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Alexander A. Baker - One of the best experts on this subject based on the ideXlab platform.
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Dependence of spin pumping and spin transfer torque upon Ni81Fe19 thickness in Ta/Ag/Ni81Fe19/Ag/Co2MnGe/Ag/Ta spin-valve structures
Physical Review B, 2017Co-Authors: C. J. Durrant, L. R. Shelford, R. A. J. Valkass, R. J. Hicken, Adriana I. Figueroa, Alexander A. Baker, G. Van Der Laan, L. B. Duffy, P. Shafer, Christoph KleweAbstract:Author(s): Durrant, CJ; Shelford, LR; Valkass, RAJ; Hicken, RJ; Figueroa, AI; Baker, AA; Van Der Laan, G; Duffy, LB; Shafer, P; Klewe, C; Arenholz, E; Cavill, SA; Childress, JR; Katine, JA | Abstract: © 2017 American Physical Society. Spin pumping has been studied within Ta / Ag / Ni81Fe19 (0-5 nm) / Ag (6 nm) / Co2MnGe (5 nm) / Ag / Ta large-area spin-valve structures, and the transverse spin current absorption of Ni81Fe19 Sink Layers of different thicknesses has been explored. In some circumstances, the spin current absorption can be inferred from the modification of the Co2MnGe source Layer damping in vector network analyzer ferromagnetic resonance (VNA-FMR) experiments. However, the spin current absorption is more accurately determined from element-specific phase-resolved x-ray ferromagnetic resonance (XFMR) measurements that directly probe the spin transfer torque (STT) acting on the Sink Layer at the source Layer resonance. Comparison with a macrospin model allows the real part of the effective spin mixing conductance to be extracted. We find that spin current absorption in the outer Ta Layers has a significant impact, while Sink Layers with thicknesses of less than 0.6 nm are found to be discontinuous and superparamagnetic at room temperature, and lead to a noticeable increase of the source Layer damping. For the thickest 5-nm Sink Layer, increased spin current absorption is found to coincide with a reduction of the zero frequency FMR linewidth that we attribute to improved interface quality. This study shows that the transverse spin current absorption does not follow a universal dependence upon Sink Layer thickness but instead the structural quality of the Sink Layer plays a crucial role.
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Effect of Sink Layer thickness on damping in CoMnGe (5 nm) / Ag (6 nm) / NiFe (x nm) spin valves
2016Co-Authors: R. A. J. Valkass, C. J. Durrant, L. R. Shelford, Adriana I. Figueroa, Alexander A. Baker, Padraic Shafer, Elke Arenholz, Jeffrey R. Childress, Jordan A. Katine, Gerrit Van Der LaanAbstract:We thank the Advanced Light Source for access to beamlines 4.0.2 and 6.3.1 (ALS-06433, ALS-07116). The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
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Anisotropic Absorption of Pure Spin Currents
Physical review letters, 2016Co-Authors: Alexander A. Baker, Adriana I. Figueroa, Christopher Love, Stuart A. Cavill, Thorsten Hesjedal, G. Van Der LaanAbstract:Spin transfer in magnetic multiLayers offers the possibility of ultrafast, low-power device operation. We report a study of spin pumping in spin valves, demonstrating that a strong anisotropy of spin pumping from the source Layer can be induced by an angular dependence of the total Gilbert damping parameter, α, in the spin Sink Layer. Using lab- and synchrotron-based ferromagnetic resonance, we show that an in-plane variation of damping in a crystalline Co_{50}Fe_{50} Layer leads to an anisotropic α in a polycrystalline Ni_{81}Fe_{19} Layer. This anisotropy is suppressed above the spin diffusion length in Cr, which is found to be 8 nm, and is independent of static exchange coupling in the spin valve. These results offer a valuable insight into the transmission and absorption of spin currents, and a mechanism by which enhanced spin torques and angular control may be realized for next-generation spintronic devices.
