847 research outputs found
Structure and magnetic properties of f-electron compounds and their hydrides
No full textTitle: Structure and magnetic properties of f-electron compounds and their hydrides Author: Silvie Mašková Department: Deparment of Condensed Matter Physics Supervisor: Doc. RNDr. Ladislav Havela, CSc., Deparment of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Prague, The Czech Republic Abstract: Magnetic properties were studied in several types of actinide- and lanthanide-based ternary compounds. We have shown indirect that anisotropy of compressibility and thermal expansion can be related to the direction of magnetic moments at U-compounds with "soft" directions (where the closest U-U links are) perpendicular to the moments direction. Comparison of U and RE compounds of the 2-2-1 type indicates that contrary to U compounds, RE compounds can absorb much more hydrogen. The involvement of the f-states in metallic bond, which takes place at actinides and not in lanthanides, makes the U-based compounds apparently more stable against hydrogenation. Basic electronic properties were established for ζ -Pu19Os, which is a close analogy to β-Pu, and for its low-temperature variety η -Pu19Os. The results confirm that the volume is not the main parameter driving Pu properties, as β-Pu with intermediate volume is the most strongly correlated Pu phase. Keywords: uranium compounds,..
Vývoj aktinoidového magnetismu v hydridech na bázi uranu a dalších vybraných systémech
Get PDFTitle: Variations of actinide magnetism in uranium-base hydrides and other selected systems. Author: Anna Maria Adamska Department / Institute: Department of Condensed Matter Physics Supervisor of the doctoral thesis: Doc. RNDr. Ladislav Havela, CSc., the Department of Condensed Matter Physics Faculty of Mathematics and Physics Charles University, Prague, Czech Republic and Assoc. Prof. Dr. hab. Nhu-Tarnawska Hoa Kim Ngan, Institute of Physics, Pedagogical University, Kraków, Poland. Abstract: Actinide magnetism was studied in three different types of systems. Variations of magnetic properties of UTGe hydrides as a function of hydrogen concentration prove that doping of U intermetallics by interstitial hydrogen leads to stronger magnetic properties, primarily caused by an increase of the inter-uranium separation. Sputter-deposited UFe2+x films, which are derived from the UFe2 Laves phase but have an amorphous structure, exhibit an increase of the Curie temperarture (to more than 400 K) with the Fe excess, which could not be achieved in the bulk. This is understood as a result of the prominent role of the 3d magnetism of Fe. Notoriously weakly magnetic plutonium was studied in the form of the alloy in the ζ-phase, which exists between 35 and 70 % U in Pu. Its susceptibility increases in a comparison to pure...Název práce: Vývoj aktinoidového magnetismu v hydridech na bázi uranu a dalších vybraných systémech. Autor: Anna Maria Adamska Katedra / Ústav: Katedra fyziky kondenzovaných Vedoucí doktorské práce: Doc. RNDr. Ladislav Havela, CSc., Katedra fyziky kondenzovaných látek, Matematicko-fyzikální fakulta, Karlova Univerzita, Praha, Česká republika a Assoc. Prof. Dr. hab. Nhu-Tarnawska Hoa Kim Ngan, Fyzikální ústav, Pedagogická Univerzita, Krakov, Polsko. Abstrakt: Magnetismus aktinoidů byl studován ve třech rozličných typech systémů. Vývoj magnetických vlastností hydridů sloučenin UTGe v závislosti na koncentraci vodíku prokazuje, že dopování intermetalik uranu intersticiálním vodíkem vede k výraznějším magnetickým vlastnostem, které jsou primárně důsledkem vyšších meziuranových vzdáleností. UFe2+x filmy, připravené naprašováním, jsou sice odvozeny z Lavesovy fáze UFe2, avšak jejich struktura je amorfní. Jejich Curieva teplota vzrůstá (nad 400 K) s nadbytkem Fe, což není možno dosáhnout v masivních vzorcích. Lze to chápat jako potvrzení dominantní role 3d magnetismu Fe. Běžně slabě magnetické plutonium bylo studováno ve formě slitiny, tzv. ζ-fáze, existující mezi 35 a 70 % U v Pu. Suceptibilita této fáze je ve srovnání s fázemi čistého Pu vyšší, i když se nevytvářejí lokální magnetické momenty. To prokazuje, že...Katedra fyziky kondenzovaných látekDepartment of Condensed Matter PhysicsFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult
