Steplike metamagnetic transitions in a honeycomb lattice antiferromagnet Tb${}_2$Ir${}_3$Ga${}_9$

Abstract

Single crystals of a honeycomb lattice antiferromagnet, Tb${}_2$Ir${}_3$Ga${}_9$ were synthesized, and the physical properties have been studied. From magnetometry, a long-range antiferromagnetic ordering at $\approx$12.5 K with highly anisotropic magnetic behavior was found. Neutron powder diffraction confirms that the Tb spins lie along the $\va $-axis, parallel to the shortest Tb-Tb contact. Two field-induced spin-flip transitions are observed when the field is applied parallel to this axis, separated by a plateau corresponding roughly to M$\approx$M${}_{\mathrm{s}}$/2. Transport measurements show the resistivity to be metallic with a discontinuity at the onset of Néel order. Heat capacity shows a $\lambda$-like transition confirming the bulk nature of the magnetism. We propose a phenomenological spin-Hamiltonian that describes the magnetization plateau as a result of strong Ising character arising from a quasidoublet ground state of the Tb${}^{3+}$ ion in a site of \textit{C${}_s$} symmetry and expressing a significant bond dependent anisotropy.

11 pages, 9 figures