search query: @supervisor Karppinen, Maarit / total: 42
results-list
reference: 10 / 42
« previous | next »
Author:Mustonen, Otto
Title:Vanadium Doped Chromium Dioxide: Magnetic Properties and Electronic Structure Calculations
Vanadiinilla substituoitu kromidioksidi; Magneettiset ominaisuudet ja elektronirakennelaskuja
Publication type:Master's thesis
Publication year:2013
Pages:x + 140      Language:   eng
Department/School:Kemian laitos
Main subject:Epäorgaaninen kemia   (Kem-35)
Supervisor:Karppinen, Maarit
Instructor:Vasala, Sami
Electronic version URL: http://urn.fi/URN:NBN:fi:aalto-201603081465
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
Instructions
close

Reading digital theses in the closed network of the Aalto University Harald Herlin Learning Centre

In the closed network of Learning Centre you can read digital and digitized theses not available in the open network.

The Learning Centre contact details and opening hours: https://learningcentre.aalto.fi/en/harald-herlin-learning-centre/

You can read theses on the Learning Centre customer computers, which are available on all floors.

Logging on to the customer computers

  • Aalto University staff members log on to the customer computer using the Aalto username and password.
  • Other customers log on using a shared username and password.

Opening a thesis

  • On the desktop of the customer computers, you will find an icon titled:

    Aalto Thesis Database

  • Click on the icon to search for and open the thesis you are looking for from Aaltodoc database. You can find the thesis file by clicking the link on the OEV or OEVS field.

Reading the thesis

  • You can either print the thesis or read it on the customer computer screen.
  • You cannot save the thesis file on a flash drive or email it.
  • You cannot copy text or images from the file.
  • You cannot edit the file.

Printing the thesis

  • You can print the thesis for your personal study or research use.
  • Aalto University students and staff members may print black-and-white prints on the PrintingPoint devices when using the computer with personal Aalto username and password. Color printing is possible using the printer u90203-psc3, which is located near the customer service. Color printing is subject to a charge to Aalto University students and staff members.
  • Other customers can use the printer u90203-psc3. All printing is subject to a charge to non-University members.
Location:P1 Ark Aalto  1895   | Archive
Keywords:CrO2
half-metal
spintronics
magnetism
density funktional theory
high-pressure synthesis
spintroniikka
magnetismi
tiheysfunktionaaliteoria
korkeapainesynteesi
Abstract (eng): Spintronics is an emerging field of electronics, in which information is carried by the spin of an electron in addition to its charge.
Advantages of spintronics devices include enhanced properties such as fast switching times and low power consumption, and new functionality such as sensing of magnetic fields.
Half-metallic ferromagnets, or half-metals, are promising materials for spintronics applications.
These exotic materials behave as metallic for electrons of one spin, and as insulators for the other.

Chromium diodixe is the simplest half-metal.
It is a metastable oxide of Cr(IV), which adopts the rutile structure common in transition metal dioxides.
Electronic structure calculations first predicted CrO2 to be half-metallic.
Half-metallicity has been confirmed with spectroscopic and point contact measurements.
CrO2 is the half-metal with the highest known spin polarization of over 90% at 1.6 K.
Magnetic properties and half-metallicity of CrO2 can be manipulated by substitution of chromium with other transition metals.
Recently, vanadium doped chromium dioxide Cr1-xVxO2 has been predicted to be half-metallic.

In this work, properties of the Cr1-xVxO2 system in the composition range 0 <= x <= 0.5 are investigated with an emphasis on magnetic properties and half-metallicity.
The materials are synthesized via high-pressure synthesis.
Phase purity and crystal structure is investigated by x-ray powder diffraction.
Oxidation state of Cr, V and O is probed with x-ray absorption near edge structure spectroscopy (XANES).
The magnetic properties are measured with a superconducting quantum interference device (SQUID) magnetometer.
Furthermore, the electronic structure of Cr1-xVxO2 is investigated by first principles electronic structure calculations.

