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A magnetic resonance study of the screening of electric fields in metals

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Title: A magnetic resonance study of the screening of electric fields in metals
Author(s): Fernelius, Nils Conard
Doctoral Committee Chair(s): Slichter, C. P.
Department / Program: Physics
Discipline: Physics
Degree: Ph.D.
Genre: Dissertation
Subject(s): magnetic resonance electric field screening electric fields metals zero field resonance Ramsey-Pound magnetic field cycling
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.
Issue Date: 1966
Genre: Dissertation / Thesis
Type: Text
Language: English
URI: http://hdl.handle.net/2142/23994
Rights Information: 1966 Nils Conard Fernelius
Date Available in IDEALS: 2011-05-20
Identifier in Online Catalog: 6171405
 

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