Anomalies in the magnetic properties of some terbium-yttrium iron garnets at low temperatures

Abstract

This work is aimed to study the influence of the replacement of the magnetic cations Tb3+ by diamagnetic cations Y3+ on the low-temperature point’, TB predicted by Belov for ferrimagnets with and without magnetic compensation point, Tcomp. Isothermal magnetizations, MT(H) are carried out on single crystals of two mixed terbium-yttrium ferrite garnets TbxY3-xFe5O12 (x = 1.98 and 0.37). The measurements are performed using DC magnetic field, H up to 80 kOe applied along the <111> and <100> crystallographic directions in the 1.5-300 temperature range. From the approximation to the second order of H, the expansion of MT(H) is analyzed on the basis of the T-dependences of the spontaneous magnetization, MS, the paraprocess magnetic susceptibility, χp and the parameter, |b| of the bH2 term. The manifestation of ferromagnetic-and antiferromagnetic-type low-temperature paraprocess and other concomitant effects is observed in the temperature dependences of the derivative, dMS/dT where MS exhibits Néel’s-type curves, i.e., N-type with Tcomp = 137 K for x = 1.98 and P-type without a Tcomp point for x = 0.37). It was established that low-T anomalies appear in the area of TB = 58 K reported before for the pure TbIG. The results obtained for x = 0.37 in the case of the free sphere show that |b| undergo changes at TSR1 = 40 K, TSR2 = 140 K, and TSR3 = 232 K. Thus, we suggest that as T increase, the previous spin reorientation phase transition occurs in a wide T-range, (40-232 K) from the easy axis of magnetization <100> via stable and intermediate low-symmetry angular phases <uuw> towards the high symmetry phase <111>.