Origin of the Anomalous Magnetic Behavior in Single CrystalFe3O4Films

Antiphase boundaries (APBs) were observed in ${\mathrm{Fe}}_3{\mathrm{O}}_4$ single crystal films grown on MgO. The APBs are an intrinsic consequence of the nucleation and growth mechanism in films. Across an APB, the intrasublattice superexchange coupling is greatly strengthened, while the intersublattice superexchange coupling is weakened, reversing the dominant interaction from that found in the bulk. Thus the APB separates oppositely magnetized regions, consistent with Lorentz microscopy measurements. The APBs induce very large saturation fields and nearly random magnetization distribution in zero field.