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Tailoring of magnetic anisotropy and interfacial spin dynamics
2016Co-Authors: Alexander A. BakerAbstract:Spin transfer in magnetic multiLayers offers the possibility of a new generation of ultra-fast, low-power spintronic devices. New ways to control the resonance frequency and damping in ultrathin films are actively sought, fuelling study of the precessional dynamics and interaction mechanisms in such samples. One effect that has come under particular scrutiny in recent years is the spin-transfer torque, wherein a flow of spins entering a ferromagnet exerts a torque on the magnetisation, inducing precession. A flow of spin angular momentum is usually generated through a spin-polarised electrical current, but a promising alternative is the pure spin current emitted by a ferromagnet undergoing ferromagnetic resonance (FMR). This allows spins to be transferred without a net charge flow. The physics of the generation, transmission and absorption of pure spin currents is a developing field, and holds great promise for both industrial applications and as a means to study fundamental physical phenomena in exotic materials. This thesis presents an investigation into the magnetodynamics of ferromagnetic thin films and heterostructures grown by molecular beam epitaxy and studied using vector-network analyser ferromagnetic resonance (VNA-FMR), x-ray magnetic circular dichroism, vibrating sample magnetometry and x-ray detected ferromagnetic resonance (XFMR). Particular attention is paid to the anisotropy of damping processes that occur in thin films, and the different coupling mechanisms that can exist across non-magnetic spacer Layers in spin valves and magnetic tunnel junctions. It is first shown that the static and dynamic magnetic properties of thin Fe films can be effectively tailored by dilute doping with Dy impurities, which introduces a sizeable anisotropy of Gilbert damping. The mechanism underlying this effect is discussed, as is the concurrent modification of the spin and orbital contributions to the magnetic moment. The focus then turns to magnetodynamics of ferromagnetic films coupled across a nonmagnetic spacer Layer, examining how different materials permit different interactions. First, an insulating MgO Layer is used to separate the FM Layers; it is found that this attenuates a spin current in under 1~nm, but permits a static interaction for at least 2 nm. XFMR measurements are used to ascertain the different contributions of the two interactions, and shed light on their interplay. Next, the same techniques are applied to spin valves with a spacer Layer of the topological insulator (TI) Bi2Se3. TIs are the subject of much attention in the physics community, as they hold the potential for dissipationless transport, extremely high spin-orbit torques, and a host of novel physical effects. Here, their ability to absorb and transmit a pure spin current is studied, testing their suitability for incorporation into existing device schemata. VNA-FMR measurements confirm that the TI functions as an efficient angular momentum Sink. XFMR measurements, however, demonstrate the presence of a weak interaction between the two ferromagnets, able to persist up to at least 8~nm, and possibly mediated by the topological surface state. Finally, the angle-dependence of spin pumping through a Cr barrier is examined, finding that a strong anisotropy of spin pumping from the source Layer can be induced by an angular dependence of the total Gilbert damping parameter in the spin Sink Layer. VNA-FMR measurements show that anisotropy is suppressed above the spin diffusion length in Cr, which is found to be 8 nm, and is independent of static exchange coupling in the spin valve. XFMR results confirm induced precession in the spin Sink Layer, with isotropic static exchange and an anisotropic dynamic exchange. Taken together, these studies provide an insight not only into the magnetisation dynamics of thin films (and ways to modify them) but a demonstration of the power of ferromagnetic resonance techniques, and their applicability across materials and concepts. The results offer valuable information on the transmission and absorption of spin currents by different materials, and several mechanisms by which enhanced spin torques and angular control of damping may be realized for next-generation spintronic devices.
