6 ebq

Nov 24, 20140 likes307 views

The document summarizes research on the electronic structure and phase stability of the magnetocaloric compound ��-MnAs. It describes how MnAs undergoes a first-order phase transition from a hexagonal NiAs-type structure (��-phase) to an orthorhombic MnP-type structure (��-phase) at 318 K. This transition is magnetically driven and results in changes to the MnAs atomic distances and magnetic moments. The research investigates the band structure of both phases and finds that the structural transition is driven by nesting of the Fermi surfaces, explaining the larger resistivity observed in ��-MnAs.

Electronic structure and phase stability of the
magnetocaloric compound (B31) ��-MnAs"
K. Sachtleben, C. B. Dias de G��es, and C. Paduani
Dept. of Physics, UFSC, SC, Florian��polis, Brazil.
E-mail: kewinsachtleben@gmail.com
The MnAs compound has the hexagonal NiAs-type B81 structure (��-phase, s.g. P63/mmc),
ferromagnetic at low temperatures, and which, at the Curie temperature of 318 K, exhibits a
first-order phase transition to an orthorhombic MnP-type (Pnma) B31 structure (��-phase),
one of the most common derivatives of the NiAs-type structure among the pnictides. The
MnP-type structure can be viewed as a distorted NiAs structure, where the unit cell contains
four (instead of two) formula units. The atomic distance between Mn and As atoms changes
from 2.479 ?, in the ��-phase, to 2.581 ? in the ��-phase. MnAs undergoes also a
structural-phase transformation from NiAs-type to a zinc-blende structure, under large
volume expansion. These characteristics put MnAs into the special class of magnetocaloric
compounds. ��-MnAs has already been reported in the literature as non ferromagnetic, as well
as unlikely to be paramagnetic. However, it has been also pointed out that the ��-�� structural
transition is magnetically driven, from the high symmetry ferromagnetic state to a lower
symmetry antiferromagnetic state. In this contribution is investigated the band structure of
MnAs in both hexagonal (B81) and orthorhombic (B31) phases. The dependence of the Mn
moment on the unit cell volume is investigated. The characteristics of the calculated Fermi
surfaces indicate that the ��-�� structural transition is driven by nesting of the Fermi surfaces,
and provide explanation for the experimentally observed larger resistivity in ��-MnAs.
Refer��ncias
[1] W. Tremel, R. Hoffmann and J. Silvestre, J. Am. Chem. Soc. 108, 5174 (1986).
[2] S. Sanvito, N.A. Hill, Phys. Rev. B 62, 15553 (2000).
[3] B. Sanyal, L. Bergqvist, O. Eriksson, Phys. Rev. B 68, 054417 (2003).
[4] L.J. Shi, B.G. Liu, J. Phys. Condens. Matter 17, 1209 (2005).
[5] G. Prathiba, B. Anto Naanci, M. Rajagopalan, J. Magn. Magn. Mater. 309, 251 (2007).
[6] K. Maki, T. Kaneko, H. Hiroyoshi, K. Kamigaki, J. Magn. Magn. Mater. 177181, 1361
(1998).

We have synthesized a Ba6Ge25 clathrate, substituting 3 Ge per formula unit by Fe. This chiral clathrate has Ge sites forming a framework of closed cages and helical tunnel networks. Fe atoms randomly occupy these sites, and exhibit high-spin magnetic moments. A ferromagnetic transition is observed with Tc5170 K, the highest observed Tc for a magnetic clathrate. However, the magnetic phase is significantly disordered, and exhibits a transformation to a reentrant spin glass phase. This system has a number of features in common with other dilute magnetic semiconductors.

Normas para submiss?o de resumo1IFCE

O documento apresenta as normas e cronograma para submiss?o de resumos no II Simp��sio do NUPFARQ sobre a populariza??o da ci��ncia para promover o desenvolvimento social e tecnol��gico do Maranh?o. Os resumos devem descrever pesquisas ou experi��ncias conclu��das e ser?o avaliados por uma comiss?o cient��fica, com os melhores trabalhos apresentados tamb��m na forma oral. O prazo final para submiss?o de resumos �� 11 de outubro de 2014.

