Electron-nuclear double resonance ofFe3+57in RbAl and RbGa sulfate alums

Abstract

The electron-nuclear double resonance (ENDOR) of the $S$-state ion ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}_{}^{3+}{}_{}{}^{}$ is studied in the trigonally distorted octahedral si es of the hydrated crystals RbAl${\left(\mathrm{S}{\mathrm{O}}_4\right)}_2$·12${\mathrm{H}}_2$O and RbGa${\left(\mathrm{S}{\mathrm{O}}_4\right)}_2$·12${\mathrm{H}}_2$O. ENDOR frequencies from all four inequivalent sites in the unit cell of the crystals were measured and fitted to an appropriate spin Hamiltonian, which included higher-order trigonal terms of the type $S{}_{}{}^3{}_{}{}^{}I$. Exact diagonalization of the spin Hamiltonian expressed in trigonal symmetry adequately described the observed frequencies for measurements with the magnetic field along two directions in the crystals.