RESARCH


Enhanced interface perpendicular magnetic anisotropy

 - Interface perpendicular magnetic anisotropy increases upon doping the Ta underlayer with nitrogen.
- Nitrogen doped Ta shows smaller magnetic dead layer thickness than that of pure Ta.
- Out of plane bulk magnetic anisotropy found in many films.


Reference
J. Sinha, M. Hayashi, A. Kent, S. Fukami, M. Yamanouchi, H. Sato, S. Ikeda, S. Mitani, S. Yang, S. S. P. Parkin and H. Ohno.
Enhanced interface perpendicular magnetic anisotropy in Ta-CoFeB-MgO using nitrogen doped Ta underlayers.
Appl. Phys. Lett. 102, 242405 (2013).




Vector measurments of current induced torques in magnetic heterostructures

 - Current induced effective field in Ta|CoFeB|MgO magnetic heterostructure.
- Vector measurements of the effective field (fields parallel and transerse to the current direction).
- Effective field increases with Ta thickness.
- Sign changes at low Ta thickness.
- Transverse field is larger than the longitudinal field for thick Ta regime, i.e. a large field-like term.
- Field like term is opposite to the conventional field like term for spin Hall spin torque.


Reference
J. Kim, J. Sinha, M. Hayashi, M. Yamanouchi, S. Fukami, T. Suzuki, S. Mitani, and H. Ohno.
Layer thickness dependence of the current induced effective field vector in Ta|CoFeB|MgO.
Nature Mater. 12, 240 (2013).

Related materials
APS March meeting, Baltimore (2013).




Spin Hall angle of Pt and Pd

 - Thickness dependence of the spin current-induced ferromagnetic resonance in Ni80Fe20/nonmagnetic (Pt,Pd) bilayer thin films.
- Spin Hall angle of Pt~0:022 and Pd~0:008.
- Spin diffusion length of Pt~1:2nm and Pd~2:0nm.


Reference
Evaluation of spin Hall angle and spin diffusion length by using spin current-induced ferromagnetic resonance.
K. Kondou, H. Sukegawa, S. Mitani, K. Tsukagoshi, S. Kasai.
APEX. 5, 073002 (2012).




Magnetic Tunnel Junctions with Perpendicular Co2FeAl Heusler Alloy

 - Perpendicularly magnetized magnetic tunnel junctions (p-MTJs) with an ultrathin Co2FeAl (CFA) full-Heusler alloy electrode.
- Out-of-plane tunnel magnetoresistance (TMR) ratio of 53% at room temperature in CFA/MgO/Co20Fe60B20 p-MTJs.
- TMR ratio enhanced to 91% by inserting a 0.1-nm-thick Fe layer between the MgO and /Co20Fe60B20 layers.
- Bias voltage dependence of differential conductance did not clearly show coherent tunneling characteristics.


Reference
Magnetic Tunnel Junctions with Perpendicular Anisotropy Using a Co2FeAl Full-Heusler Alloy.
Z. C. Wen, H. Sukegawa, S. Kasai, M. Hayashi, S. Mitani, and K. Inomata.
Appl. Phys. Exp. 5, 063003 (2012).




Resonant domain wall nucleation

 - Domain wall nucleation with microwave field in permalloy nanowires.
- Resonance frequency coincides with the excitation frequency for the FMR uniform mode.
- Nucleation field drops by a factor of two compared to off resonant nucleation.


Reference
M. Hayashi, Y. K. Takahashi, and S. Mitani.
Microwave assisted resonant domain wall nucleation in permalloy nanowires.
Appl. Phys. Lett., 101, 172406 (2012).




Spin-transfer switching in full-Heusler Co2FeAl-based magnetic tunnel junctions

 - Magnetic tunnel junctions (MTJs) with a full-Heusler alloy Co2FeAl (CFA).
- "CFA-free": CFA(1.5 nm)/MgO/CoFe(4 nm) and "CFA-reference": CFA(30 nm)/MgO/CoFeB(2 nm) MTJs on Cr(001) layer.
- "CFA-free": JC0=2.9x107 A/cm2.
- "CFA-reference": JC0=7.1x106 A/cm2.
- Large Gilbert damping of ~0.4 in "CFA-free" due to the Cr layer.


Reference
Spin-transfer switching in full-Heusler Co2FeAl-based magnetic tunnel junctions.
H. Sukegawa, Z. C. Wen, K. Kondou, S. Kasai, S. Mitani, and K. Inomata.
Appl. Phys. Lett. 100 (2012) 182403.




Realtime detection of the Spinmotive force

 - Time resolved measurements of the voltage (spinmotive force) generated when a domain wall propagates along a magnetic nanowire.
- Spinmotive force in permalloy nanowires.
- Generated voltage scales with the driving magnetic field.
- Voltage sign changes when the domain wall propagation direction is reversed.
- Scaling of the voltage with magnetic field indicates current spin polarization of 0.55-0.69.


