Evidence of anomalous switching of the in-plane magnetic easy axis with temperature in Fe3O4 film on SrTiO3:Nb by v-MOKE and ferromagnetic resonance.

The evolution of the magnetic anisotropy directions has been studied in a magnetite (Fe3O4) thin film grown by infrared pulsed-laser deposition on SrTiO3(100):Nb substrate. The magnetic easy axes at room temperature are found along the in-plane 〈100〉 film directions, which means a rotation of the easy axis by 45° with respect to the directions typically reported for bulk magnetite and films grown on single-crystal substrates. Moreover, when undergoing the Verwey transition temperature, TV, the easy axis orientation evolves to the 〈110〉 film directions. This anomalous behavior has been demonstrated by measuring first the angular dependence of coercivity and remanence well above and below TV by high-resolution vectorial magneto-optical Kerr effect (v-MOKE). Ferromagnetic resonance (FMR) measurements have additionally proven a well-defined fourfold magnetic anisotropy induced during growth with confirmed easy axis directions along 〈100〉 for T > TV and 〈110〉 for T < TV. These results provide a clear proof of the possibility of tuning magnetic anisotropy in Fe3O4 thin films by proper control on the growth parameters and substrate choice.