Room-temperature Ferromagnetism in the Bi Transition-metal-oxide Bilayer BiMnO3/BiFeO3

Abstract

We grow BiMnO3/BiFeO3 bilayer films on SrTiO3 substrates by using the pulsed laser deposition method. While both BiMnO3 and BiFeO3 show the same ferroelectricity with transition temperatures far above room temperature, their magnetic structures are completely different. BiFeO3 has an antiferromagnetic Neel temperature of around 620 K whereas BiMnO3 becomes ferromagnetic at about 100 K. In accord with these facts, no ferromagnetic signature is detected at temperatures above 150 K in the as-grown bilayer films. Remarkably, it is possible to induce ferromagnetism by intermixing Mn and Fe ions by post-annealing the bilayer film at 620 degrees C. The ferromagnetism remains for temperatures Lip to 450 K, well above room temperature. We also note that just a few monolayers of BiFeO3 may be used as a buffer to grow an epitaxial BiMnO3 film on a SrTiO3 substrate.