New mechanism of first order magnetization process in many-sublattice rare-earth compounds

First-order field-induced spin reorientation transitions in multisublattice intermetallic compounds are considered within an anisotropic Heisenberg model. Unlike previous works, only leading-order anisotropy constants of the sublattices are included. The exchange interactions both between the rare-earth (RE) and transition metal (TM) sublattices and within the RE sublattice play an important role in the model. The latter interaction results in the occurrence of metastable states. One of the minima corresponds to the non-collinear magnetic structure where the RE subsystem is divided into two sublattices, and their moments deviate in opposite directions from the TM moment direction. The possible FOMP scenarios for R$_2$Fe$_{17}$, HoFe$_{11}$Ti, and TbMn$_6$Sn$_6$ systems are discussed.