Room temperature ferromagnetism in CrGaN: Dependence on growth conditions in rf N-plasma molecular beam epitaxy

Here, we report the influence of the growth conditions for CrGaN grown with the N-polarity on sapphire (0 0 0 1) using radio frequency N plasma-assisted molecular beam epitaxy. Samples are grown under different Ga/N flux ratio of 0.65-1.0 at substrate temperatures of 650 and 700°C. The Cr/Ga flux ratio is set to either 3% or 5%. These growth parameters allow to vary over a range of growth conditions from N-rich to Ga-rich. It is shown that the surface condition during growth influences the surface morphology and magnetic properties of CrGaN. In particular, we show that N-rich and metal-rich growth conditions result in room temperature ferromagnetism. Also discussed are the influence of Cr on the surface reconstruction and also the influence of annealing on the properties of the CrGaN film.