47 research outputs found
Antiferromagnetism in semiconducting KFe0.85Ag1.15Te2 single crystals
We have synthesized single crystals of K1.00(3)Fe0.85(2)Ag1.15(2)Te2.0(1).
The materials crystallizes in the ThCr2Si2 structure with I4/mmm symmetry and
without K and Fe/Ag deficiencies, unlike in KxFe2-ySe2 and KxFe2-yS2. In
contrast to theoretical prediction for higher Tc in KFe2Te2, KFe0.85Ag1.15Te2
is a semiconductor with long-range antiferromagnetic transition at TN = 35 K.Comment: 4 pages, 4 figure
Magnetism in La2O3(Fe1-xMnx)2Se2 tuned by Fe/Mn ratio
We report the evolution of structural and magnetic properties in
La2O3(Fe1-xMnx)2Se2. Heat capacity and bulk magnetization indicate an increased
ferromagnetic component of the long-range magnetic order and possible increased
degree of frustration. Atomic disorder on Fe(Mn) sites suppresses the
temperature of the long-range order whereas intermediate alloys show a rich
magnetic phase diagram.Comment: 7 pages, 7 figure
Unconventional order-disorder phase transition in improper ferroelectric hexagonal manganites
The improper ferroelectricity in YMnO and other related multiferroic
hexagonal manganites are known to cause topologically protected ferroelectric
domains that give rise to rich and diverse physical phenomena. The local
structure and structural coherence across the ferroelectric transition,
however, were previously not well understood. Here we reveal the evolution of
the local structure with temperature in YMnO using neutron total scattering
techniques, and interpret them with the help of first-principles calculations.
The results show that, at room temperature, the local and average structures
are consistent with the established ferroelectric symmetry. On
heating, both local and average structural analyses show striking anomalies
from K up to the Curie temperature consistent with increasing
fluctuations of the order parameter angle. These fluctuations result in an
unusual local symmetry lowering into a \textit{continuum of structures} on
heating. This local symmetry breaking persists into the high-symmetry non-polar
phase, constituting an unconventional type of order-disorder transition.Comment: 10 pages, 5 figure
Detailed Mapping of the Local Ir⁴⁺ Dimers through the Metal-Insulator Transitions of CuIr₂S₄ Thiospinel by X-ray Atomic Pair Distribution Function Measurements
The evolution of the short-range structural signature of the Ir 4+ dimer state in CuIr2S4 thiospinel has been studied across the metal-insulator phase transitions as the metallic state is induced by temperature, Cr doping, and x-ray fluence. An atomic pair distribution function (PDF) approach reveals that there are no local dimers that survive into the metallic phase when this is invoked by temperature and doping. The PDF shows Ir4+ dimers when they exist, regardless of whether or not they are long-range ordered. At 100 K, exposure to a 98 keV x-ray beam melts the long-range dimer order within a few seconds, though the local dimers remain intact. This shows that the metallic state accessed on warming and doping is qualitatively different from the state obtained under x-ray irradiation
Phase Diagram of KxFe2-ySe2-zSz and the Suppression of its Superconducting State by an Fe2-Se/S Tetrahedron Distortion
We report structurally tuned superconductivity in KxFe2-ySe2-zSz (0<=z<=2)
phase diagram. Superconducting Tc is suppressed as S is incorporated into the
lattice, eventually vanishing at 80% of S. The magnetic and conductivity
properties can be related to stoichiometry on poorly occupied Fe1 site and the
local environment of nearly fully occupied Fe2 site. The decreasing Tc
coincides with the increasing Fe1 occupancy and the overall increase in Fe
stoichiometry from z = 0 to z = 2. Our results indicate that the irregularity
of Fe2-Se/S tetrahedron is an important controlling parameter that can be used
to tune the ground state in the new superconductor family.Comment: 5 pages, 4 figure