Field-induced 3D-LRO of Haldane-gap antiferromagnet NDMAZ

Abstract The heat capacity and magnetization measurements of the single crystal of Haldane-gap antiferromagnet NDMAZ were carried out at low temperatures down to 0.1 K and under magnetic fields up to 14 T. We have observed three-dimensional long-range ordering of NDMAZ at around T ⋍ 0.3 K above H ⋍ 13 T ( H | c ), which is ascribed to both the field-induced gap quenching and the existence of finite interchain interaction. Applying the higher external field, the transition temperature reaches up to 0.6 K at H = 14 T, showing a negative curvature with respect to the external field.