Antiferromagnetic resonance and dielectric properties of rare-earth ferroborates in the submillimeter frequency range
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ISORDER, AND PHASE TRANSITION IN CONDENSED SYSTEM
Antiferromagnetic Resonance and Dielectric Properties of Rareearth Ferroborates in the Submillimeter Frequency Range A. M. Kuz’menkoa, A. A. Mukhina,*, V. Yu. Ivanova, A. M. Kadomtsevab, S. P. Lebedeva, and L. N. Bezmaternykhc a Institute
of General Physics, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 119991 Russia *email: [email protected] b Moscow State University, Moscow, 119991 Russia c Kirensky Institute of Physics, Siberian Branch, Russian Academy of Sciences, Akademgorodok, Krasnoyarsk, 660036 Russia Received December 10, 2010
Abstract—The magnetoresonance and dielectric properties of a number of crystals of a new family of multi ferroics, namely, rareearth ferroborates RFe3(BO3)4 (R = Y, Eu, Pr, Tb, Tb0.25Er0.75), are studied in the sub millimeter frequency range (ν = 3–20 cm–1). Ferroborates with R = Y, Tb, and Eu exhibit permittivity jumps P3121 phase transition. at temperatures of 375, 198, and 58 K, respectively, which are caused by the R32 Antiferromagnetic resonance (AFMR) modes in the subsystem of Fe3+ ions are detected in the range of anti ferromagnetic ordering (T < TN = 30–40 K) in all ferroborates that have either an easyplane (Y, Eu) or easy axis (Pr, Tb, Tb0.25Er0.75) magnetic structure. The AFMR frequencies are found to depend strongly on the magnetic anisotropy of a rareearth ion and its exchange interaction with the Fe subsystem, which determine the type of magnetic structure and the sign and magnitude of an effective anisotropy constant. The basic parameters of the magnetic interactions in these ferroborates are found, and the magnetoelectric contribu tion to AFMR is analyzed. DOI: 10.1134/S106377611105013X
INTRODUCTION Rareearth ferroborates RFe3(BO3)4 (R = Y, La⎯Lu) have recently attracted considerable interest due to the discovery of multiferroelectric phenomena in them [1, 2] and to their interesting magnetic, opti cal, and other properties caused by the exchange inter action between the iron and rareearth magnetic sub systems [3, 4]. At sufficiently high temperatures, all rareearth ferroborates have a noncentrosymmetric trigonal structure belonging to space group R32 [5, 6], which remains unchanged in a number of ferroborates with a large ionic radius of an R ion (La–Sm) down to low temperatures. In ferroborates with a smaller ionic radius of an R ion (Eu–Er, Y), a phase transition into a lowsymmetry trigonal crystal structure of space group P3121 takes place when temperature decreases [7, 8]. At temperatures below TN = 30–40 K, antiferromag netic ordering occurs in the iron ion subsystem in ferrob orates: depending on the type of R ion, iron ion spins are oriented in either plane ab (R = Nd, Sm, Eu, Er, Y) [4, 9, 10] or along trigonal axis c (R = Pr, Tb, Dy) [11–14]. In this case, a magnetic order is also induced in the rare earth subsystem due R–Fe to exchange; it plays an important role in stabilizing an easyplane or uniaxial magnetic structure, and the role of a rather weak R–R interaction here is in
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