Pressure-induced structural transition and antiferromagnetism in elemental terbium

Structural and magnetic properties of rare-earth Tb metal have been studied by means of neutron powder diffraction at pressures up to 9 GPa in the temperature range 7-290 K. A structural phase transition from the initial hexagonal close-packed (hcp) to the Sm-type rhombohedral phase develops gradually at high pressures above 4 GPa. The initial ferromagnetic state in the hcp phase is suppressed and an antiferromagnetic state is developed in the pressure-induced phase. In the Sm-type structure and the temperature range below T-MO = 110K (at 9 GPa) down to 50 K, long-range order of Tb magnetic moments located in the layers resembling hexagonal close-packing type is formed with a propagation vector k(AF1) = (0 0 1/2), while the layers resembling cubic close-packing type remain disordered. This partial disorder disappears at temperatures below 50 K when magnetic order, including the moments in the latter layers, develops with a propagation vector k(AF2) = (1/2 0 1/2). The relative stability of the hcp and Sm-type structures under pressure was examined by density functional theory calculations, providing significant support to the experimental findings. The calculated bulk moduli of the hcp and Sm-type phases are close to the experimentally determined ones and the estimate P-0 approximate to 4GPa obtained for the equilibrium transition pressure is close to the onset pressure found in real material. The volume collapse at the hcp to Sm-type transition was evaluated to amount to 0.4 angstrom(3) per atom.

Automated summary

The rare-earth Tb metal undergoes a structural phase transition from hcp to Sm-type phase under high pressures, resulting in changes in its magnetic properties. Density functional theory calculations support the experimental findings and provide estimates for volume collapse and transition pressures in real materials.