Magnetic superelasticity and inverse magnetocaloric effect in Ni-Mn-In

Applying a magnetic field to a ferromagnetic Ni$_{50}$Mn$_{34}$In$_{16}$ alloy in the martensitic state induces a structural phase transition to the austenitic state. This is accompanied by a strain which recovers on removing the magnetic field giving the system a magnetically superelastic character. A further property of this alloy is that it also shows the inverse magnetocaloric effect. The magnetic superelasticity and the inverse magnetocaloric effect in Ni-Mn-In and their association with the first order structural transition is studied by magnetization, strain, and neutron diffraction studies under magnetic field.Comment: 6 pages, 8 figures. Published in the Physical Review

Magnetic superelasticity and inverse magnetocaloric effect in Ni-Mn-In

Applying a magnetic field to a ferromagnetic Ni$_{50}$Mn$_{34}$In$_{16}$ alloy in the martensitic state induces a structural phase transition to the austenitic state. This is accompanied by a strain which recovers on removing the magnetic field giving the system a magnetically superelastic character. A further property of this alloy is that it also shows the inverse magnetocaloric effect. The magnetic superelasticity and the inverse magnetocaloric effect in Ni-Mn-In and their association with the first order structural transition is studied by magnetization, strain, and neutron diffraction studies under magnetic field.Comment: 6 pages, 8 figures. Published in the Physical Review

Comparison of hospital-wide and unit-specific cumulative antibiograms in hospital- and community-acquired infection

Background: Empirical antibacterial therapy in hospitals is usually guided by local epidemiologic features reflected by institutional cumulative antibiograms. We investigated additional information inferred by aggregating cumulative antibiograms by type of unit or according to the place of acquisition (i.e. community vs. hospital) of the bacteria. Materials and methods: Antimicrobial susceptibility rates of selected pathogens were collected over a 4-year period in an university-affiliated hospital. Hospital-wide antibiograms were compared with those selected by type of unit and sampling time (48h after hospital admission). Results: Strains isolated >48h after admission were less susceptible than those presumably arising from the community (48h after admission. When compared to hospital-wide antibiograms, susceptibility rates were lower in the ICU and surgical units for Escherichia coli to amoxicillin-clavulanate, enterococci to penicillin, and Pseudomonas aeruginosa to anti-pseudomonal beta-lactams, and in medical units for Staphylococcus aureus to oxacillin. In contrast, few differences were observed among strains isolated within 48h of admission. Conclusions: Hospital-wide antibiograms reflect the susceptibility pattern for a specific unit with respect to community-acquired, but not to hospital-acquired strains. Antibiograms adjusted to these parameters may be useful in guiding the choice of empirical antibacterial therap

Transport and magnetic properties of GdBaCo_{2}O_{5+x} single crystals: A cobalt oxide with square-lattice CoO_2 planes over a wide range of electron and hole doping

Single crystals of the layered perovskite GdBaCo_{2}O_{5+x} (GBCO) have been grown by the floating-zone method, and their transport, magnetic, and structural properties have been studied in detail over a wide range of oxygen contents. The obtained data are used to establish a rich phase diagram centered at the "parent'' compound GdBaCo_{2}O_{5.5} -- an insulator with Co ions in the 3+ state. An attractive feature of GBCO is that it allows a precise and continuous doping of CoO_{2} planes with either electrons or holes, spanning a wide range from the charge-ordered insulator at 50% electron doping (x=0) to the undoped band insulator (x=0.5), and further towards the heavily hole-doped metallic state. This continuous doping is clearly manifested in the behavior of thermoelectric power which exhibits a spectacular divergence with approaching x=0.5, where it reaches large absolute values and abruptly changes its sign. At low temperatures, the homogeneous distribution of doped carriers in GBCO becomes unstable, and both the magnetic and transport properties point to an intriguing nanoscopic phase separation. We also find that throughout the composition range the magnetic behavior in GBCO is governed by a delicate balance between ferromagnetic (FM) and antiferromagnetic (AF) interactions, which can be easily affected by temperature, doping, or magnetic field, bringing about FM-AF transitions and a giant magnetoresistance (MR) phenomenon. An exceptionally strong uniaxial anisotropy of the Co spins, which dramatically simplifies the possible spin arrangements, together with the possibility of continuous ambipolar doping turn GBCO into a model system for studying the competing magnetic interactions, nanoscopic phase separation and accompanying magnetoresistance phenomena.Comment: 31 pages, 32 figures, submitted to Phys. Rev.

