Magnetic X-ray spectroscopy studies of dilute magnetic semiconductors
Dilute magnetic semiconductors are an important family of materials that have many potential applications in spintronics; (Ga,Mn)As, (In,Ga,Mn)As and (Ga,Mn)N are of major interest. This thesis investigates dierent aspects of these, using the synchrotron radiation techniques of x-ray magnetic circul...
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| Format: | Thesis (University of Nottingham only) |
| Language: | English |
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2009
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| Online Access: | https://eprints.nottingham.ac.uk/10839/ |
| _version_ | 1848791139249815552 |
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| author | Freeman, Adam Alexander |
| author_facet | Freeman, Adam Alexander |
| author_sort | Freeman, Adam Alexander |
| building | Nottingham Research Data Repository |
| collection | Online Access |
| description | Dilute magnetic semiconductors are an important family of materials that have many potential applications in spintronics; (Ga,Mn)As, (In,Ga,Mn)As and (Ga,Mn)N are of major interest. This thesis investigates dierent aspects of these, using the synchrotron radiation techniques of x-ray magnetic circular dichroism (XMCD) and x-ray magnetic linear dichroism (XMLD), supported by superconducting quantum interference device (SQUID) magnetometry and magnetotransport measurements.
A large anisotropic XMLD signal is observed for the Mn L-edge in (Ga,Mn)As. In unannealed (Ga,Mn)As, an apparently reduced Mn magnetic moment is commonly observed. It is thought to be related to compensation of both carriers and magnetic moment, caused by interstitial Mn. This issue is investigated using combined data from XMCD, XMLD and SQUID magnetometry. The findings suggest that substitutional and interstitial Mn form `non-magnetic' pairs which do not have a preferred spin orientation.
(Ga,Mn)N is studied by x-ray absorption and field-dependent XMCD at the Mn L-edge. Two distinct Mn congurations are identified: Mn2+ is prevalent towards the surface with nearly paramagnetic behaviour, while a weakly ferromagnetic Mn2+/Mn3+ mixed valence exists within the bulk. The weak ferromagnetism, often observed in (Ga,Mn)N, is attributed to coupling between the impurities by the double exchange mechanism.
Finally, XMCD is used to measure the orbital polarization of As 4p states of (III,Mn)As materials. These states correspond to those of the holes involved in the itinerant exchange interaction in ferromagnetic semiconductors. The coupling between the localized d states of the magnetic impurities and the valence band p states of the host is demonstrated by an anisotropy in the orbital moment of these states. This is experimental confirmation of the origin of the magnetocrystalline anisotropy in dilute magnetic semiconductors. |
| first_indexed | 2025-11-14T18:23:45Z |
| format | Thesis (University of Nottingham only) |
| id | nottingham-10839 |
| institution | University of Nottingham Malaysia Campus |
| institution_category | Local University |
| language | English |
| last_indexed | 2025-11-14T18:23:45Z |
| publishDate | 2009 |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | nottingham-108392025-02-28T11:09:54Z https://eprints.nottingham.ac.uk/10839/ Magnetic X-ray spectroscopy studies of dilute magnetic semiconductors Freeman, Adam Alexander Dilute magnetic semiconductors are an important family of materials that have many potential applications in spintronics; (Ga,Mn)As, (In,Ga,Mn)As and (Ga,Mn)N are of major interest. This thesis investigates dierent aspects of these, using the synchrotron radiation techniques of x-ray magnetic circular dichroism (XMCD) and x-ray magnetic linear dichroism (XMLD), supported by superconducting quantum interference device (SQUID) magnetometry and magnetotransport measurements. A large anisotropic XMLD signal is observed for the Mn L-edge in (Ga,Mn)As. In unannealed (Ga,Mn)As, an apparently reduced Mn magnetic moment is commonly observed. It is thought to be related to compensation of both carriers and magnetic moment, caused by interstitial Mn. This issue is investigated using combined data from XMCD, XMLD and SQUID magnetometry. The findings suggest that substitutional and interstitial Mn form `non-magnetic' pairs which do not have a preferred spin orientation. (Ga,Mn)N is studied by x-ray absorption and field-dependent XMCD at the Mn L-edge. Two distinct Mn congurations are identified: Mn2+ is prevalent towards the surface with nearly paramagnetic behaviour, while a weakly ferromagnetic Mn2+/Mn3+ mixed valence exists within the bulk. The weak ferromagnetism, often observed in (Ga,Mn)N, is attributed to coupling between the impurities by the double exchange mechanism. Finally, XMCD is used to measure the orbital polarization of As 4p states of (III,Mn)As materials. These states correspond to those of the holes involved in the itinerant exchange interaction in ferromagnetic semiconductors. The coupling between the localized d states of the magnetic impurities and the valence band p states of the host is demonstrated by an anisotropy in the orbital moment of these states. This is experimental confirmation of the origin of the magnetocrystalline anisotropy in dilute magnetic semiconductors. 2009-05 Thesis (University of Nottingham only) NonPeerReviewed application/pdf en arr https://eprints.nottingham.ac.uk/10839/1/Adam_Thesis_Corrected_print_singlesided.pdf Freeman, Adam Alexander (2009) Magnetic X-ray spectroscopy studies of dilute magnetic semiconductors. PhD thesis, University of Nottingham. |
| spellingShingle | Freeman, Adam Alexander Magnetic X-ray spectroscopy studies of dilute magnetic semiconductors |
| title | Magnetic X-ray spectroscopy studies of dilute magnetic semiconductors |
| title_full | Magnetic X-ray spectroscopy studies of dilute magnetic semiconductors |
| title_fullStr | Magnetic X-ray spectroscopy studies of dilute magnetic semiconductors |
| title_full_unstemmed | Magnetic X-ray spectroscopy studies of dilute magnetic semiconductors |
| title_short | Magnetic X-ray spectroscopy studies of dilute magnetic semiconductors |
| title_sort | magnetic x-ray spectroscopy studies of dilute magnetic semiconductors |
| url | https://eprints.nottingham.ac.uk/10839/ |