Enhancement of low-frequency spin-orbit-torque ferromagnetic resonance signals by frequency tuning observed in Pt/Py, Pt/Co, and Pt/Fe bilayers

DC voltages via spin rectification effect (SRE), VDC, under microwave irradiation are investigated for three platinum (Pt)/ferromagnetic metal (FM) bilayer structures: Pt/Ni₈₀Fe₂₀, Pt/Co, and Pt/Fe. At the microwave frequency region lower than the resonant frequency, large VDC is obtained at zero DC magnetic field for all devices. In frequency dependence just around the resonant frequency, sharp rise and drop of magnitude in VDC are observed. These behaviors are well explained by the numerically calculated magnetic susceptibility. It is also found that the magnitude of VDC is strongly dependent on the slope of magnetoresistance spectrum. These findings lead to developments of sensitive detection technique for nano-scale magnetization switching

SPIN INJECTION INTO FERROMAGNETIC METAL FROM HEAVY METAL OWING TO SPIN HALL EFFECT

When a current flows through a heavy metal (HM), the spin of the current carriers is polarized by the spin Hall effect (SHE). In a junction of a HM and a ferromagnetic metal (FM), the spin current flows into the FM from the HM and gives spin-transfer torque to the magnetic moments of the FM. We calculate the spin current in a layer of HM/FM with the SHE. We use a spin-resolved electrochemical potential including the SHE in the calculation of the spin current. The spin current flowing into the FM depends strongly on the thickness of the HM.This work was supported by JSPS KAKENHI Grant Number JP20H0260

Electronic structures and magnetic moments of Co3FeN thin films grown by molecular beam epitaxy

We evaluated electronic structures and magnetic moments in Co3FeN epitaxial films on SrTiO3(001). The experimentally obtained hard x-ray photoemission spectra of the Co3FeN film have a good agreement with those calculated. Site averaged spin magnetic moments deduced by x-ray magnetic circular dichroism were 1.52 μ B per Co atom and 2.08 μ B per Fe atom at 100 K. They are close to those of Co4N and Fe4N, respectively, implying that the Co and Fe atoms randomly occupy the corner and face-centered sites in the Co3FeN unit cell

DEPTH-DEPENDENCE OF MAGNETIZATION AT A FERROMAGNET EDGE UNDER THE INTERFACIAL DZYALOSHINSKII-MORIYA INTERACTION

The interfacial Dzyaloshinskii-Moriya interaction (I-DMI) occurs in a ferromagnetic wire on a heavy metal. Magnetic moments (MMs) at the edge of the wire are forcibly canted by the I-DMI. The influence of the canting MM at the wire edge on the wire interior is unclear. Here, we theoretically investigate the MMs under the I-DMI. The effect of the canting of MMs at the edge of the interior is shown to increase with a smaller exchange energy and a larger perpendicular anisotropy. A cosine of the cant angle of the MMs decreases exponentially with distance from the edge.We are grateful to the Kansai University Fund for Supporting Young Scholars 2019.研究課題「スピンホール効果によるスピン注入を用いたナノ磁石磁化反転の高速化に向けた研究

Electrical detection of magnetic domain wall in Fe4N nanostrip by negative anisotropic magnetoresistance effect

The magnetic structure of the domain wall (DW) of a 30-nm-thick Fe4N epitaxial film with a negative spin polarization of the electrical conductivity is observed by magnetic force microscopy and is well explained by micromagnetic simulation. The Fe4N film is grown by molecular beam epitaxy on a SrTiO3(001) substrate and processed into arc-shaped ferromagnetic nanostrips 0.3 μm wide by electron beam lithography and reactive ion etching with Cl2 and BCl3 plasma. Two electrodes mounted approximately 12 μm apart on the nanostrip register an electrical resistance at 8 K. By changing the direction of an external magnetic field (0.2 T), the presence or absence of a DW positioned in the nanostrip between the two electrodes can be controlled. The resistance is increased by approximately 0.5 Ω when the DW is located between the electrodes, which signifies the negative anisotropic magnetoresistance effect of Fe4N. The electrical detection of the resistance change is an important step toward the electrical detection of current-induced DW motion in Fe4N