Magnetic aftereffect following first order magnetostructural phase transitions

The H- and T-induced magnetic aftereffect associated with first order magnetostructural phase transitions has been studied experimentally. The alloys La(Fe, Co, Al)₁₃, Fe_0.49Rh_0.51 doped with Ni and Pd, as well as the compound ζ-Mn₅Ge₂ have been investigated. These materials have various magnetic phase H-T diagrams, various magnetoactive ions, various types of magnetic structures before and after the transitions. However, common magnetic aftereffect relationships have been established for them. A relationship between such an aftereffect and the characteristics (shapes of branches) of quasistatic hysteresis loops (strain in our case) has been revealed. It is shown that the aftereffect is of fluctuational nature: on the steep parts of hysteresis loop branches one observes so called "anomalous" and "giant" fluctuational aftereffects for which the linear dependence of deformation vs. In t does not hold. The existence of a fluctuational aftereffect following a change of temperature has been observed for the first time. The theory of fluctuational aftereffect has been generalized for the case of strain aftereffect with first order magnetostructural phase transitions. Such a theory describes the experimental relationships quite satisfactorily.