Two-dimensional magnetism in the Cu-containing planes of metatorbenite

Advances in coordination chemistry have led to the discovery of new architectures which can be described by different model magnetic systems. Here we focus on metatorbenite, a mineral with a crystal structure which consists of alternating layers of (1) uranyl phosphate and (2) a network of spin-1/2 Cu2+ ions linked by a hydrogen-bonded network of water. The diamagnetic uranyl phosphate layers serve to effectively magnetically insulate the magnetic layers, meaning that this compound is expected to be a model two-dimensional Heisenberg square-lattice antiferromagnet. To estimate the inter-sheet coupling J' it is important to measure the Neel temperature, but this is difficult to do with bulk techniques since the system is so anisotropic; it is well-known that muons, on the other hand, are ideally suited to detecting magnetic order in highly anisotropic systems.