Experimental studies of weakly magnetic transition metal compounds

Experimental studies of the weakly magnetic d-electron systems MnSi, ZrZn₂ and Mn₃Si reviewed here, reveal unexpected deviations from Fermi-liquid behavior and the conventional assumptions underlying standard spin fluctuation theory. Properties of the weakly ferromagnetic compounds are inconsistent with Landau damping of spin fluctuations, expected for the high purity of the samples investigated, but are instead suggestive of diffusive spin dynamics. The spin-density-wave antiferromagnet Mn₃Si exhibits exceptional stability at high magnetic field indicative of two vastly different energy scales and a novel mechanism that controls the onset of long-range magnetic coherence. It is speculated that these properties are of similar origin and hint of a break-up of single-electron excitations.