Field evolution of the spin-liquid candidate YbMgGaO_4

摘要

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 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 μ_0H = 1.0-2.5 T for H ‖ c and 2-5 T for H ⊥ c. Using Monte Carlo simulations of a realistic spin Hamiltonian, we ascribe these features to nonmonotonic changes in the magnetization and the 1/2 plateau that is smeared out by the random distribution of exchange couplings in YbMgGaO_4.