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We investigate the ferromagnetic resonance (FMR) of a single chiral structure of a ferromagnetic metal-the magnetochiral (MCh) metamolecule. Using a strain-driven self-coiling technique, micrometersized MCh metamolecules of metallic permalloy (Py) are fabricated without any residual Py films. The magnetization curves of ten Py MCh metamolecules obtained by an alternating gradient magnetometer show soft magnetic behavior. In cavity FMR with a magnetic-field sweep and coplanar-waveguide (CPW) FMR with a frequency sweep, the Kittel-mode FMR of the single Py metamolecule is observed. The CPW-FMR results, which are consistent with the cavity-FMR results, bring about the effective g factor, effective magnetization, and Gilbert damping of the single metamolecule. Together with calculations using these parameters, the angle-resolved cavity FMR reveals that the magnetization in the Py MCh metamolecule is most likely to be the hollow-bar type of configuration when the external magnetic field is applied parallel to the chiral axis, although the expected magnetization state at remanence is the corkscrew type of configuration.

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Compositional dependence of spin–orbit torque (SOT) of the bilayer comprised of Ta and ferrimagnetic GdFeCo was investigated. Critical current density of SOT switching Jsw of the GdFeCo/Ta bilayers did not vary with Gd composition x, and were found to exhibit roughly Jsw = 11 MA cm−2. Two orthogonal components of SOT, damping-like torque τDL and field-like torque τFL were estimated by measuring harmonic Hall resistance under in-plane fields parallel and perpendicular to the AC current, respectively. The absolute values of SOT, ∣τ DL∣ and ∣τFL∣, were confirmed to be roughly constant within 22 ≤ x ≤ 28. On the other hand, the sign of τFL changed across the compensation composition. These results suggest that the injected spin current is considered to exert a torque to the transition metal FeCo moment rather than to the rare earth Gd moment.

Time-resolved magneto-optical Kerr effect (MOKE) measurement was demonstrated on a sample of the Au/Fe/Au heterostructure with the Fe layer of 0.35 nm thickness under Fe M-edge resonance condition. An ultrabrilliant free electron laser (FEL) in the soft X-ray range was facilitated for the detection of transient signals of resonant MOKE from the ultrathin Fe film. A variation in the Kerr rotation angle was successfully observed on the femtosecond timescale. This technique enables us to reveal the transient magnetization dynamics of such a-few-monolayer magnetic films, which promote the development of spintronic devices.

5 nm- and 15 nm-thick (001) oriented MnAl films were fabricated on CoGa buffer layers with various thermal treatments. The insertion of the CoGa layer was effective to obtain the square out-of-plane hysteresis loop even in the MnAl thickness of 5 nm. Highly (001) oriented MnAl film was obtained by depositing Mn and Al on CoGa at a substrate temperature of 200°C followed by annealing at 500°C. The perpendicular magnetic anisotropy was estimated to be 7.4±0.2 and 8.5±0.4 Merg/cc for 5 nm- and 15 nm-thick MnAl, respectively. Lower anisotropy in 5 nm-thick MnAl may be due to the interdiffusion between the MnAl and CoGa layers.

The critical current density (J c0 ) and thermal stability factor Δ for the spin transfer torque switching of [Pt/Co] 6 /Cu/[Co/Pd] 3 nanopillars with various Co/Pd layer compositions were investigated. Moreover, the Gilbert damping constants α of Co/Pd and Co/Pt multilayers (MLs) with various layer compositions were also studied to understand the variations in the J c0 and Δ of the nanopillars. The J c0 and Δ of Co/Pd MLs were found to be almost independent of the pillar diameters, and the effective reversal size contributing to Δ was found to be much smaller than the physical pillar diameter. From the spin transfer torque (STT) switching of Co/Pd MLs with various layer compositions, J c0 was found to gradually increase with increasing thickness ratio of Pd and Co layers, t Pd /t Co , up to t Pd /t Co = 2, and further increase in t Pd /t Co resulted in the decrease in J c0 . On the other hand, Δ was roughly independent of the thickness ratio. The Gilbert damping constants α of Co/Pd and Co/Pt MLs increased with increasing thickness ratio of noble metal and Co layers, t NM /t Co . The large damping constant of the Co/Pt ML compared with that of the Co/Pd ML means that Co/Pt and Co/Pd MLs are appropriate for use as reference and memory layers, respectively. The increase in α with t Pd /t Co is considered to be responsible for the increase in J c0 up to t Pd /t Co = 2.