We have investigated the effective magnetic anisotropy in CVD-grown epitaxial $\mathrm{Cr}{\mathrm{O}}_2$ thin films and ${\mathrm{Cr}}_2{\mathrm{O}}_3∕\mathrm{Cr}{\mathrm{O}}_2$ bilayers using resonant radio-frequency transverse susceptibility (TS). While $\mathrm{Cr}{\mathrm{O}}_2$ is a highly spin polarized ferromagnet, ${\mathrm{Cr}}_2{\mathrm{O}}_3$ is known to exhibit magnetoelectric effect and orders antiferromagnetically just above room temperature. In $\mathrm{Cr}{\mathrm{O}}_2$, 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 $\mathrm{Cr}{\mathrm{O}}_2∕{\mathrm{Cr}}_2{\mathrm{O}}_3$ bilayers $M\text{−}H$ 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 $K_{\mathrm{eff}}$ values were observed depending on the fraction of ${\mathrm{Cr}}_2{\mathrm{O}}_3$ present. This anomalous behavior, observed for the first time, cannot be accounted for by the variable thickness of $\mathrm{Cr}{\mathrm{O}}_2$ alone and is indicative of possible exchange coupling between $\mathrm{Cr}{\mathrm{O}}_2$ and ${\mathrm{Cr}}_2{\mathrm{O}}_3$ phases that significantly affects the effective magnetic anisotropy.

• Received 7 January 2006

DOI:https://doi.org/10.1103/PhysRevB.74.024420