ESR studies of Cu²⁺ Doped in Na<inf>2</inf>SO<inf>4</inf> single crystals

The ESR spectrum of Cu2+ has been observed in the host single crystal Na2SO4. Copper enters the lattice substitutionally and is trapped at four chemically as well as magnetically inequivalent sites. The centers have tetragonally distorted octahedral symmetry with a small orthorhombic distortion, having fx2 - y2 > as the ground state. Forbidden transitions of the type |m1 = ±1 are analyzed and the quadrupole interaction parameter is obtained as Q = 8.8 G. Superhyperfine structure with one sodium nucleus is observed, having an s character of 0.85 %. and a p character of 1.84 %. The spin Hamiltonian parameters are analyzed both from the measurements on single crystals and polycrystalline samples. Copper is surrounded by six nearest oxygen atoms which form polyhedra and the observed direction cosines of the four sites are in agreement with the calculated NaNa directions. The optical absorption band observed at 12,800 cm -1 is assigned as the ground state (eg→t2g) transition. There is about 34% reduction in the spin-orbit coupling constant as deduced from the results of ESR and optical spectroscopy. © 1974.