Exchange anisotropy in epitaxial Fe3O4/CoO and Fe3O4/COxFe3-xO4 bilayers grown by pulsed laser deposition

Magnetic exchange anisotropy has been studied in epitaxial Fe3O4 based bilayers grown by pulsed laser deposition on MgO substrates. Measurements of the exchange biasing of the Fe3O4 magnetization curves were performed on (100)- and (111)-oriented Fe3O4 (20 nm)/CoO (20 nm) bilayers and (100)-oriented Co0.16Fe2.84O4 (190 nm)/Fe3O4 (40-370 nm) bilayers. The effective exchange bias field H-eb and coupling energy were found to be 10-10(2) kA/m and 1-2 mJ/m(2), respectively. The dependence of H-eb on the thickness d of the soft magnetic component (magnetite) of the cobalt ferrite/magnetite bilayer H(eb)similar to 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-eb for the Fe3O4/CoO bilayers are similar to those of bilayers prepared by molecular beam epitaxy. (C) 1998 American Institute of Physics. [S0021-8979(98)09420-1].