A correlation length measured by zero-field muon spin relaxation in disordered magnets

Abstract

Muon spin relaxation, as a local magnetic probe, is not normally expected to be able to provide measurements of any magnetic correlation length. When anomalously shallow static zero-field muon spin relaxation functions were observed for CeNi1-xCuxSn and a small number of other highly disordered magnetic systems, however, and a `Gaussian-broadened Gaussian' relaxation function shown to fit them, it was suggested that an unusual short-range correlation among local moments in the material was acting. `Range-correlated moment magnitude variation', in which ion-moment orientations are completely random, but moment magnitude varies slowly from place to place, is shown by Monte Carlo numerical simulation on a lattice of moments to generate the qualitative form of shallow static zero-field relaxation observed. Thus, the shape of the zero-field muon spin relaxation function is sensitive to a correlation length.