Struktura a magnetické vlastnosti sloučenin s f-elektrony a jejich hydridů
Get PDFTitle: Structure and magnetic properties of f-electron compounds and their hydrides Author: Silvie Mašková Department: Deparment of Condensed Matter Physics Supervisor: Doc. RNDr. Ladislav Havela, CSc., Deparment of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Prague, The Czech Republic Abstract: Magnetic properties were studied in several types of actinide- and lanthanide-based ternary compounds. We have shown indirect that anisotropy of compressibility and thermal expansion can be related to the direction of magnetic moments at U-compounds with "soft" directions (where the closest U-U links are) perpendicular to the moments direction. Comparison of U and RE compounds of the 2-2-1 type indicates that contrary to U compounds, RE compounds can absorb much more hydrogen. The involvement of the f-states in metallic bond, which takes place at actinides and not in lanthanides, makes the U-based compounds apparently more stable against hydrogenation. Basic electronic properties were established for ζ -Pu19Os, which is a close analogy to β-Pu, and for its low-temperature variety η -Pu19Os. The results confirm that the volume is not the main parameter driving Pu properties, as β-Pu with intermediate volume is the most strongly correlated Pu phase. Keywords: uranium compounds,...Název práce: Struktura a magnetické vlastnosti sloučenin s f-elektrony a jejich hydridů Autor: Silvie Mašková Katedra: Katedra fyziky kondenzovaných látek Vedoucí dizertační práce: Doc. RNDr. Ladislav Havela, CSc., Katedra fyziky kondenzovaných látek, Matematicko-fyzikální fakulta, Karlova Univerzita, Praha, Česká republika Abstrakt: Magnetické vlastnosti byly studovány u několika systémů na bázi aktinoidů a vzácných zemin. Nepřímo jsme ukázali, že anizotropie kompresibility a termální expanze souvisí se směrem magnetických momentů U-sloučenin. Snadněji stlačitelný směr (směr nejkratších meziuranových vzdáleností) je kolmý na magnetické momenty. Vzácnozeminné sloučeniny typu 2-2-1 mohou absorbovat mnohem větší množství vodíku než jejich uranové protějšky. Uranové sloučeniny jsou stabilnější vůči hydrogenaci v důsledku zapojení 5f- elektronů do kovové vazby. Základní elektronové vlastnosti β-Pu byly určeny pomocí simulace sloučeninou ζ-Pu19Os. Pro porovnání byly určeny i vlastnosti nízkoteplotní variety η-Pu19Os. Bylo ukázáno, že objem není primární řídící parametr vlastností plutonia, když je β-Pu nejvíce korelovanou fází. Klíčová slova: uranové sloučeniny, vzácné zeminy, krystalová struktura, magnetické vlastnosti, hydrogenaceKatedra fyziky kondenzovaných látekDepartment of Condensed Matter PhysicsFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult
U in metastable systems: structure, magnetism, superconductivity
No full textTitle: U in metastable systems: structure, magnetism, and superconductivity Author: Volodymyr Buturlim Department / Institute: Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University Supervisor of the doctoral thesis: Doc. RNDr. Ladislav Havela, CSc., Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Prague, The Czech Republic Abstract: This thesis presents studies of U-Nb and U-Ti alloys and hydrides synthesized via different technological paths. Investigation of the microstructure of the alloys with different concentrations of Ti (Nb) allowed to find the optimum setting for stabilization of the metastable bcc U allotrope. Ultra-fast cooling accompanied by alloying leads to retention of materials with high degree of atomic disorder apparent from the studies of their transport properties. The alloys exhibit a weakly paramagnetic ground state and low-temperature superconductivity, the critical temperature of which has only moderate variations with Ti (Nb) concentrations and which has very high upper critical fields. Interaction with hydrogen allows to stabilize two distinctive forms of hydride: β-UH3 and UTi2Hx. β-UH3 alloyed by Ti (Nb) orders ferromagnetically with transition temperatures exceeding 170 K, weakly influenced..
