Tuneable magnetic behaviour, electronic structure and nitrogen vacancy formation in Gd$_{x}$Sm$_{1-x}$N
The rare earth nitrides are the only series of intrinsic ferromagnetic semiconductors where the interplay of spin and unquenched orbital angular momentum provides access to a range of magnetic behaviour. Furthermore, the magnetic properties can be finely tuned through the combination of multiple lanthanide ions in the nitride. Here we present a combined computational and experimental study on the electronic and magnetic properties of Gd$_x$Sm$_{1-x}$N and discuss the effect of cation substitution on the internal exchange field and band structure. We find that as the coercive field of Gd$_x$Sm$_{1-x}$N changes over orders of magnitude via cation substitution the internal exchange field changes by $\sim$20%. Control of these material properties is vital in the field of superconducting spintronics. Finally, motivated by an enhanced concentration of nitrogen vacancies in films with higher Sm content, we investigate computationally the formation of nitrogen vacancy defects in Gd$_x$Sm$_{1-x}$N finding that the formation energy is significantly reduced for vacancy sites adjacent to Sm ions rather than Gd ions.