Magnetic Dipole−Dipole Interactions and Single-Ion Anisotropy:  Revisiting a Classical Approach to Magnets

The weak classical through-space magnetic dipolar interactions have, in general, not been an important component in stabilizing bulk magnets, as the strong quantum-mechanical through-bond exchange couplings dominate. We show that for materials composed of strongly exchange-coupled magnetic chains with very weak interchain exchange, the interchain dipolar interactions may dominate, leading to sizable ordering temperatures. The single-ion anisotropy together with the anisotropy of the dipole interaction determine the magnetic ordering directions. The family of [Mn(porphyrin)] + [cyanocarbon] - magnets is shown to order due to classical interchain dipolar interaction in combination with the single-ion anisotropy, resulting in canted magnetic structures.