Magnetism study on a triangular lattice antiferromagnet Cu2(OH)3Br

Magnetism of Cu-2(OH)(3)Br single crystals based on a triangular lattice is studied by means of magnetic susceptibility, pulsed-field magnetization, and specific heat measurements. There are two inequivalent Cu2+ sites in an asymmetric unit. Both Cu2+ sublattices undergo a long-range antiferromagnetic (AFM) order at T-N = 9.3 K. Upon cooling, an anisotropy crossover from Heisenberg to XY behavior is observed below 7.5 K from the anisotropic magnetic susceptibility. The magnetic field applied within the XY plane induces a spin-flop transition of Cu2+ ions between 4.9 T and 5.3 T. With further increasing fields, the magnetic moment is gradually increased but is only about half of the saturation of a Cu2+ ion even in 30 T. The individual reorientation of the inequivalent Cu2+ spins under field is proposed to account for the magnetization behavior. The observed spin-flop transition is likely related to one Cu site, and the AFM coupling among the rest Cu spins is so strong that the 30 T field cannot overcome the anisotropy. The temperature dependence of the magnetic specific heat, which is well described by a sum of two gapped AFM contributions, is a further support for the proposed scenario.