Two vanadyl phosphates have recently been prepared in superheated aqueous solutions. These materials crystallize as infinite chains of corner sharing VO6 octahedra. The magnetic susceptibility of NaVOPO4 and NH4VOPO4 has been recorded over the 2-300 K temperature region. At higher temperatures, both compounds exhibit Curie-Weiss paramagnetism, where C=0.416 emu K/mole, θ=-31 K; C=0.417 emu K/mole, θ=-4.7 K, for NaVOPO4 and NH4VOPO4, respectively. At lower temperatures, there is a maximum in the temperature-dependent magnetic susceptibility of each compound. The data for the two compounds have been successfully analyzed following the Bonner-Fisher numerical calculations that describe the magnetic behavior of antiferromagnetically coupled S=1/2 one-dimensional chains. The results of the Bonner-Fisher analysis of the magnetic data are g=2.00, J/k=-18.6 for NaVOPO4; and g=2.1, J/k=-3.26 K, for NH4VOPO4. The theoretical analysis of the NH4VOPO4 analog also required the addition of a molecular field correction (zJ'/k=-2.1 K) to the Bonner-Fisher calculation in order to adequately fit the data. The trans crosslinking via phosphate bridges of the magnetic chains in NH 4VOPO4 gives rise to the onset of long-range antiferromagnetic ordering at TAF=3.71 K.
ASJC Scopus subject areas
- Physics and Astronomy(all)