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Masashi Sahashi - One of the best experts on this subject based on the ideXlab platform.
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Soft magnetic characteristics of an ultrathin CoFeNi Free Layer in spin-valve films
Journal of Magnetism and Magnetic Materials, 2006Co-Authors: H. Fukuzawa, Hitoshi Iwasaki, K. Koi, Masashi SahashiAbstract:Abstract We have investigated the soft magnetic characteristics of an ultrathin Co-rich CoFeNi Free Layer in spin-valve films. By addition of Ni to a Co-rich CoFe Free Layer, magnetostriction ( λ ) of the films increased positively with Ni concentration, in contrast to which a Co90Fe10 Free Layer showed a negatively large λ . However, Ni addition also caused an increase in coercivity of the easy axis direction (Hce.a.). To avoid this problem, a slight decrease in the Co contents of a CoFeNi Free Layer was found to be effective for decreasing Hce.a.. In order to satisfy both the small λ and Hce.a., a Free Layer of (Co86Fe14)88−94Ni12−6 proved to be an optimum composition in spin-valve films. Moreover, the zero λ composition of the CoFeNi Free Layer was changed by a high-conductance Cu Layer deposited on the Free Layer, which was considered to come from the lattice strain of a Free Layer.
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Saturation magnetostriction of an ultrathin CoFe Free-Layer on double-Layered underLayers
Journal of Applied Physics, 2002Co-Authors: H. Fukuzawa, Hitoshi Iwasaki, Yuzo Kamiguchi, K. Koi, Masashi SahashiAbstract:We investigated the saturation magnetostriction (λs) of an ultrathin CoFe Free-Layer on double-Layered underLayers of Ru/Cu. By increasing the Ru underLayer thickness, λs becomes positively large; on the other hand, λs becomes negatively large by increasing the Cu underLayer thickness. This tendency can be explained by the model where λs is changed by the film strain. The λs sensitivity on the Cu underLayer thickness becomes large with increasing the Co concentration of the CoFe Free-Layer. This indicates that CoFe λs becomes sensitive to strain with increasing Co concentration. In order to realize small magnetostriction spin-valve films with an ultrathin CoFe Free-Layer, we have to take care of the lattice strain of the film.
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Spin-filter spin-valve films with an ultrathin CoFe Free Layer
Journal of Applied Physics, 2001Co-Authors: H. Fukuzawa, Hitoshi Iwasaki, Yuzo Kamiguchi, K. Koi, Masashi SahashiAbstract:The concept of spin-filter spin-valve (SFSV) films is reviewed. The dependence of the Free Layer structure on the spin-filter effect was investigated by using model films and two types of Free Layers were compared, a single CoFe Layer and a conventional NiFe/Co Free Layer. At the same magnetic thickness of the Free Layer, the SFSV films with a CoFe Free Layer showed a larger magnetoresistance (MR) ratio than those with a NiFe/Co Free Layer. This is partly attributed to the thinner CoFe Free Layer thickness, which is due to the fact that the CoFe Free Layer has higher Bs than the NiFe/Co Free Layer. Moreover, SFSV films with a CoFe Free Layer still showed a larger MR ratio when the Free Layer thickness was the same. It suggests that other factors contribute to the high MR performance, such as the quality of the interface between a Free Layer and a high conductance Layer. Film performance of MR 9% to 10%, ΔRs 1.5–2.0 Ω, Hcea∼3 Oe, and λs⩽±0.5 ppm was obtained with a single CoFe Free Layer and synthetic anti...
Hiroshi Imamura - One of the best experts on this subject based on the ideXlab platform.
