Room Temperature Exchange Bias in BiFeO 3 /Co–Fe Bilayers

Thin highly epitaxial BiFeO3 films were prepared on SrTiO3 (100) substrates by reactive magnetron cosputtering. Detailed magneto-optic Kerr effect (MOKE) measurements on BiFeO3/Co–Fe bilayers were performed to investigate the exchange bias as a function of film thicknesses and Co–Fe stoichiometries. We found a maximum exchange bias of $H_{\mathrm {eb}}=92$ Oe and a coercive field of $H_{c}=89$ Oe for a 12.5 nm-thick BiFeO3 film with a 2 nm-thick Co layer. The unidirectional anisotropy is clearly visible in in-plane rotational MOKE measurements. Anisotropic magnetoresistance measurements reveal a strongly increasing coercivity with decreasing temperature, but no significant change in the exchange bias field.