MAGNETIC PROPERTIES OF Co-DOPED IRON OXIDE FILMS PREPARED BY SOL-GEL METHOD

摘要

Thin films of iron-oxide based magnetic materials are being investigated due to their application as high density recording and magneto-optical materials. Of the several techniques viz. Chemical vapour deposition (CVD), ferrite plating, laser evaporation etc., the preparation by sol-gel method [1,2] is gaining importance because of their high homogeneity in molecular level, low cost and simplicity in production. Cobalt substituted iron-oxide films were prepared using sol-gel technique. Weighed quantitites of iron (III) nitrate and cobalt(II) nitrate were dissolved in methoxy ethanol in the ratio 4:3. The gel solution was prepared by constantly stirring the solution at 50°C in the nitrogen atmosphere. A few drops of the gel solution was poured on the glass substrate fixed to the spinner. After each coating films were dried at 100°C in air for 10 minutes. The optical quality and thickness of films were monitered for various spin speeds. The thickness of each layer as measured by stylus technique was found to be around 600 A. The as grown films are amorphous in nature. The magnetic properties viz. the magnetization and the coercivity were measured using a vibrating sample magnetometer (VSM). Hysteresis loop of the as deposited and hydrogen reduced (at 250°C and 2 hrs) films of thickness 3000 A (five layers) with magnetic field parallel to the film surface are shown in Fig.1. The reduced films yield a value of coercivity (H_(C))=250 Oe as compared to H_(C)=16 Oe for as grown films. The oxidation (at 350°C for 2 hrs) of hydrogen reduced films shows further increase in the coercivity. The saturation magnetization (M_(S)) also shows increase in its value after reducing the films in hydrogen atmosphere as shown in Fig.1.