On the ferromagnetic structure of the intermetallic borocarbide TbCo2B2C

TL;DR

This study reveals that TbCo2B2C exhibits a ferromagnetic transition at 6.3 K with a tetragonal-to-orthorhombic distortion, differing from similar compounds due to exchange coupling variations influenced by lattice and electronic structure.

Contribution

It provides detailed experimental evidence of the ferromagnetic structure and phase transition in TbCo2B2C, highlighting differences from related borocarbides and linking them to exchange interactions.

Findings

TbCo2B2C undergoes a ferromagnetic transition at 6.3 K.

No field-induced splitting of Co 3d orbitals up to 90 kOe.

The magnetic behavior differs from TbNi2B2C due to exchange coupling variations.

Abstract

Based on magnetization, specific heat, magnetostriction, and neutron diffraction studies on single-crystal TbCo2B2C, it is found out that the paramagnetic properties, down to liquid nitrogen temperatures, are well described by a Curie-Weiss behavior of the Tb+3 moments. Furthermore, below Tc= 6.3 K, the Tb-sublattice undergoes a ferromagnetic (FM) phase transition with the easy axis being along the (100) direction and, concomitantly, the unit cell undergoes a tetragonal-to-orthorhhombic distortion. For fields up to 90 kOe, no field-induced splitting of the Co 3d orbitals was observed; as such the internal field must be well below the critical value needed to polarize the Co 3d subsystem. The manifestation of a FM state in TbCo2B2C is unique among all other isomorphous borocarbides, in particular TbNi2B2C (Tn=15 K, incommensurate modulated magnetic state) even though the Tb-ions in both isomorphs have almost the same crystalline electric field properties. The difference in the magnetic modes of these Tb-based isomorphs is attributed to a difference in their exchange couplings caused by a variation in their lattice parameters and in the position of their Fermi levels.