Dynamics of a collinear two-position multisublattice ferrimagnet in a three-sublattice model as applied to yttrium iron garnet

Abstract

Results of investigations of magnetoelectric effects in substances with a ferrimagnetic ordering are reported. The consideration is performed on the example of yttrium iron garnet (YIG) belonging to the space group Oh10. In the unit cell of the crystal structure of YIG, the magnetic Fe ions occupy 16 positions of the a type and 24 positions of the d type. It is shown that the magnetoelectric effects in YIG can be described in the model of three (rather than 20) magnetic sublattices, namely Ma, Md1 and Md2. The magnetization vector Ma is determined by Fe ions located in a positions. The Fe ions in d positions are located in two sublattices (d1 and d2) related by a symmetry center. In such a three-sublattice model of a two-position ferrimagnet, one more branch (antimagnon) appears in the spectrum apart from two ferromagnon branches. The third branch is caused by vibrations of only antiferromagnetism vector L = Md1 − Md2. This branch is associated with changes in the dielectric permittivity and refraction index of the ferrimagnetic medium that are responsible for the magnetoelectric effects.