Neutron scattering studies of rare earth alloys and compounds
Neutron scattering studies of rare earth alloys and compounds
The major part of this thesis is concerned with the experimental investigation by neutron scattering of some physical properties of rare earth materials. The occurrence of fibre texture in polycrystalline samples of some RCo compounds (R = Nd,Tb,Ho) prepared b argon arc melting has been studied. In NdCo2 the crystallite [110 axes were found to lie preferentially along the cooling direction and other evidence suggests that, in general, the phenomenon of preferred alignment is caused by the presence of the unwanted phase RCo3. The investigation of the RCo, compounds is continued by a powder neutron diffraction experiment to find the temperature dependence of the rare earth and cobalt sub-lattice magnetisations. The previously reported two step magnetisation process was not found to be an intrinsic property of the material but originated instead from unwanted extra phases. The magnetic moment values were extracted from the diffraction profiles using a simplified Rietveld method for two phases. The cobalt moment remained fairly constant up to the ordering temperature and its value decreased between compounds when the substituted rare earth moment was reduced.Using the technique of inelastic neutron scattering themagnon dispersion relations along the hexagonal axis were found for the intermediate rare earth alloy Ho(50%) Th(50%). Measurements were taken at several temperatures to include the ferromagnetic and helical phases as well as a high temperature ferromagnetic phase induced by an externally applied magnetic field. The interplanar exchange parameters were extracted from the results using a theoretical model and these are used to discuss the stability of the magnetic structures. The results are compared with those of the element Dysprosium.The final chapter contains an attempt to understand theoretically the origins of the magnetostrictive distortions found in cubic materials where the rare earth ion is the dominant source of anisotropy. A strain dependent crystal field Hamiltonian was developed and the point charge model was used to apply this to some RCo2 compounds. An explanation for the observed magnetostriction in HoCo2 and NdCo2 is given. Some RA12 and RFe2 compounds are also considered and the possibility of internal distortions is recognised. The simpler CsCl-type RZn compounds are also discussed and a calculation is presented for ThZn.
University of Southampton
1977
Hendy, Paul
(1977)
Neutron scattering studies of rare earth alloys and compounds.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
The major part of this thesis is concerned with the experimental investigation by neutron scattering of some physical properties of rare earth materials. The occurrence of fibre texture in polycrystalline samples of some RCo compounds (R = Nd,Tb,Ho) prepared b argon arc melting has been studied. In NdCo2 the crystallite [110 axes were found to lie preferentially along the cooling direction and other evidence suggests that, in general, the phenomenon of preferred alignment is caused by the presence of the unwanted phase RCo3. The investigation of the RCo, compounds is continued by a powder neutron diffraction experiment to find the temperature dependence of the rare earth and cobalt sub-lattice magnetisations. The previously reported two step magnetisation process was not found to be an intrinsic property of the material but originated instead from unwanted extra phases. The magnetic moment values were extracted from the diffraction profiles using a simplified Rietveld method for two phases. The cobalt moment remained fairly constant up to the ordering temperature and its value decreased between compounds when the substituted rare earth moment was reduced.Using the technique of inelastic neutron scattering themagnon dispersion relations along the hexagonal axis were found for the intermediate rare earth alloy Ho(50%) Th(50%). Measurements were taken at several temperatures to include the ferromagnetic and helical phases as well as a high temperature ferromagnetic phase induced by an externally applied magnetic field. The interplanar exchange parameters were extracted from the results using a theoretical model and these are used to discuss the stability of the magnetic structures. The results are compared with those of the element Dysprosium.The final chapter contains an attempt to understand theoretically the origins of the magnetostrictive distortions found in cubic materials where the rare earth ion is the dominant source of anisotropy. A strain dependent crystal field Hamiltonian was developed and the point charge model was used to apply this to some RCo2 compounds. An explanation for the observed magnetostriction in HoCo2 and NdCo2 is given. Some RA12 and RFe2 compounds are also considered and the possibility of internal distortions is recognised. The simpler CsCl-type RZn compounds are also discussed and a calculation is presented for ThZn.
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Published date: 1977
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Local EPrints ID: 467249
URI: http://eprints.soton.ac.uk/id/eprint/467249
PURE UUID: 9db6a792-b009-441f-953e-591ba32565b5
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Date deposited: 05 Jul 2022 08:16
Last modified: 05 Jul 2022 08:16
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Author:
Paul Hendy
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