56365695 programacao-semicIFCE

Economic Order Quality Eoqsikander kushwaha

The document discusses the economic order quantity (EOQ) model, which aims to minimize total inventory costs by determining the optimal order quantity. It defines EOQ as the order quantity that balances ordering costs and carrying costs. The key assumptions of the EOQ model are constant demand, lead time, and costs. The document presents the mathematical formula for calculating EOQ and provides an example calculation. It also describes two EOQ models: the 'Q' model with fixed reorder quantities and the 'P' model with periodic reviews and orders.

User Interfaces beyond the screenJason Mesut

Untangling the customer journeyMark Schaefer

OgilvyRED - Dollars and Sense of ConnectivityOgilvy

Mobile connectivity has the potential to provide significant economic and social benefits globally, but its impact depends on factors like infrastructure development and affordability. The mobile connectivity ecosystem involves infrastructure providers (carriers), services/content providers, and consumers. While carriers play a pivotal role by operating networks, the benefits are not evenly distributed. In developed nations, higher bandwidth enables services like video streaming but in developing areas, basic connectivity can improve access to information, resources and opportunities that positively impact areas like health, education and economic growth. Ensuring widespread affordable access remains an ongoing challenge.

Magnon crystallization in kagom�� antiferromagnetsRyutaro Okuma

This document summarizes research on magnon crystallization in kagom�� antiferromagnets. Key points include: 1) Observation of a series of magnetization plateaus up to 160 T in CdK and a 1/3 magnetization plateau over 150 T in herbertsmithite. 2) Theoretical calculation showing hexagonal magnon localization and crystallization phases with different magnetization values as the field is increased. 3) Experimental studies of the S=1/2 kagom�� magnets volborthite, herbertsmithite, and Cd-kapellasite using ultra-high magnetic fields up to 200 T to observe magnon crystallization phenomena.

A first principle study of pressure induced structural and electronic propert...Alexander Decker

This article summarizes a study that examines the pressure-induced structural and electronic properties of neptunium monobismuthide (NpBi) using first-principles calculations. The authors find that at ambient pressure, NpBi is stable in the NaCl crystal structure. However, they predict that NpBi undergoes a phase transition from the NaCl structure to the CsCl structure at a pressure of around 11 GPa. The calculations also show that NpBi exhibits metallic behavior. The predicted equilibrium lattice parameters and bulk modulus are in good agreement with available experimental data.

Presentation of Licentiate in Physics Engineering of Francisco AlmeidaFrancisco Almeida

Research Inventy : International Journal of Engineering and Scienceresearchinventy

Research Inventy : International Journal of Engineering and Science is published by the group of young academic and industrial researchers with 12 Issues per year. It is an online as well as print version open access journal that provides rapid publication (monthly) of articles in all areas of the subject such as: civil, mechanical, chemical, electronic and computer engineering as well as production and information technology. The Journal welcomes the submission of manuscripts that meet the general criteria of significance and scientific excellence. Papers will be published by rapid process within 20 days after acceptance and peer review process takes only 7 days. All articles published in Research Inventy will be peer-reviewed.

Superconductivity in Al-substituted Ba8Si46 clathratesYang Li

There is a great deal of interest vested in the superconductivity of Si clathrate compounds with sp3 network, in which the structure is dominated by strong covalent bonds among silicon atoms, rather than the metallic bonding that is more typical of traditional superconductors. A joint experimental and theoretical investigation of superconductivity in Al-substituted type-I silicon clathrates is reported. Samples of the general formula Ba8Si46xAlx, with different values of x were prepared. With an increase in the Al composition, the superconducting transition temperature TC was observed to decrease systematically. The resistivity measurement revealed that Ba8Si42Al4 is superconductive with transition temperature at TC=5.5 K. The magnetic measurements showed that the bulk superconducting Ba8Si42Al4 is a type II superconductor. For x=6 sample Ba8Si40Al6, the superconducting transition was observed down to TC=4.7K which pointed to a strong suppression of superconductivity with increasing Al content as compared with TC=8K for Ba8Si46. Suppression of superconductivity can be attributed primarily to a decrease in the density of states at the Fermi level, caused by reduced integrity of the sp3 hybridized networks as well as the lowering of carrier concentration. These results corroborated by first-principles calculations showed that Al substitution results in a large decrease of the electronic density of states at the Fermi level, which also explains the decreased superconducting critical temperature within the BCS framework. The work provided a comprehensiveunderstanding of the doping effect on superconductivity of clathrates.

