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Physical properties of magnetic as-grown and oxygen annealed SnO2:Co thin films.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Physical properties of magnetic as-grown and oxygen annealed SnO2:Co thin films./
作者:	Stoian, Gratiela M.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2013,
面頁冊數:	131 p.
附註:	Source: Dissertations Abstracts International, Volume: 75-10, Section: B.
Contained By:	Dissertations Abstracts International75-10B.
標題:	Condensed matter physics. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3612507
ISBN:	9781303740978

Physical properties of magnetic as-grown and oxygen annealed SnO2:Co thin films.
Stoian, Gratiela M.

Physical properties of magnetic as-grown and oxygen annealed SnO2:Co thin films. - Ann Arbor : ProQuest Dissertations & Theses, 2013 - 131 p.

Source: Dissertations Abstracts International, Volume: 75-10, Section: B.

Thesis (Ph.D.)--The Florida State University, 2013.

This item must not be added to any third party search indexes.

Dilute magnetic semiconductor oxides are complex systems in which ferromagnetic and semiconducting properties coexist, potentially making these materials suitable for Spintronics applications. Understanding the fundamental physical processes taking place in these intricate materials could offer a better way to implement these structures into real life Spintronic devices. This dissertation is based on the study of the physical properties of a magnetic oxide system, namely SnO2 thin films doped with a few atomic percent Co, grown by two different methods. The ultimate goal of this study is to understand the physical mechanisms of high temperature ferromagnetism (RTFM) in SnO2-δ:Co. Two different methods for growing epitaxial SnO2-δ: Co thin films were employed: pulsed laser deposition (PLD) and RF Sputtering. In both cases, films were deposited on R-cut Al2O3 substrates under well controlled growth conditions in order to produce epitaxial thin films which behave ferromagnetically at room temperature and are semiconducting. Detailed structural and magnetic characterization demonstrates that PLD SnO 2-δ:Co films grown under optimal oxygen pressure are single phase SnO2 with no presence of Co-based nanoclusters in the oxide matrix. Moreover, a direct relationship between structure, resistivity and magnetization is demonstrated, the number of structural defects influencing greatly the electromagnetic properties of the studied materials. Highly crystalline samples have a larger resistivity than less ordered materials. In addition, films grown with an optimal deposition rate have a saturation magnetization that is comparable to the Co2+ low spin state (1&mgr;B/Co). This is consistent with the XPS measurements which suggest that the valence of Co in SnO2 is +2, proving that Co2+ ions substitute for octahedral Sn4+ ions in the SnO2 lattice. Temperature dependent magnetic investigations indicate the presence of a granular-type magnetism, which is believed to occur due to formation of small Co-doped SnO 2 grains with different particle sizes and blocking temperatures, existing in a dielectric matrix. Annealing samples in O2 enhances the ferromagnetism dramatically due to the strong intergranular interaction produced after the thermal treatment. Electrical transport data reveal there is a hopping-type activated conduction mechanism up to room temperature. Non-diffusive electrical transport is observed up to 350 K. The study done on RF sputtered films deposited by two methods: RF co-sputtering and sputtering from a 5 at.% Co - doped target, has shown that by changing the deposition parameters, one can produce films which are highly crystalline and insulating, some of which exhibit a paramagnetic signature, originating from the presence of noninteracting Co2+ ions. It was concluded that the magnetism in sputtered SnO2:Co thin films is not carrier mediated but is due to the superexchange interaction which couples the nearest neighbor Co spins antiferromagnetically, depending on the local lattice distortions and the spin environment. The moments per Co ion in these films determined from magnetic measurements are lower than the theoretical value of low spin state Co2+ ions. Moreover, XPS and TEM analysis suggests that Sn4+ is substituted by Co 2+ ions. Annealing some of the samples in oxygen environment modifies their structure and enhances the magnetic moment per Co ion. The sputtered materials studied in this project may not be suitable for Spintronics applications since magnetism is not carrier mediated due to the very low carrier concentration achieved in these samples. The deposition process was found to be unreliable because of the difficulty to control the growth. This yielded discrepancies in the structural and magnetic properties, characteristics that will be outlined in this thesis.

