Helimagnets by disorder: Its role on the high-temperature magnetic spiral in the YBaCuFeO5 perovskite

Most of the spiral magnetoelectric multiferroics investigated in recent years are geometrically or exchangefrustrated magnets, where the presence of triangular or other frustrated spin networks produce low magnetic transition temperatures. This critically limits their potential uses. The exceptional stability of the spiral magnetic order (at TS) in the layered structure of the YBaCuFeO5 double perovskite involves a nonconventional mechanism: spiral order by disorder. The model has been theoretically developed by Scaramucci et al. [Phys.Rev.Res. 2, 013273 (2020)] after the discovery of a huge impact of cation disorder on TS [M. Morin et al., Nat. Commun. 7, 13758 (2016)]. In this work the influence of disorder (and only disorder) on the magnetic phase diagram is studied on a quantitative basis extending the range of previous studies. We thoroughly investigate the impact of frustration due to B-site disorder (nd) on the magnetic spirals in the reference composition YBaCuFeO5.The interplay between disorder, stability, and the detailed features of the incommensurate spiral magnetic orders were systematic, quantitative, and methodically investigated in samples of identical composition, spanning a wide range of nd values. Three different regimes are distinguished in the YBaCuFeO5 phase diagram versus disorder. A triple point is found in YBaCuFeO5 driven by Fe/Cu disorder that sets limits to TS and the cycloidal component of the helicoidal order. These layered materials appear as a very efficient realization of the avenue “spiral order by disorder” to supply functional helimagnets at normal working temperatures

Mechano-Chemical Synthesis, Structural Features and Optical Gap of Hybrid CH3NH3CdBr3 Perovskite

Hybrid methyl-ammonium (MA:CH3 NH3+) lead halide MAPbX3 (X = halogen) perovskites exhibit an attractive optoelectronic performance that can be applied to the next generation of solar cells. To extend the field of interest of these hybrid materials, we describe the synthesis by a solvent-free ball-milling procedure, yielding a well crystallized, pure and moisture stable specimen of the Cd tribromide counterpart, MACdBr3, which contains chains of face-sharing CdBr6 octahedra in a framework defined in the Cmc21 (No 36) space group. The details of the structural arrangement at 295 K have been investigated by high angular resolution synchrotron x-ray diffraction (SXRD), including the orientation of the organic MA units, which are roughly aligned along the c direction, given the acentric nature of the space group. UV-vis spectra unveil a gap of 4.6 eV, which could be useful for ultraviolet detectors.Fil: Alonso, José Antonio. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Kayser, Paula. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Hong, Bo Kyung. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Álvarez Galván, María Consuelo. Consejo Superior de Investigaciones Científicas; EspañaFil: Fauth, Francois. No especifíca;Fil: Lopez, Carlos Alberto. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Área Química General e Inorgánica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; Argentin

The Electronic and Magnetic Properties of Cation Ordered Sr2Mn2.23Cr0.77As2O2

ACKNOWLEDGMENT This research is supported by the EPSRC (research grant EP/L002493/1). We also acknowledge the UK Science and Technology Facilities Council (STFC) for provision of beam time at the ILL.Peer reviewedPostprin

Non-linear effects and Joule heating in I-V curves in manganites

We study the influence of the Joule effect on the non-linear behavior of the transport I-V curves in polycrystalline samples of the manganite Pr0.8Ca0.2MnO3 by using the crystalline unit cell parameters as an internal thermometer in X-ray and neutron diffraction. We develop a simple analytical model to estimate the temperature profile in the samples. Under the actual experimental conditions we show that the internal temperature gradient or the difference between the temperature of the sample and that of the thermal bath are at the origin of the non-linearity observed in the I-V curves. Consequences on other compounds with colossal magnetoresistance are also discussed.Comment: accepted in Journal of Applied Physic

Sodium vanadium titanium phosphate electrode for symmetric sodium-ion batteries with high power and long lifespan

Sodium-ion batteries operating at ambient temperature hold great promise for use in grid energy storage owing to their significant cost advantages. However, challenges remain in the development of suitable electrode materials to enable long lifespan and high rate capability. Here we report a sodium super-ionic conductor structured electrode, sodium vanadium titanium phosphate, which delivers a high specific capacity of 147 mA h g−1 at a rate of 0.1 C and excellent capacity retentions at high rates. A symmetric sodium-ion full cell demonstrates a superior rate capability with a specific capacity of about 49 mA h g−1 at 20 C rate and ultralong lifetime over 10,000 cycles. Furthermore, in situ synchrotron diffraction and X-ray absorption spectroscopy measurement are carried out to unravel the underlying sodium storage mechanism and charge compensation behaviour. Our results suggest the potential application of symmetric batteries for electrochemical energy storage given the superior rate capability and long cycle life

