Magnetic clusters in Sm 6(Mn 1− xFe x) 23 compounds

Abstract

At temperatures below the magnetic ordering temperature T c the compounds Sm 6(Mn 1− x Fe x ) 23 with 0.33 < x < 0.87 exhibit magnetic properties characteristic of mictomagnetic alloys, e.g. a thermomagnetic history effect, a time dependence of magnetization and a displacement of the hysteresis loop with respect to the origin. At temperatures in a wide range above T c , these compounds do not obey the Curie-Weiss law and the magnetic susceptibility shows a strong field dependence. The results of the magnetic investigations were analysed in terms of the concept of magnetic clusters with temperature-dependent magnetic moments and concentrations. This analysis indicated the formation of magnetic clusters of iron atoms in the spin glass matrix of manganese atoms for compounds with x > 0.2. The appearance of long-range magnetic order in compounds with x > 0.87 is believed to be due to an increase in the magnetic moments of the clusters with increasing x. It is shown that the presence of magnetic clusters causes high initial magnetic susceptibilities at temperatures ranging from T c up to the temperature at which the largest magnetic cluster in the compound disappears.