Strongly Correlated Oxides - Half-metallicity in Chromium-based Rutiles and Quantum Magnetism in Copper-based Double Perovskites

Otto Mustonen

Strongly Correlated Oxides - Half-metallicity in Chromium-based Rutiles and Quantum Magnetism in Copper-based Double Perovskites

Julkaisun otsikon käännös: Voimakkaan elektronikorrelaation oksidit: Spin-metallisuus kromipohjaisissa rutiileissa ja kvanttimagnetismi kuparipohjaisissa kaksoisperovskiiteissa

Otto Mustonen

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Voimakkaan korrelaation materiaaleissa on huomattavia elektroni-elektroni –korrelaatioita johtuen lokalisoituneiden elektronien välisestä sähköisestä hylkimisestä. Tästä ilmiöstä johtuen näiden materiaalien ominaisuuksien ennustaminen on vaikeaa, mutta toisaalta niillä voi olla kiinnostavia kokonaan uudenlaisia ominaisuuksia. Tässä väitöskirjassa tutkittiin kahdentyyppisiä voimakkaasti korreloituneita materiaaleja: spin-metalleja ja kvanttispinnesteitä. Kromidioksidi on tunnetuin spin-metalli. Se on samanaikaisesti ferromagneettinen sekä erinomainen sähkönjohde, mikä on tärkeä yhdistelmä spintroniikkasovelluksiin. Tässä väitöskirjassa tutkittiin kemiallista substituutiota CrO2-VO2 –systeemissä tapana etsiä uusia spin-metalleja. Tiheysfunktionaaliteoria ennusti näiden substituoitujen yhdisteiden olevan spin-metalleja, mutta niiden todettiin kokeellisesti olevan antiferromagneettisia. Tämä korostaa hapetusasteiden ennustamisen vaikeutta etsittäessä uusia spin-metalleja tiheysfunktionaaliteorian avulla. Spin-1/2 ionien neliöhilojen kvanttimagnetismi on ollut erittäin suuren teoreettisen ja kokeellisen kiinnostuksen kohteena jo kolme vuosikymmentä. Tämä johtuu korkean lämpötilan suprajohtavuuden havaitsemista näissä materiaaleissa 1980-luvulla. Neliöhiloissa on myös ennustettu erikoisen kvanttitilan, kvanttispinnesteen, muodostuminen, kun kilpailevat magneettiset vuorovaikutukset estävät magneettisen järjestäytymisen. Tässä väitöskirjassa esitetään ensimmäiset kokeelliset havainnot tällaisesta tilasta neliöhilayhdisteessä. A2CuB''O6 kaksoisperovskiitit ovat ideaali systeemi spin-1/2 neliöhilojen tutkimiseen. Tässä väitöskirjassa kehitettiin menetelmä magneettisten vuorovaikutusten räätälöintiin hyödyntämällä ei-magneettisia d10/d0 kationeja. Tällöin voitiin ensimmäistä kertaa muokata yhdisteen perustila kvanttikriittiselle alueelle. Kvanttispinnesteen kaltainen tila havaittiin yhdisteessä Sr2Cu(Te0.5W0.5)O6. Magneettisen järjestäytymisen estyminen havaittiin laajalla alueella Sr2Cu(Te1-xWx)O6 –systeemissä.

Julkaisun otsikon käännös	Voimakkaan elektronikorrelaation oksidit: Spin-metallisuus kromipohjaisissa rutiileissa ja kvanttimagnetismi kuparipohjaisissa kaksoisperovskiiteissa
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Karppinen, Maarit, Vastuuprofessori Karppinen, Maarit, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-60-7992-9
Sähköinen ISBN	978-952-60-7993-6
Tila	Julkaistu - 2018
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

spin-metalli
kvanttispinneste
kvanttimagnetismi

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http://urn.fi/URN:ISBN:978-952-60-7993-6Lisenssi: Määrittelemätön

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@phdthesis{094d466ea5fb484394f0fbafb077ab78,

title = "Strongly Correlated Oxides - Half-metallicity in Chromium-based Rutiles and Quantum Magnetism in Copper-based Double Perovskites",

abstract = "Strongly correlated oxides are materials with significant electron-electron correlation effects arising from the Coulomb repulsion between localized electrons. While very difficult to model by theory, these materials exhibit a wide range of novel properties and phenomena of both fundamental and technological interest in solid state chemistry and physics. In this thesis two types of strongly correlated materials are investigated: half-metallic ferromagnets and quantum spin liquids. Chromium dioxide is an archetypical half-metallic ferromagnet. It is simultaneously ferromagnetic and metallic, a property of significance in spintronics applications. In this thesis, chemical substitution tuning was investigated in the CrO2-VO2 system as a route for discovering new half-metals. While density functional theory calculations predicted the V-for-Cr substituted phases to be half-metallic similar to CrO2, in practice the materials became antiferromagnetic. This revealed a significant potential pitfall in the search for new half-metals by entirely ab initio methods: the difficulty of correctly predicting oxidation states in materials with multiple transition metals. Quantum magnetism on spin-1/2 square lattices has been of significant theoretical and experimental interest in condensed matter physics for three decades. This is due to the discovery of high-temperature superconductivity in these materials in the 1980's. Specifically, a quantum disordered ground state has been predicted to emerge when nearest-neighbor and next-nearest neighbor interactions compete. In this dissertation, the first experimental evidence of such a state is presented. The perovskite compounds A2CuB''O6 are an ideal system for studying spin-1/2 square-lattice antiferromagnetism. A method for tuning magnetic exchange using diamagnetic d10/d0 cations on the B'' site was developed in this dissertation. This d10/d0 method allowed the tuning of the ground state into the quantum critical regime for the first time. Spin-liquid-like behavior was observed in the compound Sr2Cu(Te0.5W0.5)O6. A thorough investigation of the Sr2Cu(Te1-xWx)O6 system revealed the suppression of magnetic order in a wide composition range.",