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high emission power and q factor in spin torque vortex oscillator consisting of feb Free Layer
Applied Physics Express, 2014Co-Authors: Sumito Tsunegi, Hitoshi Kubota, Akio Fukushima, Hiroshi Imamura, Kay Yakushiji, Makoto Konoto, Shingo Tamaru, Hiroko Arai, Eva Grimaldi, Romain LebrunAbstract:Microwave oscillation properties of spin torque vortex oscillators (STVOs) consisting of an FeB vortex Free Layer were investigated. Because of a high MR ratio and large DC current, a high emission power up to 3.6 µW was attained in the STVO with a thin FeB Free Layer of 3 nm. In STOs with a thicker FeB Layer, e.g., 10 nm thick, we obtained a large Q factor greater than 6400 while maintaining a large integrated emission power of 1.4 µW. Such excellent microwave performance is a breakthrough for the mutual phase locking of STVOs by electrical coupling.
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Minimization of the Switching Time of a Synthetic Free Layer in Thermally Assisted Spin Torque Switching
Applied Physics Express, 2011Co-Authors: Tomohiro Taniguchi, Hiroshi ImamuraAbstract:We theoretically studied the thermally assisted spin torque switching of a synthetic Free Layer and showed that the switching time is minimized if the condition H_J=|H_s|/(2 alpha) is satisfied, where H_J, H_s and alpha are the coupling field of two ferromagnetic Layers, the amplitude of the spin torque, and the Gilbert damping constant. We also showed that the coupling field of the synthetic Free Layer can be determined from the resonance frequencies of the spin-torque diode effect.
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Angular dependence of spin transfer torque on magnetic tunnel junctions with synthetic ferrimagnetic Free Layer
Journal of Physics: Conference Series, 2010Co-Authors: Masahiko Ichimura, Saburo Takahashi, Hiroshi Imamura, Tomoyuki Hamada, Sadamichi MaekawaAbstract:Based on a spin-polarized Free-electron model, spin and charge transports are analyzed in magnetic tunnel junctions with synthetic ferrimagnetic Layers in the ballistic regime, and the spin transfer torque is derived. We characterize the synthetic ferrimagnetic Free Layer by extending an arbitrary direction of magnetizations of the two Free Layers forming the synthetic ferrimagnetic Free Layer. The synthetic ferrimagnetic configuration exerts the approximately optimum torque for small magnetization angle of the first Layer relative to that of the pinned Layer. For approximately anti-parallel magnetization of the first Layer to that of the pinned Layer, the parallel magnetization of two magnetic Layers is favorable for magnetization reversal rather than the synthetic ferrimagnetic configuration.
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dependence of critical current of spin transfer torque driven magnetization dynamics on Free Layer thickness
Journal of Applied Physics, 2009Co-Authors: Tomohiro Taniguchi, Hiroshi ImamuraAbstract:The dependence of the critical current of spin transfer torque-driven magnetization dynamics on the Free Layer thickness was studied by taking into account both the finite penetration depth of the transverse spin current and spin pumping. We showed that the critical current remains finite in the zero-thickness limit of the Free Layer for both parallel and antiparallel alignments. We also showed that the remaining value of the critical current of parallel to antiparallel switching is larger than that of antiparallel to parallel switching.
H. Fukuzawa - One of the best experts on this subject based on the ideXlab platform.
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Soft magnetic characteristics of an ultrathin CoFeNi Free Layer in spin-valve films
Journal of Magnetism and Magnetic Materials, 2006Co-Authors: H. Fukuzawa, Hitoshi Iwasaki, K. Koi, Masashi SahashiAbstract:Abstract We have investigated the soft magnetic characteristics of an ultrathin Co-rich CoFeNi Free Layer in spin-valve films. By addition of Ni to a Co-rich CoFe Free Layer, magnetostriction ( λ ) of the films increased positively with Ni concentration, in contrast to which a Co90Fe10 Free Layer showed a negatively large λ . However, Ni addition also caused an increase in coercivity of the easy axis direction (Hce.a.). To avoid this problem, a slight decrease in the Co contents of a CoFeNi Free Layer was found to be effective for decreasing Hce.a.. In order to satisfy both the small λ and Hce.a., a Free Layer of (Co86Fe14)88−94Ni12−6 proved to be an optimum composition in spin-valve films. Moreover, the zero λ composition of the CoFeNi Free Layer was changed by a high-conductance Cu Layer deposited on the Free Layer, which was considered to come from the lattice strain of a Free Layer.
