(31)P NMR study of Na(2)CuP(2)O(7): an S = 1/2 two dimensional Heisenberg antiferromagnetic system.

The magnetic properties of Na(2)CuP(2)O(7) were investigated by means of (31)P nuclear magnetic resonance (NMR), magnetic susceptibility, and heat capacity measurements. We report the (31)P NMR shift, the spin-lattice [Formula: see text], and spin-spin (1/T(2)) relaxation rate data as a function of temperature T. The temperature dependence of the NMR shift K(T) is well described by the S = 1/2 square lattice Heisenberg antiferromagnetic model with an intraplanar exchange of [Formula: see text] K and a hyperfine coupling A = 3533 ± 185 Oe /μ(B). The (31)P NMR spectrum was found to broaden abruptly below T∼10 K, signifying some kind of transition. However, no anomaly was noticed in the bulk susceptibility data down to 1.8 K. The heat capacity appears to have a weak maximum around 10 K. With decrease in temperature, the spin-lattice relaxation rate 1/T(1) decreases monotonically and appears to agree well with the high temperature series expansion expression for a S = 1/2 2D square lattice.