Electronic structure and magnetic anisotropy of Sm$_2$Fe$_{17}$N$_x$

Electronic structure and magnetic properties of Sm$_2$Fe$_{17}$N$_x$ are studies on the basis of the first-principles electronic structure calculation in the framework of the density functional theory within the local density and coherent potential approximations. The magnetic anisotropy of the system as a function of nitrogen concentration $x$ is discussed by taking account not only of the crystal field effects but also of the effects of the f-electron transfer from Sm to the neighboring sites. Also discussed is the magnetic transition temperature that is estimated by mapping the system into a Heisenberg model. The results show the crystalline magnetic anisotropy changes its direction from in-plane to uniaxial ones as x increases. It takes the maximum value near $x\sim 2.8$ and then decreases slightly towards $x=3$. The mechanism for these behaviors is discussed in the light of the results of detailed calculations on the bonding properties between Sm and its neighboring N.