G. Van Der Laan - One of the best experts on this subject based on the ideXlab platform.
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Dependence of spin pumping and spin transfer torque upon Ni81Fe19 thickness in Ta/Ag/Ni81Fe19/Ag/Co2MnGe/Ag/Ta spin-valve structures
Physical Review B, 2017Co-Authors: C. J. Durrant, L. R. Shelford, R. A. J. Valkass, R. J. Hicken, Adriana I. Figueroa, Alexander A. Baker, G. Van Der Laan, L. B. Duffy, P. Shafer, Christoph KleweAbstract:Author(s): Durrant, CJ; Shelford, LR; Valkass, RAJ; Hicken, RJ; Figueroa, AI; Baker, AA; Van Der Laan, G; Duffy, LB; Shafer, P; Klewe, C; Arenholz, E; Cavill, SA; Childress, JR; Katine, JA | Abstract: © 2017 American Physical Society. Spin pumping has been studied within Ta / Ag / Ni81Fe19 (0-5 nm) / Ag (6 nm) / Co2MnGe (5 nm) / Ag / Ta large-area spin-valve structures, and the transverse spin current absorption of Ni81Fe19 Sink Layers of different thicknesses has been explored. In some circumstances, the spin current absorption can be inferred from the modification of the Co2MnGe source Layer damping in vector network analyzer ferromagnetic resonance (VNA-FMR) experiments. However, the spin current absorption is more accurately determined from element-specific phase-resolved x-ray ferromagnetic resonance (XFMR) measurements that directly probe the spin transfer torque (STT) acting on the Sink Layer at the source Layer resonance. Comparison with a macrospin model allows the real part of the effective spin mixing conductance to be extracted. We find that spin current absorption in the outer Ta Layers has a significant impact, while Sink Layers with thicknesses of less than 0.6 nm are found to be discontinuous and superparamagnetic at room temperature, and lead to a noticeable increase of the source Layer damping. For the thickest 5-nm Sink Layer, increased spin current absorption is found to coincide with a reduction of the zero frequency FMR linewidth that we attribute to improved interface quality. This study shows that the transverse spin current absorption does not follow a universal dependence upon Sink Layer thickness but instead the structural quality of the Sink Layer plays a crucial role.
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Anisotropic Absorption of Pure Spin Currents
Physical review letters, 2016Co-Authors: Alexander A. Baker, Adriana I. Figueroa, Christopher Love, Stuart A. Cavill, Thorsten Hesjedal, G. Van Der LaanAbstract:Spin transfer in magnetic multiLayers offers the possibility of ultrafast, low-power device operation. We report a study of spin pumping in spin valves, demonstrating that a strong anisotropy of spin pumping from the source Layer can be induced by an angular dependence of the total Gilbert damping parameter, α, in the spin Sink Layer. Using lab- and synchrotron-based ferromagnetic resonance, we show that an in-plane variation of damping in a crystalline Co_{50}Fe_{50} Layer leads to an anisotropic α in a polycrystalline Ni_{81}Fe_{19} Layer. This anisotropy is suppressed above the spin diffusion length in Cr, which is found to be 8 nm, and is independent of static exchange coupling in the spin valve. These results offer a valuable insight into the transmission and absorption of spin currents, and a mechanism by which enhanced spin torques and angular control may be realized for next-generation spintronic devices.
Adriana I. Figueroa - One of the best experts on this subject based on the ideXlab platform.
