Low- and high-temperature electron paramagnetic resonance studies on Cu2+-doped monopyrazine zinc sulphate trihydrate single crystal: observation of the Jahn-Teller effect

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Abstract
Electron paramagnetic resonance studies on a single crystal of Cu2+-doped monopyrazine zinc sulphate trihydrate (PZST) have been made over an extended temperature range (4.2-375 K). Three physically equivalent, but magnetically inequivalent, Cu2+ complexes have been observed. The spin-Hamiltonian parameters are rigorously evaluated at 334, 295, 77 and 4.2 K, by the method of least-squares fitting, utilising numerical diagonalisation of the spin-Hamiltonian matrix on a digital computer. The principal values of the g- and A-tensors indicate that, in PZST, the Cu2+ ion experiences an octahedral symmetry with orthorhombic distortion. The data are interpreted to conclude the occurrence of both static and dynamic Jahn-Teller effects over the temperature range of investigation, the transition from static to dynamic Jahn-Teller effect occurring at 334+or-1 K.