Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userStructural and Magnetic Phase Transitions in NdCoAsO under High Pressures
129
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We have investigated structural and magnetic phase transitions under high pressures in a quaternary rare earth transition metal arsenide oxide NdCoAsO compound that is isostructural to high temperature superconductor NdFeAsO. Four-probe electrical resistance measurements carried out in a designer diamond anvil cell show that the ferromagnetic Curie temperature and anti-ferromagnetic Neel temperature increase with an increase in pressure. High pressure x-ray diffraction studies using a synchrotron source show a structural phase transition from a tetragonal phase to a new crystallographic phase at a pressure of 23 GPa at 300 K. The NdCoAsO sample remained anti-ferromagnetic and non-superconducting to temperatures down to 10 K and to the highest pressure achieved in this experiment of 53 GPa. A P-T phase diagram for NdCoAsO is presented to a pressure of 53 GPa and low temperatures of 10 K.
rate research
Read More
SrRh2As2 exhibits structural phase transitions reminiscent to those of BaFe2As2, but crystallizes with three polymorphs derived from the tetragonal ThCr2Si2-type structure. The structure of alpha-SrRh2As2 is monoclinic with a = 421.2(1) pm, b = 1105.6(2) pm, c = 843.0(1) pm and beta = 95{deg} and was refined as a partially pseudo meroedric twin in the space group P21/c with R1 = 0.0928. beta-SrRh2As2 crystallizes with a modulated structure in the (3+1) dimensional superspace group Fmmm(10gamma)sigma 00 with the unit cell parameters a = 1114.4(3) pm, b = 574.4(2) pm and c = 611.5(2) pm and an incommensurable modulation vector q = (1, 0, 0.3311(4)). High temperature single crystal diffraction experiments confirm the tetragonal ThCr2Si2-type structure for gamma-SrRh2As2 above 350{deg}C. Electronic band structure calculations indicate that the structural distortion in alpha-SrRh2As2 is caused by strong Rh-Rh bonding interactions and has no magnetic origin as suggested for isotypic BaFe2As2.
At ambient pressure CaFe2As2 has been found to undergo a first order phase transition from a high temperature, tetragonal phase to a low temperature orthorhombic / antiferromagnetic phase upon cooling through T ~ 170 K. With the application of pressure this phase transition is rapidly suppressed and by ~ 0.35 GPa it is replaced by a first order phase transition to a low temperature collapsed tetragonal, non-magnetic phase. Further application of pressure leads to an increase of the tetragonal to collapsed tetragonal phase transition temperature, with it crossing room temperature by ~ 1.7 GPa. Given the exceptionally large and anisotropic change in unit cell dimensions associated with the collapsed tetragonal phase, the state of the pressure medium (liquid or solid) at the transition temperature has profound effects on the low temperature state of the sample. For He-gas cells the pressure is as close to hydrostatic as possible and the transitions are sharp and the sample appears to be single phase at low temperatures. For liquid media cells at temperatures below media freezing, the CaFe2As2 transforms when it is encased by a frozen media and enters into a low temperature multi-crystallographic-phase state, leading to what appears to be a strain stabilized superconducting state at low temperatures.
The coexistence and competition between superconductivity and electronic orders, such as spin or charge density waves, have been a central issue in high transition-temperature (${T_{rm c}}$) superconductors. Unlike other iron-based superconductors, FeSe exhibits nematic ordering without magnetism whose relationship with its superconductivity remains unclear. More importantly, a pressure-induced fourfold increase of ${T_{rm c}}$ has been reported, which poses a profound mystery. Here we report high-pressure magnetotransport measurements in FeSe up to $sim9$ GPa, which uncover a hidden magnetic dome superseding the nematic order. Above ${sim6}$ GPa the sudden enhancement of superconductivity (${T_{rm c}le38.3}$ K) accompanies a suppression of magnetic order, demonstrating their competing nature with very similar energy scales. Above the magnetic dome we find anomalous transport properties suggesting a possible pseudogap formation, whereas linear-in-temperature resistivity is observed above the high-${T_{rm c}}$ phase. The obtained phase diagram highlights unique features among iron-based superconductors, but bears some resemblance to that of high-${T_{rm c}}$ cuprates.
Recently, natural van der Waals heterostructures of (MnBi2Te4)m(Bi2Te3)n have been theoretically predicted and experimentally shown to host tunable magnetic properties and topologically nontrivial surface states. In this work, we systematically investigate both the structural and electronic responses of MnBi2Te4 and MnBi4Te7 to external pressure. In addition to the suppression of antiferromagnetic order, MnBi2Te4 is found to undergo a metal-semiconductor-metal transition upon compression. The resistivity of MnBi4Te7 changes dramatically under high pressure and a non-monotonic evolution of r{ho}(T) is observed. The nontrivial topology is proved to persists before the structural phase transition observed in the high-pressure regime. We find that the bulk and surface states respond differently to pressure, which is consistent with the non-monotonic change of the resistivity. Interestingly, a pressure-induced amorphous state is observed in MnBi2Te4, while two high pressure phase transitions are revealed in MnBi4Te7. Our combined theoretical and experimental research establishes MnBi2Te4 and MnBi4Te7 as highly tunable magnetic topological insulators, in which phase transitions and new ground states emerge upon compression.
We report on the structural phase transitions in the S doped FeSe superconductor by powder synchrotron X ray diffraction at high pressures up to 18.5 GPa under compression and decompression modes. In order to create high quasi hydrostatic pressures, diamond anvil cells filled with helium as a pressure transmitting medium were used. It was found that at ambient pressure and room temperature, S doped FeSe has a tetragonal structure. Under compression, in the region of 10 GPa, a phase transition from the tetragonal into the orthorhombic structure is observed, which persists up to 18.5 GPa. Our results strongly suggest that, at decompression, as the applied pressure decreases to 6 GPa and then is completely removed, most of the sample recrystallizes into the hexagonal phase of the structural type NiAs. However, the other part of the sample remains in the high pressure orthorhombic phase, while the tetragonal phase is not restored. These observations illustrate a strong hysteresis of the structural properties of S doped FeSe during a phase transition under pressure.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