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Dependence of spin pumping and spin transfer torque upon Ni81Fe19 thickness in Ta/Ag/Ni81Fe19/Ag/Co2MnGe/Ag/Ta spin-valve structures
Physical Review B, 2017Co-Authors: C. J. Durrant, L. R. Shelford, R. A. J. Valkass, R. J. Hicken, Adriana I. Figueroa, Alexander A. Baker, G. Van Der Laan, L. B. Duffy, P. Shafer, Christoph KleweAbstract:Author(s): Durrant, CJ; Shelford, LR; Valkass, RAJ; Hicken, RJ; Figueroa, AI; Baker, AA; Van Der Laan, G; Duffy, LB; Shafer, P; Klewe, C; Arenholz, E; Cavill, SA; Childress, JR; Katine, JA | Abstract: © 2017 American Physical Society. Spin pumping has been studied within Ta / Ag / Ni81Fe19 (0-5 nm) / Ag (6 nm) / Co2MnGe (5 nm) / Ag / Ta large-area spin-valve structures, and the transverse spin current absorption of Ni81Fe19 Sink Layers of different thicknesses has been explored. In some circumstances, the spin current absorption can be inferred from the modification of the Co2MnGe source Layer damping in vector network analyzer ferromagnetic resonance (VNA-FMR) experiments. However, the spin current absorption is more accurately determined from element-specific phase-resolved x-ray ferromagnetic resonance (XFMR) measurements that directly probe the spin transfer torque (STT) acting on the Sink Layer at the source Layer resonance. Comparison with a macrospin model allows the real part of the effective spin mixing conductance to be extracted. We find that spin current absorption in the outer Ta Layers has a significant impact, while Sink Layers with thicknesses of less than 0.6 nm are found to be discontinuous and superparamagnetic at room temperature, and lead to a noticeable increase of the source Layer damping. For the thickest 5-nm Sink Layer, increased spin current absorption is found to coincide with a reduction of the zero frequency FMR linewidth that we attribute to improved interface quality. This study shows that the transverse spin current absorption does not follow a universal dependence upon Sink Layer thickness but instead the structural quality of the Sink Layer plays a crucial role.
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Effect of Sink Layer thickness on damping in CoMnGe (5 nm) / Ag (6 nm) / NiFe (x nm) spin valves
2016Co-Authors: R. A. J. Valkass, C. J. Durrant, L. R. Shelford, Adriana I. Figueroa, Alexander A. Baker, Padraic Shafer, Elke Arenholz, Jeffrey R. Childress, Jordan A. Katine, Gerrit Van Der LaanAbstract:We thank the Advanced Light Source for access to beamlines 4.0.2 and 6.3.1 (ALS-06433, ALS-07116). The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
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Anisotropic Absorption of Pure Spin Currents
Physical review letters, 2016Co-Authors: Alexander A. Baker, Adriana I. Figueroa, Christopher Love, Stuart A. Cavill, Thorsten Hesjedal, G. Van Der LaanAbstract:Spin transfer in magnetic multiLayers offers the possibility of ultrafast, low-power device operation. We report a study of spin pumping in spin valves, demonstrating that a strong anisotropy of spin pumping from the source Layer can be induced by an angular dependence of the total Gilbert damping parameter, α, in the spin Sink Layer. Using lab- and synchrotron-based ferromagnetic resonance, we show that an in-plane variation of damping in a crystalline Co_{50}Fe_{50} Layer leads to an anisotropic α in a polycrystalline Ni_{81}Fe_{19} Layer. This anisotropy is suppressed above the spin diffusion length in Cr, which is found to be 8 nm, and is independent of static exchange coupling in the spin valve. These results offer a valuable insight into the transmission and absorption of spin currents, and a mechanism by which enhanced spin torques and angular control may be realized for next-generation spintronic devices.
David G. Cahill - One of the best experts on this subject based on the ideXlab platform.
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Thermal spin-transfer torque driven by the spin-dependent Seebeck effect in metallic spin-valves
Nature Physics, 2015Co-Authors: Gyung-min Choi, Chul-hyun Moon, Byoung-chul Min, Kyung-jin Lee, David G. CahillAbstract:The coupling of spin and heat gives rise to new physical phenomena in nanoscale spin devices. In particular, spin-transfer torque (STT) driven by thermal transport provides a new way to manipulate local magnetization. We quantify thermal STT in metallic spin-valve structures using an intense and ultrafast heat current created by picosecond pulses of laser light. Our result shows that thermal STT consists of demagnetization-driven and spin-dependent Seebeck effect (SDSE)-driven components; the SDSE-driven STT becomes dominant after 3 ps. The sign and magnitude of the SDSE-driven STT can be controlled by the composition of a ferromagnetic Layer and the thickness of a heat Sink Layer. The spin-dependent Seebeck effect converts thermal gradients into spin currents. It is now shown that this effect can be used to drive spin-transfer torques on picosecond timescales using the heat currents created by ultrafast pulses of laser light.
