Exchange bias in polycrystalline Bi1−xLaxFeO3/NiFe bilayers

The well saturated ferroelectric hysteresis and exchange bias with a ferromagnetic layer are the important prerequisites for multiferroic applications of BiFeO3 in spintronics. Mn substitution has significantly suppressed the current leakage and improved the ferroelectric properties of BiFeO3, but the exchange bias on NiFe has been strongly suppressed [J. Allibe, et al., Appl. Phys. Lett. 95, 182503 (2009)]. Pure phase Bi1−xLaxFeO3 films with x up to 0.40 have been prepared on LaNiO3 buffered surface oxidized Si substrates by pulsed laser deposition. With 10% La substitution, the Bi0.90La0.10FeO3 film shows well-saturated ferroelectric hysteresis loop with remnant polarization Pr of 34 μC/cm2. Furthermore, with La substitution concentration x below the structural transition point from rhombohedral to orthorhombic (x=0.20), maximum exchange bias field of about 28 Oe has been obtained with 3.6 nm NiFe layer on Bi0.90La0.10FeO3 (20 Oe on pure BiFeO3 under the same conditions).