Effects of a “weak” sublattice magnetization longitudinal quantum fluctuations on spin waves’ dynamics in ferrimagnets

Ferrimagnets (FIMs) with antiferromagnetically coupled magnetic sublattices are promising materials for magnonics. Compared to ferromagnets, they possess both right-handed and left-handed spin waves (SWs) and thus can store information as spin-up and spin-down electrons. Experiments indicate that at finite temperatures, the quantum fluctuations of a “weak” sublattice magnetization make a unique and significant contribution to SWs’ characteristics. These effects are fundamental to understanding the microscopic mechanisms determining clockwise and counterclockwise magnons’ energy and chiral asymmetry of magnons damping. We discuss the temperature renormalization of SW’s spectrum in FIM with two antiferromagnetically coupled sublattices based on the diagrammatic technique for spin operators developed by V. G. Bar’yakhtar and coauthors. The effects of magnetization longitudinal fluctuations on SWs characteristics are demonstrated on the classical FIM, namely, gadolinium iron garnet. The quantum description of SWs’ dynamics reveals individual magnetic sublattices’ contribution to their characteristics, clearly identifying their origin and features.