Large single-ion anisotropy and ferromagnetic intrachain interaction in four Ni-compounds of formula Ni X2L2 with X = Cl, Br; L = N 2C 3H 4, NC 5H 5

Abstract

The specific heat has been measured of powdered samples of Ni X 2 L 2 ( X = Cl, Br; L = pyrazole, pyridine), compounds which can be considered as weakly antiferromagnetically coupled ferromagnetic chains with large uniaxial single-ion anisotropy. The intrachain exchange constants and the zero-field splitting parameters for the four compounds have been deduced from the specific heat data, using accurate numerical calculations for the isotropic Heisenberg spin S = 1 linear chain model with uniaxial single-ion anisotropy.