Paramagnetic scattering studies of the short-range order above TC in 3d transition metal compounds and pure iron

Abstract

For 3d metals the atomic moments derived from Curie‐Weiss susceptibility are often significantly larger than the value obtained in the ferromagnetic state from the saturation magnetization. Indeed the Heisenberg model is known to be inappropriate for metallic systems which in general are better described by band theory. The ground state properties of metallic magnets, particularly the occurrence of nonintegral moments, are well accounted for using the Stoner theory, but the model is less satisfactory at elevated temperatures. The persistence of spin waves above T_C and the observation of paramagnetic moments indicate that the 3d band remains split in the paramagnetic phase in contradiction with mean field theory. A direct way of establishing the existence of paramagnetic moments is by the paramagnetic scattering of neutrons. The technique is particularly enhanced if polarization analysis is employed to obtain a unique estimate of the magnetic cross section. In the present paper, we report the results of recent polarization analysis measurements on transition metal compounds and on pure iron. The magnitude of the atomic moments were found to be temperature independent, remaining close to the saturation magnetization values. Considerable short‐range order persisting up to many times T_C was observed and it is these correlations which give rise to the large paramagnetic moment extracted from the Curie constant.