High pressure Mössbauer studies of magnetic interactions in palladium-cobalt alloys

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Year dc:date

2011

Author dc:creator

• Cohen, Joel Alan

Contributors dc:contributor

• Drickamer, H.G.

• high pressure Mossbauer
• magnetic interactions
• palladium-cobalt alloys

Statement dc:rights

• 1968 Joel Alan Cohen

Language dc:language

en

Identifier

6081612

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/25756