Nanocrystalline magnetite thin films grown by dual ion-beam sputtering

•We have grown tensile and compressive strained nanocrystalline magnetite thin films by dual ion beam sputtering.•The magnetic and thermoelectric properties can be controlled by the deposition conditions.•The magnetic anisotropy depends on the crystalline grain size.•The thermoelectric properties depend on the type of strain induced in the films.•In plane uniaxial magnetic anisotropy develops in magnetite thin films with grain sizes ⩽20 nm.

We have explored the influence of an ion-assisted beam in the thermoelectric and magnetic properties of nanocrystalline magnetite thin films grown by ion-beam sputtering. The microstructure has been investigated by XRD. Tensile and compressive strained thin films have been obtained as a function of the parameters of the ion-assisted beam. The evolution of the in-plane magnetic anisotropy was attributed to crystalline grain size. In some films, magneto-optical Kerr effect measurements reveal the existence of uniaxial magnetic anisotropy induced by the deposition process related with a small grain size (⩽20 nm). Isotropic magnetic properties have observed in nanocrystalline magnetite thin film having larger grain sizes. The largest power factor of all the films prepared (0.47 μW/K2 cm), obtained from a Seebeck coefficient of −80 μV/K and an electrical resistivity of 13 mΩ cm, is obtained in a nanocrystalline magnetite thin film with an expanded out-of-plane lattice and with a grain size ≈30 nm.