A study was made of the electron paramagnetic resonance spectrum, of 1.5at% of the [Ni(H2O)6]2+ complex in crystals of the fluoroborate at 77K, by using an X-band spectrometer. The magnetic field was directed along the distortion axis of the crystal field with trigonal symmetry. It was found that the spectrum exhibited satellite lines that were close to the 2 expected main lines. The former lines were explained as being due to magnetically coupled pairs between nearest neighbors. An explicit account of dipolar and isotropic exchange interactions was introduced into the spin Hamiltonian of the pairs, and the exact eigenvalues were calculated. The dipolar and exchange interaction parameters were determined, directly from the line positions, to be equal to 98G and -194G (ferromagnetic), respectively. This result indicated that the dipolar interaction that was usually excluded in magnetic interaction studies of the [Ni(H2O)6]2+ complex was not negligible. This quantitative determination of magnetic interactions was made possible by using a combination of electron paramagnetic resonance and magnetic dilution techniques.

W.Sano, J.A.Ochi, J.B.Domiciano: Physical Review B, 1996, 53[6], 3436-9