Studies of magnetic critical phenomena in gadolinium
Studies of magnetic critical phenomena in gadolinium
An automatic adiabatic calorimeter has been developed to measure the critical specific heat of gadolinium. A survey of different techniques for measuring heat capacities preceeds the description of the calorimeter and its automation using a PET minicomputer. Reviews of the theory of phase transitions and the results of experimental measurements on magnetic systems focus special attention on gadolinium, and the a (specific heat) exponent in particular. A detailed analysis of the measurements from these experiments on a single crystal of gadolinium has been carried out using a systematic approach based on the method of least squares. Satisfactory fits to the data can be obtained with the equation y e (A±/a)ItI + B± + Ct, where t is the reduced temperature, only when e + B7. A typical set of results is Tc a 293.46K, a - -0.26, A+ - 8.33/mole/K, A - 14.6 J/mole/K, B+ - 49 J/mole/K, 8 - 75 J/mole/K and C - -44 J/mole/K. This represents a significant departure from the theoretical, renormalization group, predictions; and is supported by the analysis of earlier specific heat and thermal expansion data. Various possible perturbations in gadolinium have been considered to see if they could cause crossover to a new fixed point. Finally, the results of measurements on a large polycrystalline sample are reported. They reveal a considerable smearing of the transition and the need to use good single crystals to investigate the critical region in gadolinium.
University of Southampton
1981
Baker, David Paul
(1981)
Studies of magnetic critical phenomena in gadolinium.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
An automatic adiabatic calorimeter has been developed to measure the critical specific heat of gadolinium. A survey of different techniques for measuring heat capacities preceeds the description of the calorimeter and its automation using a PET minicomputer. Reviews of the theory of phase transitions and the results of experimental measurements on magnetic systems focus special attention on gadolinium, and the a (specific heat) exponent in particular. A detailed analysis of the measurements from these experiments on a single crystal of gadolinium has been carried out using a systematic approach based on the method of least squares. Satisfactory fits to the data can be obtained with the equation y e (A±/a)ItI + B± + Ct, where t is the reduced temperature, only when e + B7. A typical set of results is Tc a 293.46K, a - -0.26, A+ - 8.33/mole/K, A - 14.6 J/mole/K, B+ - 49 J/mole/K, 8 - 75 J/mole/K and C - -44 J/mole/K. This represents a significant departure from the theoretical, renormalization group, predictions; and is supported by the analysis of earlier specific heat and thermal expansion data. Various possible perturbations in gadolinium have been considered to see if they could cause crossover to a new fixed point. Finally, the results of measurements on a large polycrystalline sample are reported. They reveal a considerable smearing of the transition and the need to use good single crystals to investigate the critical region in gadolinium.
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Published date: 1981
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Local EPrints ID: 460464
URI: http://eprints.soton.ac.uk/id/eprint/460464
PURE UUID: f2946543-b023-4083-8e07-31a800676785
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Date deposited: 04 Jul 2022 18:22
Last modified: 04 Jul 2022 18:22
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Author:
David Paul Baker
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