The magnetism and electronic structure of 3d and 4d ions in metals exhibit qualitative differences in sp metal hosts compared to hosts with d band electrons. 3d and 4d ions in sp metal hosts, in particular in alkali metals, reflect the phenomena of well-defined ionic ground states, large orbital magnetism, mixed valence, and crystal field splittings smaller than the LS coupling. Magnetic 3d and 4d states in sp metals cannot be described by one-electron approaches based on Anderson type models but require an analysis based on ionic configurations where the tendencies towards reduced magnetism can be well reproduced by increasing spin fluctuation rates. The behavior of d ions in sp metals exhibit basic common features to the physics of stable and unstable f states in metals. In contrast, the local moment formation of Fe, Co and Ni ions in transition metal hosts, in Cu, Ag, Au, and even in Hg is governed by inter-atomic interactions of the magnetic d states with host d band electrons. As the leading contribution to magnetic stability an effectively ferromagnetic interaction between impurity d states and host d band electrons has been suggested, which in certain hosts successfully suppress spin fluctuations arising from antiferromagnetic d-sp exchanges. All host dependent trends of moment stability of 3d and also of 4d ions in metals are consistent with this proposal.
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