Stress Effects CoCr₂O₄ Film on MgO and MgAl₂O₄ Grown by RF-Sputter Process

Multiferroic $CoCr_2O_4$ film was deposited on MgO and $MgAl_2O_4$ substrates by the rf-sputtering process. The films were prepared at an RF-magnetron sputtering power of 50 W and a pressure of 10 mtorr (20 sccm in Ar), and at substrate temperatures of $550^{\circ}C$. The crystal structure was determined to be a spinel (Fd-3m) structure by means of X-ray diffraction (XRD) with Cu $K{\yen}{\acute{a}}$ radiation. The thickness and morphology of the films were measured by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The magnetic properties were measured using a Superconducting Quantum Interference Device (SQIUD) magnetometer. While the ferrimagnetic transitions were observed at about 93 K, which was determined as the Neel temperature, the magnetic properties all show different behaviors. The differences between the magnetic properties can be explained by the stress effects between $CoCr_2O_4$ and the substrates of MgO and $MgAl_2O_4$.