Elastic, magnetic, and magnetoelectric properties of the CaBaCo 4 O 7 multiferroic
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ISORDER, AND PHASE TRANSITION IN CONDENSED SYSTEM
Elastic, Magnetic, and Magnetoelectric Properties of the CaBaCo4O7 Multiferroic Z. A. Kazeia*, V. V. Snegireva, G. P. Vorob’eva, Yu. F. Popova, D. K. Vyalykha, L. P. Kozeevab, and M. Yu. Kamenevab a Moscow
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State University, Moscow, 119992 Russia Nikolaev Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia *e-mail: [email protected] Received January 25, 2016
Abstract—The structural, elastic, magnetic, and magnetoelectric properties of the CaBaCo4O7 multiferroic are experimentally studied and compared with the properties of the related YBaCo4O7 cobaltite, where Y3+ ions substitute for Ca2+ ions. Unlike the frustrated YBaCo4O7 magnet, the softening of Young’s modulus and the hysteresis in the ΔE(T)/E0 curve of ferrimagnetic CaBaCo4O7 in the paramagnetic region are weak, and the anomaly during the magnetic transition increases by almost an order of magnitude. This difference can point to different characters of the development of a long-range magnetic order in these two cobaltites. The distortion of the crystal structure that removes the frustrations of exchange interactions is found to correlate with the magnetic behavior of the cobaltites under study. The magnetization curves of the Ca cobaltite have two steps below 15 K, which can point to the presence of a metastable state in a high magnetic field. The study of the longitudinal and transverse magnetoelectric effects in a pulsed magnetic field demonstrates that their magnitudes are maximal near TC and change their character from linear to quadratic during passage through this temperature. DOI: 10.1134/S106377611611011X
1. INTRODUCTION The family of cobaltites LnBaCo4O7 + δ (Ln is a lanthanide, Y, or Ca), which exhibit unusual magnetic behavior due to the frustration of exchange interactions and mixed valence in the 3d subsystem, has been extensively studied in the last decade [1–6]. The LnBaCo4O7 cobaltites (family 114) have a framework tetrahedral crystal structure, in which the magnetic lattice of Co with high-spin cations Co2+/Co3+ in CoO4 tetrahedra is described as the packing of triangles layers and Kagome layers alternating along trigonal axis c [1, 2, 7, 8]. The two-dimensional Kagome lattice, which consists of corner-sharing triangles, is well known as the structural topology that causes a geometric frustration. The geometric frustrations that are inherent in both the Kagome lattice and the triangle lattice and can be lifted as a result of a structural phase transition accompanied by the deformation of CoO4 octahedra induce the formation of nontrivial magnetic states in the LnBaCo4O7 cobaltites [9, 10]. The crystal structure of the cobaltites at high temperatures is described by hexagonal space group P63mc [11–13] or trigonal group P31c [14, 15], which is a subgroup of group P63mc. Hexagonal structure P63mc is formed by vortex-connected CoO4 tetrahedra, where
Ln and Ba cations occupy the octahedral and tetrahedral sites, respectively, in a 3D t
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