Magnetostriction Behaviors of Ni 100− x Fe x and Ni 100− y Co y (001) Single-Crystal Films with fcc Structure under Rotating Magnetic Fields

Ni 100− x Fe x ( $x = 0$ , 20 at.%) and Ni 100− y Co y ( $y = 0$ , 25, 50, 75, and 100 at.%) alloy single-crystal films of fcc(001) orientation are prepared through heteroepitaxial growth on Cu(001) single-crystal underlayers at 300 °C. The effects of Fe/Ni and Co/Ni compositions on the magnetic anisotropy and the magnetostriction behavior under rotating magnetic fields are investigated. The Ni single-crystal film shows a nearly isotropic in-plane magnetic property. The Ni 80 Fe 20 and Ni 100− y Co y ( $y = 25$ –100) single-crystal films show fourfold symmetries in in-plane magnetic anisotropy. The easy magnetization direction is observed along [110] and [ $1\bar {1}0$ ] for the Ni 80 Fe 20 and the Ni 100− y Co y ( $y = 50$ –100) films, whereas that is recognized along [100] and [010] for the Ni 75 Co 25 film. The easy magnetization axis varies depending on the Co/Ni composition. The in-plane magnetic anisotropy increases with increasing the Co content. Triangular output waveforms of magnetostriction appear when the Ni 80 Fe 20 and Ni 100− y Co y ( $y = 25$ –100) films are measured under low rotating magnetic fields. The magnetostriction behavior is related to the magnetization direction in a magnetically unsaturated film with in-plane magnetic anisotropy. As the rotating magnetic field increases, the magnetization approaches saturation and the waveform gradually changes to a usual sinusoidal shape. As the in-plane anisotropy increases, a higher rotating field is required to obtain a sinusoidal waveform. On the contrary, sinusoidal waveforms are observed for the Ni film, even when the magnetization is not saturated. The waveform of magnetostriction is affected by the symmetry and the strength of in-plane magnetic anisotropy.