A magnetic resonance study of the screening of electric fields in metals
Fernelius, Nils Conard
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https://hdl.handle.net/2142/23994
Description
Title
A magnetic resonance study of the screening of electric fields in metals
Author(s)
Fernelius, Nils Conard
Issue Date
1966
Doctoral Committee Chair(s)
Slichter, C.P.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
magnetic resonance
electric field screening
electric fields metals
zero field resonance
Ramsey-Pound magnetic field cycling
Language
en
Abstract
We have observed zero field resonance in zinc-doped aluminum
samples by means of the Ramsey-Pound magnetic field cycling
technique. Experiments were performed near 1.2o K in order to
obtain Tl sufficiently long to perform a cycle in a time less than
Tl , Near 53.5 kc/sec and 27 kc/sec we see pure quadrupole resonance
from aluminum atoms near to the zinc, as is shown by the dependence
of the absorption strength on zinc concentration at constant power
level. Assuming that these are the 3/2-5/2 and 1/2-3/2 transitions
of aluminum nearest neighbors to zinc, these are about half the
values predicted by Blandin and Friedel's field gradients, viz.
122 kc/sec and 61 kc/sec for axial symmetry. No other clearly
discernable resonance was observed between 54 kc/sec and 150 kc/sec.
Work of T. J. Rowland sets an upper limit of about 185 kc/sec for
the pure quadrupole resonance of aluminum in the largest field
gradient near to the zinc impurity. Presumably this is at nearest
neighbor sites. Perhaps weak resonances were seen around 80 kc/sec
and 40 kc /sec. The saturation of the 53.5 kc/sec resonance was analyzed with
respect to impurity concentration and Hl power level using the model
of two coupled spin systems developed by R. T. Schumacher. This
model views the power absorbed from the applied alternating field
as absorbed by either the 53.5 kc/sec quadrupole resonance or by a
system composed of nuclear moments in local magnetic fields with
additional weak quadrupole splittings. The two systems are weakly
coupled together so that heat flows from one system to the other
whenever there is a temperature imbalance. A cross relaxation time
was determined from the analysis which decreases with increasing
impurity concentration.
We made studies of the broadening of non-resonant spin
absorption due to the weaker quadrupole splittings. The observed
second moment fits the expression:
(sv 2> = (A7I~ + c (D:l/Q2)
Pure
The second moment of the doped samples extrapolated to the value
measured in a 99.999~ pure aluminum sample. This value is still
much larger than the theoretical Van Vleck second moment as has been
observed by other researchers and is still unexplained.
Zeeman perturbation on pure quadrupole resonance was treated
theoretically. Powder pattern lineshapes were calculated. Some
inconclusive experiments were made.
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