ISBN: 9781303740978Subjects--Topical Terms:

3173567
Condensed matter physics.
Subjects--Index Terms:

Defects

Physical properties of magnetic as-grown and oxygen annealed SnO2:Co thin films.
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100 1 $a Stoian, Gratiela M. $3 3545314
245 1 0 $a Physical properties of magnetic as-grown and oxygen annealed SnO2:Co thin films.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 2013
300 $a 131 p.
500 $a Source: Dissertations Abstracts International, Volume: 75-10, Section: B.
500 $a Publisher info.: Dissertation/Thesis.
500 $a Advisor: von Molnar, Stephan;Stampe, Patricia A.
502 $a Thesis (Ph.D.)--The Florida State University, 2013.
506 $a This item must not be added to any third party search indexes.
506 $a This item must not be sold to any third party vendors.
520 $a Dilute magnetic semiconductor oxides are complex systems in which ferromagnetic and semiconducting properties coexist, potentially making these materials suitable for Spintronics applications. Understanding the fundamental physical processes taking place in these intricate materials could offer a better way to implement these structures into real life Spintronic devices. This dissertation is based on the study of the physical properties of a magnetic oxide system, namely SnO2 thin films doped with a few atomic percent Co, grown by two different methods. The ultimate goal of this study is to understand the physical mechanisms of high temperature ferromagnetism (RTFM) in SnO2-δ:Co. Two different methods for growing epitaxial SnO2-δ: Co thin films were employed: pulsed laser deposition (PLD) and RF Sputtering. In both cases, films were deposited on R-cut Al2O3 substrates under well controlled growth conditions in order to produce epitaxial thin films which behave ferromagnetically at room temperature and are semiconducting. Detailed structural and magnetic characterization demonstrates that PLD SnO 2-δ:Co films grown under optimal oxygen pressure are single phase SnO2 with no presence of Co-based nanoclusters in the oxide matrix. Moreover, a direct relationship between structure, resistivity and magnetization is demonstrated, the number of structural defects influencing greatly the electromagnetic properties of the studied materials. Highly crystalline samples have a larger resistivity than less ordered materials. In addition, films grown with an optimal deposition rate have a saturation magnetization that is comparable to the Co2+ low spin state (1&mgr;B/Co). This is consistent with the XPS measurements which suggest that the valence of Co in SnO2 is +2, proving that Co2+ ions substitute for octahedral Sn4+ ions in the SnO2 lattice. Temperature dependent magnetic investigations indicate the presence of a granular-type magnetism, which is believed to occur due to formation of small Co-doped SnO 2 grains with different particle sizes and blocking temperatures, existing in a dielectric matrix. Annealing samples in O2 enhances the ferromagnetism dramatically due to the strong intergranular interaction produced after the thermal treatment. Electrical transport data reveal there is a hopping-type activated conduction mechanism up to room temperature. Non-diffusive electrical transport is observed up to 350 K. The study done on RF sputtered films deposited by two methods: RF co-sputtering and sputtering from a 5 at.% Co - doped target, has shown that by changing the deposition parameters, one can produce films which are highly crystalline and insulating, some of which exhibit a paramagnetic signature, originating from the presence of noninteracting Co2+ ions. It was concluded that the magnetism in sputtered SnO2:Co thin films is not carrier mediated but is due to the superexchange interaction which couples the nearest neighbor Co spins antiferromagnetically, depending on the local lattice distortions and the spin environment. The moments per Co ion in these films determined from magnetic measurements are lower than the theoretical value of low spin state Co2+ ions. Moreover, XPS and TEM analysis suggests that Sn4+ is substituted by Co 2+ ions. Annealing some of the samples in oxygen environment modifies their structure and enhances the magnetic moment per Co ion. The sputtered materials studied in this project may not be suitable for Spintronics applications since magnetism is not carrier mediated due to the very low carrier concentration achieved in these samples. The deposition process was found to be unreliable because of the difficulty to control the growth. This yielded discrepancies in the structural and magnetic properties, characteristics that will be outlined in this thesis.
590 $a School code: 0071.
650 4 $a Condensed matter physics. $3 3173567
653 $a Defects
653 $a Dilute magnetic semiconductor oxide
653 $a Ferromagnetism
653 $a High curie temperature
653 $a SnO2:Co
653 $a Spintronics
690 $a 0611
710 2 $a The Florida State University. $b Physics. $3 2099202
773 0 $t Dissertations Abstracts International $g 75-10B.
790 $a 0071
791 $a Ph.D.
792 $a 2013
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3612507