Ferro2016Ryan Herchig

The document summarizes research on the electrocaloric effect in ferroelectric nanowires compared to bulk materials. Key findings include: 1) The maximum electrocaloric response is reduced in nanowires compared to bulk, due to decreased spontaneous polarization and dielectric constant from reduced correlation length. 2) In polydomain nanowires, both the BaTiO3 and KNbO3 nanowires lose their electrocaloric properties, as the electric field is not well aligned with polarization in each domain. 3) The largest electrocaloric response occurs near phase transition temperatures where crystal structure changes and entropy is maximized, as shown in simulations of the electrocaloric temperature change.

Materials Science Exam HelpLive Exam Helper

I am Abdullah A. I am a Material Science Exam Helper at liveexamhelper.com. I hold a Ph.D. Degree in Material Science from University of Chicago, USA. I have been helping students with their exams for the past 14 years. You can hire me to take your exam in Material Science. Visit liveexamhelper.com or email info@liveexamhelper.com.You can also call on +1 678 648 4277 for any assistance with the Material Science exams.

Exchange Bias National Tsing Hua University

This document summarizes a review article on exchange bias in ferromagnetic-antiferromagnetic systems. Exchange bias is a phenomenon where cooling a system through the Neel temperature of an antiferromagnet in the presence of a ferromagnet induces an anisotropy (exchange bias) in the ferromagnet. The key findings of the review are: 1. Exchange bias was first discovered in 1956 when studying cobalt particles embedded in cobalt oxide. 2. It has since been observed in small particles, inhomogeneous materials, ferromagnetic films on antiferromagnetic single crystals, and thin films. 3. Various theoretical models have been proposed to explain exchange bias based on interface coupling, anisotropies, and domain formation.

Electronic structure of strongly correlated materials Part III V.AnisimovABDERRAHMANE REGGAD

This document discusses results from DFT+DMFT calculations on various strongly correlated materials. It summarizes calculations showing a strongly correlated metal state in SrVO3 with a lower Hubbard band, a Mott insulator transition in V2O3 accompanied by a small structural change, and heavy fermion behavior in Li2VO4 without f-electrons. It also discusses calculations of the charge transfer insulator NiO, pressure-induced transitions in MnO and Fe2O3, correlated covalent insulators FeSi and FeSb2, superconductivity in LaOFeAs, Jahn-Teller distortions and orbital ordering in KCuF3, and f-electron localization in cerium. The document

Global-12Vijay Bist

This paper studies the dielectric properties of order-disorder type crystals like KH2PO4. It derives expressions for the dielectric constant and tangent loss using the soft mode dynamical model and double time temperature dependent Green's function techniques. It calculates the transverse dielectric constant, observed dielectric constant, and tangent loss for KH2PO4 in the paraelectric phase using model parameters. The calculated results agree well with experimental data from several other studies on the temperature dependence of the dielectric constant and tangent loss of KH2PO4. The paper finds that phonon anharmonicity contributes significantly to the observed loss at higher temperatures.

Science Talk-091102-��nccuscience

Through ab initio calculations, researchers discovered the mechanism behind the Verwey transition in magnetite, solving a decades-old problem. The calculations revealed an ordering of t2g orbitals on the iron sublattice in the low-temperature phase. This orbital ordering leads to charge ordering consisting of alternating Fe2+ and Fe3+ ions. Resonant x-ray scattering experiments confirmed these findings. The discovery explains the long-standing mystery of the entropy change at the Verwey transition.

symposium 2016Rajesh Kodur

This study compares quasi-fission in the nuclear reactions 19F + 169Tm and 64Ni + 124Sn, which form the same compound nucleus of 188Pt. The 19F + 169Tm system is more asymmetric with a lower ZPZT value and shows good agreement between experimental evaporation residue cross sections and statistical calculations. However, for the more symmetric 64Ni + 124Sn system, the experimental data deviates significantly from calculations above the Coulomb barrier, likely due to the onset of quasi-fission. A comparative study shows the more symmetric system has a decreased evaporation residue cross section, suggesting stronger quasi-fission that prevents the formation of an equilibrated compound nucleus.

