Magnetic anomalies in single crystal Fe3O4 thin films

Abstract
Fe3O4 thin films were reactively sputtered onto 〈100〉 and 〈110〉 MgO substrates. X‐ray diffraction data indicate single crystal Fe3O4 films under a tensile stress. Magnetization data show good agreement with bulk Fe3O4 for Ms, but also show the presence of a large anisotropy component manifest in the lack of saturation in fields up to 70 kOe. Conversion electron Mössbauer spectroscopy data taken at zero field also show good agreement with bulk Fe3O4 for the values of the hyperfine fields and isomer shifts of the two Fe3O4 sites, indicate good stoichiometry, but indicate the presence of a large anisotropy component randomizing the moments. In‐plane torque measurements on 〈100〉 oriented Fe3O4 are consistent with bulk Fe3O4 magnetocrystalline anisotropy. However, in‐plane torque measurements on 〈110〉 oriented Fe3O4 show the presence of a uniaxial anisotropy superimposed on the crystalline terms. This anisotropy, modeled as being due to the stress induced by epitaxy, changes the easy axis from the 〈111〉 directions to the 〈110〉 directions in the (110) plane. Since the directional dependence of the crystal and stress anisotropy are measurable the ‘‘large anisotropy’’ component is considered to be random.