Anomalous magnetic reordering in magnetodielectric terbium iron garnet at low temperatures

The paper deals with five topics: i) the single three-dimensional irreductible representation (Gamma(4g) = T-1g) of the paramagnetic space group Ia (3) over bard No. 230 is chosen according to the representation analysis of Bertaut for the interpretation of the neutron powder diffraction experiments performed on terbium iron garnet (Tb3Fe5O12); ii) the use of the method of the "symmetry lowering device" of Bertaut in order to select the appropriate rhombohedral subgroup of Ia (3) over bard which allows to deal with the case where the cubic description provides an incomplete answer to the changes observed below 160 K in the ferrimagnetic structure around the [1 1 1] axis from the Neel model toward the "double umbrella" observed at 13 K; iii) the magnetic modes belonging to the one-dimensional irreductible representation A(2g) of the highest rhombohedral subgroup R (3) over barc No. 167 are able to describe the occurrence of its anisotropic character which steeply increases below 160 K due to the concomitant anisotropic effects; iv) the broad anomaly observed near 54 K in the temperature dependences of the components of both sublattices of the Tb3+ ions in the Wyckoff positions (6e) and (6e') is explained partially on the basis of the concept of Belov of the strong paraprocess which has been termed "exchange-enhanced paramagnetism" at the so-called "low-temperature point" (T-B); v) the results are related to the magnetodielectric effect in low magnetic field and to the significant coupling between exchange magnons and ligand-field excitations reported recently in this compound. (C) 2014 Elsevier B.V. All rights reserved.