Long-time decay of thermoremanent magnetization through stepwise changes of the reentrant spin-glass-like state in the Ni₂In-type Mn₇Sn₄

The zero-field-cooled magnetization at the magnetic field H = 300 Oe shows anomolous kinks at T_A and T_B (> TA) far below the reentrant spin-glass-like transition temperature T_f (above which a long-range ferrimagnetic ordering is set up). The irreversibility between the zero-field-cooled and the field-cooled magnetizations, and the time decay of the thermoremanent magnetization (σ_TRM) are observed below the ferrimagnetic Curie temperature T_c. The decay feature can be described by Ogielski's power law σ_TRM = At^-α whose α exhibits peaks at T_A, T_B, T_f and T_C. The peak of α at T_C can be fitted by the combination of Ising type and Ginzburg-Landan type expressions. Three stepwise changes of the spin-glass-like state below T_f and the feature of the coexistence of short-range spin-glass and long-range magnetic ordering components above T_f are discussed.