{"id":{"repo_id":"aachen","oai_identifier":"oai:publications.rwth-aachen.de:60680"},"canonical_url":"https://search.dev.ndltd.org/etd/aachen/oai:publications.rwth-aachen.de:60680","repository":{"repo_id":"aachen","name":"RWTH Aachen University","base_url":"https://publications.rwth-aachen.de/oai2d"},"display":{"title":"Spin-gap materials from first principles: properties and applications of half-metallic ferromagnets","abstract":"Half-metallic ferromagnets, discovered in 1983 by de~Groot and collaborators,have given a strong boost to the research in the field of spintronics.The main characteristic of these materials is a different behavior in the two spin bands: while the majority spin band shows a typical metallic behavior, the minority spin band is semiconducting. Thus, the spin polarization at the Fermi level is 100%, maximizing the efficiency of magnetoelectronic devices. In this thesis we address the half-metallicity of materials from the electronic structure point of view. We focus on the structural, electronic, and magnetic aspects of the half-metallic Heusler alloys and the zincblende compounds. Among the Heusler alloys we focus particularly on NiMnSb. The investigations arebased on the Density Functional Theory (DFT), the most successful ab-initio theory for real solid state materials. We investigate the bulk properties, the properties of selected low index surfaces and for the case of NiMnSb/InP also a junction with a semiconductor. The importance of the spin-orbit interaction in reducing the polarization at the Fermi energy is considered. The calculations are carried out with the full-potential augmented linearized plane-wave method (FLAPW), one of the most precise density functional methods for multicomponentmaterials, open structures and surfaces.Particular effort is made to address the finite temperature properties of half-metals. This is a challenge, as the local-density approximation and the generalized gradient approximation to DFT are theories which address the systems at zero temperature. To bridge the temperature gap, we calculate theinteratomic exchange parameters from first principles, using the frozen magnon calculations which employ the spin spiral formalism as implemented in the FLEUR code. These parameters are then used in a Heisenberg model which describes the system at finite temperatures. Besides applying the random phase and the mean-field approximation, we seek the finite temperature properties by Monte Carlosimulations. To describe the system NiMnSb properly, we extend the Heisenberg model to include the longitudinal fluctuations in addition to the transverse ones. This leads to the surprising result that, although the magnetic moment of Ni is lost at a temperature around 1/10 of the Curie point, the half-metallicity is preserved. However, the width of the half-metallic gap is reduced and the Fermi level is slightly shifted. Finally, we present an analysis of possible applications of half-metals in giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) junctions, concluding that in the TMR case interface states can completely compensate the half-metallic property rendering it useless. A possible application of zincblende half-metals in ideal spin-valves, found to be free of interfacestates, is described.","abstract_html":"Half-metallic ferromagnets, discovered in 1983 by de~Groot and collaborators,have given a strong boost to the research in the field of spintronics.The main characteristic of these materials is a different behavior in the two spin bands: while the majority spin band shows a typical metallic behavior, the minority spin band is semiconducting. Thus, the spin polarization at the Fermi level is 100%, maximizing the efficiency of magnetoelectronic devices. In this thesis we address the half-metallicity of materials from the electronic structure point of view. We focus on the structural, electronic, and magnetic aspects of the half-metallic Heusler alloys and the zincblende compounds. Among the Heusler alloys we focus particularly on NiMnSb. The investigations arebased on the Density Functional Theory (DFT), the most successful ab-initio theory for real solid state materials. We investigate the bulk properties, the properties of selected low index surfaces and for the case of NiMnSb/InP also a junction with a semiconductor. The importance of the spin-orbit interaction in reducing the polarization at the Fermi energy is considered. The calculations are carried out with the full-potential augmented linearized plane-wave method (FLAPW), one of the most precise density functional methods for multicomponentmaterials, open structures and surfaces.Particular effort is made to address the finite temperature properties of half-metals. This is a challenge, as the local-density approximation and the generalized gradient approximation to DFT are theories which address the systems at zero temperature. To bridge the temperature gap, we calculate theinteratomic exchange parameters from first principles, using the frozen magnon calculations which employ the spin spiral