High pressure Mössbauer studies of magnetic interactions in palladium-cobalt alloys
Cohen, Joel Alan
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https://hdl.handle.net/2142/25756
Description
Title
High pressure Mössbauer studies of magnetic interactions in palladium-cobalt alloys
Author(s)
Cohen, Joel Alan
Issue Date
1968
Doctoral Committee Chair(s)
Drickamer, H.G.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
high pressure Mossbauer
magnetic interactions
palladium-cobalt alloys
Language
en
Abstract
The pressure dependence of the Fe57 hyper fine field has
been studied by means of the Mossbauer effect in a series of PdCo
alloys consisting of 5, 8, 9, 12, and 15 atomic percent Co, up to
180 kilobarsat 297 oK. The Curie temperatures (Tc) of the 8%
and 9% alloys are observed to increase with pressure. A molecular
field approximation is employed, along with data on the pressure
dependence of T for the 12% alloy (which also increases), to calculate the pressure variation of the T = 0 hyper fine Field (H ) for
the 12% and 15% alloys. It is found that IHol decreases linearly
with volume in the high-pressure region and may pass through a
maximum near p = 30 kilobars. The pressure dependences of both T c
and H are similar to those which obtain in pure Co. Since Tis
known to decrease with pressure in the more dilute alloys, where
the Co moments couple indirectly via the pd host, it is concluded
that a direct Co-Co exchange interaction which is not prominent in
the very dilute cases becomes important at concentrations somewhere
between 4% and 8% Co in Pd.
Isomer shift data are also obtained and show a composition independent
pressure dependence which is similar to that of Fe57 in
Pd, Co, and other close-packed transition metals. This result is
briefly related to current theories concerning a pressure induced
increase of s-like conduction-electron density at the Fe57 nucleus
and a relative s-to-d shift of the character of the itinerant band
electrons.
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