Effect of spin-polarisation on the crystal field of lanthanide ions

Abstract

It is shown that covalency provides a positive contribution to the ck parameters describing the spin-correlated crystal field (SCCF). Estimates of the magnitude of this contribution are made which are consistent with experiment. A simple method of calculating the matrix elements of the SCCF is described and some examples are given in the hope that the SCCF can be routinely included in crystal field fits in future.