Layered Mixed-Metal Phenylphosphonates,Mn_(#chi#)Co_(1-#chi#)(O_3PC_6H_5)·H_2O: Structure and Magnetic Properties

摘要

Mixed metal phenylphosphonates of composition Mn_(#chi#)Co_(1-#chi#)(O_3PC_6H_5)·H_2O were perpared with 0<=#chi#<=1. Atomic absorption,X-ray powder diffraction, and electron paramagnetic resonance measurements indicate that the mixedmetal solid solutions are homogeneous and isostructueal with the single-metal-parent compounds over the entire concentration range, with a small, systematic evolution of the #alpha# and c in-plane unit cell parameters. The temperature dependence of the magnetic data ofr the pure Mn~(2+) (#chi# = 1) and pure Co~(2+) (#chi# = 0) samples was fitted by standard 2D Heisenberg and 2D Ising models, respectively, yielding nearest-neighbor exchange interaction energies of J = -2.27+-0.02 K for Mn(O_3PC_6H_5)·H_2O and J = -2.43+-0.05 K for Co(O_3PC_6H_5)·H_2O. T he magnetic phase diagram, down to 2K, was constructed over the entire composition range. Both dc and ac magnetic susceptibilities were used to identify the transitions to low temperature, long-range-ordered antiferromagnetic states. In the Mn~(2+)- and Co~(2+)- fich regions, the ordering temperature, T_N decreases relative to the pure materials, as expected for magnetic ion impurity doping. For intermediate values of #chi#, Mn~(2+)-Mn~(2+) interactions dominate, resulting in a minimum in T_N near #chi# = 0.25.A weak negative magnetization was observed for #chi# < 0.25. No evidence of spin glass behavior was observed for any concentration at any temperature.