Structural phase transition study of NiCl22H2O by EPR

A single EPR line of isotropic and Lorentzian form was observed in a crystal of NiCl₂2H₂O between 113 and 300 K. During a cooling run a sudden line broadening was observed at 200 K associated with a known crystallographic phase transition. On heating, the corresponding transition temperature was 220 K. The EPR spectra are interpreted in terms of a modified Anderson and Weiss model. The crystal field parameter is determined as D = 0.81 K and D = 1.07 K above and below the transition temperature, respectively.