Spin Dynamics for Antiferromagnets and Ultrafast Spintronics
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ynamics for Antiferromagnets and Ultrafast Spintronics B. A. Ivanova,b,c,* a
Institute of Magnetism, National Academy of Sciences of Ukraine and Ministry of Education and Science of Ukraine, Kiev, 03142 Ukraine b Taras Shevchenko National University of Kiev, Kiev, 03127 Ukraine c National University of Science and Technology MISIS, Moscow, 119049 Russia *e-mail: [email protected] Received March 3, 2020; revised March 3, 2020; accepted April 3, 2020
Abstract—A brief review is given of the physical properties of antiferromagnets (AFMs) that can be used as active elements of terahertz and subterahertz range nanooscillators based on the excitation of spin oscillations by spin transfer torque. Possible schemes of such devices are considered. The analysis is carried out from a unified point of view on the basis of the nonlinear sigma model for the antiferromagnetic vector with regard to the magnetic symmetry of real AFMs. Specific properties of AFMs, first of all, the possibility of faster (compared to ferromagnets) spin dynamics, as well as the manifestations of antiferromagnetic ordering in galvanomagnetic and optical effects, are described. The history of the development of AFM physics is briefly discussed, first of all, those aspects of it that may be important for the practical application of AFMs, in particular, in ultrafast spintronics. DOI: 10.1134/S1063776120070079
tures is the existence of weak ferromagnetism due to the deviation of the magnetizations M1 and M2 from the purely antiparallel orientation and the appearance of a sufficiently small magnetic moment M ⊥ L even in the ideal AFM structure [8]. Antiferromagnets with weak ferromagnetism are also called canted AFMs. The theory of weak antiferromagnetism based on a consistent analysis of magnetic symmetry was developed by Dzyaloshinskii [9, 10]. The concept of magnetic symmetry proved extremely fruitful to describe antiferromagnetism; in particular, it made it possible to predict the piezomagnetic effect in AFMs [11], which was discovered experimentally by BorovikRomanov [12]. In fact, at that time, the foundation was laid for studying “nonmagnetic” properties of AFMs, such as optical, galvanomagnetic, and acoustic ones. In the same years, it was experimentally established that the magnetic resonance frequencies of AFMs are much higher than those for ferromagnets [13, 14]. It became clear that AFMs have unique physical properties, often absent for ferromagnets or ferrimagnets, and the physics of AFMs is a significant and important part of the fundamental physics of magnetism. In the early 1960s, Borovik-Romanov wrote the first monograph devoted exclusively to AFM physics [15]. In this monograph, he was actually the first to formulate the criterion of antiferromagnetism based on the symmetry definition of antiferromagnetism, rather than on the condition M = 0. According to this definition, a
1. INTRODUCTION The study of antiferromagnets (AFMs) began in the 1930s [1–5]. It was found that an AFM is characterized by a special type of magnetic ordering, w
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