Research

Research

Spintronics is an emerging field as a new branch of electronics, in which the charges and spins of electrons are utilized. We are studying and developing new magnetic materials and spin-based functionalities for high-density nonvolatile solid-state memory and logic devices. In addition, fundamental studies on new phenomena and characterization methods in spintronics have been performed. These new spintronic devices are expected to contribute to the realization of low power consumption in the future electronics.
  • Large perpendicular magnetic anisotropy at Fe/MgO interfaces
  • Enhanced interface perpendicular magnetic anisotropy
  • Vector measurments of current induced torques in magnetic heterostructures
  • Enhanced tunnel magnetoresistance in a spinel oxide tunnel barrier with cation site disorder
  • Spin Hall angle of Pt and Pd
  • Magnetic Tunnel Junctions with Perpendicular Co2FeAl Heusler Alloy
  • Resonant domain wall nucleation
  • Spin-transfer switching in full-Heusler Co2FeAl-based magnetic tunnel junctions
  • Realtime detection of the Spinmotive force
  • Spatial control of magnetic anisotropy
  • Perpendicular magnetic anisotropy in Co2FeAl Heusler alloy
  • Narrow linewdith spin torque oscillators using Co2Fe(Ge0.5Ga0.5) Heusler alloy
  • Spin dependent resonant tunneling
  • Magnetic tunnel junctions with Spinel MgAl2O4 barrier
  • Spin transfer magnetization switching in full-Heusler Co2FeAl0.5Si0.5 spin valves
  • Large perpendicular magnetic anisotropy at Fe/MgO interfaces

    - Fe(5ML)/MgO[100] bilayer structures were prepared.
    - Small amount of absorbate on Fe(100) enhances interface perpendicular magnetic anisotropy.
    - Maximum PMA energy density of Keff = 14 Merg/cm3 was obtained.
    Reference
    J. W. Koo, S. Mitani, T. T. Sasaki, H. Sukegawa, Z. C. Wen, T. Ohkubo, T. Niizeki, K. Inomata and K. Hono.
    Large perpendicular magnetic anisotropy at Fe/MgO interfaces.
    Appl. Phys. Lett. 103, 192401 (2013)..

    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).

    Enhanced tunnel magnetoresistance in a spinel oxide tunnel barrier with cation site disorder

    - Large tunnel magnetoresistance of 308% at RT (479% at 15 K) was obtained by introducing cation site disorder into spinel oxide (MgAl2O4) tunnel barrier.
    - The enhancement can be interpreted as a band-folding effect in Fe.
    Reference
    H. Sukegawa, Y. Miura, S. Muramoto, S. Mitani, T. Niizeki, T. Ohkubo, K. Abe, M. Shirai, K. Inomata and K. Hono.
    Enhanced tunnel magnetoresistance in a spinel oxide barrier with cation-site disorder.
    Phys. Rev. B 86, 184401 (2012)..

    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).
    Page top