduce the unwanted stray field and improving the out-of-plane anisotropy even for relatively thicker soft layer. (c) 2015 AIP Publishing LLC.
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| 10. |
- Spicer, T. M., et al.
(författare)
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Spatial mapping of torques within a spin Hall nano-oscillator
- 2018
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 98:21
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved scanning Kerr microscopy (TRSKM) was used to study precessional magnetization dynamics induced by a radio frequency (RF) current within a Al2O3/Py(5 nm)/Pt(6 nm)/Au(150 nm) spin Hall nano-oscillator structure. The Au layer was formed into two needle-shaped electrical contacts that concentrated the current in the center of a Py/Pt mesa of 4 mu m diameter. Due to the spin Hall effect, current within the Pt layer drives a spin current into the Py layer, exerting a spin transfer torque (STT). By injecting RF current and exploiting the phase sensitivity of TRSKM and the symmetry of the device structure, the STT and Oersted field torques have been separated and spatially mapped. The STT and torque due to the in-plane Oersted field are observed to exhibit minima at the device center that is ascribed to spreading of RF current that is not observed for DC current. Torques associated with the RF current may destabilize the position of the self-localized bullet mode excited by the DC current and inhibit injection locking. The present study demonstrates the need to characterize both DC and RF current distributions carefully.
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