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Saturation magnetostriction of an ultrathin CoFe Free-Layer on double-Layered underLayers
Journal of Applied Physics, 2002Co-Authors: H. Fukuzawa, Hitoshi Iwasaki, Yuzo Kamiguchi, K. Koi, Masashi SahashiAbstract:We investigated the saturation magnetostriction (λs) of an ultrathin CoFe Free-Layer on double-Layered underLayers of Ru/Cu. By increasing the Ru underLayer thickness, λs becomes positively large; on the other hand, λs becomes negatively large by increasing the Cu underLayer thickness. This tendency can be explained by the model where λs is changed by the film strain. The λs sensitivity on the Cu underLayer thickness becomes large with increasing the Co concentration of the CoFe Free-Layer. This indicates that CoFe λs becomes sensitive to strain with increasing Co concentration. In order to realize small magnetostriction spin-valve films with an ultrathin CoFe Free-Layer, we have to take care of the lattice strain of the film.
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Spin-filter spin-valve films with an ultrathin CoFe Free Layer
Journal of Applied Physics, 2001Co-Authors: H. Fukuzawa, Hitoshi Iwasaki, Yuzo Kamiguchi, K. Koi, Masashi SahashiAbstract:The concept of spin-filter spin-valve (SFSV) films is reviewed. The dependence of the Free Layer structure on the spin-filter effect was investigated by using model films and two types of Free Layers were compared, a single CoFe Layer and a conventional NiFe/Co Free Layer. At the same magnetic thickness of the Free Layer, the SFSV films with a CoFe Free Layer showed a larger magnetoresistance (MR) ratio than those with a NiFe/Co Free Layer. This is partly attributed to the thinner CoFe Free Layer thickness, which is due to the fact that the CoFe Free Layer has higher Bs than the NiFe/Co Free Layer. Moreover, SFSV films with a CoFe Free Layer still showed a larger MR ratio when the Free Layer thickness was the same. It suggests that other factors contribute to the high MR performance, such as the quality of the interface between a Free Layer and a high conductance Layer. Film performance of MR 9% to 10%, ΔRs 1.5–2.0 Ω, Hcea∼3 Oe, and λs⩽±0.5 ppm was obtained with a single CoFe Free Layer and synthetic anti...
P P Freitas - One of the best experts on this subject based on the ideXlab platform.
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Reduction of critical current in magnetic tunnel junctions with CoFeB/Ru/CoFeB synthetic Free Layer
Journal of Physics: Conference Series, 2010Co-Authors: A. J. Zaleski, Witold Skowroński, Maciej Czapkiewicz, Jarosław Kanak, Tomasz Stobiecki, Rita Macedo, Susana Cardoso, P P FreitasAbstract:Reduction of the critical current density (Jc) in magnetic tunnel junctions (MTJs) can be achieved by replacing the standard Co40Fe40B20 Free Layer with a synthetic antiferromagnet. Patterned MTJs prepared by ion-beam assisted deposition (nanopillars, sizes down to 60 nm × 80 nm) with 2 nm CoFeB Free Layer and Co40Fe40B20/Ru (tRu)/ Co40Fe40B20 as a synthetic Free Layer (SyF) were studied. We have measured critical current density of CIMS in thermally activated switching regime (long current pulses). Values of switching current densities for standard MTJs with SyF were of the order 106 A/cm2, whilst MTJs with standard Free Layer demonstrated up to four times higher values of Jc.
