Observation of Magnetism of Fe at an Interstitial Site in a Metal Host

Magnetic behavior of interstitial Fe impurities in divalent Ca, Sr, and Yb hosts

“…Since the d states at the Fe impurity are not totally occupied, non-spin-polarized calculations yield a sharp peak at the Fermi level, high values of N(E F ) and a strong tendency towards magnetism. The spinpolarized results confirm this tendency and, in agreement with previous calculations, 14,19,20 yield large values for the local moments. In Table I we show RS-LMTO-ASA values for the local moments at a substitutional Fe site in divalent Yb, Ca, and Sr hosts.…”

“…21,32,33 To obtain values for the first-neighbor relaxations, we fixed the impurity and its second neighbors to their unrelaxed positions and allowed the six host atoms closest to the impurity to move radially under the forces generated by the pair potentials, until equilibrium was reached. Later, we realized that for the soft divalent hosts considered here, Lennard-Jones-like potentials probably underestimate the relaxation 14 and decided that it would be useful to obtain results considering larger values for the relaxations. In Table III we show values of the local moment at the interstitial impurity site ͑in units of B ) for two different values of the lattice ralaxation: the Lennard-Jones relaxation ͑LJ͒ and with a value approximately 20% larger ͑LJϩ20%͒.…”

“…Under these conditions the presence of lattice relaxation around the impurity should not significantly change the magnetic behavior at the impurity site. Therefore, as done in previous calculations, 14,19,20 lattice relaxation around the substitutional impurity site was not included. To investigate moment formation at the impurity site we have performed non-spin-polarized calculations for the substitutional Fe impurities in the three hosts.…”

“…In the case of interstitial impurities we assume that the impurity occupies the octahedral site of the fcc structure and, to accommodate the Fe in the interstice, first-neighbor lattice relaxation around the impurity is included. Interstitial transition-metal impurities in Ca and Sr do exist and some, as in the case of interstitial Fe in divalent Yb, 14 are probably magnetic. We hope that the present investigation will contribute to a better understanding of the mechanisms which lead to moment formation at interstitial impurity sites in metallic hosts.…”

“…Normally the sites have very different isomer shift values and can be clearly identified as Fe impurities occupying substitutional or interstitial positions in the host lattice. 14,15 Substitutional Fe impurities in metals have been studied using several different ab initio approaches and the agreement between theory and experiment regarding moment formation at the impurity site is impressive. The mechanisms which govern moment formation in transition metal and simple metal hosts may differ considerably.…”