The mechanism of the magnetic interaction in the β phase of the p-(nitro)phenyl nitronyl nitroxide (KAXHAS). A bottom-up study using only ab initio data

Abstract

The magnetism of the β phase of p-(nitro)phenyl nitronyl nitroxide (KAXHAS) crystal has been studied using a recently developed theoretical approach ‘J. Phys. Chem. A 106 (2002) 1299’. This approach is a bottom-up study based on the evaluation of the magnetic interaction between all pairs of radicals (JAB), which allows the definition of the magnetic structure of the crystal. With only such knowledge, one solves an algebraic Heisenberg Hamiltonian on a properly chosen finite subset of the magnetic structure and then computes the magnetic susceptibility χ(T) and/or heat capacity Cp(T) curves for the crystal. This method is applied here to the KAXHAS crystal. The theoretical χ(T) and Cp(T) results are in very good agreement with the available experimental data. This theoretical methodology is first reviewed here on physical terms, and then used to rationalize the bulk ferromagnetic behavior of KAXHAS in terms of its corresponding microscopic JAB pair interactions.