Magnetic Measurements of RE-Doped Cobalt Ferrite Thin Films

Cobalt ferrite is a ferrimagnetic material with properties which support its use in different types of devices. In bulk form CoFe₂O₄ presents the highest magnetostriction coefficient relative to other ferrites making it a good candidate for sensors and actuators. Due to the industries miniaturization trend, several research groups focused their study on obtaining novel thin films with high magnetostriction coefficient. The aim of this work was to investigate the influence of the substrate temperature and rare earth addition on the properties of cobalt ferrite thin films deposited by pulsed laser deposition. CoFe₂O₄, CoFe_1.8Gd_0.2O₄ and CoFe_1.8La_0.2O₄ thin films were deposited using an Nd-YAG laser (532 nm) with a 10 Hz repetition rate and 10 ns pulse duration. The target-substrate distance of 2.5 cm and laser fluence of 10 J/cm² were kept constant. The substrate temperature was varied from 200 °C to 600 °C. The structural properties of the thin films obtained by Raman spectroscopy and scanning electron microscopy indicated the formation of a single cobalt ferrite structure. Hysteresis loops for both in-plane and out-of-plane configuration were obtained using a vibrating sample magnetometer. These results showed an increase in coercive field and maximum magnetization as the substrate temperature was raised from 200 °C to 400 °C. Vibrating sample magnetometer measurements of the cobalt ferrite thin film deposited at 400 °C revealed a tendency of the particles to a perpendicular magnetic arrangement.