Exchange bias in tetragonal-like BiFeO3/Sr2FeMoO6 bilayer

Exchange bias in the bilayer of half-metallic La0.7Sr0.3MnO3 and multiferroic BiFeO3 has been applied for the electric field control of magnetization, which is strongly limited by the much low blocking temperature of about 100 K (Phys. Rev. Lett. 105, 027201 (2010)). One possible solution is to strengthen the interfacial exchange coupling, thus another half-metallic oxide Sr2FeMoO6 is selected. Tetragonal-like BiFeO3 has been successfully fabricated on (0 0 1) SrTiO3 substrate using Sr2FeMoO6 as buffer layer. By replacing the exchange coupling between Fe and Mn ions in BiFeO3/La0.7Sr0.3MnO3 bilayer, stronger exchange couplings between Fe and Fe ions are established at the interface, and the blocking temperature has been significantly increased to 160 K. A second blocking temperature at 110 K due to the exchange coupling between Fe and Mo ions is also observed. Detailed magnetization measurements confirm the conventional mechanism of exchange coupling between ferromagnetic and antiferromagnetic layers and exclude the contribution from surface spin glass. Furthermore, BiFeO3 still retains excellent ferroelectric properties with Sr2FeMoO6 acting as ferromagnetic conducting electrode, which may have important applications in multiferroic spintronics devices.