Contents I. Introduction
Several high magnetic field facilities for solid-state research have been developed in the world [Kyoko 2002]. High fields are especially useful for the studies of various alloys of rare earths (R) and Fe. The R–Fe intermetallics are indispensable for production of permanent magnets, as well as magnetostrictive, magnetocaloric, magnetoelectric, and other functional materials [Tereshina 2018]. Experiments carried out using high magnetic fields permit studies of magnetization processes in the R–Fe-type compounds both with high and low R content. If R is a heavy rare earth metal (from Gd on), the magnetic moment of the R sublattice orders are antiparallel to the Fe sublattice's moment, thereby decreasing the total magnetization of the ferrimagnet. If the magnetic field is sufficiently high, it is capable of breaking the antiparallel alignment of the moments by turning them (in an abrupt or continuous fashion) in the same direction. The ultimate goal is a field-induced ferromagnetic state in the compound with the maximum magnetization. For different classes of the R–Fe alloys, external magnetic fields required to observe a field-induced ferromagnetism often exceed 100 T. Such fields can be obtained using a special technology, destructive or semidestructive [Portugall 1999, Zherlitsyn 2012]. Analysis of the magnetization processes with the aid of analytical methods allows us to extract information on the crystal field and exchange interaction parameters [Kato 1995, Kostyuchenko 2015] for the functional R–Fe materials.
