Magneto-structural correlation in Cu(NH_3)_2Ag_2(CN)_4. Crystal structure, magnetic and thermodynamic properties of an S = 1/2 low-dimensional Heisenberg antiferromagnet

摘要

Crystal structure, thermodynamic properties and electron spin resonance spectra of Cu(NH_3)_2Ag_2(CN)_4 have been studied. The structure of the studied compound consists of interpenetrating wave-shaped two-dimensional (2d) arrays, in which CuN_4N_2 octahedra axially elongated due to the Jahn-Teller effect are linked by diamagnetic [Ag(CN)_2]~- anions forming a square lattice. Although the susceptibility and specific heat data confirm the existence of short-range order at about 2 K, quantitative analysis of the experimental data reveals that the magnetic behavior differs from that of the crystal structure expected for 2d Heisenberg magnet on the square lattice. Structural features responsible for the observed difference are discussed. In addition, it is suggested, that additional degrees of freedom contribute to the thermodynamic equilibrium properties in the millikelvin temperature range.