Field evolution of the spin-liquid candidate YbMgGaO${}_4$

Abstract

We report magnetization, heat capacity, thermal expansion, and magnetostriction measurements down to millikelvin temperatures on the triangular antiferromagnet YbMgGaO${}_4$. Our data exclude the formation of the distinct $\frac{1}{3}$ plateau phase observed in other triangular antiferromagnets, but reveal plateaulike features in second derivatives of the free energy, magnetic susceptibility and specific heat, at $\hat{I}{¼}_{0}H$ = 1.0 - 2.5 T for $H\parallel c$ and 2 - 5 T for $H\perp c$. Using Monte-Carlo simulations of a realistic spin Hamiltonian, we ascribe these features to nonmonotonic changes in the magnetization and the $\frac{1}{2}$ plateau that is smeared out by the random distribution of exchange couplings in YbMgGaO${}_4$.