인공고관절의 세라믹 볼 헤드의 기계적 안정성 평가를 위한 3 차원 유한요소 해석

The response of the worldwide scientific community to the discovery in 2008 of superconductivity at T c = 26 K in the Fe-based compound LaFeAsO1−x F x has been very enthusiastic. In short order, ot...

The puzzle of high temperature superconductivity in layered iron pnictides and chalcogenides

Colossal magnetoresistance (CMR) phenomena are observed in the perovskite-type hole-doped manganites in which the double-exchange ferromagnetic metal phase and the charge–orbital ordered antiferromagnetic phase compete with each other. The quenched disorder arising from the inherent chemical randomness or the intentional impurity doping may cause major modifications in the electronic phase diagram as well as in the magnetoelectronic properties near the bicritical point that is formed by such a competition of the two phases. One is the phase separation phenomenon on various time-scales (from static to dynamic) and on various length-scales (from glass-like nano to grain-like micron). The other is the enhanced phase fluctuation with anomalous reduction in the transition temperatures of the competing phases (and hence in the bicritical-point temperature). The highly effective suppression of such a phase fluctuation by an external magnetic field is assigned here to the most essential ingredient of the CMR physics. Such profound and dramatic features as appearing in the bicritical region are extensively discussed in this paper with ample examples of the material systems specially designed for this purpose. The unconventional phase-controls over the competing phases in terms of magnetic/electric fields and photo-excitations are also exemplified.

https://iopscience.iop.org/article/10.1088/0034-4885/69/3/R06/pdf

Critical features of colossal magnetoresistive manganites

Manganese-activated fluoride phosphors for high-efficacy warm white light-emitting diodes have been limited by low photoluminescence quantum yields. Here, Zhu et al. use an efficient cation exchange reaction to synthesize manganese phosphors with photoluminescence quantum yields as high as 98%.

/pdf/highly-efficient-non-rare-earth-red-emitting-phosphor-for-3wgxp231in.pdf

Highly efficient non-rare-earth red emitting phosphor for warm white light-emitting diodes

The manipulation of magnetic properties by an electric field in magnetoelectric multiferroic materials has driven significant research activity, with the goal of realizing their transformative technological potential. Here, we review progress in the fundamental understanding and design of new multiferroic materials, advances in characterization and modelling tools to describe them, and the exploration of devices and applications. Focusing on the translation of the many scientific breakthroughs into technological innovations, we identify the key open questions in the field where targeted research activities could have maximum impact in transitioning scientific discoveries into real applications. Magnetoelectric multiferroics, where magnetic properties are manipulated by electric field and vice versa, could lead to improved electronic devices. Here, advances in materials, characterisation and modelling, and usage in applications are reviewed.

Advances in magnetoelectric multiferroics.

Synthesis, structure and magnetic properties of Ba2CrMoO6

The rare earth vanadium oxynitride perovskites RVO3−xNx (R = La, Pr, Nd; 0 ≤ x ≤ 1) have been prepared by treatment of RVO4 precursors in NH3. The ammonolysis reactions proceed through an initial reduction of RVO4 precursors to RVO3 perovskites that are progressively nitrided and reoxidised to RVO3−xNx materials with varying proportions of V4+/V3+. Variable temperature neutron diffraction studies show that NdVO2N and PrVO2.24N0.76 have orthorhombic Pbnm symmetry between 3.5 and 300 K, but LaVO2.11N0.89 undergoes a broad Pbnm to Rc structural transition over this temperature range. In LaVO3−xNx samples the proportion of the Rc phase at room temperature increases with the nitrogen content. The partial anion order indicative of planes of cis-VN2 chains found in NdVO2N is also present in PrVO2.24N0.76, and is thus robust to the disorder created by non-stoichiometry. Magnetic measurements reveal spin freezing transitions at low temperatures in LaVO2.09N0.91 and PrVO2.24N0.76, but NdVO2N is paramagnetic.

Synthesis, anion order and magnetic properties of RVO3−xNx perovskites (R = La, Pr, Nd; 0 ≤ x ≤ 1)

Incomplete transformations from ferromagnetic to charge ordered states in manganite perovskites lead to phase-separated microstructures showing colossal magnetoresistances. However, it is unclear whether electronic matter can show spontaneous separation into multiple phases distinct from the high temperature state. Here we show that paramagnetic CaFe3O5 undergoes separation into two phases with different electronic and spin orders below their joint magnetic transition at 302 K. One phase is charge, orbital and trimeron ordered similar to the ground state of magnetite, Fe3O4, while the other has Fe2+/Fe3+charge averaging. Lattice symmetry is unchanged but differing strains from the electronic orders probably drive the phase separation. Complex low symmetry materials like CaFe3O5 where charge can be redistributed between distinct cation sites offer possibilities for the generation and control of electronic phase separated nanostructures. Electronic phase separation is an important feature of many correlated perovskite compounds but hasn’t been seen in other complex oxides with similar physical behaviour such as magnetite. Hong et al. find phase separation between a magnetite-like charge ordered phase and a charge averaged phase in CaFe3O5.

/pdf/long-range-electronic-phase-separation-in-cafe3o5-1is4222g6n.pdf

Long range electronic phase separation in CaFe3O5

Synchrotron X-ray, neutron powder diffraction, and magnetic susceptibility measurements have been used to characterize the Ln2LiRuO6 (Ln = Pr, Nd, Sm, Eu, Gd, and Tb) double perovskites. All compos...

Coupled Spin Ordering in the Ln(2)LiRuO(6) Double Perovskites

The nature of triclinic to orthorhombic phase transition, at which colossal negative thermal expansion is observed, and the magnetic ordering of Bi${}_{1\ensuremath{-}x}$La${}_{x}$NiO${}_{3}$ have been investigated with neutron powder diffraction (NPD) and x-ray absorption spectroscopy techniques. The presence of a charge-transfer transition from (Bi/La)${}^{3+}$${}_{0.5}$Bi${}^{5+}$${}_{0.5}$Ni${}^{2+}$O${}_{3}$ to (Bi/La)${}^{3+}$Ni${}^{3+}$O${}_{3}$, accompanied by the simultaneous structural distortion, was confirmed. The NPD data also revealed that magnetic ordering is present only in the insulating triclinic phase. The metallic orthorhombic phase was found to be nonmagnetic down to 10 K.

/pdf/intermetallic-charge-transfer-transition-in-bi-1-x-la-x-nio-za8sbldpj5.pdf

J. Paul Attfield

Papers

Synthesis, structure and magnetic properties of Ba2CrMoO6

Synthesis, anion order and magnetic properties of RVO3−xNx perovskites (R = La, Pr, Nd; 0 ≤ x ≤ 1)

Long range electronic phase separation in CaFe3O5

Coupled Spin Ordering in the Ln(2)LiRuO(6) Double Perovskites

Intermetallic charge-transfer transition in Bi 1 − x La x NiO 3 as the origin of the colossal negative thermal expansion