We focus on accurate representations of hysteretic phenomena under pulse width modulation (PWM) inverter excitation using strong-coupling analysis of the magnetic field and the electric circuit. We perform the strong-coupling analysis by applying a dynamic hysteresis model (play model with the Cauer circuit) to a circuit simulator. We show that, by accounting for dead time properties, the numerical voltage waveforms obtained in our study are consistent with those obtained experimentally. Further, the accurate representations of the voltage waveform and of the high and wide band frequency indicate that the hysteresis curves simulated by our proposed strong-coupling analysis agree well with the measured results.

  10-nm-thick FePt alloy films without and with MgO, VC, and VN cap-layers of 2 nm thickness are prepared on MgO, VC, and VN single-crystal underlayers of (001) orientation by using a two-step method consisting of low-temperature deposition at 200 °C followed by high-temperature annealing at 600 °C. The surface energies of MgO and vanadium compounds (VC, VN) are respectively lower and higher than that of FePt alloy. The influences of combination of underlayer and cap-layer materials on the surface flatness, the lattice deformation, the degree of L1₀ ordering, and the magnetic anisotropy are investigated. FePt(001) single-crystal films without and with MgO, VC, and VN(001) single-crystal cap-layers grow epitaxially on all the underlayers. The in-plane lattice of FePt film is expanded in accommodation of lattice mismatch with underlayer and/or cap-layer. The lattice deformation aligns the c-axis perpendicular to the substrate surface and enhances L1₀ ordering. A higher order degree and a stronger perpendicular magnetic anisotropy are obtained by using a combination of VN underlayer and MgO cap-layer. The present study shows that employment of underlayer and cap-layer materials whose surface energies are respectively higher and lower than that of FePt alloy is effective in enhancing order degree and magnetic anisotropy.

  The thermal stability factor K_umV_m /kT and the anisotropy constant ratio K_u /K_bulk necessary for 10 years of archiving in heat-assisted magnetic recording of 2 Tbpsi are evaluated by employing a bit error rate calculation using a grain error probability P. Although the attempt frequency f₀ in P is a function of the Gilbert damping constant, the Curie temperature, K_u /K_bulk , the grain volume, and temperature, f₀ can be treated as a constant. The Gilbert damping constant and the Curie temperature variation are parameters with little impact. On the other hand, the grain size variation, the grain number per bit n, the mean Curie temperature T_cm , and the storage temperature T are parameters with a strong impact on bit error rate. Although K_umV_m /kT decreases as n increases due to a statistical problem, a larger K_u /K_bulk is necessary as n increases due to a smaller grain size. A larger K_u /K_bulk is also necessary as T_cm decreases. The bit error rate increases rapidly as T increases.

  We systematically investigated perpendicular magnetic anisotropy (PMA) in bilayers comprising ultrathin full-Heusler Co₂FeSi (CFS) alloy and MgO as an insulator. The MgO layer was fabricated using two different sputtering techniques: reactive sputtering and radio-frequency sputtering. The characteristics of the layers fabricated using the different methods were compared. Irrespective of the MgO fabrication technique, the CFS/MgO bilayers exhibited PMA when the CFS surface was exposed to oxygen, which resulted in additional Fe–O bonds at the interface. Additionally, we characterized PMA in the bilayers while varying the substrate temperature T_S for CFS sputtering. CFS samples that were 0.6-nm thick exhibited PMA when they were formed at T_S as high as 300°C. The bilayer formed at 350°C exhibited in-plane magnetic anisotropy. Quantitative analysis of the magnetic anisotropy energy density revealed that the dominant magnetic anisotropy contribution in PMA differed between the bilayers formed at 300°C and 350°C. We expect these findings to be useful in the further development of high spin-polarized ferromagnetic electrodes containing PMA for next-generation spintronics devices.

To improve the fuel efficiency of electric vehicles, it is necessary to reduce the weight of the wireless power transfer coil in the vehicles. Resistance due to the skin effect or the proximity effect increases during wireless power transfer, decreasing the transmission efficiency. This study aims to reduce the weight of the coil by replacing it with an aluminum plate coil, which is easy to manufacture and inexpensive. The weight of the coil was reduced by 3/4 (from 1.9 to 0.44 kg) when compared with copper Litz wire. Furthermore, the AC resistance was reduced by applying magnetic coating to the same coil. Consequently, the transmission efficiency increased from 88.2% to 89.3%, an improvement of 1.1%. The optimal material for magnetic coating was revealed in an analysis.