Magnetic anisotropy in detwinned Tb0.9Dy0.1BaCo2O5.5 single crystal

Magnetic properties of detwinned Tb0.9Dy0.1BaCo2O5.5 single crystals have been studied. The admixture of Dy, introduced only for technological reasons, has no essential influence on the behaviour of the rare earth subsystem of this compound, which is determined by the electronic structure of the Tb3+ ions. It is shown that the Co3+ ions are Ising ions, with the easy axis along the a axis, in the temperature range 2-276 K (T-C). The Tb3+ ions in the AFM phase (T < T-N2 = 3.4 K) are strongly anisotropic, with easy axes [101] and [101]. The magnetic field induced phase transitions have been studied, and it is shown that they are determined by anisotropic Co3+-Tb3+ exchange interactions. It is shown that the Co3+ subsystem is ferrimagnetically ordered within the range T-N < T < T-C (T-N = 250 K, T-C = 275.5 K) and that the ferrimagnet-antiferromagnet phase transition is of first order, whereas the ferrimagnet-paramagnet phase transition is of second order. In the region of antiferromagnetic ordering of the Co3+ ions, metamagnetic phase transitions have been observed for H parallel to a. In the temperature range 2 K < T < 170 K, a small ferromagnetic component along the a axis has been observed. This could indicate partial lack of compensation of the antiferromagnetic order. The magnetic susceptibility in the vicinity of the metal-insulator transition (340 K) has been measured. It is found that this transition is accompanied by a structural phase transition responsible for the essential changes of the magnetic anisotropy of Co ions.