Exploring the magnetic phase diagram of a metal-organic S = 1 triangular spin system.

We report on magnetic properties of a novel metal-organic S = 1 antiferromagnetic triangular spin compound with isolated Ni2+ triangles entitled as BHAP-Ni3. Specific heat measurements reflect an onset of magnetic correlation at low temperatures without any long-range order down to 300 mK, indicating the presence of an unusual magnetic ground state. ESR measurements performed at 1.5 K advocate this ground state to be a gapped one. Field-dependent magnetization measured on the single crystal shows anisotropic behavior with field applied parallel and perpendicular to the triangle plane. However, a clear plateau-like region is seen in both directions above 8 T which corresponds to half of the fully polarized value of Ni2+ moment. The presence of such half-magnetization plateau is quite unusual in the family of triangular magnets. High-field magnetization measurements using pulsed magnet show another field-induced plateau above 30 T corresponding to the fully polarized state of S = 1 triangles.