Characteristic Features of the Anomalous Magnetic Properties of Some Mixed Terbium–Yttrium Ferrite Garnets at Low Temperatures

Mahieddine Lahoubi,Wei Wang,Xiangyu Wang,Assia Boutaba

doi:10.1109/tmag.2020.3019015

Abstract

This article is devoted to the experimental investigation of the occurrence of the so-called “low-temperature Belov point” T B predicted previously for the mixed rare earth-yttrium iron garnet compounds RE x Y 3- x Fe 5 O 12 possessing or not a magnetic compensation point T comp . Isothermal magnetizations MT(H) of two single crystals of Tb x Y 3-x Fe 5 O 12 with rare-earth (RE) = Tb, and x = 1.98, 0.37, were measured in the 4.2-300 K range, using dc magnetic field H up to 100 kOe applied in one or more of the three main crystallographic directions. Anomalies are observed in the region of T B TbIG ≈ 58 K, the previous estimated value for TbIG (x = 3), in the temperature dependences of the paraprocess susceptibility χ p , the parameter |b| of the bH 2 term of the quadratic expansion of MT(H) curves, and other pertinent magnetic characteristics. For x = 1.98 with T comp = 137 K and when H is applied along (110), the χ p - and |b|-maxima take place close to T B TbIG . The anisotropy of the χ p -data gives evidence for a spontaneous noncollinear structure around the easy axis of magnetization (111) at 4.2 K. For x = 0.37 which has no T comp point and when H is applied along (100), the χ p - and |b|-maxima are clearly disturbed by the sign anomalies caused by the noncollinear structure instability mechanism due to the crossing of the Tb 3+ levels at the critical point T* = 16 K and by the lower continuous change from the easy axis <;100> to a low-symmetry angular phase (uuw) due to the first spontaneous spin reorientation phase transition at T SR1 = 40 K. When x decreases from 3 to 0.37, it is found that despite different anisotropy effects of the Tb 3+ ion, its magnetic moment m Tb close to T B TbIG is practically constant (~4.99 in μ B per Tb 3+ ion).

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