Magnetization and thermal expansion measurements on the Ising magnet SmPt2 Si2: Potential coexistence of spin glass and antiferromagnetic states

The Ising magnet SmPt2Si2 undergoes an antiferromagnetic (AFM) transition at TN1 = 5.6 K, but the magnetic moments of some Sm ions remain disordered even below TN1. 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 Tg≈ 2.4 K. These results suggest that the partially disordered state of the Sm ions becomes a cluster spin glass below Tg 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.