Re-entrant Spin Glass Behavior in U2NiSi3

Abstract

The results of DC magnetization, AC susceptibility, specific heat and magnetic relaxation measurements on a well-annealed polycrystalline U2NiSi3 sample are reported. The temperature dependencies of the DC magnetization and AC susceptibility show a cusp at a characteristic temperature Tf and a weak ferromagnetic transition at TC>Tf. The temperature Tf strongly depends on the applied magnetic field and frequency. Below Tf the magnetic relaxation measurements reveal a decay of the isothermal remanent magnetization versus time which is drastically slower than above Tf. No anomalies around Tf are observed in the specific heat data which rules out the existence of usual long-range spatial magnetic order at Tf. These results can be considered as clear evidence for the formation of a re-entrant spin glass state in U2NiSi3. The necessary randomness in the U-U magnetic exchange interactions arises from a statistical distribution of Ni and Si atoms on the crystallographic sites of the U2NiSi3 crystal lattice.