Film thickness and temperature dependence of the magnetic properties of pulsed-laser-deposited Fe3O4 films on different substrates -: art. no. 205413

We report a systematic study of (100) epitaxial films of magnetite (Fe3O4) of thickness 300-2000 Angstrom, grown on single-crystal substrates (MgO, MgAl2O4, and SrTiO3) using pulsed laser deposition. The magnetic state was explored by measuring magnetization, conversion-electron Mossbauer spectroscopy, and ferromagnetic resonance. At 300 K, films grown on MgAl2O4 and SrTiO3 are, more or less, normal for all thicknesses. That is, the in-plane anisotropy is fourfold. The films on MgO, however, show no in-plane anisotropy if the thickness is less than similar to 800 Angstrom. In contrast to some previous claims, the present films exhibit magnetic saturation at quite modest (less than or equal to2 kOe) fields. We propose simple models to account for a variety of observations. In addition to the shape anisotropy, strains appear to play the major role in determining the variation of the magnetic behavior with thickness, substrate, and temperature.