Formation of local moments on iron in alkali-metal hosts

Abstract

Spin-polarized, self-consistent-field, scattered-wave calculations have been performed on Fe${M}_{14}$, Fe${M}_{26}$, and ${\mathrm{FeCa}}_{18}$ clusters (M=Li,Na,K,Rb) modeling local environments of an isolated Fe impurity in bcc (M) and fcc (Ca) alkali-metal hosts. No stable moment is observed for the Ca host, while a spin moment of 2${\ensuremath{\mu}}_{B}$ is seen for Fe in the Li host which grows to over 3${\ensuremath{\mu}}_{B}$ in the Rb host. Orbital moments are also likely to be important because of the extreme atomic nature of the Fe d states. We infer these moments by consideration of the calculated 3${d}^{7}$ ground state. A configuration of nearly 3${d}^{7}$ for the Fe atom is inferred for all the alkali-metal hosts. Moment trends are explained in terms of nearly vanishing s-d hybridization in Rb but increasing s-d hybridization up the column to Li.