Reference
M. Hayashi, J. Ieda, Y. Yamane, J.Ohe, Y. K. Takahashi, S. Mitani, and S. Maekawa.
Time-Domain Observation of the Spinmotive Force in Permalloy Nanowires.
Phys. Rev. Lett. 108, 147202 (2012).





Spatial control of magnetic anisotropy

 - Spatial patterning of magnetic anisotropy in CoFeB|MgO.
- Anisotropy of the CoFeB layer determined by the amount of etching of the MgO layer.
- Regions where MgO is half-etched show in-plane easy axis, otherwise it is out of plane.
- In-plane|out of plane domains form 90 deg domain walls.
- Presence of the 90 deg domain walls allows current induced injection of domain walls.


Reference
Spatial control of magnetic anisotropy for current induced domain wall injection in perpendicularly magnetized CoFeB|MgO nanostructures.
M. Hayashi, M. Yamanouchi, S. Fukami, J. Sinha, S. Mitani, and H. Ohno.
Appl. Phys. Lett. 100, 192411 (2012).




Perpendicular magnetic anisotropy in Co2FeAl Heusler alloy

 - Perpendicular magnetization in full-Heusler alloy Co2FeAl (CFA) films using CFA|MgO and MgO|CFA structures.
- Interfacial magnetic anisotropy at the CFA|MgO interface.
- Perpendicular magnetic anisotropy energy density (KU) of 2-3x106 erg/cm3.


Reference
Perpendicular magnetization of Co2FeAl full-Heusler alloy films induced by MgO interface
Z. C. Wen, H. Sukegawa, S. Mitani and K. Inomata
Appl. Phys. Lett. 98, 242507 (2011).




Narrow linewdith spin torque oscillators using Co2Fe(Ge0.5Ga0.5) Heusler alloy

 - Microwave emission from pseudo spin valve nanopillars with Heusler alloy Co2Fe(Ge0.5Ga0.5) electrodes.
- Large emission amplitude exceeding 150 nV/Hz0.5 and narrow generation linewidth below 10MHz.
- Reduced non-linear phase noise by tuing the applied field magnitude and its angle within the film plane.


Reference
Large amplitude microwave emission and reduced nonlinear phase noise in Co2Fe(Ge0.5Ga0.5) Heusler alloy based pseudo spin valve nanopillars
J. Sinha, M. Hayashi, Y. K. Takahashi, T. Taniguchi, M. Drapeko, S. Mitani and K. Hono
Appl. Phys. Lett. 99, 162508 (2011).




Spin dependent resonant tunneling

 - Fully epitaxial Cr(001)/ultrathin Fe(001)/MgO(001)/Fe(001) tunnel junctions.
- Sharp resonant conductance peaks due to the Fe quantum-well layer.
- Symmetry-selective transport via MgO barrier.



Reference
Correlation between symmetry-selective transport and spin-dependent resonant tunneling in fully epitaxial Cr/ultrathin-Fe/MgO/Fe(001) magnetic tunnel junctions
T. Niizeki, H. Sukegawa, S. Mitani, N. Tezuka and K. Inomata
Appl. Phys. Lett. 99, 182508 (2011).




Magnetic tunnel junctions with Spinel MgAl2O4 barrier

 - Fully epitaxial Fe/MgAl2O4/Fe(001) magnetic tunnel junctions.
- MgAl2O4: (001)-oriented spinel-type structure.
- A small lattice mismatch (~1%) between Fe and MgAl2O4.
- Tunnel magnetoresistance (TMR) ratios up to 117% (165%) obtained at room temperature (15 K).
- Large Vhalf, ranging from 1.0 to 1.3 V at room temperature.



Reference
Tunnel Magnetoresistance with Improved Bias Voltage Dependence in Lattice-Matched Fe/Spinel MgAl2O4/Fe(001) Junctions
H. Sukegawa, H. Xiu, T. Ohkubo, T. Furubayashi, T. Niizeki, W. Wang, S. Kasai, S. Mitani, K. Inomata, and K. Hono
Appl. Phys. Lett. 96, 212505 (2010).




Spin transfer magnetization switching in full-Heusler Co2FeAl0.5Si0.5 spin valves

 - Epitaxial spin-valve nanopillar with a half-metallic full-Heusler Co2FeAl0.5Si0.5 (CFAS) alloy.
- Giant magnetoresistance ratio of 7%-9% in CFAS/Ag/CFAS.
- Spin-transfer switching with a relatively small dc current (~106 A/cm2).
- Statistical analysis based on a thermal activation model.
- Averaged critical current density JC0 of 9.3x106 A/cm2 with a thermal stability factor KV/kBT of 40.



Reference
Spin-transfer switching in an epitaxial spin-valve nanopillar with a full-Heusler Co2FeAl0.5Si0.5 alloy
H. Sukegawa, S. Kasai, T. Furubayashi, S. Mitani, and K. Inomata
Appl. Phys. Lett. 96, 042508 (2010).

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