Non-Heisenberg Anisotropic Ferrimagnet
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DISORDER, AND PHASE TRANSITION IN CONDENSED SYSTEM
Non-Heisenberg Anisotropic Ferrimagnet A. V. Krivtsovaa, Ya. Yu. Matyuninaa, and Yu. A. Fridmana,* a
Vernadsky Crimean Federal University, Simferopol, Crimea, 295007 Russia *e-mail: [email protected]
Received December 31, 2019; revised February 7, 2020; accepted February 7, 2020
Abstract—The static and dynamic properties of an anisotropic ferrimagnet, which has sublattices with S = 1 and σ = 1/2 and is characterized by a non-Heisenberg (spin bilinear or biquadratic) exchange interaction for the sublattice with S = 1, are studied. The anisotropy is determined by the Ising interaction of the sublattices. When the non-Heisenberg exchange interaction of the sublattice with S = 1 is taken into account, the anisotropic system is shown to be in a phase with vector order parameters (ferrimagnetic phase) and in a phase characterized by both vector and tensor order parameters (quadrupole-ferrimagnetic phase). The type of the phase transition between these phases and the condition of compensating the magnetic moments of the sublattices are determined. DOI: 10.1134/S1063776120060059
1. INTRODUCTION Ferrimagnets are the magnetic materials the properties of which are intermediate between ferromagnets and antiferromagnets. As antiferromagnets, ferrimagnets contain magnetic sublattices with antiparallel magnetization. As ferromagnets, ferrimagnets have a nonzero total magnetization, which can vanish at a compensation point. Ferrimagnets are always considered as important magnetic electronics materials, and new interesting properties are constantly revealed in them. Early in the 21st century, a new promising field formed in the fundamental and applied physics of magnetism. It was called femtomagnetism and was based on the possibility to manipulate the spin system of a magnet using femtosecond laser pulses [1–4]. An ultrafast (in a few picoseconds) magnetization reversal in the sublattices of a ferrimagnet (rare-earth–transition metal alloy GdFeCo) was detected under the action of a laser pulse shorter than 100 fs [5, 6]. This effect was found to be directly related to the presence of two sublattices and to be substantially dependent on the exchange-interaction-induced change in the moduli of the magnetic moments of the sublattices M1(t) and M2(t) so that their sum remains constant [7, 8]. Therefore, the purely longitudinal evolution of the magnetic moments of the sublattices is substantial for describing this effect. Interest in compensated magnets has been recently quickened in the new and rapidly developing field of applied physics of magnetism, namely, spintronics [9–11] due to the fact that their dynamic parameters (magnetic resonance frequency, domain wall velocity) are exchange enhanced. The possibility of spin pumping of antiferromagnets was demonstrated for the first
time in [12], where a spin current was shown to strongly affect magnetically ordered systems with a zero total magnetic moment. In principle, this finding can be used to increase the speed of operatio
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