The spin-Hamiltonian and line widths in nickel Tutton salts

Abstract

An account is given of the derivation and properties of a spin-Hamiltonian which has recently been used to describe the results of magnetic resonance experiments on nickel Tutton salts. It is obtained on the assumption that the nickel ions are situated in a field of rhombic symmetry. A theory of line widths is then developed and a comparison is made with experimental results obtained for nickel ammonium selenate. Agreement is only obtained if it is assumed that in addition to dipolar couplings between the ions there are exchange interactions of comparable magnitudes. The sign of the exchange is found to be that associated with ferromagnetism and its magnitude is of order 0⋅025 cm -1 .