Ab initio calculation of electronic structure, crystal field, and intrinsic magnetic properties of Sm2Fe17, Sm2Fe17N3, Sm2Fe17C3, and Sm2Co17

In a comparative study we calculated the spin and orbital moments, spin and charge densities, and 4f crystal field (CF) parameters of the rare-earth transition-metal intermetallics Sm(2)Fe(17)Z(3) (Z=C,N) and Sm2Co17 using a relativistic optimized linear combination of atomic orbitals method. The itinerant valence electron states were treated in the local-spin- density approximation (LSDA), whereas the localized 4f states were described as open core states within the self-interaction-corrected LSDA. The calculations yield magnetic moments in good agreement with experiment. While all local moments of Sm2Fe17 increase upon lattice expansion, the moments of atoms neighbouring the interstitial sites decrease and those of more distant Fe atoms increase upon insertion of interstitial N or C. In N interstitial atoms all 2p(alpha) orbitals are polarized antiparallel to their respective Fe and Sm neighbor atoms in the bond directions, whereas in C all 2p(alpha) orbitals are polarized antiparallel to the Fe atoms neighboring the interstitial site. The second-order CF parameters A(2)(0) dominating the rare-earth magnetocrystalline anisotropy are found to have the same sign and order of magnitude as those derived from magnetization data. In accordance with experiment the calculated negative A(2)(0) is larger for the Co compound than for the Fe parent compound and is largely strongly increased upon insertion of interstitial N or C. The agreement between theory and experiment is improved by taking into account the CF contribution arising from the asphericity of the exchange-correlation potential of the non-4f states.