Field-Induced Partially Disordered State in Yb2Pt2Pb

The physical properties of Yb2Pt2Pb, which has been considered to be a geometrically frustrated antiferromagnet with the Shastry-Sutherland lattice, are investigated by magnetization and specific heat measurements under magnetic fields. Unconventional H-T phase diagrams, which markedly vary according to the direction of the applied magnetic field, are presented. When the magnetic field is applied along the [110] direction, a partially disordered state appears. Such unconventional H-T phases of Yb2Pt2Pb are deduced to be ascribed to the Ising-like nature of the ground-state Kramers doublet and the characteristic crystal structure.