Charge and Orbital Ordering and Spin State Transition Driven by Structural Distortion in YBaCo_2O_5

We have investigated electronic structures of antiferromagnetic YBaCo_2O_5 using the local spin-density approximation (LSDA) + U method. The charge and orbital ordered insulating ground state is correctly obtained with the strong on-site Coulomb interaction. Co^{2+} and Co^{3+} ions are found to be in the high spin (HS) and intermediate spin (IS) state, respectively. It is considered that the tetragonal to orthorhombic structural transition is responsible for the ordering phenomena and the spin states of Co ions. The large contribution of the orbital moment to the total magnetic moment indicates that the spin-orbit coupling is also important in YBaCo_2O_5.Comment: 4 pages including 4 figures, Submitted to Phys. Rev. Let

Magnetic Structures of High Temperature Phases of TbBaCo2O5.5

Neutron diffraction studies have been carried out on a single crystal of oxygen-deficient perovskite TbBaCo2O5.5 in the temperature range of 7-370 K. There have been observed several magnetic or structural transitions. Among these, the existence of the transitions to the insulating phase from the metallic one at ~340 K, to the one with the ferromagnetic moment at ~280 K and possibly to the antiferromagnetic one at ~260 K, with decreasing temperature T correspond to those reported in former works. We have studied the magnetic structures at 270 K and 250 K and found that all Co3+ ions of the CoO6 octahedra are in the low spin state and those of the CoO5 pyramids carry spins which are possibly in the intermediate spin state. Non-collinear magnetic structures are proposed at these temperatures. Two other transitions have also been observed at the temperatures, ~100 K and ~250 K.Comment: 9 pages, 2 tables, 10 figure

Field-temperature phase diagram of the enigmatic Nd2(Zr1−xTix)2O7 pyrochlore magnets

By combining neutron scattering and magnetization measurements down to 80 mK, we determine the (H, T ) phase diagram of the Nd2(Zr1−xTix )2O7 pyrochlore magnet compounds. In those samples, Zr is partially substituted by Ti, hence tuning the exchange parameters and testing the robustness of the various phases. In all samples, the ground state remains all in/all out, while the field induces phase transitions toward new states characterized by two in–two out or one out–three in/one in–three out configurations. These transitions manifest as metamagnetic singularities in the magnetization versus field measurements. Strikingly, it is found that moderate substitution reinforces the stability of the all in/all out phase: the Néel temperature, the metamagnetic fields along with the ordered magnetic moment, are higher in substituted samples with x < 10%

Polymorphs of Rb3ScF6: X-ray and Neutron Diffraction, Solid-State NMR, and Density Functional Theory Calculations Study

The crystal structures of three polymorphs of Rb3ScF6 have been determined through a combination of synchrotron, laboratory X-ray, and neutron powder diffraction, electron diffraction, and multinuclear high-field solid-state NMR studies. The room temperature (RT; α) and medium-temperature (β) structures are tetragonal, with space groups I41/a (Z = 80) and I4/m (Z = 10) and lattice parameters a = 20.2561(4) Å, c = 36.5160(0) Å and a = 14.4093(2) Å, c = 9.2015(1) Å at RT and 187 °C, respectively. The high-temperature (γ) structure is cubic space group Fm3¯ m (Z = 4) with a = 9.1944(1) Å at 250 °C. The temperatures of the phase transitions were measured at 141 and 201 °C. The three α, β, and γRb3ScF6 phases are isostructural with the α, β, and δforms of the potassium cryolite. Detailed structural characterizations were performed by density functional theory as well as NMR. In the case of the β polymorph, the dynamic rotations of the ScF6 octahedra of both Sc crystallographic sites have been detailed. © 2021 American Chemical Society.For DFT calculations, we thank the “Centre de Calcul Scientifique en region Centre” (Orléans, France). We acknowledge the Interface, Confinement, Materials and Nanostructures (Orléans, France) for access to their transmission electron microscope. Financial support from the IR-RMN-THC Fr3050 CNRS for conducting the research is gratefully acknowledged. This study was also financially supported by VEGA-2/0060/18 and ITMS project (code 313021T081, Research & Innovation Operational Programme funded by the ERDF). We thank also Dr. F. Vivet, Dr. F. Fayon, and Dr. D. Massiot for useful discussions

Sauver Byzance de la barbarie du monde

Il volume ripercorre la trattazione del mitema di Bisanzio nella letteratura francese e francofona dalle origini ai giorni nostr

Crystal growth and superconductivity of FeSe_x

Single crystals FeSe_x have been grown in evacuated sealed quartz tube using a NaCl/KCl flux. The products include two crystal structures of tetragon and hexagon. The electronic transport and magnetic properties measurements of FeSe_x single crystal exhibits a superconducting transition at about 10K.Comment: 9 pages, 4 Figure