Local character of magnetic coupling in ionic solids

Abstract

Magnetic interactions in ionic solids are studied using parameter-free methods designed to provide accurate energy differences associated with quantum states defining the Heisenberg constant J. For a series of ionic solids including ${\mathrm{KNiF}}_{3},$ ${\mathrm{K}}_{2}{\mathrm{NiF}}_{4},$ ${\mathrm{KCuF}}_{3},$ ${\mathrm{K}}_{2}{\mathrm{CuF}}_{4},$ and high- ${T}_{c}$ parent compound ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4},$ the J experimental value is quantitatively reproduced. This result has fundamental implications because J values have been calculated from a finite cluster model whereas experiments refer to infinite solids. The present study permits us to firmly establish that in these wide-gap insulators, J is determined from strongly local electronic interactions involving two magnetic centers only thus providing an ab initio support to commonly used model Hamiltonians.