keywords = "half-metals, frustrated magnetism, spin liquids, quantum magnetism, spin-metalli, kvanttispinneste, kvanttimagnetismi, half-metals, frustrated magnetism, spin liquids, quantum magnetism",

author = "Otto Mustonen",

year = "2018",

language = "English",

isbn = "978-952-60-7992-9",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "93",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - Strongly Correlated Oxides - Half-metallicity in Chromium-based Rutiles and Quantum Magnetism in Copper-based Double Perovskites

AU - Mustonen, Otto

PY - 2018

Y1 - 2018

N2 - Strongly correlated oxides are materials with significant electron-electron correlation effects arising from the Coulomb repulsion between localized electrons. While very difficult to model by theory, these materials exhibit a wide range of novel properties and phenomena of both fundamental and technological interest in solid state chemistry and physics. In this thesis two types of strongly correlated materials are investigated: half-metallic ferromagnets and quantum spin liquids. Chromium dioxide is an archetypical half-metallic ferromagnet. It is simultaneously ferromagnetic and metallic, a property of significance in spintronics applications. In this thesis, chemical substitution tuning was investigated in the CrO2-VO2 system as a route for discovering new half-metals. While density functional theory calculations predicted the V-for-Cr substituted phases to be half-metallic similar to CrO2, in practice the materials became antiferromagnetic. This revealed a significant potential pitfall in the search for new half-metals by entirely ab initio methods: the difficulty of correctly predicting oxidation states in materials with multiple transition metals. Quantum magnetism on spin-1/2 square lattices has been of significant theoretical and experimental interest in condensed matter physics for three decades. This is due to the discovery of high-temperature superconductivity in these materials in the 1980's. Specifically, a quantum disordered ground state has been predicted to emerge when nearest-neighbor and next-nearest neighbor interactions compete. In this dissertation, the first experimental evidence of such a state is presented. The perovskite compounds A2CuB''O6 are an ideal system for studying spin-1/2 square-lattice antiferromagnetism. A method for tuning magnetic exchange using diamagnetic d10/d0 cations on the B'' site was developed in this dissertation. This d10/d0 method allowed the tuning of the ground state into the quantum critical regime for the first time. Spin-liquid-like behavior was observed in the compound Sr2Cu(Te0.5W0.5)O6. A thorough investigation of the Sr2Cu(Te1-xWx)O6 system revealed the suppression of magnetic order in a wide composition range.

AB - Strongly correlated oxides are materials with significant electron-electron correlation effects arising from the Coulomb repulsion between localized electrons. While very difficult to model by theory, these materials exhibit a wide range of novel properties and phenomena of both fundamental and technological interest in solid state chemistry and physics. In this thesis two types of strongly correlated materials are investigated: half-metallic ferromagnets and quantum spin liquids. Chromium dioxide is an archetypical half-metallic ferromagnet. It is simultaneously ferromagnetic and metallic, a property of significance in spintronics applications. In this thesis, chemical substitution tuning was investigated in the CrO2-VO2 system as a route for discovering new half-metals. While density functional theory calculations predicted the V-for-Cr substituted phases to be half-metallic similar to CrO2, in practice the materials became antiferromagnetic. This revealed a significant potential pitfall in the search for new half-metals by entirely ab initio methods: the difficulty of correctly predicting oxidation states in materials with multiple transition metals. Quantum magnetism on spin-1/2 square lattices has been of significant theoretical and experimental interest in condensed matter physics for three decades. This is due to the discovery of high-temperature superconductivity in these materials in the 1980's. Specifically, a quantum disordered ground state has been predicted to emerge when nearest-neighbor and next-nearest neighbor interactions compete. In this dissertation, the first experimental evidence of such a state is presented. The perovskite compounds A2CuB''O6 are an ideal system for studying spin-1/2 square-lattice antiferromagnetism. A method for tuning magnetic exchange using diamagnetic d10/d0 cations on the B'' site was developed in this dissertation. This d10/d0 method allowed the tuning of the ground state into the quantum critical regime for the first time. Spin-liquid-like behavior was observed in the compound Sr2Cu(Te0.5W0.5)O6. A thorough investigation of the Sr2Cu(Te1-xWx)O6 system revealed the suppression of magnetic order in a wide composition range.

KW - half-metals

KW - frustrated magnetism

KW - spin liquids

KW - quantum magnetism

KW - spin-metalli

KW - kvanttispinneste

KW - kvanttimagnetismi

KW - half-metals

KW - frustrated magnetism

KW - spin liquids

KW - quantum magnetism

M3 - Doctoral Thesis

SN - 978-952-60-7992-9

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -

Strongly Correlated Oxides - Half-metallicity in Chromium-based Rutiles and Quantum Magnetism in Copper-based Double Perovskites

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