Electron paramagnetic resonance of Mn2+ in single crystals of hexaquonitrates of nickel and magnesium

An EPR study has been carried out on Mn2+-doped single crystals of hexaquonitrates of Mg and Ni, Mg(OH2)6.(NO3)2 and Ni(OH2)6.(NO3)2, at room temperature ( approximately 300K) and at X-band. Mn2+ substituting for Mg2+ in Mg(OH2)6.(NO3)2 exhibits two identical, but differently oriented, magnetic complexes, whose z axes make an angle of approximately 15+or-1 degrees with each other in the zx plane. However, Mn2+-doped Ni(OH2)6.(NO3)2 crystals exhibit only one single thirty-line spectrum indicating the equivalency of two Ni(OH2)62+ complexes per unit cell. The EPR spectra are analysed using a spin-Hamiltonian of orthorhombic symmetry to get the best fit parameters. These studies reveal that the two crystals are not isomorphous and that the site symmetry at the cation sites is very low.