A two-step field-induced magnetic transition in a novel layered cobalt diphosphonate

Compound Na6Co7(hedp)(2)(hedpH)(4)(H2O)(4).8H(2)O (hedp = 1-hydroxyethylidenediphosphonate) with a novel layer structure is reported in this paper. The layer maybe viewed as made up from two types of chains each of composition Co-3(hedp)(2) and Co-2(hedpH)(2). Magnetic measurements at 1.8 K reveal a metamagnetic transition at ca. 6.5 kOe, followed by a second transition to a ferromagnetic state at ca. 30 kOe.