Anomalously large ferromagnetic Curie temperature of epitaxial Bi2 CoMn O6 thin films

Abstract

We present the structural and physical properties of epitaxial Bi2 CoMn O6 films grown on SrTi O3 and LaAl O3. They display magnetic hysteresis loop with 170 Oe coercivity and a 3.1 μB f.u. saturation magnetization which indicates a disordered CoMn state. Nevertheless, these films display an unusually large ferromagnetic Curie temperature of about 800 K. We propose that the large Curie temperature is the result of a strong coupling between the magnetization and the polarization order parameters of Bi2 CoMn O6 promoted by substantial structural changes in the films with respect to the bulk. These structural modifications amplify the overlap of the electronic wave functions of the Mn-O-Mn, Mn-O-Co and Co-O-Co bonds and the Bi 6 s2 lone pair electrons providing the long-range spin order through the minimization of the magnetoelastic energy. © 2008 American Institute of Physics.