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field detection in mgo magnetic tunnel junctions with superparamagnetic Free Layer and magnetic flux concentrators
Journal of Applied Physics, 2009Co-Authors: J M Almeida, P P FreitasAbstract:Magnetic tunnel junctions (MTJs) were deposited with CoFeB Free Layer thickness ranging from 1.3 to 3 nm. The samples were processed with areas of 10, 100, and 1000 μm2, presented RA products of ∼10 kΩ μm2, and tunneling magnetoresistance ratio values varying from ∼10% (t=1.3 nm) to ∼210% (t=3 nm). All the samples with t<1.5 nm presented linear responses (coercivity of <1 Oe) for all the studied areas; this behavior was associated with the CoFeB Free Layer transition from ferromagnetic to superparamagnetic. Noise measurements made in samples with superparamagnetic Free Layer showed negligible magnetic noise in the sensitive region. The sensitivity loss caused by the reduced Free Layer thickness was partially recovered using magnetic flux concentrators (MFCs). The MFC had a maximum gain of ∼3, a limited value to ensure a uniform gain for the MTJs with larger area (up to 1000 μm2). The MFC’s influence on the sensor’s noise behavior appears to increase with the sensor area, for both white noise background an...
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Field detection in MgO magnetic tunnel junctions with superparamagnetic Free Layer and magnetic flux concentrators
Journal of Applied Physics, 2009Co-Authors: J M Almeida, P P FreitasAbstract:Magnetic tunnel junctions (MTJs) were deposited with CoFeB Free Layer thickness ranging from 1.3 to 3 nm. The samples were processed with areas of 10, 100, and 1000 μm2, presented RA products of ∼10 kΩ μm2, and tunneling magnetoresistance ratio values varying from ∼10% (t=1.3 nm) to ∼210% (t=3 nm). All the samples with t
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1 f magnetic noise dependence on Free Layer thickness in hysteresis Free mgo magnetic tunnel junctions
IEEE Transactions on Magnetics, 2008Co-Authors: P Wisniowski, J M Almeida, P P FreitasAbstract:The noise spectrum of MgO magnetic tunnel junctions with linear transfer curves for varying CoFeB Free Layer thickness was studied. For continuous ferromagnetic Free Layers (tCoFeB ges 15.5 A), the noise spectrum in the linear range is dominated by 1/f magnetic noise and random telegraph noise. When superparamagnetic behavior sets on the Free Layer (tCoFeB < 14.5 A) the junctions do not present 1/f magnetic noise. This cancellation of 1/f magnetic noise is done at the expense of field sensitivity. In terms of field detection limit, the junctions with thin and thick Free Layer show the same detection limit of 25 nT/Hz1/2 low frequency (500 Hz). At high frequency (100 kHz), however, junctions with thicker Free Layer show detection limit of 1.5 nT/Hz1/2, which is three times better than for thin Free Layer.
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effect of Free Layer thickness and shape anisotropy on the transfer curves of mgo magnetic tunnel junctions
Journal of Applied Physics, 2008Co-Authors: P Wiśniowski, Susana Cardoso, J M Almeida, N P Barradas, P P FreitasAbstract:A study of the combined effect of CoFeB Free Layer thickness, shape anisotropy, and annealing temperature on the transfer curves of MgO based magnetic tunnel junctions is presented. The response of the Free Layer changes gradually as its thickness decreases and shows hysteresis-Free response for CoFeB⩽15.5A. For junctions with CoFeB=15.5A, the onset of hysteresis-Free response depends on junction area and annealing temperature. Linearized magnetic tunnel junctions with dimensions down to 1.5×3μm2 and sensitivity as high as 7.7%∕Oe were achieved.
A D Kent - One of the best experts on this subject based on the ideXlab platform.
