Yuta Sasaki

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

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.

Evaluation of Thin Film Noise Suppressor Applied to Noise Emulator Chip Implemented in 65 nm CMOS Technology

This paper reports the shielding effect of soft magnetic film as a thin film noise suppressor applied to a test chip implemented in 65 nm seven metal CMOS technology. This test chip is equipped with a noise generator circuit. The 0.2-1- μm-thick magnetic films, which are integrated with polyimide substrates, are mounted onto the noise generator circuit in the test chip, and 2-μm-thick magnetic film is directly integrated to the passivation of the test chip. These films are deposited by RF magnetron spattering. The shield effect is evaluated by magnetic near-field measurement using planar shielded loop probe and 3-D full-wave electromagnetic field simulation. As a result, we successfully demonstrate a shield effect of 7.7 dB at a crock frequency of 200 MHz with 2-μ m-thick CoZrNb film. Furthermore, the result of the thickness dependence of the shielding effect revealed that a permeability-thickness product (μr × tm) of 1 950 μ m is required as the design target for obtaining 10 dB suppression.

Ultrafast demagnetization of L10 FePt and FePd ordered alloys

The cause of the time scale for ultrafast demagnetization induced by irradiation using a fs pulse laser remains an open issue. Spin-flip mediated by electron–phonon scattering due to spin–orbit interactions is one major theory proposed to explain ultrafast demagnetization. Ultrafast demagnetization in Ni, FePd, and FePt films was investigated in order to systematically study the influence of heavy elements on the demagnetization time. The ultrafast demagnetization in these systems was analyzed using the microscopic three temperature model, which is a theory based on spin-flip mediated by electron–phonon scattering. The spin-flip probability () values for the Ni, FePd, and FePt films were evaluated in the low pump fluence regime. It was found that the value for the Ni film was larger than that for the FePd and FePt films. Thus, there is no correlation between the value and the spin–orbit coupling strength. Fast demagnetization of the FePd film was also observed due to large electron–phonon scattering. In addition, it was found that the values decreased with increasing magnetization quenching for all the films.

All-optical detection of magnetization precession in tunnel junctions under applied voltage

An all-optical time-resolved magneto-optical Kerr effect measurement of a micron-sized tunnel junction with a CoFeB electrode was performed. The femtosecond (fs) laser-induced magnetization precession was clearly observed at various magnetic field angles. The frequency f and relaxation time τ of the magnetization precession varied with the voltage applied via a MgO barrier. The precession dynamics were in accordance with Kittels ferromagnetic resonance mode, and the voltage-induced changes in f and τ were well explained by the voltage-induced change in the perpendicular magnetic anisotropy of −36 fJ/Vm.

Modulation of magnetization dynamics in an epitaxial Heusler ferromagnet due to pure spin current in a laterally configured structure

Using a laterally configured structure, we demonstrate modulation of the magnetization dynamics of an epitaxial Heusler ferromagnet, Fe3Si, by nonlocally injecting pure spin currents. From the ferromagnetic resonance signals, the effective Gilbert damping constant ([Formula: see text]) of the epitaxial Fe3Si nanomagnet is estimated to be  ∼0.003 at room temperature. By using the lateral and nonlocal spin injection, the [Formula: see text] value of the epitaxial Fe3Si nanomagnet can be modulated from 0.0034 to 0.0024. This study will open a way for control of the magnetization dynamics of high-performance ferromagnetic Heusler alloys due to pure spin currents even in laterally configured structures.

Spatially Resolved Pump-probe Magneto-optical Kerr Effect in Permalloy Films

Measurement set-up of the spatially resolved pump-probe magneto-optical Kerr effect was constructed to investigate laser-induced spin-wave propagation in micrometer region. One dimensional-space and time mapping of laser-induced change in Kerr rotation angle was successfully obtained in permalloy films and the wave packet propagation was clearly observed, which may be attributed to the spin-wave prop-