Evidence of two-fold and four-fold anisotropies by ferromagnetic resonance in zinc ferrite thin films*

By means of ferromagnetic resonance (FMR) technique the magnetic properties of ZnFe₂O₄ (ZFO) films grown on Si(111), MgO(100), and STO(100) were investigated. By using a model that takes into consideration the relevant contributions to the energy, we were able to extract the following parameters: effective magnetization M_eff, cubic magnetocrystalline anisotropy field, in-plane, and out-of-plane uniaxial anisotropy fields, as well as the g factor. The samples deposited on Si showed a twofold in-plane anisotropy while a fourfold magnetic anisotropy was observed for the ZFO/MgO and ZFO/SrTiO₃ samples. All samples showed a strong perpendicular uniaxial anisotropy above 1 kOe and low in-plane uniaxial and cubic anisotropy field, of the order of tenths of Oe. The FMR linewidth (ΔH) fitted from FMR data show values above 190 Oe for all samples, indicating high damping of this material to be ∼10^-2.