The Cr1-xVxO2 solid solutions are confirmed to be single-phase with XRD.
The lattice parameter a increases linearly with increasing vanadium content in agreement with Vegard's law.
XANES measurements reveal that the oxidation state of chromium decreases from Cr(IV) towards Cr(III) with increasing vanadium content.
Magnetic ordering is found to dramatically change from ferromagnetic (CrO2, Cr0.9V0.1O2 to ferrimagnetic Cr0.8V0.2O2 to antiferromagnetic (Cr0.7V0.3O2, Cr0.6V0.4O2, Cr0.5V0.5O2) resulting in the elimination of half-metallicity in the system.
Electronic structure calculations predict Cr0.875V0.125O2 to be half-metallic with reduced spin polarization compared to CrO2, and Cr0.5V0.5O2 to be an antiferromagnetic metal
Abstract (fin): Spintroniikka on nouseva elektroniikan ala, jossa sekä elektronin spin että varaus valittavat informaatiota.
Spintroniikan sovellusten etuja ovat komponenttien parantuneet ominaisuudet, kuten logiikan nopea muutosaika ja matala virrankulutus, sekä kokonaan uudenlainen toiminnallisuus kuten magneettisten kenttien havaitseminen.
Spin-metallit (half-metal) ovat lupaavia materiaaleja spintroniikkasovelluksiin.
Nämä materiaalit käyttäytyvät kuin metallit elektroneille, joilla on tietty spin, ja kuin eristeet elektroneille, joilla on päinvastainen spin.

Kromidioksi on yksinkertaisin spin-metalli.
Se on metastabiili kromi(IV)-yhdiste, jolla on rutiilirakenne.
Elektronirakennelaskut ennustivat ensimmäisen kerran kromidioksidin olevan spinmetalli.
Spin-metallisuus on myöhemmin vahvistettu spektroskooppisin ja pistekontaktimenetelmin.
Kromidioksidin spin-polarisaatio on korkein tunnetuista spin-metalleista.
Kromidioksidin magneettisiin ominaisuuksiin ja spin-metallisuuteen voidaan vaikuttaa substituoimalla kromia muilla siirtymämetalleilla.
Vanadiinilla substituoidun kromidioksidin Cr1-xVxO2 on äskettäin ennustettu olevan myös spin-metalli.

Tässä työssä tutkitaan Cr1-xVxO2 -systeemin (0 <= x <= 0.5) ominaisuuksia.
Erityistä huomiota kiinnitetään magneettisiin ominaisuuksiin ja spin-metallisuuteen.
Näytteet valmistetaan korkeapainesynteesillä.
Niiden faasipuhtautta ja kiderakennetta tarkastellaan röntgendiffraktion avulla.
Hapen, vanadiinin ja kromin hapetusastetta tutkitaan XANES-spektroskopialla.
Magneettiset ominaisuudet mitataan SQUID-magnetometrillä.
Lisaksi materiaalin elektronirakennetta mallinnetaan tiheysfunktionaaliteorian avulla.

Röntgendiffraktio osoittaa Cr1-xVxO2 -näytteiden olevan faasipuhtaita.
Hilaparametri a kasvaa lineaarisesti vanadiinipitoisuuden noustessa Vegardin lain mukaisesti.
XANES-mittaukset osoittavat, että kromin hapetusaste laskee kromi(IV):stä kromi(III):a kohti vanadiinipitoisuuden noustessa.
Vanadiinilla substituointi muuttaa merkittävästi Cr1-xVxO2 magneettista järjestäytymistä ferromagneettisesta (CrO2, Cr0.9V0.1O2) ferrimagneettiseen (Cr0.8V0.2O2) ja antiferromagneettiseen (Cr0.7V0.3O2, Cr0.6V0.4O2 ja Cr0.5V0.5O2) tuhoten spin-metallisuuden.
Elektronirakennelaskut ennustavat Cr0.875V0.125O2 olevan spin-metalli ja Cr0.5V0.5O2 olevan antiferromagneettinen metalli.
ED:2013-05-20
INSSI record number: 46158
+ add basket
« previous | next »
INSSI