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Title:Strain-modified spin-lattice relaxation rates in some rare earth salts
Author(s):Young, Byron Arlen
Doctoral Committee Chair(s):Stapleton, H.J.
Department / Program:Physics
Subject(s):strain-modified spin-lattice relaxation
rare earth salts
spin system
Abstract:An examination was made of the electron spin-lattice relaxation rates of Ce and Er in LaCl3 progressively strained by replacing a small fraction of the ct ions by Br and also Nd in lanthanum magnesium nitrate (LMN) similarly strained with Zn replacing Mg in order to test our proposal that strain-induced excited level energy widths in rare earth crystals could explain the discrepancies in excited state energy levels as determined by optical and spin-lattice relaxation data. If the distribution of first excited state energy levels throughout a crystal is assumed Gaussian with a standard deviation a about an optically-determined value 6, then the temperature dependence of the Orbach relaxation rate is (B)f(a,6,T) expC(-6 + a 2/2kT)/kT]" where f(a,6,T) is a function nearly equal to 63 Relaxation times were measured in the temperature range 1.5 OK to 4.2 OK using a pulsed-power X-band microwave spectrometer. A better fit to the data is obtained using this two parameter (B and a; 6 = optical value) equation than by the conventional two parameter (B and 6, a = 0). approach. The data can be analyzed so that Band cr are determined almost independently. The results indicate that for 2% Ce in a LaCl3 lattice, cr2 is 43, 65, and 95 °K2 for Br concentrations of 0, 5, and 10% respectively, and for 1% Er in a LaC£3 lattice, cr2 is 7 and 31 °K2 for Br concentrations of 3% and 6% respectively providing strong evidence for the validity of our proposal. For Nd in LMN with 0% and 10% Zn, cr2 is about 11 °K2 indicating the ion substitution had little effect on the crystal field splittings. (B)f(cr,6,T) is found to diminish more rapidly with cr than expected from a simple theory. Changing the Ce concentration in LaCl3 doped with 10% Br gives results that indicate this can be explained in part by a strain modification of the spin-spin interaction. Results of damaging LaCl3 containing 2% Ce by neutron radiation suggest strain-modification of the phonon system as another explanation. The effects of a distribution of splittings on 6- 2 appearing in the expression for the direct process coefficient A are qualitatively considered to account for the increase in A with large strain. The differences in anisotropies in A for Ce in LaCl3 containing 0% and 10% Br are discussed in terms of these effects. A is concentration-independent for 0% Br but drops by a factor of 20 for 10% Br when the Ce concentration is decreased from 2% to 1%. The g values for 2% Ce in LaBr3 were measured to be: gil = 4.068 ± .006, g~ = .13 ± .14. The EPR absorptions of Ce in the LaBr3 and LaCl3 samples have satellite lines of unknown origin. Their separations appear to be independent of the type of halide ion.
Issue Date:1967
Genre:Dissertation / Thesis
Rights Information:1967 Byron Arlen Young
Date Available in IDEALS:2011-07-08
Identifier in Online Catalog:6087143

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