235 research outputs found
Origin of ferromagnetism in CsAgF: importance of Ag - F covalency
The magnetic nature of CsAgF, an isoelectronic and isostructural
analogue of LaCuO, is analyzed using density functional calculations.
The ground state is found to be ferromagnetic and nearly half metallic. We find
strong hybridization of Ag- and F- states. Substantial moments reside on
the F atoms, which is unusual for the halides and reflects the chemistry of the
Ag(II) ions in this compound. This provides the mechanism for ferromagnetism,
which we find to be itinerant in character, a result of a Stoner instability
enhanced by Hund's coupling on the F
TaIrTe4 a ternary Type-II Weyl semi-metal
In metallic condensed matter systems two different types of Weyl fermions can
in principle emerge, with either a vanishing (type-I) or with a finite
(type-II) density of states at the Weyl node energy. So far only WTe2 and MoTe2
were predicted to be type-II Weyl semi-metals. Here we identify TaIrTe4 as a
third member of this family of topological semi-metals. TaIrTe4 has the
attractive feature that it hosts only four well-separated Weyl points, the
minimum imposed by symmetry. Moreover, the resulting topological surface states
- Fermi arcs connecting Weyl nodes of opposite chirality - extend to about 1/3
of the surface Brillouin zone. This large momentum-space separation is very
favorable for detecting the Fermi arcs spectroscopically and in transport
experiments
Collinear order in a frustrated three-dimensional spin- antiferromagnet LiCuWO
Magnetic frustration in three dimensions (3D) manifests itself in the
spin- insulator LiCuWO. Density-functional band-structure
calculations reveal a peculiar spin lattice built of triangular planes with
frustrated interplane couplings. The saturation field of 29 T contrasts with
the susceptibility maximum at 8.5 K and a relatively low N\'eel temperature
K. Magnetic order below is collinear with the propagation
vector and an ordered moment of 0.65(4) according to
neutron diffraction data. This reduced ordered moment together with the low
maximum of the magnetic specific heat () pinpoint strong
magnetic frustration in 3D. Collinear magnetic order suggests that quantum
fluctuations play crucial role in this system, where a non-collinear spiral
state would be stabilized classically.Comment: published version with supplemental material merged into the tex
Antiferromagnetic ground state in the MnGa intermetallic compound
Magnetism of the binary intermetallic compound MnGa is re-investigated.
Band-structure calculations predict antiferromagnetic behavior in contrast to
Pauli paramagnetism reported previously. Magnetic susceptibility measurements
on single crystals indeed reveal an antiferromagnetic transition at
K. Neutron powder diffraction and Ga nuclear quadrupole resonance
spectroscopy show collinear antiferromagnetic order with magnetic moments
alligned along the [111] direction of the cubic unit cell. The magnetic moment
of 0.80(3) at 1.5 K extracted from the neutron data is in good agreement
with the band-structure results
Possible re-entrant superconductivity in EuFe2As2 under pressure
We studied the temperature-pressure phase diagram of EuFe2As2 by measurements
of the electrical resistivity. The antiferromagnetic spin-density-wave
transition at T_0 associated with the FeAs-layers is continuously suppressed
with increasing pressure, while the antiferromagnetic ordering temperature of
the Eu 2+ moments seems to be nearly pressure independent up to 2.6 GPa. Above
2 GPa a sharp drop of the resistivity, \rho(T), indicates the onset of
superconductivity at T_c \approx 29.5 K. Surprisingly, on further reducing the
temperature \rho(T) is increasing again and exhibiting a maximum caused by the
ordering of the Eu 2+ moments, a behavior which is reminiscent of re-entrant
superconductivity as it is observed in the ternary Chevrel phases or in the
rare-earth nickel borocarbides
Frequent strandings of dolphins and whales along the gulf of Mannar coast
The present observations no specific reason could be attributed towards the frequent strandlngs of marine mammals in the Gulf of Meinnar region. It Is inferred that any one factor as given above or more would have
contributed towards the strandlngs. As the Indian Ocean is declared as a sanctuary for whales,the frequent stranding of whales eind dolphins emphasise the need for Intensive study on conservation measures. The scientific Information on the extent of strandlngs of marine mammals all along the coast needs consolidation
Pressure-induced phase transitions and high-pressure tetragonal phase of Fe1.08Te
We report the effects of hydrostatic pressure on the temperature-induced
phase transitions in Fe1.08Te in the pressure range 0-3 GPa using synchrotron
powder x-ray diffraction (XRD). The results reveal a plethora of phase
transitions. At ambient pressure, Fe1.08Te undergoes simultaneous first-order
structural symmetry-breaking and magnetic phase transitions, namely from the
paramagnetic tetragonal (P4/nmm) to the antiferromagnetic monoclinic (P2_1/m)
phase. We show that, at a pressure of 1.33 GPa, the low temperature structure
adopts an orthorhombic symmetry. More importantly, for pressures of 2.29 GPa
and higher, a symmetry-conserving tetragonal-tetragonal phase transition has
been identified from a change in the c/a ratio of the lattice parameters. The
succession of different pressure and temperature-induced structural and
magnetic phases indicates the presence of strong magneto-elastic coupling
effects in this material.Comment: 11 page
Pressure-induced ferromagnetism due to an anisotropic electronic topological transition in Fe1.08Te
A rapid and anisotropic modification of the Fermi-surface shape can be
associated with abrupt changes in crystalline lattice geometry or in the
magnetic state of a material. In this study we show that such an electronic
topological transition is at the basis of the formation of an unusual
pressure-induced tetragonal ferromagnetic phase in FeTe. Around 2 GPa,
the orthorhombic and incommensurate antiferromagnetic ground-state of
FeTe is transformed upon increasing pressure into a tetragonal
ferromagnetic state via a conventional first-order transition. On the other
hand, an isostructural transition takes place from the paramagnetic
high-temperature state into the ferromagnetic phase as a rare case of a `type
0' transformation with anisotropic properties. Electronic-structure
calculations in combination with electrical resistivity, magnetization, and
x-ray diffraction experiments show that the electronic system of FeTe
is instable with respect to profound topological transitions that can drive
fundamental changes of the lattice anisotropy and the associated magnetic
order.Comment: 7 pages, 4 figur
Bulk and surface electronic properties of SmB6: a hard x-ray photoelectron spectroscopy study
We have carried out bulk-sensitive hard x-ray photoelectron spectroscopy
(HAXPES) measurements on in-situ cleaved and ex-situ polished SmB6 single
crystals. Using the multiplet-structure in the Sm 3d core level spectra, we
determined reliably that the valence of Sm in bulk SmB6 is close to 2.55 at ~5
K. Temperature dependent measurements revealed that the Sm valence gradually
increases to 2.64 at 300 K. From a detailed line shape analysis we can clearly
observe that not only the J=0 but also the J=1 state of the Sm 4f 6
configuration becomes occupied at elevated temperatures. Making use of the
polarization dependence, we were able to identify and extract the Sm 4f
spectral weight of the bulk material. Finally, we revealed that the oxidized or
chemically damaged surface region of the ex-situ polished SmB6 single crystal
is surprisingly thin, about 1 nm only.Comment: 11 pages, 8 figure
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