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.