2,463 research outputs found
Electron Confinement, Orbital Ordering, and Orbital Moments in - Oxide Heterostructures
The (SrTiO)/(SrVO) multilayer system is studied
with first principles methods through the observed insulator-to-metal
transition with increasing thickness of the SrVO layer. When correlation
effects with reasonable magnitude are included, crystal field splittings from
the structural relaxations together with spin-orbit coupling (SOC) determines
the behavior of the electronic and magnetic structures. These confined slabs of
SrVO prefer =() orbital ordering of and
() orbitals within the plane, accompanied by
=(0,0) spin order (ferromagnetic alignment). The result is a
SOC-driven ferromagnetic Mott insulator. The orbital moment of 0.75
strongly compensates the spin moment on the sublattice. The
insulator-metal transition for (occurring between =4 and
=5) is reproduced. Unlike in the isoelectronic TiO/VO
(rutile structure) system and in spite of some similarities in orbital
ordering, no semi-Dirac point [{\it Phys. Rev. Lett.} {\bf 102}, 166803 (2009)]
is encountered, but the insulator-to-metal transition occurs through a
different type of unusual phase. For n=5 this system is very near (or at) a
unique semimetallic state in which the Fermi energy is topologically determined
and the Fermi surface consists of identical electron and hole Fermi circles
centered at =0. The dispersion consists of what can be regarded as a
continuum of radially-directed Dirac points, forming a "Dirac circle".Comment: 9 pages, 8 figure
Statistics on Graphs, Exponential Formula and Combinatorial Physics
The concern of this paper is a famous combinatorial formula known under the
name "exponential formula". It occurs quite naturally in many contexts
(physics, mathematics, computer science). Roughly speaking, it expresses that
the exponential generating function of a whole structure is equal to the
exponential of those of connected substructures. Keeping this descriptive
statement as a guideline, we develop a general framework to handle many
different situations in which the exponential formula can be applied
CCRS proposal for evaluating LANDSAT-D MSS and TM data
Accomplishments in the evaluation of LANDSAT 4 data are reported. The objectives of the Canadian proposal are: (1) to quantify the LANDSAT-4 sensors and system performance for the purpose of updating the radiometric and geometric correction algorithms for MSS and for developing and evaluating new correction algorithms to be used for TM data processing; (2) to compare and access the degree to which LANDSAT-4 MSS data can be integrated with MSS imagery acquired from earlier LANDSAT missions; and (3) to apply image analysis and information extraction techniques for specific user applications such as forestry or agriculture
Antiferromagnetic coupling of the single-molecule magnet Mn12 to a ferromagnetic substrate
We investigate magnetic coupling between a monolayer of prototype
single-molecule magnets Mn12 and a ferromagnetic Ni(111) substrate through S,
using density-functional theory (DFT) and a DFT+U method. Our DFT and DFT+U
calculations show that the Mn12 molecules favor antiferromagnetic coupling to
the Ni substrate, and that they possess magnetic moments deviated from the
magnetic moments of isolated Mn12 molecules. We find that the magnetic easy
axis of the Mn12 on Ni (whole system) is dictated by that of the Ni substrate.
The antiferromagnetic coupling is, dominantly, caused by superexchange
interactions between the magnetic moments of the Mn and the Ni substrate via
the S, C, and O anions. Our findings can be observed from x-ray magnetic
circular dichroism or scanning tunneling microscopy
Structural, orbital, and magnetic order in vanadium spinels
Vanadium spinels (ZnV_2O_4, MgV_2O_4, and CdV_2O_4) exhibit a sequence of
structural and magnetic phase transitions, reflecting the interplay of lattice,
orbital, and spin degrees of freedom. We offer a theoretical model taking into
account the relativistic spin-orbit interaction, collective Jahn-Teller effect,
and spin frustration. Below the structural transition, vanadium ions exhibit
ferroorbital order and the magnet is best viewed as two sets of
antiferromagnetic chains with a single-ion Ising anisotropy. Magnetic order,
parametrized by two Ising variables, appears at a tetracritical point.Comment: v3: streamlined introductio
Phase Competition in Ln0.5a0.5mno3 Perovskites
Single crystals of the systems Pr0.5(Ca1-xSrx)0.5MnO3,
(Pr1-yYy)0.5(Ca1-xSrx)0.5MnO3, and Sm0.5Sr0.5MnO3 were grown to provide a
series of samples with fixed ratio Mn(III)/Mn(IV)=1 having geometric tolerance
factors that span the transition from localized to itinerant electronic
behavior of the MnO3 array. A unique ferromagnetic phase appears at the
critical tolerance factor tc= 0.975 that separates charge ordering and
localized-electron behavior for t<tc from itinerant or molecular-orbital
behavior for t>tc. This ferromagnetic phase, which has to be distinguished from
the ferromagnetic metallic phase stabilized at tolerance factors t>tc,
separates two distinguishable Type-CE antiferromagnetic phases that are
metamagnetic. Measurements of the transport properties under hydrostatic
pressure were carried out on a compositions t a little below tc in order to
compare the effects of chemical vs. hydrostatic pressure on the phases that
compete with one another near t=tc.Comment: 10 pages. To be publised in Phys. Rev.