Q. Y. Jin - One of the best experts on this subject based on the ideXlab platform.
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Role of the Heat Sink Layer Ta for Ultrafast Spin Dynamic Process in Amorphous TbFeCo Thin Films
2017Co-Authors: Y. Ren, Zongzhi Zhang, T. Min, Q. Y. JinAbstract:The ultrafast demagnetization processes (UDP) in Ta (t nm)/TbFeCo (20 nm) films have been studied using the time-resolved magneto-optical Kerr effect (TRMOKE). With a fixed pump fluence of 2 mJ/cm2, for the sample without a Ta underLayer (t=0nm), we observed the UDP showing a two-step decay behavior, with a relatively longer decay time (τ2) around 3.0 ps in the second step due to the equilibrium of spin-lattice relaxation following the 4f occupation. As a 10nm Ta Layer is deposited, the two-step demagnetization still exists while τ2 decreases to ∼1.9ps. Nevertheless, the second-step decay (τ2=0ps) disappears as the Ta Layer thickness is increased up to 20 nm, only the first-step UDP occurs within 500 fs, followed by a fast recovery process. The rapid magnetization recovery rate strongly depends on the pump fluence. We infer that the Ta Layer provides conduction electrons involving the thermal equilibrium of spin-lattice interaction and serves as heat bath taking away energy from spins of TbFeCo alloy film in UDP.
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Role of the Heat Sink Layer Ta for Ultrafast Spin Dynamic Process in Amorphous TbFeCo Thin Films
SPIN, 2017Co-Authors: Y. Ren, Z. Z. Zhang, T. Min, Q. Y. JinAbstract:The ultrafast demagnetization processes (UDP) in Ta ([Formula: see text] nm)/TbFeCo (20 nm) films have been studied using the time-resolved magneto-optical Kerr effect (TRMOKE). With a fixed pump fluence of 2 mJ/cm2, for the sample without a Ta underLayer ([Formula: see text][Formula: see text]nm), we observed the UDP showing a two-step decay behavior, with a relatively longer decay time ([Formula: see text] around 3.0 ps in the second step due to the equilibrium of spin-lattice relaxation following the 4[Formula: see text] occupation. As a 10[Formula: see text]nm Ta Layer is deposited, the two-step demagnetization still exists while [Formula: see text] decreases to [Formula: see text]1.9[Formula: see text]ps. Nevertheless, the second-step decay ([Formula: see text]) disappears as the Ta Layer thickness is increased up to 20 nm, only the first-step UDP occurs within 500 fs, followed by a fast recovery process. The rapid magnetization recovery rate strongly depends on the pump fluence. We infer that the Ta Layer provides conduction electrons involving the thermal equilibrium of spin-lattice interaction and serves as heat bath taking away energy from spins of TbFeCo alloy film in UDP.
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Effect of heat Sink Layer on ultrafast magnetization recovery of FeCo films
Journal of Physics D: Applied Physics, 2008Co-Authors: Yun-zhu Ren, J Q Zhao, Zongzhi Zhang, Q. Y. Jin, S M ZhouAbstract:For FeCo alloy thin films with Ag, Cu, Pt, Ta and Cr as heat Sink Layers, ultrafast demagnetization and recovery processes of transient magnetization have been studied by the time-resolved magneto-optical Kerr effect. For all samples, the ultrafast demagnetization process is accomplished within almost the same time interval of 500 fs, which is independent of the heat Sink Layer material and the pump fluence. The recovery rate of the FeCo film grown on the Si(1 0 0) substrate is enhanced with a heat Sink Layer. In addition, the recovery rate is found to be independent of the heat Sink Layer thickness; it decreases with increasing pump fluence. Among all heat Sink Layers, the sample with the Cr Layer achieves the highest recovery rate because it has the same bcc structure as that of the FeCo Layer and the small lattice mismatch. The sample with the Ta Layer, has the largest damage threshold of pump fluence because of the highest melting point.