Foreword: Nuclear methods in magnetism

Abstract

Usually, the occurrence of magnetism on isolated, substitutional 3d, 4d and 5d impurity ions in metals is restricted to certain 3d ions (mainly Cr, Mn, Fe, Co, Ni) in alloying metallic systems. The application of the perturbed γ-ray distribution method following heavy ion reactions and recoil implantation has offered an experimental technique for producing and investigating new magnetic systems. Of special importance are nonalloying systems, which can exhibit extreme variations of e.g. density of states and atomic volume in the probe–host combinations produced by recoil implantation. Recent developments in this field include the following: Magnetism and the Kondo effect observed for ⁴³Sc ions in alkali metal hosts are found to be consistent with a nearly localised, ionic 3d¹ single-electron configuration, and parallel the behaviour observed in certain Ce systems. More generally, essential features of the magnetism of 3d and 4d ions in sp metal hosts are similar to those of 4f systems. Recent experimental and theoretical studies of ⁵⁴Fe in d-band metal hosts are of key importance for an understanding of the basic features of local moment formation on substitutional Fe ions in transition metal hosts in general.

In many nonalloying ⁵⁴Fe probe-host combinations, (at least) two different magnetic responses have been detected. These components correspond to substitutional and interstitial sites of the implanted probes, as has been verified by in-beam Mössbauer spectroscopy of ⁵⁷Fe in a series of host metals. This provides new insight into lattice site occupation as a function of host properties and allows directed investigations of the magnetic behaviour of Fe (and Mo) ions on interstitial lattice sites. Depending on the host metal, interstitial Fe is found to be nonmagnetic, e.g. in Zr, or magnetic, e.g. in Yb. Surprisingly, even the 4d ion Mo can be magnetic on interstitial sites. The experimental results for the substitutional as well as the interstitial sites can be compared to extensive theoretical work within the framework of local spin density calculations.