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

Mixed metal phenylphosphonates of composition MnxCo1-x(O3PC6H5).H2O were pr epared with 0 less than or equal to x less than or equal to 1. Atomic absor ption, X-ray powder diffraction, and electron paramagnetic resonance measur ements indicate that the mixed-metal solid solutions are homogeneous and is ostructural with the single-metal-parent compounds over the entire concentr ation range, with a small, systematic evolution of the a and c in-plane uni t 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 H eisenberg and 2D Ising models, respectively, yielding nearest-neighbor exch ange 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 t o 2 K, was constructed over the entire composition range. Both de and ac ma gnetic susceptibilities were used to identify the transitions to low temper ature, long-range-ordered antiferromagnetic states, In the Mn2+- and Co2+-r ich regions, the ordering temperature, T-N, decreases relative to the pure materials, as expected for magnetic ion impurity doping. For intermediate v alues 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 t emperature. (C) 2001 Academic Press.