Frustrated magnetism of the triangular-lattice antiferromagnets α-CrOOH and α-CrOOD

We report a comprehensive investigation of the frustrated magnetism on the delafossite oxides, α -CrOOH and α -CrOOD, which experimentally realize the S = 3/2 nearly-Heisenberg antiferromagnetic ( J 1 > 0) model on a triangular lattice with weak single-ion anisotropy ( D ). The electron spin resonance (ESR), neutron scattering, and specific heat ( C m ) measurements on both α -CrOOH and α -CrOOD consistently indicate that the long-range 120° Néel order is significantly suppressed and both systems are in the vicinity of a spin-liquid phase with C m ∼ T 2 at low temperatures. The strength of D is quantitatively determined from fitting the high-temperature ESR linewidth and magnetic susceptibility, and its minus sign ( D < 0, easy-axis type) is suggested by the low-energy ( E ⩽ 2 meV) spin excitations. This easy-axis anisotropy ( D / J 1 ∼ −5%) competes with the 120° Néel order and thus enhances the quantum spin fluctuations at low temperatures.