formalism as implemented in the FLEUR code. These parameters are then used in a Heisenberg model which describes the system at finite temperatures. Besides applying the random phase and the mean-field approximation, we seek the finite temperature properties by Monte Carlosimulations. To describe the system NiMnSb properly, we extend the Heisenberg model to include the longitudinal fluctuations in addition to the transverse ones. This leads to the surprising result that, although the magnetic moment of Ni is lost at a temperature around 1/10 of the Curie point, the half-metallicity is preserved. However, the width of the half-metallic gap is reduced and the Fermi level is slightly shifted. Finally, we present an analysis of possible applications of half-metals in giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) junctions, concluding that in the TMR case interface states can completely compensate the half-metallic property rendering it useless. A possible application of zincblende half-metals in ideal spin-valves, found to be free of interfacestates, is described.","abstract_has_math":false,"creators":["Ležaic, Marjana"],"institution":"Publikationsserver der RWTH Aachen University","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":["Blügel, Stefan"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2006,"date_issued":"2006","date_published":"2006","updated_at":"2026-07-30T19:42:56Z","subjects":["info:eu-repo/classification/ddc/530","Physik","Half-metallic ferromagnets","Heusler alloys","spintronics"],"languages":["eng"],"rights":["info:eu-repo/semantics/openAccess"],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-122375%22"],"render_values":[{"text":"https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-122375%22","href":"https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-122375%22","code":true}]}]},"links":{"outbound_url":"https://publications.rwth-aachen.de/record/60680","outbound_label":"Repository record","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Blügel, Stefan"]},{"key":"dc:creator","label":"Author","values":["Ležaic, Marjana"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:coverage","label":"Dc Coverage","values":["DE"]},{"key":"dc:date","label":"Dc Date","values":["2006"]},{"key":"dc:publisher","label":"Institution","values":["Publikationsserver der RWTH Aachen University"]},{"key":"dc:relation","label":"Dc Relation","values":["info:eu-repo/semantics/altIdentifier/urn/urn:nbn:de:hbz:82-opus-13594"]},{"key":"dc:type","label":"Dc Type","values":["info:eu-repo/semantics/doctoralThesis","info:eu-repo/semantics/publishedVersion"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["info:eu-repo/classification/ddc/530","Physik","Half-metallic ferromagnets","Heusler alloys","spintronics"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["info:eu-repo/semantics/openAccess"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://publications.rwth-aachen.de/record/60680","https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-122375%22"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Half-metallic ferromagnets, discovered in 1983 by de~Groot and collaborators,have given a strong boost to the research in the field of spintronics.The main characteristic of these materials is a different behavior in the two spin bands: while the majority spin band shows a typical metallic behavior, the minority spin band is semiconducting. Thus, the spin polarization at the Fermi level is 100%, maximizing the efficiency of magnetoelectronic devices. In this thesis we address the half-metallicity of materials from the electronic structure point of view. We focus on the structural, electronic, and magnetic aspects of the half-metallic Heusler alloys and the zincblende compounds. Among the Heusler alloys we focus particularly on NiMnSb. The investigations arebased on the Density Functional Theory (DFT), the most successful ab-initio theory for real solid state materials. We investigate the bulk properties, the properties of selected low index surfaces and for the case of NiMnSb/InP also a junction with a semiconductor. The importance of the spin-orbit interaction in reducing the polarization at the Fermi energy is considered. The calculations are carried out with the full-potential augmented linearized plane-wave method (FLAPW), one of the most precise density functional methods for multicomponentmaterials, open structures and surfaces.Particular effort is made to address the finite temperature properties of half-metals. This is a challenge, as the local-density approximation and the generalized gradient approximation to DFT are theories which address the systems at zero temperature. To bridge the temperature gap, we calculate theinteratomic exchange parameters from first principles, using the frozen magnon calculations which employ the spin spiral formalism as implemented in the FLEUR code. These parameters are then used in a Heisenberg model which describes the system at finite temperatures. Besides applying the random phase and the mean-field approximation, we seek the