Spontaneous Magnetodielectric Effect and Its Coupling to the Lattice Dynamics in Fluoroperovskites
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neous Magnetodielectric Effect and Its Coupling to the Lattice Dynamics in Fluoroperovskites R. M. Dubrovina,* and R. V. Pisareva a Ioffe
Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia *e-mail: [email protected]
Received February 19, 2020; revised February 19, 2020; accepted March 6, 2020
Abstract—Experimental results on temperature dependences of the low-frequency dielectric permittivity of the group of magnetic fluoroperovskites with different crystal and magnetic structures are presented. Orthorhombic NaCoF3 and NaNiF3, cubic RbFeF3, hexagonal RbNiF3 and tetragonal K2CoF4 and K2NiF4 were investigated. The analysis of experimental results in combination with those of our previous studies of other fluoroperovskites was carried out taking into account the influence of the spontaneous magnetodielectric effect on lattice dynamics. It revealed the role of the spin-phonon coupling and the anharmonic contribution, which leads an increase of dielectric permittivity at heating, and contribution of the hidden structural instability manifested as an increase of the dielectric permittivity at cooling. It was established that the relative contributions of these three main mechanisms to the temperature dependence of dielectric permittivity are significantly different in all fluoroperovskites under study but they are well correlated with the tolerance factor t, which characterizes a relation between ionic radii and is a measure of stability of AMF3 perovskite crystal structure. The obtained results and their analysis reliably demonstrate that the low-frequency dielectric spectroscopy is a highly sensitive method to study particular features of the lattice dynamics of fluoroperovskites at magnetic and structural phase transitions. DOI: 10.1134/S1063776120070043
1. INTRODUCTION The materials that exhibit a coupling between the electric, magnetic, and deformation degrees of freedom are of particular interest of the condensed-matter physics, since they open up new opportunities in the manifestation of the diverse and unusual linear and nonlinear physical phenomena induced by the interaction between various subsystems. Along with fundamental problems, such materials with crossed types of susceptibility are of deep interest for developing multifunctional technological devices, such as tunable filters, electric and magnetic transducers, and converters. Such materials and the related structures are called multiferroics and magnetoelectrics, and the state of the art of their fundamental investigations and potential practical applications was described in many reviews [1–11]. Several tens of thousands of papers in this field was published in the last two decades, which reflects keen interest of a wide scientific society in these materials from both a fundamental standpoint and a viewpoint of their potential applications for creating multifunctional devices. Among the numerous studies reflected in those reviews, the linear magnetoelectric effect (ME), which manifests itself in the appearance of electric polar
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