Yuki Hisamatsu

Spin motive force induced in Fe3O4 thin films with negative spin polarization

Spin motive force (SMF) is induced by a time and spatial derivative of magnetizations and is dependent on spin polarization. We compare the SMF in FeNi with positive spin polarization with that in a magnetite (Fe3O4) with negative spin polarization. We observe the SMF induced by a nonuniform ferromagnetic resonance in Fe3O4 and find that the SMF in Fe3O4 is opposite to that in FeNi. This result originates from the negative spin polarization of Fe3O4. Our clear observation of the SMF depending on the sign of the spin polarization agrees well with the framework of the SMF theory.

Effect of lattice strain on cobalt ferrite Co0.75Fe2.25O4(111) thin films

We report the optimum conditions for the epitaxial growth of Co x Fe3− x O4 (CFO) (111) thin films with x = 0.75 on an α-Al2O3(0001) substrate via reactive RF magnetron sputtering. The lattice strain evaluated by X-ray diffraction measurements is as small as 0.11% in spite of the large lattice mismatch between CFO(111) and α-Al2O3(0001). The CFO(111) thin films grown under the optimal conditions exhibit magnetic anisotropy with the easy axis of magnetization perpendicular to the films. The induced uniaxial anisotropy energy can be quantitatively explained by the magnetoelastic effect.