Kazuya Suzuki

Structure and magnetic properties of Bi-Zn-Fe-O amorphous films

Strong ferromagnet-like glasses have been prepared by rapidly quenching the molten mixture of antiferromagnetic BiFeO 3 and ZnFe 2 O 4 and by depositing simultaneously the ionized clusters of Bi, Zn and Fe atoms in a low pressure oxygen gas atmosphere. The Curie temperature of the glasses appears at 460-510 K and the magnetization reaches about 15-20 emu/g at 10 kOe at room temperature. Based on the Mossbauer effect and EXAFS measurements, the glass is concluded to be a speromagnet consisting of magnetic spins localized on each Fe atom tetrahedrally surrounded by four 0 atoms.

Laser-induced THz magnetization precession for a tetragonal Heusler-like nearly compensated ferrimagnet

Laser-induced magnetization precessional dynamics was investigated in epitaxial films of Mn

TETRAGONAL HEUSLER-LIKE Mn–Ga ALLOYS BASED PERPENDICULAR MAGNETIC TUNNEL JUNCTIONS

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Magnetic properties of ultrathin tetragonal Heusler D022-Mn3Ge perpendicular-magnetized films

Ge, which is a tetragonal Heusler-like nearly compensated ferrimagnet. The ferromagnetic resonance (FMR) mode was observed, the precession frequency for which exceeded 0.5 THz and originated from the large magnetic anisotropy field of approximately 200 kOe for this ferrimagnet. The effective damping constant was approximately 0.03. The corresponding effective Landau-Lifshitz constant of approximately 60 Mrad/s and is comparable to those of the similar Mn-Ga materials. The physical mechanisms for the Gilbert damping and for the laser-induced excitation of the FMR mode were also discussed in terms of the spin-orbit-induced damping and the laser-induced ultrafast modulation of the magnetic anisotropy, respectively.

Current-induced spin–orbit torque magnetization switching in a MnGa/Pt film with a perpendicular magnetic anisotropy

Films of the Mn-based tetragonal Heusler-like alloys, such as Mn–Ga, exhibit a large perpendicular magnetic anisotropy (PMA), small damping constant, small saturation magnetization and large spin polarizations. These properties are attractive for the application to the next generation high density spin-transfer-torque (STT) magnetic random access memory (STT-MRAM). We reviewed the structure, magnetic properties and Gilbert damping of the alloy films with large PMA, and the current status of research on tunnel magnetoresistance (TMR) in perpendicular magnetic tunnel junctions (p-MTJs) based on Mn-based tetragonal Heusler-like alloy electrode, and also discuss the issues for the application of those to STT-MRAM.

Magnetic tunnel junctions with an equiatomic quaternary CoFeMnSi Heusler alloy electrode

We investigated the crystal structure and magnetic properties of Manganese-germanium (Mn3Ge) films having the tetragonal D022 structure, with varied thicknesses (5–130 nm) prepared on chromium (Cr)-buffered single crystal MgO(001) substrates. A crystal lattice elongation in the in-plane direction, induced by the lattice mismatch between the D022-Mn3Ge and the Cr buffer layer, increased with decreasing thickness of the D022-Mn3Ge layer. The films exhibited clear magnetic hysteresis loops with a squareness ratio close to unity, and a step-like magnetization reversal even at a 5-nm thickness under an external field perpendicular to the films plane. The uniaxial magnetic anisotropy constant of the films showed a reduction to less than 10 Merg/cm3 in the small thickness range (≤20 nm), likely due to the crystal lattice elongation in the in-plane direction.

Room temperature magnetoresistance in an organic spin valve with an aromatic hydrocarbon macrocycle

Current-induced magnetization switching is demonstrated in a micron sized Hall bar consisting of Pt-capped ultrathin ferrimagnetic MnGa films. The films showed a low magnetization M s 150 kA/m and a large perpendicular magnetic anisotropy (PMA) field T, indicating a PMA thickness t product mJ/m2, which is relatively larger than those reported for other material films with PMA. Magnetization switching induced by an in-plane electrical current was examined with the application of an in-plane magnetic field. The phase diagram of the switching current vs the in-plane magnetic field is qualitatively consistent with that of the torque due to the spin-Hall effect in the Pt layer.

Magnetic relaxation for Mn-based compounds exhibiting the Larmor precession at THz wave range frequencies

Tunnel magnetoresistance (TMR) in MgO-based magnetic tunnel junctions (MTJs) with equiatomic quaternary CoFeMnSi Heusler and CoFe alloy electrodes is studied. The epitaxial MTJ stacking structures were prepared using ultrahigh-vacuum magnetron sputtering, where the CoFeMnSi electrode has a full B2 and partial L21 ordering crystal structure. Maximum TMR ratios of 101% and 521% were observed at room temperature and 10 K, respectively, for the MTJs. The large bias voltage dependence of the TMR ratio was also observed at low temperature (LT), as similarly observed in Co2MnSi Heusler alloy-based MTJs in the past. The physical origins of this relatively large TMR ratio at LT were discussed in terms of the half-metallicity of CoFeMnSi.

Engineered Heusler Ferrimagnets with a Large Perpendicular Magnetic Anisotropy

Aromatic hydrocarbon macrocycles, which have a conjugated π-electron system, are potentially useful for various organic device applications, although there have been no attempts to apply them to organic spin valves (OSVs). Here, we studied OSVs with [6]cyclo-2,7-naphthylene (CNAP), a type of aromatic hydrocarbon macrocycle. OSV stacking structures of Co/AlOx/CNAP/Ni80Fe20 with different CNAP thicknesses were fabricated, and the transport properties of the OSVs were measured from 300 to 5 K. A magnetoresistance of approximately 1%-2% at 300 K (4%-6% at 5 K) was observed for 15-nm-thick OSVs, showing the potential for organic spintronics based on aromatic hydrocarbon macrocycles.

Magneto-optical Kerr effect characterization of a uniform nanocrystalline Fe3O4 monolayer fabricated on a silicon substrate functionalized with catechol groups

Mn-based hard magnets are potentially suitable for advanced ultra-high frequency spintronics applications because they exhibit the Larmor precession of magnetization at THz wave-range frequencies with low magnetic relaxation. However, the low magnetic relaxation properties are not well understood; thus, a more detailed study is necessary. In this study, magnetization precessions in L10 Mn1.54Ga, D022 Mn2.12Ga, and C38 MnAlGe epitaxial films grown on MgO substrates were investigated using an all-optical pump-probe method under a magnetic field of ∼20 kOe. The coherent magnetization precessions at frequencies of more than 0.1, 0.2, and 0.3 THz for the C38 MnAlGe, L10 Mn1.54Ga, and D022 Mn2.12Ga films, respectively, were clearly measured. The effective damping constant for the C38 MnAlGe film was smaller than the previously reported value measured at 10 kOe by a factor of 2, whereas those showed a large angular dependence. The effective damping constants for the L10 Mn1.54Ga and D022 Mn2.12Ga films were inde...