Spectroscopy ofRFe₃(BO₃)₄multiferroics: phase transitions, spin-phonon interaction, coupled electron-phonon modes

Abstract

Abstract. Review of the work performed in the author's laboratory is given, on high-resolution Fourier spectroscopy studies of multiferroics from the family of rare-earth iron borates with the structure of the natural mineral huntite. For these multiferroics, we reveal spectral signatures of interactions between electronic, spin, and lattice degrees of freedom. We have observed and investigated coupled electron-phonon modes in PrFe3(BO3)4 and TbFe3(BO3)4. The structure of the magnetically ordered phase of EuFe3(BO3)4 is determined.Multiferroics, i.e., materials, in which at least two order parameters coexist, are interesting both for the fundamental solid state physics and in view of possible applications. As a rule, different subsystems (electronic, spin, lattice) of a multiferroic strongly interact with each other. This, in particular, opens a possibility to control an electric polarization by a magnetic field and vice versa. The history of multiferroics goes back to the P. Curie's paper of 1894 but only in the middle of the last century Soviet scientists at first predicted in what compounds (named by them "magnetoelectrics") the magnetoelectric effect can be observed and then observed it for the first time. These studies are summarized in the review [1]. The word "multiferroics" appeared in 1994, it allows considering other than magnetic and electric order parameters. At the beginning of this century, a new burst of interest in multiferroics was caused by the synthesis of compounds with a large magnetoelectric effect and by a discovery of new classes of multiferroics (see, e.g., the reviews [2] and [3]). At the same time, linear and nonlinear optical spectroscopy of multiferroics develops; new magneto-optical effects characteristic just for multiferroics are discovered.In our laboratory, starting from the beginning of 2000-ies, studies of different multiferroics are carried out by the method of the broad-band high-resolution Fourier spectroscopy. Below, we review several our works on the study of new multiferroics from the family of the rare-earth (RE) iron borates with structural type of the natural mineral huntite. These compounds possess a noncentrosymmetric trigonal structure which incorporates helical chains of the FeO6 octahedra joined by their edges, running along the c axis. The chains are linked by BO6 triangles and RO6 prisms. All RE iron borates antiferromagnetically order at TN = 30 -40 K. Those of them that have an ionic radius of the R 3+ ion smaller than the one of Sm 3+ undergo a structural phase transition. We have

Химическое сжатие, структурная нестабильность и ИК-активные фононы в ряду редкоземельных аналогов францисита Cu-=SUB=-3-=/SUB=-RE(SeO-=SUB=-3-=/SUB=-)-=SUB=-2-=/SUB=-O-=SUB=-2-=/SUB=-Cl

“…Такие взаимодействия могут приводить как к образованию связанных мод, так и к необычному поведению фононов. В работах профессора Марины Поповой, юбилею которой посвящена данная работа, получены важные результаты по исследованиям мультифункциональных материалов при помощи спектроскопии колебательных состояний в области динамики решетки [1][2][3][4][5][6][7], структурных [8][9][10] и магнитоструктурных переходов [6,[11][12][13], спин-фононных [4,9,[14][15][16], электрон-фононных [17][18][19][20] и межионных (давыдовских) [21] взаимодействий, магнито-диэлектрических [18] и изотопических [22] эффектов, связанных электрон-фононных [14,19] и магнонфононных мод [3]. В данной работе, опираясь на опыт, полученный благодаря совместной с юбиляром работе, мы проводим первое исследование спектра инфракрасноактивных фононов новых редкоземельных соединений из семейства францисита.…”