To improve the coercivity of Sm(Fe-Co)₁₂-B thin film, a Sm seed layer was introduced between a V buffer layer and a Sm(Fe-Co)₁₂-B layer, and the thickness of the Sm(Fe-Co)₁₂-B layer was varied. From the result of XRD patterns measured in an out-of-plane configuration, peaks from (002) and (004) of the ThMn₁₂-type crystal structure were observed for all samples. The intensity of these peaks was reduced by decreasing the thickness of the Sm(Fe-Co)₁₂-B layer; however, it was recovered by introducing a Sm seed layer. Although the coercivity was decreased due to the reduction in the thickness of the Sm(Fe-Co)₁₂-B layer, a large coercivity of 1.87 T was obtained in an Al-diffused thin film, which was thinned to 50 nm while introducing a Sm seed layer.

  We present a microwave transmission theory for recently proposed ultrastrong-coupled magnon-polariton (MP) in dynamical inductors which consist of a coil involving a magnetic insulator. Combining with the RLC-circuit and Landau-Lifshitz-Gilbert equations, we formulate the electric impedance of MP as a coupled oscillator under the corresponding principle. Based on the transmission (ABCD or F) matrix approach, we further calculate S₂₁ being a scattering parameter for the microwave transmission measurement passing through an RLC-circuit with the dynamical inductor. By tunning the size of the dynamical inductor, we theoretically demonstrate an on-chip ultrastrong-coupled MP at room temperature, which reaches a coupling ratio about 0.55 and cooperativity about 2×10⁵ with material parameters of Y₃Fe₅O₁₂. This work paves the way for quasi-two-dimensional circuit/wave-guide based magnonics for quantum information technology.

  We investigate unidirectional spin Hall magnetoresistance (USMR) in Ta/Co bilayer systems with various Co thicknesses. A negative USMR is observed when the thickness of Co is thin due to the negative spin Hall angle of Ta, as expected from the conventional framework. However, as the Co thickness increases, the amplitude of USMR becomes strongly suppressed, and the sign of USMR becomes positive, which cannot be explained by theoretical calculation considering only the spin Hall effect (SHE) in the Ta layer. We successfully explain the anomalous thickness dependence of USMR by considering USMR induced by SHE in the Co layer. This work verifies the significant influence of SHE in ferromagnets on the measurement of USMR and will contribute to a better understanding of USMR.

  A novel type of giant magneto-resistance (GMR) sensor utilizing domain wall displacement (DWD) modulation and a closed-loop current-field feedback technique was investigated. In this paper, a Ni₈₀Fe₂₀ free layer was used for the GMR sensor since the uniaxial anisotropy of Ni₈₀Fe₂₀ is smaller than that of the (Co₉₀Fe₁₀)₉₂B₈ used in the previous study, resulting in a larger wall displacement with a smaller field. When the domain wall was modulated by a modulation field H_mod = 94 μT_rms, the sensitivity of the sensor increased to 2.6 mV/μT in open-loop mode compared with a sensitivity of 0.98 mV/μT for the sensor without H_mod. Moreover, a significant improvement in the linearity of the output was obtained by operating the DWD GMR sensor in closed-loop mode, and the sensitivity was also increased up to 4.2 mV/μT. The improvement in linearity is considered to be due to the suppression of the displacement of the average position of the domain walls by the current-field feedback. The noise floor of the output of the DWD GMR sensor under closed-loop operation was estimated to be 300 pT/Hz^1/2 at 10 Hz.