The use of the electron paramagnetic resonance of Gd3+ impurity ions and infrared spectra to study the phase transitions in NH4Ce(SO4)2∙4H2O single crystals

The 9.4 GHz electron paramagnetic resonance (epr) of Gd3+ impurity ions in NH4Ce(SO4)2∙4H2O single crystals has been studied at 97–304 K. The Gd3+ impurity ion is found to substitute for the trivalent lanthanide ion in two inequivalent magnetic complexes corresponding to the tetramolecular unit cell. The epr spectra at 304 K have been analyzed using an orthorhombic symmetry spin-Hamiltonian. The observation of resolved Gd3+ impurity ion spectra in the presence of paramagnetic Ce3+ ions has been interpreted in terms of a random modulation of the interaction between the Gd3+ impurity and Ce3+ host ions by rapid spin–lattice relaxation of Ce3+ ions. The 304 K spin–lattice relaxation time of the Ce3+ ions has been estimated from the impurity ion epr linewidths and is found to be consistent with an Orbach process. It has been shown for the first time that NH4Ce(SO4)2∙4H2O single crystals have a phase transition sequenceThe infrared spectra of NH4Ce(SO4)2∙4H2O were studied at 120 and 303 K and the results are r...