Spin-glass behaviour with extended short-range ferromagnetic order in U2RhSi3

For U2RhSi3, which crystallizes in a disordered derivative of the hexagonal AlB2-type structure, we present a detailed investigation of magnetic properties by measurements of AC and DC susceptibility, magnetization, magnetic relaxation, specific heat and electrical resistivity. The results provide evidence for the formation of extended short-range ferromagnetic order at the temperature T-C approximate to 25 K, as indicated by a specific heat anomaly, and for a low-temperature spin-glass state with a freezing temperature T-f = 19.6 K. According to systematic specific heat experiments on isostructural spin-glass systems, short-range ferromagnetic correlations above the spin-freezing temperature are observed in U2RhSi3 (T-C approximate to 25 K, T-f = 19.6 K) and U2CoSi3 (T-C approximate to 10 K, T-f approximate to 8 K), but not in U2PdSi3 (T-f = 13.5 K) and U2NiSi3 (T-f approximate to 22 K). Different degrees of structural disorder of transition metal and silicon atoms, both on the same crystallographic site, seem to be the origin for the distinct different magnetic behaviour.