Magnetization and thermal expansion measurements on the Ising magnet SmPt2Si2: Potential coexistence of spin glass and antiferromagnetic states

The Ising magnet SmPt2Si2 undergoes an antiferromagnetic (AFM) transition at T-N1 = 5.6 K, but the magnetic moments of some Sm ions remain disordered even below T-N1. Here, we report the results of measurements of thermal expansion, magnetostriction, and dc magnetization of SmPt2Si2 in the temperature range from 0.26 to 7 K. The magnetization and thermal expansion results show clear irreversible phenomena at temperatures below T-g approximate to 2.4 K. These results suggest that the partially disordered state of the Sm ions becomes a cluster spin glass below T-g and coexists with the AFM long-range order. However, unlike the conventional coexistence of spin glass and antiferromagnetism, the isothermal magnetization process at 0.26 K shows a hysteresis curve with almost no remanent magnetization. This observation suggests that the cluster spin glass state is an unusual state with a short relaxation time at zero field.