Superconductivity and electronic properties of y-U alloys and their hydrides
No full textTitle: Superconductivity and electronic properties of γ-U alloys and their hydrides. Author: Ilya Tkach Department / Institute: Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University Supervisor of the doctoral thesis: Doc. RNDr. Ladislav Havela, CSc., Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Prague, The Czech Republic Abstract: Low-temperature electronic properties for U-Mo and U-Zr splats stabilized in γ-U were investigated. Magnetic measurements revealed Pauli paramagnetic behavior with temperature independent susceptibility for U-Mo alloys. U-Mo and U- Zr splats become superconducting at low temperatures with Tc up to 2.1 K and critical field 5-6 T. The superconductivity of -U can be considered as a bulk effect and can be described by the BCS theory, while -U superconductivity is not a real bulk effect. U-Mo and U-Zr alloys absorb hydrogen at high pressures (p ≥ 4.5 bar) and form hydrides with stoichiometry analogous to UH3. The hydrides with Mo have an amorphous structure based on β-UH3 phase, while hydrides with Zr have a crystalline structure of the -UH3 type. (UH3)1-xMox hydrides are ferromagnetic with enhanced TC up to 202 K and magnetic moments 1.1 μB/U in comparison with pure β-UH3 (175 K; 0.87 μB/U)...
U-based thin films: electronic structure and physical properties
No full textTitle: U-based thin films: electronic structure and physical properties Author: Oleksandra Koloskova Department / Institute: Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University Supervisor of the doctoral thesis: Doc. RNDr. Ladislav Havela, CSc., Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Prague, The Czech Republic Abstract: This thesis presents studies of U-based thin films synthesized by means of the DC sputter deposition, which allows to vary the composition and microstructure and perform in photoelectron spectroscopy studies. The subjects are U-Mo and U-Zr alloys, Uranium hydrides (UH3 and UH2), and U hydrides with Zr/Mo substitution. In-situ analysis was followed by ex-situ studies of structure, magnetic and transport properties. Despite the superconducting ground state of the U-T alloys, only one film (U0.92Mo0.08) exhibited superconductivity, with the transition at 0.55 K. All hydrides are ferromagnetic, with Curie temperatures around 120 K for UH2 and 170 K for both α- and β-UH3. This ferromagnetism is robust and independent of structural details. By varying sputtering parameters, one can obtain UH2 (nonexistent in bulk form), β-UH3, or a mix of UH2 and α-UH3 (first observed in film form). Inclusion of..
U v metastabilních systémech: struktura, magnetismus a supravodivost
Get PDFNázev práce: U v metastabilních systémech: struktura, magnetismus a supravodivost Autor: Volodymyr Buturlim Katedra / Ústav: Katedra fyziky kondenzovaných látek Vedoucí doktorské práce: Doc. RNDr. Ladislav Havela, CSc. Abstrakt: Tato práce představuje studium slitin a hydridů U-Nb a U-Ti syntetizovaných různými technologickými postupy. Výzkum mikrostruktury slitin s různými koncentracemi Ti (Nb) umožnil najít optimální parametry pro udržení metastabilní bcc alotropní fáze uranu. Ultrarychlé chlazení doprovázené legováním vede ke stabilizaci materiálů s vysokým stupněm neupořádanosti na atomové úrovni, prokázané studiem transportních vlastností. Tyto slitiny vykazují slabě paramagnetický základní stav a nízkoteplotní supravodivost, která slabě závisí na koncentraci Ti (Nb) a vykazuje velmi vysoké hodnoty kritického magnetického pole. Interakce s vodíkem umožňuje stabilizovat dvě charakteristické formy hydridu: β-UH3 a UTi2Hx. β-UH3 legovaný Ti (Nb) se uspořádává feromagneticky s teplotami přechodu přesahujícími 170 K a slabě ovlivněnými koncentrací tranzitivních prvků. Vývoj hustoty elektronových stavů na Fermiho mezi byl sledován také studiem specifického tepla. Výsledky byly interpretovány v kontextu změn vzdáleností mezi atomy uranu. UTi2Hx reprezentuje kubickou Lavesovu fázi AB2, která se však v tomto...Title: U in metastable systems: structure, magnetism, and superconductivity Author: Volodymyr Buturlim Department / Institute: Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University Supervisor of the doctoral thesis: Doc. RNDr. Ladislav Havela, CSc., Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Prague, The Czech Republic Abstract: This thesis presents studies of U-Nb and U-Ti alloys and hydrides synthesized via different technological paths. Investigation of the microstructure of the alloys with different concentrations of Ti (Nb) allowed to find the optimum setting for stabilization of the metastable bcc U allotrope. Ultra-fast cooling accompanied by alloying leads to retention of materials with high degree of atomic disorder apparent from the studies of their transport properties. The alloys exhibit a weakly paramagnetic ground state and low-temperature superconductivity, the critical temperature of which has only moderate variations with Ti (Nb) concentrations and which has very high upper critical fields. Interaction with hydrogen allows to stabilize two distinctive forms of hydride: β-UH3 and UTi2Hx. β-UH3 alloyed by Ti (Nb) orders ferromagnetically with transition temperatures exceeding 170 K, weakly influenced...Katedra fyziky kondenzovaných látekDepartment of Condensed Matter PhysicsMatematicko-fyzikální fakultaFaculty of Mathematics and Physic
