Disappearance of spin glass behavior in ThCr2Si2-type intermetallic PrAu2Si2

Abstract

It is unexpected that a spin-glass transition, which generally occurs only in the system with some form of disorder, was observed in the ThCr 2 Si 2 -type compound PrAu 2 Si 2 at a temperature of ∼3 K. This puzzling phenomenon was later explained based on a novel dynamic frustration model that does not involve static disorder. We present the results of re-verification of the reported spin-glass behaviors by measuring the physical properties of three polycrystalline PrAu 2 Si 2 samples annealed under different conditions. Indeed, in the sample annealed at 827 • C for one week, a spin-glass transition does occur at a temperature of T f ∼ 2.8 K as that reported previously in the literature. However, it is newly found that the spin-glass effect is actually more pronounced in the as-cast sample, and almost completely disappears in the well-annealed (at 850 • C for 4 weeks) sample. The apparent sample dependence of the magnetic characteristics of PrAu 2 Si 2 is discussed by comparing it with similar phenomena observed in the isomorphic compounds URh 2 Ge 2 and CeAu 2 Si 2 . Our experimental results strongly suggest that the spin-glass behavior observed in the as cast and insufficient annealed samples is most likely due to the presence of small amount of crystalline impurities and/or partial site disorder on the Au and Si sublattices, and thus is not the inherent characteristic of ideal ThCr 2 Si 2 -type PrAu 2 Si 2 . The perfectly ordered PrAu 2 Si 2 should be regarded as a paramagnetic system with obvious crystal-field effects.