141 research outputs found
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
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
Thermal evolution of antiferromagnetic correlations and tetrahedral bond angles in superconducting FeTeSe
It has recently been demonstrated that dynamical magnetic correlations
measured by neutron scattering in iron chalcogenides can be described with
models of short-range correlations characterized by particular {choices of
four-spin plaquettes, where the appropriate choice changes as the} parent
material is doped towards superconductivity. Here we apply such models to
describe measured maps of magnetic scattering as a function of two-dimensional
wave vectors obtained for optimally superconducting crystals of
FeTeSe. We show that the characteristic antiferromagnetic wave
vector evolves from that of the bicollinear structure found in underdoped
chalcogenides (at high temperature) to that associated with the stripe
structure of antiferromagnetic iron arsenides (at low temperature); {these can
both be described with the same local plaquette, but with different
inter-plaquette correlations}. While the magnitude of the low-energy magnetic
spectral weight is substantial at all temperatures, it actually weakens
somewhat at low temperature, where the charge carriers become more itinerant.
The observed change in spin correlations is correlated with the dramatic drop
in the electronic scattering rate and the growth of the bulk nematic response
on cooling. Finally, we also present powder neutron diffraction results for
lattice parameters in FeTeSe indicating that the tetrahedral bond
angle tends to increase towards the ideal value on cooling, in agreement with
the increased screening of the crystal field by more itinerant electrons and
the correspondingly smaller splitting of the Fe orbitals
Pressure tuning of structure, superconductivity and novel magnetic order in the Ce-underdoped electron-doped cuprate T'-Pr_1.3-xLa_0.7Ce_xCuO_4 (x = 0.1)
High-pressure neutron powder diffraction, muon-spin rotation and
magnetization studies of the structural, magnetic and the superconducting
properties of the Ce-underdoped superconducting (SC) electron-doped cuprate
system T'-Pr_1.3-xLa_0.7Ce_xCuO_4 with x = 0.1 are reported. A strong reduction
of the lattice constants a and c is observed under pressure. However, no
indication of any pressure induced phase transition from T' to T structure is
observed up to the maximum applied pressure of p = 11 GPa. Large and non-linear
increase of the short-range magnetic order temperature T_so in
T'-Pr_1.3-xLa_0.7Ce_xCuO_4 (x = 0.1) was observed under pressure.
Simultaneously pressure causes a non-linear decrease of the SC transition
temperature T_c. All these experiments establish the short-range magnetic order
as an intrinsic and a new competing phase in SC T'-Pr_1.2La_0.7Ce_0.1CuO_4. The
observed pressure effects may be interpreted in terms of the improved nesting
conditions through the reduction of the in-plane and out-of-plane lattice
constants upon hydrostatic pressure.Comment: 11 pages, 10 figure
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