Geodynamic setting and origin of the Oman/UAE ophiolite
The ~500km-long mid-Cretaceous Semail nappe of the Sultanate of Oman and UAE (henceforth referred to as the Oman ophiolite) is the largest and best-preserved ophiolite complex known. It is of particular importance because it is generally believed to have an internal structure and composition closely comparable to that of crust formed at the present-day East Pacific Rise (EPR), making it our only known on-land analogue for ocean lithosphere formed at a fast spreading rate. On the basis of this assumption Oman has long played a pivotal role in guiding our conceptual understanding of fast-spreading ridge processes, as modern fast-spread ocean crust is largely inaccessible
Bridging the Gap:Parent and Child Perspectives of Living With Cerebral Visual Impairments
Cerebral Visual Impairment (CVI) is an umbrella term which includes abnormalities in visual acuity, or contrast sensitivity or colour; ocular motility; visual field and the conscious and unconscious filtering or processing of visual input. Children with CVI have specific needs and problems relating to their development from infancy to adulthood which can impact on their wellbeing. Recent research indicates the complexities of living with CVI but there remains limited information of the full impact of CVI on families’ everyday lives. The qualitative interviews reported here explored families’ experiences to discover the impact of CVI on all aspects of everyday life. Parents and children (aged 6–18) were invited to participate in semi-structured interviews, either face to face, by phone or video call between January 2018 and February 2019. Topics covered everyday practicalities of living with CVI, focusing on challenges and what worked well at school and home. Interviews were audio-recorded and subject to thematic analysis to look for patterns across the data. Twenty families took part in interviews, with eight children/young people within those families contributing interviews of their own. Four themes were developed from the interviews: (1) Assessment and understanding implications of CVI, (2) Education, (3) Family life, (4) Psychological wellbeing and quality of life. The interviews provide valuable insights into the impact of living with CVI and highlight the need for more awareness of the condition among professionals in both health and education settings
Suppression of Ferromagnetic Double Exchange by Vibronic Phase Segregation
From Raman spectroscopy, magnetization, and thermal-expansion on the system
La2/3(Ca1-xSrx)1/3MnO3, we have been able to provide a quantitative basis for
the heterogeneous electronic model for manganites exhibiting colossal
magnetoresistance (CMR). We construct a mean-field model that accounts
quantitatively for the measured deviation of TC(x) from the TC predicted by de
Gennes double exchange in the adiabatic approximation, and predicts the
occurrence of a first order transition for a strong coupling regime, in
accordance with the experiments. The existence of a temperature interval
TC<T<T* where CMR may be found is discussed, in connection with the occurrence
of an idealized Griffiths phase.Comment: Replaced with the final version accepted in Physical Review Letter
Magneto-elastic coupling and unconventional magnetic ordering in triangular multiferroic AgCrS2
The temperature evolution of the crystal and magnetic structures of
ferroelectric sulfide AgCrS2 have been investigated by means of neutron
scattering. AgCrS2 undergoes at TN = 41.6 K a first-order phase transition,
from a paramagnetic rhombohedral R3m to an antiferromagnetic monoclinic
structure with a polar Cm space group. In addition to being ferroelectric below
TN, the low temperature phase of AgCrS2 exhibits an unconventional collinear
magnetic structure that can be described as double ferromagnetic stripes
coupled antiferromagnetically, with the magnetic moment of Cr+3 oriented along
b within the anisotropic triangular plane. The magnetic couplings stabilizing
this structure are discussed using inelastic neutron scattering results.
Ferroelectricity below TN in AgCrS2 can possibly be explained in terms of
atomic displacements at the magneto-elastic induced structural distortion.
These results contrast with the behavior of the parent frustrated
antiferromagnet and spin-driven ferroelectric AgCrO2
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