Structure dependence of magnetic properties of Pr5Si2Ge2

The crystal structure and magnetic and electronic transport properties of the ternary intermediate compound Pr5Si2Ge2 were investigated by means of x-ray powder diffraction, magnetic and electrical resistance measurements. The compound has two polymorphs: alpha-Pr5Si2Ge2 crystallizing in a monoclinic structure with space group P112(1)/a, for the as-cast sample, and alpha-Pr5Si2Ge2 crystallizing in a tetragonal structure with space group P4(1)2(1)2, for. the sample annealed at 1273 K. The average interatomic distances of magnetic Pr atoms and the amounts of covalent (Si, Ge)-(Si, Ge) bond pairs in these two phases are different, which may be, responsible for their different magnetic properties. The Curie temperatures T-C of alpha-Pr5Si2Ge2 and beta-Pr5Si2Ge2 are 38 and 50 K, respectively. An irreversibility between zero-field-cooling and field-cooling magnetization curves is observed. The zero-field resistance of these two phases exhibits an anomaly near T-C. On the basis of the results of magnetic and electrical resistance measurements, it is inferred that both of these phases exhibit spin-glass-like behaviour. The magnetic properties and structure dependence of the Pr5Si2Ge2 can be elucidated well using the Ruderman-Kittel-Kasuya-Yosida model.