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Title:Anisotropic spin-lattice relaxation times of trivalent rare earth ions in anhydrous lanthanum trichloride
Author(s):Mikkelson, Raymond Charles
Doctoral Committee Chair(s):Stapleton, H.J.
Department / Program:Physics
Discipline:Physics
Degree:Ph.D.
Genre:Dissertation
Subject(s):anisotropic spin-lattice relaxation times
trivalent rare earth ions
anhydrous lanthanum trichloride
cerium
praseodymium
neodymium
saraium
terbium
erbium
single crystals
Abstract:Measurements of the temperature and angular dependence oft,he spin-lattice relaxation time Tl have been made for cerium, praseodymium, neodymium, samarium, terbium, and erbium , in single crystals of anhydrous lanthanum tric~loride. The experiments were performed on samples cqntaining ~ 2 at.% rpre earth doping using pulse-saturation techniques at X-ba~d frequencies. Angular m~asurements at constant temperature and microwave ~requency were made for.,magnetic field orientations between 0° and 90° ~ith respect to the crystal c-axis in"the temperature range 1065 to 402°K. The "results are interpreted as involving an angular d~pendent direct process and isotropic Orbach and Raman mechanisms. They are compared with theoretically predicted rates obtainedfrom our computer calculations which are ba~ed upon Orbach's approach and require a knowledge of the d9t.atic c~stal field param,aters"., Since the rare earth trichlorides have been the oboject of much optical investigation, these parameters 'are available for all the ioris we trea,\ except cerium. '. Except· for the ions cerium and samarium~ nearly all the predicted relaxation rate temperature dependencies agree with experimental results within a factor of five or less~ Theoretical treatments which involve the mixing of excited state wave functions into the ground magnetic doublet through the anisotropic Zeeman interaction are required to expla~n the observed angular dependence.. The theoretical·anisotropies are followed almost exactly in every case.. One of the ions, praseodymium, exhibits a phonon limited direct process relaxation rate which is interesting because the apparent hot phonon equilibration time is about 13 nsec, corresponding to an equilibration path length of only 26 microns. Measurements made before and after a crystal was cleaved to half its original thickness gave an unaltered relaxation rate. After neutron bombardment the bottlenecked r~laxation rate changed with the phonon equilibration time app~rently reduced to 8 nsec. Prior irradiation of this same sample with 100 KeV x-rays produced no observable change in the relaxation time.
Issue Date:1965
Genre:Dissertation / Thesis
Type:Text
Language:English
URI:http://hdl.handle.net/2142/23975
Rights Information:1965 Raymond Charles Mikkelson
Date Available in IDEALS:2011-05-19
Identifier in Online Catalog:6191538


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