Magnetic anisotropy in epitaxial CrO2 and CrO2/Cr2O3 bilayer thin films

We have investigated the effective magnetic anisotropy in CVD-grown epitaxial CrO2 thin films and Cr2O3/CrO2 bilayers using resonant radio-frequency transverse susceptibility (TS). While CrO2 is a highly spin polarized ferromagnet, Cr2O3 is known to exhibit magnetoelectric effect and orders antiferromagnetically just above room temperature. In CrO2, the measured values for the room temperature anisotropy constant scaled with the film thickness and the TS data is influenced by magnetoelastic contributions at low temperature due to interfacial strain caused by lattice mismatch with the substrate. In CrO2/Cr2O3 bilayers M-H loops indicated an enhanced coercivity without appreciable loop shift and the transverse susceptibility revealed features associated with both the ferromagnetic and antiferromagnetic phases. In addition, a considerable broadening of the anisotropy fields and large K-eff values were observed depending on the fraction of Cr2O3 present. This anomalous behavior, observed for the first time, cannot be accounted for by the variable thickness of CrO2 alone and is indicative of possible exchange coupling between CrO2 and Cr2O3 phases that significantly affects the effective magnetic anisotropy. (c) 2006 American Institute of Physics.