Magnetic order in quasi-two-dimensional molecular magnets investigated with muon-spin relaxation

We present the results of a muon-spin relaxation (μ+SR) investigation into magnetic ordering in several families of layered quasi-two-dimensional molecular antiferromagnets based on transition-metal ions such as S=12 Cu2+ bridged with organic ligands such as pyrazine. In many of these materials magnetic ordering is difficult to detect with conventional magnetic probes. In contrast, μ+SR allows us to identify ordering temperatures and study the critical behavior close to TN. Combining this with measurements of in-plane magnetic exchange J and predictions from quantum Monte Carlo simulations we may assess the degree of isolation of the 2D layers through estimates of the effective inter-layer exchange coupling and in-layer correlation lengths at TN. We also identify the likely metal-ion moment sizes and muon stopping sites in these materials, based on probabilistic analysis of the magnetic structures and of muon-fluorine dipole-dipole coupling in fluorinated materials. © 2011 American Physical Society