Film thickness and temperature dependence of the magnetic properties of pulsed-laser-deposited Fe<SUB>3</SUB>O<SUB>4</SUB> films on different substrates

We report a systematic study of &lt;100&gt; epitaxial films of magnetite (Fe3O4) of thickness 300-2000 &#197;, 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 ~800 &#197;. In contrast to some previous claims, the present films exhibit magnetic saturation at quite modest ( 2 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