A frustrated ferrimagnet Cu5(VO4)2(OH)4 with a 1/5 magnetization plateau on a new spin-lattice of alternating triangular and honeycomb strips

Cu-5(VO4)(2)(OH)(4) (turanite) is a layered compound, exhibiting a copper(II) oxide layer in the [0 1 1] plane composed of edge-sharing CuO6 octahedra. Each Cu-O layer is further separated by VO4 tetrahedra. Closer scrutiny found that the copper(II) oxide layer in the compound represents a totally new geometrically-frustrated lattice, a 1/6 depleted triangular lattice. More specifically, the spin network in the [0 1 1] plane is formed by the alternate ranking of triangular and honeycomb strips. Magnetic measurements show that the Cu-5(VO4)(2)(OH)(4) behaves as a spin-1/2 ferrimagnet with a T-c = similar to 4.5 K. It exhibits an unusual 1/5 magnetization plateau arising from the competition between antiferromagnetic and ferromagnetic interactions caused by the strong frustration. The possible spin-arrangements are also suggested.