Tunable Optical Bandgap in GdN Ultrathin Films for Spin Filtering

Spintronic devices based on rare-earth nitrides (RENs) are of great interest since they present semiconducting and ferromagnetic properties suitable for exploiting carriers' spin in fundamental and applied research. GdN has been widely studied due to its high magnetic moment and spin-splitting bandgap attributed to the bandgap shrinking and the different energies for the minority and majority bands. Because of its high oxophilicity, the growth of stoichiometric GdN thin ?lms is very challenging and requires rigorous control of impurities. Besides that, to combine GdN films with novel materials for investigating interface and spin phenomena, flat surfaces with a high degree of crystallinity, well-defined bandgap, and critical temperature and magnetization saturation compatible with the bulk values are crucial. The crystal, optical and magnetic properties of GdN films depend on strain, nitrogen vacancies, and the amount of oxygen impurities which depend on the growth process and substrate choices. In this work, we investigate the optical and magnetic properties of reactively sputtered AlN(10 nm)/GdN(t)/AlN(10 nm) on sapphire substrates with different thicknesses grown under different nitrogen’s partial pressure and temperature. We observed an increase of the GdN film bandgaps under a transition from the paramagnetic to the ferromagnetic state for a thickness t ranging from 4 nm to 350 nm. Next, we have been working on observing and controlling the spin-split bandgap of these films.