Zeeman interaction cubic system

Note that the Zeeman interaction for a cubic system results in an isotropic g-value, but the combination with strain lowers the symmetry at least to axial (at least one of the 7 -, 0), and generally to rhombic. In other words, application of a general strain to a cubic system produces a symmetry identical to the one underlying a Zeeman interaction with three different g-values. In yet other words, a simple S = 1/2 system subject to a rhombic electronic Zeeman interaction only, can formally be described as a cubic system deformed by strain. 

Just like the Zeeman interaction (S B), the hyperfine interaction (.S /) is a bilinear term and its coupling to strain (T S I), which we will call A-strain (also, -strain ), should be formally similar to the g-strain (T S B) just discussed. In the early work of Tucker on the effective S = 1/2 system Co2+ in the cubic host MgO, a shift in central hyperfine splitting was found to be proportional to the strain-induced g-shift given by Equation 9.22 (Tucker 1966). 

The spin Hamiltonian encompassing electronic Zeeman plus strain interaction for a cubic S = 1/2 system is (Pake and Estle 1973 Equation 7-21) ... 

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