High-field magnetization and magnetic structure of Tb₃Co

The measurements of the magnetization in high steady and pulsed fields together with neutron diffraction measurements on a powder sample and on a single crystal have been performed to study the magnetic state of the Tb ₃Co compound. It has been shown that the modulated antiferromagnetic structure which exists in Tb₃Co below T_N ≤ 82K transforms to the incommensurate magnetic structure with a strong ferromagnetic component along the c-axis with further cooling below the critical temperature T_t≈72K. The phase transition from the high-temperature to the low-temperature magnetic state at T_t is of first order. The incommensurability of the low-temperature magnetic structure of Tb₃Co is attributed to the non-Kramers character of the Tb³⁺ ion in combination with competition between the indirect exchange interaction and the low-symmetry crystal electric field.