Layered mixed-metal phenylphosphonates, MnxCo1-x(O3PC6H5)•H2O:: Structure and magnetic properties

Mixed metal phenylphosphonates of composition MnxCo1-x(O3PC6H5).H2O were prepared with 0 less than or equal to x less than or equal to 1. Atomic absorption, X-ray powder diffraction, and electron paramagnetic resonance measurements indicate that the mixed-metal solid solutions are homogeneous and isostructural with the single-metal-parent compounds over the entire concentration range, with a small, systematic evolution of the a and c in-plane unit cell parameters, The temperature dependence of the magnetic data for the pure Mn2+ (x = 1) and pure Co2+ (x = 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(O3PC6H5).H2O and J = -2.43 +/- 0.05 K for Co(O3PC6H5).H2O. The magnetic phase diagram, down to 2 K, was constructed over the entire composition range. Both de and ac magnetic susceptibilities were used to identify the transitions to low temperature, long-range-ordered antiferromagnetic states, In the Mn2+- and Co2+-rich regions, the ordering temperature, T-N, decreases relative to the pure materials, as expected for magnetic ion impurity doping. For intermediate values of x, Mn2+-Mn2+ interactions dominate, resulting in a minimum in T-N near x = 0.25, A weak negative magnetization was observed for x < 0.25, No evidence of spin glass behavior was observed for any concentration at any temperature. (C) 2001 Academic Press.