EPR OF A VO2+-DOPED ZN(NH4)2(SO4)2.6H2O SINGLE-CRYSTAL - LIGAND SUPERHYPERFINE INTERACTION

Detailed X-band electron-paramagnetic-resonance (EPR) studies of the VO2+ ion have been carried out on a single crystal of the Tutton salt Zn(NH4)2(SO4)2 6H2O at 295, 80, and 4.2 K. The data are indicative of the presence of two physically equivalent VO2+ sites in the unit cell, each consisting of three magnetically inequivalent VO2+ ions, one of them being present with a much smaller probability. Each vanadyl hyperfine line is characterized by an anisotropic temperature-independent quintet superhyperfine (SHF) splitting, with the intensity ratios 1:4:6:4:1. The origin of the SHF splittings has been explained. The principal values and the orientations of the principal axes of the SHF-interaction tensor, as well as the density of the unpaired electron at the site of ligand protons, have been estimated. The in-plane anisotropy controversy has been resolved. © 1990 The American Physical Society.