EPR Fine Structure of S State Ions

We have recently measured the EPR fine structure spectrum of Gd in Pt and found a b4 parameter of +86 ± 3 gauss. The magnitude of this is the largest ever observed for Gd in any host and is some three times greater than in any other pure metal. We discuss the parametrisation of our spectra and then compare the available results for b4 parameters in metals and intermetallic compounds.