Magnetism On Ideal Triangular Lattices In Nabayb(Bo3)(2)

We report the anisotropic magnetic properties of single crystals of the triangular lattice magnet NaBaYb(BO3)(2). In this material, a layered [Yb(BO3)(2)](infinity) framework is sandwiched by Na+ or Ba2+ layers in alternation. The space group is centrosymmetric, R (3) over barm , with no detectable disorder and Yb3+-based easy axis Kramers doublets forming layered triangular lattice planes. A specific-heat anomaly indicates a second-order phase transition at T = 0.41(2) K that is suppressed to less than 0.15 K in a 0.1-T magnetic field. With a change in entropy of only 0.6(2)% of R ln 2 at this transition, NaBaYb(BO3)(2), however, retains 94(1)% of R ln 2 entropy to the lowest temperature accessed (T = 0.15K). Strong frustration and the potential for quantum magnetism are implied.