Two-Dimensional S = 1 Quantum Antiferromagnet (NiCl)Sr2Ta3O10

A topotactic ion-exchange reaction of a layered perovskite RbSr2Ta3O10 with NiCl2 yielded a novel two-dimensional nickel-oxyhalide (NiCl)Sr2Ta3O10, the first S = 1 compound among related series of metal-oxyhalides. The room temperature structure is isostructural with (CuCl)Ca2Nb3O10 adopting the space group P4/mmm. We found a possible structural transition at 230 K that does not lead to drastic changes in magnetic character such as nickel clustering. Despite a large Weiss temperature of θ = −125 K, magnetic long-range order is significantly suppressed down to T N1 ≈ 50 K because of two-dimensionality and strong frustration. The magnetically ordered state below T N1 has a partial volume fraction coexisting with a paramagnetic component, followed by complete long-range ordering below T N2 = 20 K. The reaction process and requirement will also be discussed.