The Mossbauer effect in iron under very high pressure
Pipkorn, David Nieman
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https://hdl.handle.net/2142/23957
Description
Title
The Mossbauer effect in iron under very high pressure
Author(s)
Pipkorn, David Nieman
Issue Date
1964
Doctoral Committee Chair(s)
Frauenfelder, Hans
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Mossbauer effect
iron
fe57
ferromagnetic
internal magnetic field
s electron density
Language
en
Abstract
The Mossbauer spectrum of Fe57 in iron metal has been measured
at pressures up to 240 kilobars at room temperature. Below 133 kilobars
the spectrum consists of the normal six lines characteristic of ferromagnetic,
body-centered cubic iron. The internal magnetic field at the
nucleus H decreases linearly with pressure; ~ = -1.6 x 10-4 kilobar-l ,
o
where H is the field at atmospheric pressure. The center of gravity of o
the spectrum shifts with pressure indicating an increase in s electron
density at the nucleus. The initial variation, -8 .3 x 10 -5 cm sec -1 kilobar -1 ,
is consistent with scaling the 4s wavefunction with volume while at higher
pressures the variation is slower. Above 133 kilobars a seventh line
appears near the center of the spectrum due to the transformation of
part of the iron source to the hexagonal-close-packed high pressure
phase. With increasing pressure this line becomes more intense and the
split spectrum disappears although the transformation is sluggish.
From the absence of splitting and from the observed linewidth we conclude
that the internal field in the hexagonal phase is (0 ~ 3) kilogauss.
There may be a small broadening due to electric quadrupole interactions
in the hexagonal lattice. The isomer shift of the hexagonal phase
relative to the cubic phase is -0.017 cm/sec (s electron density greater
in hexagonal phase). The pressure dependence of the shift in the
hexagonal phase is very slight and is not consistent with scaling the
4s wavefunction with volume. Apparatus and experimental techniques that
were developed for measuring the Mossbauer spectra of sources under
pressure are described.
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