Magnetic, magneto-optical and specific heat studies of the low temperature anomalies in the magnetodielectric DyIG ferrite garnet

摘要

Measurements of magnetization and Cotton Mouton effect (CM) under external magnetic field (H-ex) combined with specific heat experiments at H-ex = 0, were performed on dysprosium iron garnet Dy3Fe5O12 (or DyIG) single crystals. The low-temperature dependences of some magnetic, magneto-optical and thermodynamic quantities, such as spontaneous magnetization, both magnetic and CM susceptibilities and the excess specific heat due to the contribution of the Dy3+ ions only, give rise to the appearance of two types of anomalies. The first one which is related to the 'low temperature paraprocess' effect, occurs in the region of the 'Belov point' T-B predicted at 42 K. Whereas the second one, which is due to the previous first-order spin reorientation phase transition, takes place at T-SR = 15 K. The easy axis of magnetization defined by the resultant iron sublattice magnetization vector M-Fe, which remains along the 1 1 1 direction above T-SR, changes spontaneously below T-SR and becomes aligned along the low symmetry angular 'u u w' phase. The results are analyzed taking into account those reported earlier, such as the negative magnetodielectric property for H-ex 10 kOe and the Schottky effect which are related to the anomalies observed respectively in the temperature dependences of the dielectric constant at T-SR and the excess specific heat near T-B.