Hyperfine and superhyperfine EPR spectra of Tc(IV) and Re(IV) in tin dioxide single crystals

The electron paramagnetic resonance spectra of Tc(IV) and Re(IV) in tin dioxide have been observed at X- and Q-band frequencies at liquid helium temperature. Both ions with a spin ground state of S=3/2 occupy lattice sites of D2/subh/ symmetry. The hyperfine structures show large anisotropies, especially in the case of Re(IV), which can be explained by the large crystal field parameters. The spectra fit with a conventional spin Hamiltonian for orthorhombic symmetry correspond to the electron transition 1/2bold-arrow-left-right-1/2. The obtained parameters for the c-axis and the magnetic z-axis coincident are Besides the hyperfine lines, both systems exhibit a partly resolved superhyperfine structure due to an interaction of the unpaired electrons with adjacent tin nuclei