Conductivity Studies in Europium Oxide

Oliver, Manuel; McWhorter, Alan L.; Reed, T. B.

doi:10.1103/physrevb.5.1078

Cited by 233 publications

(125 citation statements)

References 26 publications

Supporting

Mentioning

111

Contrasting

Unclassified

Order By: Relevance

“…We note that these measurements suggest that the red shift of the optical absorption edge is also due to this spin-splitting rather than to a broadening of the conduction band. These results support the following picture for the metal-insulator transition in Eu-rich EuO [3]. Above T c , defect or impurity states have their energy levels located slightly below the bottom of the conduction band, and the material behaves like a semiconductor: the resistivity decreases with increasing temperatures as a result of a thermal activation of the electrons from the defect states into the conduction band.…”

supporting

confidence: 84%

Exchange Splitting and Charge Carrier Spin Polarization in EuO

et al. 2002

View full text Add to dashboard Cite

High quality thin films of the ferromagnetic semiconductor EuO have been prepared and were studied using a new form of spin-resolved spectroscopy. We observed large changes in the electronic structure across the Curie and metal-insulator transition temperature. We found that these are caused by the exchange splitting of the conduction band in the ferromagnetic state, which is as large as 0.6 eV. We also present strong evidence that the bottom of the conduction band consists mainly of majority spins. This implies that doped charge carriers in EuO are practically fully spin polarized.EuO is a semiconductor with a band gap of about 1.2 eV and is one of the very rare ferromagnetic oxides [1,2]. Its Curie temperature (T c ) is around 69 K and the crystal structure is rocksalt (fcc) with a lattice constant of 5.144Å. Eu-rich EuO becomes metallic below T c and the metal-insulator transition (MIT) is spectacular: the resistivity drops by as much as 8 orders of magnitude [3,4]. Moreover, an applied magnetic field shifts the MIT temperature considerably, resulting in a colossal magnetoresistance (CMR) with changes in resistivity of up to 6 orders of magnitude [4]. This CMR behavior in EuO is in fact more extreme than in the now much investigated La 1−x Sr x MnO 3 materials [5,6]. Much what is known about the basic electronic structure of EuO dates back to about 30 years ago and is based mainly on optical measurements [7][8][9] and band structure calculations [10]. With the properties being so spectacular, it is surprising that very little has been done so far to determine the electronic structure of EuO using more modern and direct methods like electron spectroscopies.Here we introduce spin-resolved x-ray absorption spectroscopy, a new type of spin-resolved electron spectroscopy technique to study directly the conduction band of EuO where most of the effects related to the MIT and CMR are expected to show up. Spin-resolved measurements of the conduction band could previously only be obtained by spin-polarized inverse photoemission spectroscopy. Spin-resolved x-ray absorption spectroscopy is an alternative technique which is especially well suited to study ferromagnetic oxides, a currently interesting broad class of materials. Using this technique we observed large changes in the conduction band across T c and we were able to show experimentally that these are caused by an exchange splitting of the conduction band below T c . Moreover, we found that this splitting is as large as 0.6 eV and show that the states close to the bottom of the conduction band are almost fully spin-polarized, which is very interesting for basic research in the field of spintronics.The experiments were performed using the helical undulator [11] based beamline ID12B [12] at the European Synchrotron Radiation Facility (ESRF) in Grenoble. Photoemission and Auger spectra were recorded using a 140 mm mean radius hemispherical analyzer coupled to a mini-Mott 25 kV spin polarimeter [13]. The spin detector had an efficiency (Sherman function) of 17%, and t...

show abstract

supporting

confidence: 84%

Exchange Splitting and Charge Carrier Spin Polarization in EuO

et al. 2002

View full text Add to dashboard Cite

show abstract

“…2,3 In particular, being a valuable ferromagnetic semiconductor with a band gap of about 1.12 eV, 4,5 EuO receives a lot of attention due to its higher Curie temperature (Tc) of 69 K. It has a rock salt structure, with a lattice constant of 5.144 Å at room temperature. 6 There are also some spectacular phenomena for this material with electron doping, such as a metal-to-insulator transition and colossal magnetoresistance, where the resistivity change can exceed 8-10 orders of magnitude, 7,8 much stronger than the famous manganites. The Faraday rotation (~ 5 × 10 5 °/cm at 632.8 nm) of EuO is one of the highest of any known materials.…”

Section: Introductionmentioning

confidence: 99%

“…presented a model (He-like model) to account for some of the properties in oxygen-deficient EuO, 7 in which a temperature-independent impurity level for the oxygen vacancies was proposed. It is below the conduction band at high temperatures but crossed by the spin-up conduction band as the temperature is decreased.…”

Section: Introductionmentioning

confidence: 99%

Antiferromagnetic coupling in EuO1−x

2012

View full text Add to dashboard Cite

The mechanism for the ferromagnetic order in oxygen-deficient europium monoxide EuO 1-x at temperatures higher than 69 K (the Curie temperature Tc of stoichiometric EuO) remains controversial. We have investigated the magnetization of EuO 1-x thin films prepared via pulsed laser deposition as a function of temperature and applied field. The ferromagnetic ordering above 69 K originates from the exchange coupling between the doped electrons and Eu 4f moments and is described using a magnetic polaron model. Our data show that the magnetic polarons are coupled antiferromagnetically to the Eu 4f local moments that dominate the magnetization below 69 K. The magnetic polaron state is stable below 69 K and seems to persist down to a relatively low temperature. An explanation is given to account for the antiferromagnetic coupling. We also describe the evolution of the phases of the magnetic orders as the temperature is varied in EuO 1-x .2

show abstract

“…[17][18][19] This stresses the importance of the investigation of rare earth Zintl phases, which bring new strategies and structural features towards useful functional materials. The structural complexity of Zintl phases makes them candidates for unusual electrical, thermal, structural, electronic, and optical properties.…”

mentioning

confidence: 99%

Role of the dimensionality of the [GaX]2 network in the Zintl phases EuGa2X2

Singh

Pöttgen

Schwingenschlögl

2012

Journal of Applied Physics

View full text Add to dashboard Cite

The structural, electronic, magnetic, optical, and thermoelectric properties of EuGa 2 X 2 (X ¼ P, As, and Sb) are investigated using first principles calculations (taking into account the onsite Coulomb interaction) and the semi-classical Boltzmann theory. The divalent nature of Eu fulfils the Zintl principle as is confirmed by the calculated total magnetic moments of $7 l B . A metallic behavior is obtained for all compounds. The optical spectra originate mainly from the transitions between occupied Eu 4f states and unoccupied Eu 5d states. It is demonstrated that the two-dimensional ½GaðP=AsÞ 2 network in EuGa 2 P 2 and EuGa 2 As 2 is favorable for thermoelectric applications as compared to the three-dimensional ½GaSb 2 network in EuGa 2 Sb 2 . V C 2012 American Institute of Physics. [http://dx

show abstract

Conductivity Studies in Europium Oxide

Cited by 233 publications

References 26 publications

Exchange Splitting and Charge Carrier Spin Polarization in EuO

Exchange Splitting and Charge Carrier Spin Polarization in EuO

Antiferromagnetic coupling in EuO1−x

Role of the dimensionality of the [GaX]2 network in the Zintl phases EuGa2X2

Contact Info

Product

Resources

About