Exchange anisotropy in epitaxial Fe3O4/CoO and Fe3O4/CoxFe3−xO4 bilayers grown by pulsed laser deposition

Magnetic exchange anisotropy has been studied in epitaxial ${\mathrm{Fe}}_{\mathrm{3}}{\mathrm{O}}_4$ based bilayers grown by pulsed laser deposition on MgO substrates. Measurements of the exchange biasing of the ${\mathrm{Fe}}_{\mathrm{3}}{\mathrm{O}}_4$ magnetization curves were performed on (100)- and (111)-oriented ${\mathrm{Fe}}_{\mathrm{3}}{\mathrm{O}}_4$ (20 nm)/CoO (20 nm) bilayers and (100)-oriented ${\mathrm{Co}}_{\mathrm{0.16}}{\mathrm{Fe}}_{\mathrm{2.84}}{\mathrm{O}}_4$ (190 nm)/${\mathrm{Fe}}_{\mathrm{3}}{\mathrm{O}}_4$ (40–370 nm) bilayers. The effective exchange bias field $H_{\mathrm{eb}}$ and coupling energy were found to be ${\text{10–10}}^2\hspace{0.17em}\mathrm{kA/m}$ and $\text{1–2\hspace{0.5em}}{\mathrm{mJ/m}}^2,$ respectively. The dependence of $H_{\mathrm{eb}}$ on the thickness d of the soft magnetic component (magnetite) of the cobalt ferrite/magnetite bilayer $H_{\mathrm{eb}}\text{∼1/d}$ is found to be in agreement with the predictions of a Stoner–Wohlfarth-type model. The order of magnitude and the temperature dependence of $H_{\mathrm{eb}}$ for the ${\mathrm{Fe}}_{\mathrm{3}}{\mathrm{O}}_{\mathrm{4}}\mathrm{/CoO}$ bilayers are similar to those of bilayers prepared by molecular beam epitaxy.