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ic Properties of Layered Ferrimagnetic Structures Based on Gd and Transition 3d Metals A. B. Drovosekova,*, D. I. Kholina, and N. M. Kreiniesa aKapitza

Institute for Physical Problems, Russian Academy of Sciences, Moscow, 119334 Russia *e-mail: [email protected] Received March 3, 2020; revised March 3, 2020; accepted March 4, 2020

Abstract—Magnetic properties of layered structures based on transition and rare-earth metals (TMs and REMs) such as Fe and Gd have attracted attention of researchers since 1990s. These materials are artificial ferrimagnets with reach magnetic phase diagrams, which make it possible to realize a wide spectrum of predefined properties. In recent years, a new surge of the interest in such systems was evoked by observations of new peculiar dynamic effects in these materials, including optical magnetization reversal and ultrafast motion of domain walls, as well as the possibility of realization of skyrmion magnetic states. In this article, a brief review of the most interesting features of magnetism and magnetic dynamics of layered ferromagnetic TM/REM structures is presented. The results of our investigation concerning Fe/Gd superlattices and the effects of Cr interlayers on their magnetic properties are reported. The surface cant of the magnetization in these structures has been observed directly using the magnetooptical Kerr effect, and the magnetic phase diagram of the system has been obtained. We have analyzed peculiarities of nonuniform modes of magnetic oscillations excited in the Fe/Gd superlattice by the ferromagnetic resonance method. The possibility of sign reversal of the exchange interaction of Fe and Gd layers from antiferromagnetic to ferromagnetic type upon the introduction of Cr interlayers between them has been demonstrated. DOI: 10.1134/S1063776120070031

1. PROPERTIES OF FERRIMAGNETS Ferrimagnets form a special class of magnets, which is known since the 1950s [1–3]. Classical ferrimagnets are magnetically ordered materials in which, like in antiferromagnets, there exist (at least) two antiparallel-oriented magnetic sublattices. However, in contrast to antiferromagnets, these sublattices have different magnetizations because they are formed by different magnetic ions or contain their different numbers. Therefore, the total magnetic moment of the system turns out to be nonzero. In weak magnetic fields, the sublattices orient themselves collinearly to the magnetic field, and the system behaves like a conventional ferromagnet (FM). However, when the magnetic field becomes comparable with the exchange field between the sublattices, a more complicated canted state appears, which resembles the spin flop effect in an easy-axis antiferromagnet [4]. In contrast to ferromagnets, the spontaneous magnetization of ferrimagnets exhibits a more complex dependence on temperature [5, 6]. The difference in the magnetic characteristics of ions forming the sublattices leads to different temperature dependences of their magnetic moments (Fig. 1a). For this reason, the total magnetization