Julian_Toronto_cifar_2012.pdfssuser836d21

This document summarizes quantum oscillations in strongly correlated electron systems, with a focus on applications to cuprate superconductors. Key points include: (1) quantum oscillations can be used to measure the Fermi surface and quasiparticle properties; (2) in cuprates, oscillations provide evidence of long-lived quasiparticles and Fermi surface reconstruction near optimal doping; and (3) while oscillations support a small reconstructed Fermi surface in underdoped cuprates, details like the number of pockets are still controversial.

G Type Antiferromagnetic by Singhan GangulySINGHAN GANGULY

G-type antiferromagnetism results when the spins of electrons in a material are arranged in an antiferromagnetic pattern both within planes of atoms and between neighboring planes. An analysis of SrCr2As2 using neutron diffraction and magnetic susceptibility revealed it is a G-type antiferromagnet below 590K, with chromium magnetic moments aligned along the c axis. The ordered magnetic moment was found to be 1.9��B/Cr at 12K, reduced from the localized value due to itinerant electrons from Cr-As hybridization. Even with significant antisite disorder, G-type and other antiferromagnetic phases can still be detected through their characteristic peaks in the magnetic structure factor.

Magnetic entropy change and critical exponentsMary Oliveira

1) The document analyzes the magnetic entropy change and critical exponents in the double perovskite material Y2NiMnO6, which exhibits a second-order ferromagnetic to paramagnetic transition at 86 K. 2) A maximum magnetic entropy change of -6.57 J/kg-K was measured for a field change of 80 kOe. Critical exponents were obtained from analysis of the spontaneous magnetization and inverse susceptibility, and were found to be consistent with 3D Heisenberg behavior. 3) Rietveld refinement of the crystal structure confirmed the material crystallizes in a monoclinic structure with alternating Ni2+ and Mn4+ ions along the c-axis and tilted oct

Coexistence of Superconductivity and Itinerant Ferromagnetism in Ucoge ijrap

The document presents a theoretical model for the coexistence of superconductivity and itinerant ferromagnetism in uranium-based intermetallic compounds. The model uses a Hubbard Hamiltonian and Green's function method to describe the system. It is able to obtain expressions for the superconducting order parameter, magnetic order parameter, and other observables. The theory can explain key experimental observations in uranium compounds like UCoGe, such as superconductivity only occurring in the ferromagnetic phase.

Coexistence of Superconductivity and Itinerant Ferromagnetism in Ucogeijrap

The coexistence of BCS superconductivity and itinerant ferromagnetism in uranium based intermetallic systems is analyzed using a Hubbard Hamiltonian. To obtain the superconducting transition temperatureTC and Curie temperatureTFM , we used the Green��s function method. The order parameter of superconductivity ( ? ) and ferromagnetism ( m or I) are obtained in the mean field approximation. It is found that there generally exist coexistent solutions to coupled equations of the order parameter in the temperature range ( ) T TC TFM 0 < < min , . In our model, ferromagnetism is itinerant and therefore carried by the conduction electrons. This arises from a splitting of the spin-up and spin- down band. A consequence is that the ferromagnetism and superconductivity is carried by same electrons. Expressions for specific heat, energy spectra and density of states are derived. The specific heat has linear temperature dependence as opposed to that of the exponential decrease in the BCS theory. The density of states for a finite magnetic order parameter increases as opposed to that of a ferromagnetic metal. The theory is applied to explain the observations in uranium based intermetallic compoundUCoGe . The agreement between theory and experiments is quite encouraging.

G type antiferromagnetic by singhan gangulysinghanganguly

G-type antiferromagnetism results when the spins of electrons in a material are arranged in an antiferromagnetic pattern both within atomic planes and between neighboring planes. In G-type ordering, the intra-plane and inter-plane couplings are both antiferromagnetic. Earlier studies on double perovskite materials found that increasing electron doping can drive a transition from ferromagnetic order to non-ferromagnetic states like A-type and G-type antiferromagnetic order. The presence of antisite disorder, which increases with electron doping, can disrupt magnetic order but studies show that even with significant disorder, antiferromagnetic correlations persist in these materials.

