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The origin of the electronic nematicity in FeSe is one of the most important unresolved puzzles in the study of iron-based superconductors. In both spin- and orbital-nematic models, the intrinsic magnetic excitations at Q1= (1, 0) and Q2= (0, 1) of twin-free FeSe are expected to provide decisive criteria for clarifying this issue. Although a spin-fluctuation anisotropy below 10 meV between Q1and Q2has been observed by inelastic neutron scattering at low temperature, it remains unclear whether such an anisotropy also persists at higher energies and associates with the nematic transition Ts. Here we use resonant inelastic X-ray scattering to probe the high-energy magnetic excitations of detwinned FeSe. A prominent anisotropy between the magnetic excitations along the Hand Kdirections is found to persist to E≈ 200 meV, which decreases gradually with increasing temperature and finally vanishes at a temperature around Ts. The measured high-energy spin excitations are dispersive and underdamped, which can be understood from a local-moment perspective.Taking together the large energy scale far beyond the dxz/dyzorbital splitting, we suggest that the nematicity in FeSe is probably spin-driven.

Basalt fibre (BF)/acrylonitrile–butadiene rubber (NBR) composites with various BF contents and orientations were prepared, and the curing, physical and mechanical properties and wear performance under block-on-ring abrasion conditions were evaluated. The results showed that the curing time was not obviously affected by the BFs. The addition of BFs increased the hardness but had negative influence on the tensile/tear strength of the NBR composites, especially when the BFs were oriented perpendicular to the tensile/tear direction with a high content, which should be due to the weak connection between the BFs and the rubber matrix. The coefficient of friction (COF) of the composites decreased significantly when BFs were added, whereas the content (3–30 phr) and the orientation of the fibres did not mainly affect the COF. Both parallel- and perpendicular-oriented BFs were effective at improving the wear resistance of the composites, and the former showed a better effect. With the BF content increase, the wear rate initially decreased and then remained basically stable. The COF and wear rate of the composites decreased by 27% and 35% when 12 phr BFs were added in a parallel direction. The excessive BFs, especially the perpendicularly-oriented BFs, led to fracture of the worn surface due to the abrasive grain wear caused by the crushed fibres.

Noncentrosymmetric magnets usually host intriguing magnetic interactions inherent in the crystal structure with broken inversion symmetry, which can give rise to rich magnetic behaviors. We report herein the high-pressure synthesis, crystal structure, magnetizations, and magnetic structure of a so-called Nowotny chimney ladder compound Cr4Ge7. Our analysis on the powder neutron diffraction data revises the crystal structure as a noncentrosymmetric space group (P4̅c2, No. 116). It exhibits two magnetic orders within the temperature range of 2–400 K. The first order at ∼207 K associated with a small magnetic moment of ∼0.75 μBis assigned to a commensurate ferromagnetic structure with a propagation vector k= (0, 0, 0). The weak itinerant ferromagnet nature should be caused by the complex Cr spin orders from different Wyckoff positions. The second order-like behavior at ∼18 K is assumed to arise from a competition between the Dzyaloshinskii–Moriya and Heisenberg interactions. The results provide an excellent platform for the study of intricate interactions among various magnetic exchanges as well as for the exploration of high-temperature exotic magnetic properties.

Superconductivity in FeSe emerges from a nematic phase that breaks four-fold rotational symmetry in the iron plane. This phase may arise from orbital ordering, spin fluctuations or hidden magnetic quadrupolar order. Here we use inelastic neutron scattering on a mosaic of single crystals of FeSe, detwinned by mounting on a BaFe2As2substrate to demonstrate that spin excitations are most intense at the antiferromagnetic wave vectors QAF= (±1, 0) at low energies E= 6–11 meV in the normal state. This two-fold (C2) anisotropy is reduced at lower energies, 3–5 meV, indicating a gapped four-fold (C4) mode. In the superconducting state, however, the strong nematic anisotropy is again reflected in the spin resonance (E= 3.6 meV) at QAFwith incommensurate scattering around 5–6 meV. Our results highlight the extreme electronic anisotropy of the nematic phase of FeSe and are consistent with a highly anisotropic superconducting gap driven by spin fluctuations. Extreme electronic anisotropy is revealed in the high-temperature superconductor FeSe through tour de force experiments on detwinned crystals.

