Paramagnetic resonance in diluted copper salts II. Salts with trigonal symmetry

An interesting transition in the paramagnetic resonance spectrum has been observed for a number of cupric salts with trigonal symmetry. At room temperature only a single nearly isotropic line is observed, with a small hyperfine structure. Below a certain temperature, which depends on the salt, the spectrum is that of three kinds of copper ion each with nearly axial symmetry about one of three mutually perpendicular directions. The behaviour of this spectrum is similar to that of the copper Tutton salts in the anisotropy of the (/-tensor and magnetic hyperfine structure, and in the presence of a nuclear electric quadrupole interaction. A careful analysis of the spectrum is made for (Cu, Mg)3La2(NO3)12.24D2O.