NNR IN RAPIDLY ROTATED METALS By - Nottingham eTheses ...

- 118 -
Lifetime broadening alone gives rise to a Lorentzian line-
shape in the frequency domain with a width at half-height of 1/'nT1.
Assuming that the lifetime contribution to the total width of the
residual spectrum can be separated by a simple subtraction, then
upon substituting the values for T1 recorded previously the secular
broadening of the central line becomes about 560 Hz for both iso-
topes. The above value includes a contribution from the inhomo-
geneity of the magnetic field but this was estimated to be negigible
(< 20 Hz) in comparison. Consequently the figure quoted represents
a measure of the electron coupled scalar interaction between the
cadmium nuclei. The equivalence of the linewidth for the two iso-
topes simply reflects their almost equal natural abundancies.
At room temperature the relaxation times of both isotopes are of
approximately the same magnitude as the inverse of the first and
second nearest neighbour exchange coupled constants as determined
(139)
by Alloul and Deltour. This leads to the possibility that
the isotropic magnetic exchange interaction may be time averaged by
lifetime fluctuations in the nuclear spin states. Any detailed
calculation of the Rudermann-Kittel(14) indirect exchange interact-
ion is precluded by an incomplete knowledge of the effect of these
fluctuations as well as by the preliminary nature of the results.
Consequently we content ourselves with making a simple comparison
of our results to those obtained by Alloul and Deltour from observat-
ion of the modulated structure of the spin echoes of the 113Cd reson-
ance in cadmium based alloys. Their experiment was undertaken at
liquid helium temperatures, in which region T1 contributions to the
lineshapes are negligible. The exchange coupling constants, J1
and J2, between the first and second nearest neighbours in the hexagonal