It is possible to increase the charge capacity of transition-metal (TM) oxide cathodes in alkali-ion batteries by invoking redox reactions on the oxygen. However, oxygen loss often occurs. To explore what affects oxygen loss in oxygen redox materials, we have compared two analogous Na-ion cathodes, P2-Na0.67Mg0.28Mn0.72O2and P2-Na0.78Li0.25Mn0.75O2. On charging to 4.5 V, >0.4e–are removed from the oxide ions of these materials, but neither compound exhibits oxygen loss. Li is retained in P2-Na0.78Li0.25Mn0.75O2but displaced from the TM to the alkali metal layers, showing that vacancies in the TM layers, which also occur in other oxygen redox compounds that exhibit oxygen loss such as Li[Li0.2Ni0.2Mn0.6]O2, are not a trigger for oxygen loss. On charging at 5 V, P2-Na0.78Li0.25Mn0.75O2exhibits oxygen loss, whereas P2-Na0.67Mg0.28Mn0.72O2does not. Under these conditions, both Na+and Li+are removed from P2-Na0.78Li0.25Mn0.75O2, resulting in underbonded oxygen (fewer than 3 cations coordinating oxygen) and surface-localized O loss. In contrast, for P2-Na0.67Mg0.28Mn0.72O2, oxygen remains coordinated by at least 2 Mn4+and 1 Mg2+ions, stabilizing the oxygen and avoiding oxygen loss.

The search for improved energy-storage materials has revealed Li- and Na-rich intercalation compounds as promising high-capacity cathodes. They exhibit capacities in excess of what would be expected from alkali-ion removal/reinsertion and charge compensation by transition-metal (TM) ions. The additional capacity is provided through charge compensation by oxygen redox chemistry and some oxygen loss. It has been reported previously that oxygen redox occurs in O 2p orbitals that interact with alkali ions in the TM and alkali-ion layers (that is, oxygen redox occurs in compounds containing Li+–O(2p)–Li+interactions). Na2/3[Mg0.28Mn0.72]O2exhibits an excess capacity and here we show that this is caused by oxygen redox, even though Mg2+resides in the TM layers rather than alkali-metal (AM) ions, which demonstrates that excess AM ions are not required to activate oxygen redox. We also show that, unlike the alkali-rich compounds, Na2/3[Mg0.28Mn0.72]O2does not lose oxygen. The extraction of alkali ions from the alkali and TM layers in the alkali-rich compounds results in severely underbonded oxygen, which promotes oxygen loss, whereas Mg2+remains in Na2/3[Mg0.28Mn0.72]O2, which stabilizes oxygen.

Na4−δNiTeO6is a rare example in the transition-metal tellurate family of realizing an S= 1 spin-chain structure. By performing neutron powder diffraction measurements, the ground-state magnetic structure of Na4−δNiTeO6is determined. These measurements reveal that below TN∼ 6.8(2) K, the Ni2+moments form a screwed ferromagnetic (FM) spin-chain structure running along the crystallographic aaxis but these FM spin chains are coupled antiferromagnetically along the band cdirections, giving rise to a magnetic propagation vector of k= (0, 1/2, 1/2). This zigzag magnetic order is well supported by first-principles calculations. The moment size of Ni2+spins is determined to be 2.1(1)μBat 3 K, suggesting a significant quenching of the orbital moment due to the crystalline electric field (CEF) effect. The previously reported metamagnetic transition near HC∼ 0.1 T can be understood as a field-induced spin-flip transition. The relatively easy tunability of the dimensionality of its magnetism by external parameters makes Na4−δNiTeO6a promising candidate for further exploring various types of novel spin-chain physics.