Magnetic anisotropy in epitaxial Cr O2 and Cr O2 / Cr2 O3 bilayer thin films

Abstract

We have investigated the effective magnetic anisotropy in CVD-grown epitaxial Cr O2 thin films and Cr2 O3 /Cr O2 bilayers using resonant radio-frequency transverse susceptibility (TS). While Cr O2 is a highly spin polarized ferromagnet, Cr2 O3 is known to exhibit magnetoelectric effect and orders antiferromagnetically just above room temperature. In Cr O2, 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 Cr O2 / Cr2 O3 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 Keff values were observed depending on the fraction of Cr2 O3 present. This anomalous behavior, observed for the first time, cannot be accounted for by the variable thickness of Cr O2 alone and is indicative of possible exchange coupling between Cr O2 and Cr2 O3 phases that significantly affects the effective magnetic anisotropy. © 2006 The American Physical Society.