Reductive Cyclotrimerization of Carbon Monoxide to the Deltate Dianion by an ...Owen Summerscales

Annette bussmann holder, hugo keller high tc superconductors and related tran...Edward Flores

This document provides an introduction to the scientific career and contributions of K. Alex M��ller, honoring his 80th birthday. It summarizes that while he is best known for his work discovering high-temperature superconductivity, over half of his research career focused on other areas including phase transitions, critical phenomena, electron paramagnetic resonance, and ferroelectricity. The document outlines some of his seminal contributions in these fields, including establishing a theory of phase transitions involving soft modes and elastic instabilities. It also discusses his work on the nature and dynamics of structural phase transitions and ferroelectricity in perovskite oxides.

7633426.pptSUMANKALYANSAHOO4

This document summarizes Ghanshyam Pilania's PhD dissertation proposal on the physics and chemistry of ABO3 nanostructures from first principles calculations. The proposal focuses on novel polarization states in ABO3 nanowires, including "vortex" and "axial" polarization configurations and how size, surface termination, and strain affect these states. It also discusses constructing (p,T) surface phase diagrams to model oxygen adsorption on ABO3 surfaces and remaining work on modeling the effect of electric fields, surface passivation, and environment-dependent gas adsorption. The impact of this work could include applications in non-volatile ferroelectric memory and catalytic converters.

6 ebq

1. Electronic structure and phase stability of the magnetocaloric compound (B31) ��-MnAs" K. Sachtleben, C. B. Dias de G��es, and C. Paduani Dept. of Physics, UFSC, SC, Florian��polis, Brazil. E-mail: kewinsachtleben@gmail.com The MnAs compound has the hexagonal NiAs-type B81 structure (��-phase, s.g. P63/mmc), ferromagnetic at low temperatures, and which, at the Curie temperature of 318 K, exhibits a first-order phase transition to an orthorhombic MnP-type (Pnma) B31 structure (��-phase), one of the most common derivatives of the NiAs-type structure among the pnictides. The MnP-type structure can be viewed as a distorted NiAs structure, where the unit cell contains four (instead of two) formula units. The atomic distance between Mn and As atoms changes from 2.479 ?, in the ��-phase, to 2.581 ? in the ��-phase. MnAs undergoes also a structural-phase transformation from NiAs-type to a zinc-blende structure, under large volume expansion. These characteristics put MnAs into the special class of magnetocaloric compounds. ��-MnAs has already been reported in the literature as non ferromagnetic, as well as unlikely to be paramagnetic. However, it has been also pointed out that the ��-�� structural transition is magnetically driven, from the high symmetry ferromagnetic state to a lower symmetry antiferromagnetic state. In this contribution is investigated the band structure of MnAs in both hexagonal (B81) and orthorhombic (B31) phases. The dependence of the Mn moment on the unit cell volume is investigated. The characteristics of the calculated Fermi surfaces indicate that the ��-�� structural transition is driven by nesting of the Fermi surfaces, and provide explanation for the experimentally observed larger resistivity in ��-MnAs. Refer��ncias [1] W. Tremel, R. Hoffmann and J. Silvestre, J. Am. Chem. Soc. 108, 5174 (1986). [2] S. Sanvito, N.A. Hill, Phys. Rev. B 62, 15553 (2000). [3] B. Sanyal, L. Bergqvist, O. Eriksson, Phys. Rev. B 68, 054417 (2003). [4] L.J. Shi, B.G. Liu, J. Phys. Condens. Matter 17, 1209 (2005). [5] G. Prathiba, B. Anto Naanci, M. Rajagopalan, J. Magn. Magn. Mater. 309, 251 (2007). [6] K. Maki, T. Kaneko, H. Hiroyoshi, K. Kamigaki, J. Magn. Magn. Mater. 177181, 1361 (1998).

�ݺ�ߣ

6 ebq

Recommended

More Related Content

Similar to 6 ebq (20)

6 ebq