finite temperature properties by Monte Carlosimulations. To describe the system NiMnSb properly, we extend the Heisenberg model to include the longitudinal fluctuations in addition to the transverse ones. This leads to the surprising result that, although the magnetic moment of Ni is lost at a temperature around 1/10 of the Curie point, the half-metallicity is preserved. However, the width of the half-metallic gap is reduced and the Fermi level is slightly shifted. Finally, we present an analysis of possible applications of half-metals in giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) junctions, concluding that in the TMR case interface states can completely compensate the half-metallic property rendering it useless. A possible application of zincblende half-metals in ideal spin-valves, found to be free of interfacestates, is described."]},{"key":"dc:source","label":"Dc Source","values":["Aachen : Publikationsserver der RWTH Aachen University II, 157 S. : Ill., graph. Darst. (2006). = Aachen, Techn. Hochsch., Diss., 2005"]},{"key":"dc:title","label":"Title","values":["Spin-gap materials from first principles: properties and applications of half-metallic ferromagnets"]}]}],"canonical_facts":{"dc:contributor":["Blügel, Stefan"],"dc:coverage":["DE"],"dc:creator":["Ležaic, Marjana"],"dc:date":["2006"],"dc:description":["Half-metallic ferromagnets, discovered in 1983 by de~Groot and collaborators,have given a strong boost to the research in the field of spintronics.The main characteristic of these materials is a different behavior in the two spin bands: while the majority spin band shows a typical metallic behavior, the minority spin band is semiconducting. Thus, the spin polarization at the Fermi level is 100%, maximizing the efficiency of magnetoelectronic devices. In this thesis we address the half-metallicity of materials from the electronic structure point of view. We focus on the structural, electronic, and magnetic aspects of the half-metallic Heusler alloys and the zincblende compounds. Among the Heusler alloys we focus particularly on NiMnSb. The investigations arebased on the Density Functional Theory (DFT), the most successful ab-initio theory for real solid state materials. We investigate the bulk properties, the properties of selected low index surfaces and for the case of NiMnSb/InP also a junction with a semiconductor. The importance of the spin-orbit interaction in reducing the polarization at the Fermi energy is considered. The calculations are carried out with the full-potential augmented linearized plane-wave method (FLAPW), one of the most precise density functional methods for multicomponentmaterials, open structures and surfaces.Particular effort is made to address the finite temperature properties of half-metals. This is a challenge, as the local-density approximation and the generalized gradient approximation to DFT are theories which address the systems at zero temperature. To bridge the temperature gap, we calculate theinteratomic exchange parameters from first principles, using the frozen magnon calculations which employ the spin spiral formalism as implemented in the FLEUR code. These parameters are then used in a Heisenberg model which describes the system at finite temperatures. Besides applying the random phase and the mean-field approximation, we seek the finite temperature properties by Monte Carlosimulations. To describe the system NiMnSb properly, we extend the Heisenberg model to include the longitudinal fluctuations in addition to the transverse ones. This leads to the surprising result that, although the magnetic moment of Ni is lost at a temperature around 1/10 of the Curie point, the half-metallicity is preserved. However, the width of the half-metallic gap is reduced and the Fermi level is slightly shifted. Finally, we present an analysis of possible applications of half-metals in giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) junctions, concluding that in the TMR case interface states can completely compensate the half-metallic property rendering it useless. A possible application of zincblende half-metals in ideal spin-valves, found to be free of interfacestates, is described."],"dc:identifier":["https://publications.rwth-aachen.de/record/60680","https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-122375%22"],"dc:language":["eng"],"dc:publisher":["Publikationsserver der RWTH Aachen University"],"dc:relation":["info:eu-repo/semantics/altIdentifier/urn/urn:nbn:de:hbz:82-opus-13594"],"dc:rights":["info:eu-repo/semantics/openAccess"],"dc:source":["Aachen : Publikationsserver der RWTH Aachen University II, 157 S. : Ill., graph. Darst. (2006). = Aachen, Techn. Hochsch., Diss., 2005"],"dc:subject":["info:eu-repo/classification/ddc/530","Physik","Half-metallic ferromagnets","Heusler alloys","spintronics"],"dc:title":["Spin-gap materials from first principles: properties and applications of half-metallic ferromagnets"],"dc:type":["info:eu-repo/semantics/doctoralThesis","info:eu-repo/semantics/publishedVersion"]},"updated_at":"2026-07-30T19:42:56Z"}