Reentrant magnetism: New aspects

Measurements are presented of the thermoremanent and the low-field magnetizations of an amorphous (${\mathrm{Fe}}_{78}$ ${\mathrm{Mn}}_{22}$ ${)}_{75}$ ${\mathrm{P}}_{16}$ ${\mathrm{B}}_6$ ${\mathrm{Al}}_3$ and a crystalline ${\mathrm{Ni}}_{78.4}$ ${\mathrm{Mn}}_{21.6}$ reentrant alloy as a function of temperatures. The data show evidence for two different blocking mechanisms responsible for the sharp drop in the familiar zero-field-cooled susceptibility below $T_f$. Both mechanisms are basically connected with domain-rotation effects. Our results are reasonably explained on the basis of a phenomenological free-energy model.