Defect mediated exchange bias in oriented (111) Fe3O4/(100) GaAs

Exchange bias (EB) in a single magnetic film has always been an intriguing subject to the researchers. But the quest for the origin of EB in Fe3O4 films at temperatures, T < 200 K is still contemplated. We report a thickness dependent observation of exchange bias at T < 200 K, with diminishing EB for higher thickness of oriented (111) Fe3O4 on (100) GaAs. Non-zero EB is observed to be retained even up to 55 nm of Fe3O4. Invariance of blocking temperature and the identical exponential nature of EB for different thickness of Fe3O4 suggests the origin of EB to be similar in all the films. Variation of coercivity with temperature in our case supports the disorder driven magnetic interactions in Fe3O4 films at T < TV, which is the Verwey transition of Fe3O4. Hence, the exchange bias is thought to exist between the intra-grain ferrimagnetic Fe3O4 region and the antiferromagnetic grain boundary region. Reduced island sizes with lower defect area for higher thickness of Fe3O4 further supports the claim of defect mediated exchange pinning in a thin film of single magnetic material, Fe3O4. In addition, training of exchange bias in Fe3O4 films can be carried out similar to the films consisting of traditional ferromagnetic-antiferromagnetic layers.