Low-symmetry effects in the EPR of Gd³⁺ in two double sulfates

The EPR of Gd3+ in two host single crystals K2Co(SO4)2·6H2O and K2Ni(SO4)2·6H20 is studied at room temperature using a Q-band spectrometer. Two magnetically inequivalent sites which are equivalent in the (010) plane of the crystals are observed. The spectra are characterized by the noncoincidence of the magnetic axes of the transitions for a particular site. This is attributed to a local symmetry less than orthorhombic. Approximate values of the parameters are obtained using perturbation corrections up to fifth order and an iterative least-squares method is used to evaluate the parameters precisely. It is concluded from the crystal-field parameters expressed in the principal coordinate system that the local symmetry is approximately monoclinic. By assuming that Gd3+ occupies a divalent site, it is found from the crystal structure data off (NH4)2Ni(SO4)2·6H2O that the principal z and x axes are approximately along the oxygen atom and potassium vacancy directions, respectively. The local symmetry is found to be Cs with the z axis perpendicular to the mirror plane. © 1977.