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sub nanosecond switching in a cryogenic spin torque spin valve memory element with a dilute permalloy Free Layer
Applied Physics Letters, 2019Co-Authors: Laura Rehm, Volker Sluka, Graham Rowlands, Minhhai Nguyen, Thomas A Ohki, A D KentAbstract:We present a study of pulsed current switching characteristics of spin-valve nanopillars with in-plane magnetized dilute permalloy and undiluted permalloy Free Layers in the ballistic regime at low temperatures. The dilute permalloy Free Layer device switches much faster: the characteristic switching time for a permalloy (Ni0.83Fe0.17) Free Layer device is 1.18 ns, while that for a dilute permalloy ([Ni0.83Fe0.17]0.6Cu0.4) Free Layer device is 0.475 ns. A ballistic macrospin model can capture the data trends with a reduced spin-torque asymmetry parameter, reduced spin polarization, and increased Gilbert damping for the dilute permalloy Free Layer relative to the permalloy devices. Our study demonstrates that reducing the magnetization of the Free Layer increases the switching speed while greatly reducing the switching energy and shows a promising route toward even lower power magnetic memory devices compatible with superconducting electronics.We present a study of pulsed current switching characteristics of spin-valve nanopillars with in-plane magnetized dilute permalloy and undiluted permalloy Free Layers in the ballistic regime at low temperatures. The dilute permalloy Free Layer device switches much faster: the characteristic switching time for a permalloy (Ni0.83Fe0.17) Free Layer device is 1.18 ns, while that for a dilute permalloy ([Ni0.83Fe0.17]0.6Cu0.4) Free Layer device is 0.475 ns. A ballistic macrospin model can capture the data trends with a reduced spin-torque asymmetry parameter, reduced spin polarization, and increased Gilbert damping for the dilute permalloy Free Layer relative to the permalloy devices. Our study demonstrates that reducing the magnetization of the Free Layer increases the switching speed while greatly reducing the switching energy and shows a promising route toward even lower power magnetic memory devices compatible with superconducting electronics.
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sub nanosecond switching in a cryogenic spin torque spin valve memory element with a dilute permalloy Free Layer
arXiv: Applied Physics, 2019Co-Authors: Laura Rehm, Volker Sluka, Graham Rowlands, Minhhai Nguyen, Thomas A Ohki, A D KentAbstract:We present a study of the pulsed current switching characteristics of spin-valve nanopillars with in-plane magnetized dilute permalloy and undiluted permalloy Free Layers in the ballistic regime at low temperature. The dilute permalloy Free Layer device switches much faster: the characteristic switching time for a permalloy Free (Ni0.83Fe0.17) Layer device is 1.18 ns, while that for a dilute permalloy ([Ni0.83Fe0.17]0.6Cu0.4) Free Layer device is 0.475 ns. A ballistic macrospin model can capture the data trends with a reduced spin torque asymmetry parameter, reduced spin polarization and increased Gilbert damping for the dilute permalloy Free Layer relative to the permalloy devices. Our study demonstrates that reducing the magnetization of the Free Layer increases the switching speed while greatly reducing the switching energy and shows a promising route toward even lower power magnetic memory devices compatible with superconducting electronics.
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spin transfer in biLayer magnetic nanopillars at high fields as a function of Free Layer thickness
Physical Review B, 2006Co-Authors: W Chen, M J Rooks, N Ruiz, A D KentAbstract:Spin transfer in asymmetric Co/Cu/Co biLayer magnetic nanopillars junctions has been studied at low temperature as a function of Free-Layer thickness. The phase diagram for current-induced magnetic excitations has been determined for magnetic fields up to 7.5 T applied perpendicular to the junction surface and Free-Layers thicknesses from 2 to 5 nm. The junction magnetoresistance is independent of thickness. The critical current for magnetic excitations decreases linearly with decreasing Free-Layer thickness, but extrapolates to a finite critical current in the limit of zero thickness. The limiting current is in quantitative agreement with that expected due to a spin-pumping contribution to the magnetization damping. It may also be indicative of a decrease in the spin-transfer torque efficiency in ultrathin magnetic Layers.
