ELECTRON PARAMAGNETIC RESONANCE OF CO-DOPED PBWO4

The EPR of Co-doped PbWO4 was observed at 9 GHz at temperatures below 16°K. Four sets of lines were seen, each characterized by an effective electronic spin S of 1/2 and a nuclear spin I of 72. The spectral parameters of one set in an appropriate coordinate system were as follows: gi:4.50, 6.20, and 2.07; and Ai (in GHz): 0.605, 0.970, and 0.248 (i=x,y,z). The Eulerian angles of this coordinate system with respect to the crystal axis system (caa) were: α=43.8°, β=28.0°, and γ=-65.3°. The remaining three cordinate sets are obtained by increasing α in increments of 90°. Above 16°K, the spectra gradually became broad and weak, and finally at 20°K disappeared, clearly as a result of the onset of fast spin-lattice relaxation. Below 4.2°K, the relaxation times became so long that difficulty was encountered in recording the true line shape. We believe that Co enters this lattice in a 2+ state and probably substitutes at a W site. The ground state in this site of S4 symmetry then would be A24. From relaxation data, we estimate that the separation of the two sets of Kramers doublets is several tens of wave numbers. The EPR of Co-doped PbMoO4 and PbWO4 are essentially the same. © 1969 The American Physical Society.