Magnetization dynamics of a two-sublattice ferrimagnet near the angular momentum compensation point

Abstract

The high-frequency properties of two-sublattice ferrimagnets are examined near the temperature TL at which the angular momentum of the sublattices is compensated. A diagram technique for spin operators is used, along with analytic expressions that are valid over the entire temperature range of the magnetically ordered state of the system. It is shown that near TL longitudinal fluctuations in the magnetization have a significant influence on the resonance properties of the magnet, with different temperature behaviors of the in-phase and out-of-phase precessions of the sublattice magnetization. As TL is approached the frequency of the in-phase precession increases simultaneously with a rise in the line width, while the frequency of the out-of-phase oscillations falls off significantly, so the two modes become equivalent. These results may be important for understanding the microscopic mechanisms of magnetic reversal by ultrashort laser pulses in rare earth ferrimagnets.