MAGNETIC-ANOMALIES IN SINGLE-CRYSTAL FE3O4 THIN-FILMS

Fe3O4 thin films were reactively sputtered onto [100] and [110] MgO su bstrates. X-ray diffraction data indicate single crystal Fe3O4 films u nder a tensile stress. Magnetization data show good agreement with bul k Fe3O4 for M(s), but also show the presence of a large anisotropy com ponent manifest in the lack of saturation in fields up to 70 kOe. Conv ersion electron Mossbauer spectroscopy data taken at zero field also s how good agreement with bulk Fe3O4 for the values of the hyperfine fie lds and isomer shifts of the two Fe3O4 sites, indicate good stoichiome try, but indicate the presence of a large anisotropy component randomi zing 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 presen ce of a uniaxial anisotropy superimposed on the crystalline terms. Thi s anisotropy, modeled as being due to the stress induced by epitaxy, c hanges the easy axis from the [111] directions to the [110] directions in the (110) plane. Since the directional dependence of the crystal a nd stress anisotropy are measurable the ''large anisotropy'' component is considered to be random.