Na7V3(P2O7)(4) as a high voltage electrode material for Na-ion batteries: crystal structure and mechanism of Na+ extraction/insertion by operando X-ray diffraction

International audienceThe crystal chemistry and the electrochemical properties of Na7V3(P2O7)(4) as a high voltage cathode material upon Na+ extraction/insertion were investigated. The crystal structure was solved and refined for the first time from single crystal X-ray diffraction data. Possible sodium migration pathways were determined using the bond valence energy landscape (BVEL) method based on the bond valence theory. The electrochemical behavior of the material in a wide voltage range demonstrates the activity of the V3+/V4+, V4+/V5+, and V3+/V2+ redox couples. The reversible capacity of the Na7V3(P2O7)(4) electrode is hence increased up to 118 mA h g(-1)vs. Na+/Na. Sodium extraction/insertion mechanisms are examined by operando X-ray diffraction, which provides direct information on the evolution of the material in nonequilibrium states upon electrochemical oxidation and reduction processes

From Tb3Ni2 to Tb3CoNi: The interplay between chemistry, structure, and magnetism

Formation, crystal structure, and macroscopic and microscopic magnetism of the binary Tb3Ni2 and derivative pseudobinary Tb3CoxNi2−x phases have been investigated using an array of experimental methods. While Tb3Ni2 crystallizes in the monoclinic Dy3Ni2 structure type (mS20, C2/m), the substitution of Co for Ni results in a structural transition into the rhombohedral Er3Ni2 type (hR45, R¯3h) at x(Co)≈0.34 and beyond in the Tb3CoxNi2−x system. In both the monoclinic and rhombohedral phases, the addition of Co leads to an anisotropic change of lattice parameters and unexpected reduction of the cell volume. Measurements of bulk properties reveal that these compounds order ferrimagnetically or ferromagnetically at about 100 K. Complex noncollinear ferromagnetic ordering in the Tb sublattices is weakly dependent on composition. For x > 0.34 the long-range magnetic ordering leads to a strong anisotropic magnetostriction accompanied by a symmetry reduction from rhombohedral to triclinic.</p

Structural and electrochemical studies of novel Na7V3Al(P2O7)(4)(PO4) and Na7V2Al2(P2O7)(4)(PO4) high-voltage cathode materials for Na-ion batteries

International audienceA series of Na7V4-x3+Alx(P2O7)(4)(PO4) (x = 0, 1, 2, and 4) materials were synthesized by flux crystal growth. Novel Na7V4-xAlx(P2O7)(4)(PO4) (x = 1 and 2) compositions were structurally characterized by single crystal and powder X-ray diffraction analyses using laboratory and high-resolution synchrotron X-ray sources. The investigation of the electrochemical behavior of two new mixed V/Al phases as positive electrodes in Na-based batteries was performed using charge-discharge galvanostatic tests and operando X-ray diffraction experiments. It is demonstrated that the substitution of a part of vanadium with aluminum in Na7V4(P2O7)(4)(PO4) significantly increases the gravimetric capacity of these materials: from 70.9 mA h g(-1) to 113.1 mA h g(-1) and from 48.1 mA h g(-1) to 92.7 mA h g(-1) in Na7V3Al(P2O7)(4)(PO4) and Na(7)V(2)A(2)l(P2O7)(4)(PO4), respectively thanks to the activation of the V4+/V5+ redox couple. Different degrees of reversibility of the electrochemical reactions operating on the V3+/V4+ and V4+/V5+ redox couples in Na7V3Al(P2O7)(4)(PO4) are discussed from the analysis of operando X-ray diffraction

From Tb3Ni2 to Tb3CoNi: The interplay between chemistry, structure, and magnetism

Formation, crystal structure, and macroscopic and microscopic magnetism of the binary Tb3Ni2 and derivative pseudobinary Tb3CoxNi2-x phases have been investigated using an array of experimental methods.While Tb3Ni2 crystallizes in the monoclinic Dy3Ni2 structure type (mS20, C2/m), the substitution of Co for Ni results in a structural transition into the rhombohedral Er3Ni2 type (hR45, R\uaf3h) at x(Co) 48 0.34 and beyond in the Tb3CoxNi2-x system. In both the monoclinic and rhombohedral phases, the addition of Co leads to an anisotropic change of lattice parameters and unexpected reduction of the cell volume. Measurements of bulk properties reveal that these compounds order ferrimagnetically or ferromagnetically at about 100 K. Complex noncollinear ferromagnetic ordering in the Tb sublattices is weakly dependent on composition. For x &gt; 0.34 the long-range magnetic ordering leads to a strong anisotropic magnetostriction accompanied by a symmetry reduction from rhombohedral to triclinic