Spin-flip scattering of conduction electrons from impurities
Asik, Joseph Richard
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https://hdl.handle.net/2142/23986
Description
Title
Spin-flip scattering of conduction electrons from impurities
Author(s)
Asik, Joseph Richard
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)
spin-flip scattering
conduction electrons
electrons from impurities
spin orientation lifetime
non-magnetic elemental impurities
conduction electron spin resonance (CESR)
Language
en
Abstract
"We report and analyze the results of a new type of experiment,
the effect of impurities on the spin orientation lifetime of
conduction electrons. We have made a theoretical and experimental
study of the effect of non-magnetic elemental impurities on the
conduction electron spin resonance (CESR) in metals. By measuring
the concentration dependence of the C~SR linewidth, we have
obtained the spin-flip scattering cross-sections of 14 different
impurities in Li and 7 impurities ,in Na. The mechanism of spin-flip
, ""
is proved to be the spin-orbit interaction of a conduction electron
in the electric field of the impurity atom. The smallest crosssection
observed is 6 .4 x 10- 21 cm 2 for LiMg while the largest is
2.7 x 10- 16 cm 2 for ~Tl. The range of 105 in order of magnitude
is related to the large range in the spin-orbit splittings of the
free impurity atoms. We can account for most of the cross-sections
by a simple theory which considers as a perturbation the interaction
of the conduction electron spin with its orbital motion in the -J,.
electric field of the impurity (spin-orbit coupling). Since the
spin-orbit interaction occurs well inside the ion core of the
impurity, these measurements provide information about the t > 0
terms of the conduction electron wave function in the vicinity of the
impurity nucleus. For monovalent impurities we have developed a
simple OPW theory which relates the cross-sections to the spin-orbit
splittings of the atomic core states of the impurity and to overlap
integrals between plane waves and core functions. This theory gives
excellent agreement for ~g, ~u, and ~u. For non-monovalent
impurities, the effect of screening is taken into account by solving
the problem of a conduction electron in a screened Coulomb potential.
The screened Coulomb wave functions resulting from this calculation
are then orthogonalized to the ,core functions. Excellent agreement
is obtained for impurities having valences close to 1. The crosssections
for the Group III impurities (In,Tl) and especially the
Group IV impurities (Sn,Pb) are anomalously smaller than the theory
predicts. In an attempt to resolve this discrepancy we have
developed a phase shift formulation of the spin-flip scattering
problem in the j,t representation. A formula for the spin-flip
cross-section is'found. We also derive a new Friedel sum rule which
the j, t phase shifts must satisfy for a spin-dependent interaction
of the spin-orbit type. The results of this calculation are not in
significantly better agreement with experiment."
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