Experimental and theoretical study of the magnetism and local lattice structure ofdions in alkali-metal hosts

The local susceptibility of isolated Mo ions in Na is observed to be consistent with a localized, magnetic 4$d^5$ state of ${\mathrm{Mo}}^{1+}$. Size, valence, and bonds of such ${\mathrm{Mo}}^{1+}$ cells are similar to the host ${\mathrm{Na}}^{1+}$ cells. These features allow a study of 4d magnetism by local-spin-density calculations under the premise of substitutional Mo ions in Na. The calculations yield an effective moment of more than 5${\mu }_B$ for Mo in Na. In the larger hosts, K, Rb, and Cs, we propose unusual large lattice contractions around d ions with localized d states, up to 22% for the extreme case of ${\mathrm{Fe}}^{2+}$ in Cs. This results from impurity-host bond strengths larger than those between host atoms along with the very large compressibilities of K, Rb, and Cs.