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

Abstract

We present the results of a muon-spin relaxation (${\ensuremath{\mu}}^{\text{+}}$SR) investigation into magnetic ordering in several families of layered quasi-two-dimensional molecular antiferromagnets based on transition-metal ions such as $S=\frac{1}{2}$ Cu${}^{\text{2+}}$ bridged with organic ligands such as pyrazine. In many of these materials magnetic ordering is difficult to detect with conventional magnetic probes. In contrast, ${\ensuremath{\mu}}^{\text{+}}$SR allows us to identify ordering temperatures and study the critical behavior close to ${T}_{\mathrm{N}}$. 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 ${T}_{\mathrm{N}}$. 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.