Paramagnetic resonance studies of Cu<SUP>2+</SUP> doped in NH<SUB>4</SUB>Br

Electron Paramagnetic Resonance studies of Cu<SUP>2+</SUP> doped in NH<SUB>4</SUB>Br single crystals have been carried out for the first time. The room temperature data reveal that Cu<SUP>2+</SUP> ions go predominantly to interstitial sites having square planar co-ordination of four Br- ions. For this type of complexes the bromine: superhyperfine structure: is observed on the normal hyperfine structure lines of copper. Existence of other weak spectra indicates that a relatively few Cu<SUP>++</SUP> ions go substitutionally to (NH<SUB>4</SUB>)<SUP>+</SUP> ions, and are probably associated with a first or a second nearest neighbour cation vacancy, among the two, the latter being more predominant. However, the low temperature studies corresponding to the tetragonal phase of NH<SUB>4</SUB>Br indicate that a number of Cu<SUP>2+</SUP> ions at interstitial sites get readjusted to the lattice sites after phase transformation. The spectra in both the phases are analysed by the usual spin Hamiltonian method