Strain-modified spin-lattice relaxation rates in some rare earth salts
Young, Byron Arlen
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https://hdl.handle.net/2142/25712
Description
Title
Strain-modified spin-lattice relaxation rates in some rare earth salts
Author(s)
Young, Byron Arlen
Issue Date
1967
Doctoral Committee Chair(s)
Stapleton, H.J.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
strain-modified spin-lattice relaxation
rare earth salts
spin system
Language
en
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."
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