The magnetic properties of iron-doped cobalt ferrite (Co${}_{1-x}$Fe${}_{2+x}$O${}_4$) (001) thin films grown epitaxially on MgO (001) substrates are investigated by superconducting quantum interference device magnetometry and soft x-ray magnetic linear and circular dichroisms. All Co${}_{1-x}$Fe${}_{2+x}$O${}_4$ (0.01 ⩽ $x$ ⩽ 0.63) samples have out-of-plane magnetic easy axes and large coercive fields, unlike Fe${}_3$O${}_4$, due to a large Co${}^{2+}$ orbital moment. The magnetic moments for those samples are significantly reduced from their bulk values; however, as $x$ increases, the magnetic moments tend nearer to their bulk values and increase more rapidly as $x$ approaches 1. This reduction in magnetic moment is attributed to spin canting among the Co${}^{2+}$ cations, owing to a small in-plane tensile strain in the film and to an increased antiferromagnetic alignment among all the cations caused by a partially inverse spinel cubic structure and the likely presence of antiphase boundaries. Our results show that small changes in stoichiometry can lead to significant changes in the magnetic moment of Co${}_{1-x}$Fe${}_{2+x}$O${}_4$, especially at large values of $x$.

• Received 19 May 2011

DOI:https://doi.org/10.1103/PhysRevB.84.054447