Arunava Gupta1

1, University of Alabama, Tuscaloosa, Alabama, United States

Ferrites thin films have a number of technological applications in areas such as telecommunications (microwave and millimeter wave devices), magneto-electric coupling devices and are also promising candidates for future spintronic devices. However, spinel ferrite thin films such as NiFe2O4 (NFO) suffer from a number of structural and magnetic drawbacks, e.g. formation of antiphase boundaries and high magnetic saturation fields. We show that by using substrates having similar crystal structure and low lattice mismatch, one can avoid formation of antiphase boundaries and thereby obtain magnetic properties comparable to bulk single crystal. We used spinel MgGa2O4 and CoGa2O4 substrates, which have 0.8% and 0.2% lattice mismatch, respectively, with NFO to grow epitaxial films that are essentially free of antiphase boundaries and exhibit sharp magnetic hysteresis characteristics. Moreover, ferromagnetic resonance linewidths similar to those in single crystals are obtained. We have compared these results with NFO film grown on another spinel substrate MgAl2O4, which has 3.1% lattice mismatch, that has antiphase boundaries and clearly exhibits degraded properties. We also investigated spin transport properties of the films grown on the three substrates via the longitudinal spin Seebeck effect (LSSE). An increase in the spin voltage signal with reduction in lattice mismatch is observed, which is in correspondence with similar improvements in structural and magnetic properties. Thickness and temperature dependence of the LSSE for NFO films grown on different substrates have been investigated.