Contribution to the Hyperfine Field from Cation-Cation Interactions

Two mechanisms are reported for the change in hyperfine field at the site of a magnetic ion brought about by the presence of neighboring magnetic ions: transfer of a $3d$ electron from the neighboring ion to the $4s$ level of ion in question, and orthogonalization of the antibonding orbitals of the surrounding cations to the inner $s$ cores of the magnetic ion. The total $s$-state admixture from both mechanisms results in an increase in the hyperfine field in a simple cubic antiferromagnet over that found in the dilute salt.