Tenké vrstvy na bázi uranu: elektronová struktura a fyzikální vlastnosti
Get PDFNázev práce: Tenké vrstvy na bázi uranu: elektronová struktura a fyzikální vlastnosti Autor: Oleksandra Koloskova Katedra / Ústav: Katedra fyziky kondenzovaných látek Vedoucí doktorské práce: Doc. RNDr. Ladislav Havela, CSc. Abstrakt: Tato práce se zabývá studiem tenkých vrstev na bázi uranu deponovaných pomocí DC naprašování, které umožňuje změny v kompozici a mikrostruktuře a zkoumání pomocí fotoelektronové spektroskopie. Předmětem studia jsou slitiny U-Mo a U-Zr, uranové hydridy (UH3 and UH2) a uranové hydridy se substitucí Zr/Mo. Nejprve byla provedena in-situ analýza a poté ex-situ analýzy struktury a magnetických a transportních vlastností. Navzdory supravodivému stavu U-T slitin, pouze jeden film (U0.92Mo0.08) supravodivost vykazuje, a to s přechodem při teplotě 0,55 K. Všechny hydridy jsou ferromagnetické, přičemž jejich Curieovy teploty se pohybují kolem 120 K pro UH2 a 170 K pro α- a β-UH3. Tento ferromagnetismus je robustní a nezávislý na strukturních detailech. Variací parametrů naprašování můžeme získat UH2 (který se v bulku nevyskytuje), β-UH3, nebo koexistenci UH2 and α-UH3. Inkluze atomů vodíku drasticky ovlivňuje vlastnosti. Konkrétně mění paramagnetické slitiny na ferromagnetické hydridy, a pro feromagnetismus je zde velmi důležitá U-H polární vazba. Pásově ferromagnetická povaha UH3 byla...Title: U-based thin films: electronic structure and physical properties Author: Oleksandra Koloskova Department / Institute: Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University Supervisor of the doctoral thesis: Doc. RNDr. Ladislav Havela, CSc., Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Prague, The Czech Republic Abstract: This thesis presents studies of U-based thin films synthesized by means of the DC sputter deposition, which allows to vary the composition and microstructure and perform in photoelectron spectroscopy studies. The subjects are U-Mo and U-Zr alloys, Uranium hydrides (UH3 and UH2), and U hydrides with Zr/Mo substitution. In-situ analysis was followed by ex-situ studies of structure, magnetic and transport properties. Despite the superconducting ground state of the U-T alloys, only one film (U0.92Mo0.08) exhibited superconductivity, with the transition at 0.55 K. All hydrides are ferromagnetic, with Curie temperatures around 120 K for UH2 and 170 K for both α- and β-UH3. This ferromagnetism is robust and independent of structural details. By varying sputtering parameters, one can obtain UH2 (nonexistent in bulk form), β-UH3, or a mix of UH2 and α-UH3 (first observed in film form). Inclusion of...Department of Condensed Matter PhysicsKatedra fyziky kondenzovaných látekMatematicko-fyzikální fakultaFaculty of Mathematics and Physic
Variations of actinide magnetism in uranium-base hydrides and other selected systems
No full textTitle: Variations of actinide magnetism in uranium-base hydrides and other selected systems. Author: Anna Maria Adamska Department / Institute: Department of Condensed Matter Physics Supervisor of the doctoral thesis: Doc. RNDr. Ladislav Havela, CSc., the Department of Condensed Matter Physics Faculty of Mathematics and Physics Charles University, Prague, Czech Republic and Assoc. Prof. Dr. hab. Nhu-Tarnawska Hoa Kim Ngan, Institute of Physics, Pedagogical University, Kraków, Poland. Abstract: Actinide magnetism was studied in three different types of systems. Variations of magnetic properties of UTGe hydrides as a function of hydrogen concentration prove that doping of U intermetallics by interstitial hydrogen leads to stronger magnetic properties, primarily caused by an increase of the inter-uranium separation. Sputter-deposited UFe2+x films, which are derived from the UFe2 Laves phase but have an amorphous structure, exhibit an increase of the Curie temperarture (to more than 400 K) with the Fe excess, which could not be achieved in the bulk. This is understood as a result of the prominent role of the 3d magnetism of Fe. Notoriously weakly magnetic plutonium was studied in the form of the alloy in the ζ-phase, which exists between 35 and 70 % U in Pu. Its susceptibility increases in a comparison to pure..
