Ultrafast spin dynamics and spintronics for ferrimagnets close to the spin compensation point (Review)

The possibilities of applying magnets with full or partial magnetic moment compensation in various spin groups to improve the performance of magnetic electronic devices using spin current (spintronics) are discussed. The effects of an exchange enhancement of the spin dynamics in antiferromagnets are well known. Over the past few years, antiferromagnetic spintronics has turned into an independent, rapidly developing field of applied physics of magnetism. This article provides for a detailed analysis of the possibility of using another class of magnetic materials, such as ferrimagnets close to the spin compensation point, in which the indicated acceleration effects are also detected. A comparative analysis of these two classes of magnets is conducted. The nonlinear spin dynamics of ferrimagnets are examined using a nonlinear sigma-model for the antiferromagnetic vector, describing the difference in spin densities of various spin groups. The simple conclusion derived based on this model is presented, and its real parameters for popular ferrimagnets, amorphous alloys of iron, and rare earth elements, are discussed. The different nonlinear effects of spin dynamics, ranging from homogeneous spin vibrations in small particles to the dynamics of solitons, domain walls, ferrimagnetic skyrmions, and vortices, are analyzed. The possibility of exciting such dynamic modes using spin torque, and their application in ultrafast spintronics is considered.