Antiphase boundaries induced exchange coupling in epitaxial Fe ₃O ₄ thin films

We have observed an exchange bias effect on field cooling of epitaxial magnetite, Fe ₃O ₄, films on MgO (1 0 0) substrates. We attribute this effect to the presence of antiphase boundaries (APBs). Magnitude of the exchange bias field (H _e) strongly depends on the thermo-magnetic history of the sample. The strength of the H _e was found to increase with an increase in film thickness and is attributed to the strain driven redistribution of atoms in the vicinity of APBs leading to enhanced antiferromagnetic exchange interactions.