Stress-induced magnetic anisotropy in thick oriented NiZn–ferrite films on (100) MgO substrates

Abstract

Thick films (10–12 μm) of NiZn–ferrite (Ni0.6Zn0.4Fe2O4) were grown on single-crystal (100) magnesium oxide substrates using pulsed laser deposition (PLD). The morphology, phase, orientation, strain, and magnetic properties of the as-deposited films were investigated as a function of substrate temperature (400–700 °C) and O2 background pressure (50–200 mTorr). Compositional analysis shows that the PLD NiZn–ferrite films are about 45% Zn deficient when grown using a standard polycrystalline single phase Ni0.4Zn0.6Fe2O4 target regardless of substrate temperature or O2 pressure. However, Zn-rich targets were successfully used to compensate for the Zn deficiency in the NiZn–ferrite films. PLD NiZn–ferrite films grown at 700 °C exhibit the highest degree of crystalline quality and nearly bulk saturation magnetization values (i.e., 5000 G). At low O2 pressures (<75 mTorr) the films, which were grown at 700 °C, are under a significant compressive stress. The stress decreases when the PLD NiZn–ferrite films are grown in higher O2 pressures but the crystalline quality and surface morphology deteriorate. The compressive stress produces a planar anisotropy field of about 1000–3500 Oe depending on the O2 pressure, which is consistent with the stress results from x-ray diffraction measurements on the NiZn–ferrite films. It is hypothesized that the film stress is largely the result of oxygen loss from the films during deposition.