EFFECTS OF HIGH-TEMPERATURE ANNEALING ON AMORPHOUS BIFEO3 WITH NONMAGNETIC SUBSTITUTIONS

We report on the preparation of amorphous (a-) insulators with the highest saturation induction ever achieved. Samples of a-(1 - x)BiFeO3-xABO3 (AB = PbZr, PbTi, BaTi) with x = 0-0.6 were prepared by rf sputtering techniques. As-deposited films are x-ray amorphous and are paramagnetic. Films annealed in air at temperatures T(a) = 400-750-degrees-C develop a magnetic moment. The room-temperature magnetization M increases with T(a) and shows a maximum for a specific T(a) value which is a function of the nature and amount of the nonmagnetic substitution. With further increase in T(a), the observed decrease in M is accompanied by the onset of crystallization in the films. The largest saturation induction, 4-pi-M(s) = 3.8 kG, is observed for samples substituted with 0.5 PbZrO3. The Curie temperatures are in the range 380-440-degrees-C and are well below the crystallization temperature.