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

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to the lattice directly via the time-dependent magnetic field of
the unpaired electron of the impurity ion. However most of the
nuclei are coupled only indirectly by spin diffusion through
dipole-dipole interactions. The spin-lattice relaxation time
resulting from such a process depends upon the nature of the impur-
ities and the impurity concentration. Where the concentration
of impurities is low, T1 depends upon the rate of spin diffusion.
2.3.4 INTERACTION WITH CONDUCTION ELECTRONS
This mechanism is the dominant relaxation process in metals.
The non-localized conduction electrons create relatively large
time varying local magnetic fields at a nucleus, which can induce
simultaneous but opposite flips of the electron and nuclear spins.
The resulting energy difference is made up by an increase in the
kinetic energy of the electrons. To a first approximation only
those s character electrons near the top of the Fermi distribut-
ion are able to take part in this process. From Slichter, p. 126,
the relaxation rate induced by this mechanism is given by
1 64 33222 222
T19 YeYnSt Fp (EF)kBT
where p(EF) is the density of states at the Fermi surface and kB
is Boltzmann's constant.
Xs
Y2 t1z
e
2
P(EF)
For a non-interacting electron gas
Hence equations (2.10) and (2.22) lead to the simple Korringa relat-
ionship(l7) between the Knight shift
and spin-lattice relaxation
(2.22)