Enhanced exchange bias in fully epitaxial Fe

Fully epitaxial Fe3O4/BiFeO3 bilayers were deposited on (001) LaAlO3 and SrTiO3 by magnetron sputtering. BiFeO3 remained tetragonal on highly misfit-strain LaAlO3 substrates. Obvious exchange bias with a reciprocal relation to the thickness of ferromagnetic Fe3O4 was observed in the Fe3O4/tetragonal-like BiFeO3 (Fe3O4/T-BiFeO3) bilayers below $\sim100\ \text{K}$ which is similar to that of Fe3O4/rhombohedral-like BiFeO3 (Fe3O4/R-BiFeO3) bilayers. An unexpected enhancement of exchange bias from $\sim160\ \text{Oe}$ in Fe3O4/R-BiFeO3 to $\sim320\ \text{Oe}$ in the Fe3O4/T-BiFeO3 bilayer was observed at 3 K, which could be attributed to the enhanced Fe–O–Fe interfacial superexchange (SE) interaction induced by distorted T-BiFeO3