Supravodivost a magnetické vlastnosti slitin y-U a jejich hydridů
Get PDFNázev práce: Supravodivost a magnetické vlastnosti slitin γ-U a jejich hydridů. Autor: Ilya Tkach Katedra / Ústav: Katedra fyziky kondenzovaných látek Vedoucí doktorské práce: Doc. RNDr. Ladislav Havela, CSc. Abstrakt: Byly prostudovány nízkoteplotní elektronové vlastnosti splatů U-Mo a U- Zr, ve kterých byla zachována struktura bcc (γ-U), stabilní za vysokých teplot. Magnetická studia pro U-Mo slitin prokázala Pauliho paramagnetické chování. U- Mo a U-Zr splaty přecházejí do supravodivého stavu pod teplotou Tc, která může dosáhnout až 2.1 K a vykazují kriticiká pole až 5-6 T. Supravodivost u -U může být považována za objemový efekt a je posána teorií BCS, zatímco supravodivost u -U skutečný objemový efekt není. Bcc slitiny U-Mo and U-Zr alloys absorbují vodík jen za výšených tlaků (p ≥ 4.5 bar) a vytvářejí hydridy se stechiometrií analogickou k UH3. Tyto hydridy s Mo vykazují amorfní strkturu, zalořenou na struktuře typy β-UH3, zatímco hydridy s Zr mají krystalickou struktury typu -UH3 type. Hydridy (UH3)1-xMox jsou feromagnetické s hodnotami Curievy teploty TC a magnetických momentů zvýšenými (přes 200 K a do okolí 1.1 μB/U) ve srovnání s čitým β-UH3 (165 - 175 K; 0.9 μB/U). Jsou to patrně první amorfní feromagnetika na bázi uranu s tak vysokými TC. Hodnoty koercitivního pole u (UH3)1-xMox a (UH3)1-xZrx...Title: Superconductivity and electronic properties of γ-U alloys and their hydrides. Author: Ilya Tkach Department / Institute: Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University Supervisor of the doctoral thesis: Doc. RNDr. Ladislav Havela, CSc., Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Prague, The Czech Republic Abstract: Low-temperature electronic properties for U-Mo and U-Zr splats stabilized in γ-U were investigated. Magnetic measurements revealed Pauli paramagnetic behavior with temperature independent susceptibility for U-Mo alloys. U-Mo and U- Zr splats become superconducting at low temperatures with Tc up to 2.1 K and critical field 5-6 T. The superconductivity of -U can be considered as a bulk effect and can be described by the BCS theory, while -U superconductivity is not a real bulk effect. U-Mo and U-Zr alloys absorb hydrogen at high pressures (p ≥ 4.5 bar) and form hydrides with stoichiometry analogous to UH3. The hydrides with Mo have an amorphous structure based on β-UH3 phase, while hydrides with Zr have a crystalline structure of the -UH3 type. (UH3)1-xMox hydrides are ferromagnetic with enhanced TC up to 202 K and magnetic moments 1.1 μB/U in comparison with pure β-UH3 (175 K; 0.87 μB/U)....Katedra fyziky kondenzovaných látekDepartment of Condensed Matter PhysicsMatematicko-fyzikální fakultaFaculty of Mathematics and Physic
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