AbstractsPhysics

The subject of this thesis is the work done in the Eaton Electronics Research Laboratory as a beginning of a programme of studies of double resonance. The aim of this work is to find out the conditions under which the best ENDOR signal can be obtained. A reflection cavity was used for all the results described, since the original transmission cavity developed faults. The samples used were crystals of magnesium oxide containing small amounts of cobalt impurity, present as Co++ ions. Co++ ions in MgO are known to be in surroundings of accurately cubic symmetry. Samples of 5%, 2% and 0.5% nominal concentrations were used and for each concentration, conditions for the best ENDOR signal were found and arereported. The basic spectrometer is similar in principle to that used by Feher15 for electron paramagnetic resonance measurements except that the necessary additional equipment was added for double resonance. The dependence of ENDOR signal on amount or F.M., A.M. and v2- voltage was linear, as expected, with however evidence of departures from linearity in the case of the v2-graph. The variation of ENDOR signal with microwave power showed a fairly sharp maximum, at a power dependent on the concentration of Co++ ions in the sample. A simple theory predicts a maximum when the spin temperature is doubled, and has supported by the results. F.M. was found to be preferable to A.M. for the samples used.