Chapter 4 Field induced phase transitions in ferrimagnets

Abstract

Publisher Summary This chapter discusses the high magnetic field magnetization processes in ferromagnetic compounds of the f–d type—that is, in compounds consisting of rare-earth and transition metal elements of the Fe group. The processes that are connected with the variation of mutual orientation of their magnetic sublattices and that reveal themselves through characteristic kinks and jumps in magnetization curves are focused in the chapter. Magnetic symmetry of a crystal changes when the orientation of magnetic sublattices spontaneously varies. A phase transition accompanied by a change of the magnetic symmetry takes place. The phase transitions are referred to as “field induced phase transitions” (FIPT) that may be of 1st or 2nd order. FITP connected with breaking of a collinear alignment of sublattices in ferrimagnetics are also considered in the chapter. It is assumed that the magnetic anisotropy of these materials is small in the sense that the energy of a magnetic anisotropy is smaller in comparison with the energy of the exchange interaction of sublattices. The magnetic anisotropy in such materials is best manifested near a compensation point, where critical fields of transitions to a canted phase tend to zero. In this connection, H–T phase diagrams are very complicate near Tc and composed of curves of the 1st and 2nd order phase transitions and of critical, tricritical points, and others.