magnetoelectrics and multiferroics present exciting opportunities for electric-field control of magnetism. However, there are few room-temperature ferromagnetic-ferroelectrics. Among the various types of multiferroics the bismuth ferrite system has received much attention primarily because both the ferroelectric and the antiferromagnetic orders are quite robust at room temperature. Here we demonstrate the emergence of an enhanced spontaneous magnetization in a strain-driven rhombohedral and super-tetragonal mixed phase of BiFeo 3 . using X-ray magnetic circular dichroism-based photoemission electron microscopy coupled with macroscopic magnetic measurements, we find that the spontaneous magnetization of the rhombohedral phase is significantly enhanced above the canted antiferromagnetic moment in the bulk phase, as a consequence of a piezomagnetic coupling to the adjacent tetragonal-like phase and the epitaxial constraint. Reversible electric-field control and manipulation of this magnetic moment at room temperature is also shown.

Abstract. Double perovskites Sr 2 BOsO 6 (B = Y, In, and Sc) were prepared from the respective binary metal oxides, and their structural, magnetic, and electronic properties were investigated. At room temperature all these compounds crystallize in the monoclinic space group P2 1 /n. They contain magnetic osmium (Os 5+ , t 2g 3 ) ions and are antiferromagnetic insulators with Néel temperatures T N = 53 K, 26 K, and 92 K for B = Y, In, and Sc, respectively. Powder neutron diffraction

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The role of transition-metal d and ligand p hybridization continues to be of immense interest in Li-ion battery cathode, and yet it is still poorly understood. Using combined experimental and theoretical soft X-ray absorption spectroscopic study and density functional theory calculation, we investigated the fundamental electronic structure of the high-voltage spinel LiNi x Mn2–x O4. An oxygen-participating charge rebalance between manganese and nickel ions was found; that is, the content of O 2p holes close to the Fermi level increases along with the increasing Ni content. Moreover, these unstable oxygen holes primarily congregate around the redox active dopants. The underlying mechanism accounting for this charge-compensated occurrence is the reverse of two bonding levels when manganese ions are oxidized from +3 to +4 states. On the basis of these new findings, we further exposed the role of oxygen in electrochemical performance. First, oxygen ions afford the charge variation together with the cations during Li insertion/deinsertion process. Second, the O 2p holes can largely screen the strong electrostatic repulsion between Mn4+ and Li+ ions to effectively enhance the rate capacity. Lastly, the excessive amount of O 2p holes is disadvantageous to the thermal stability associated with the O2 evolution. Also, we point out that O 2p holes concentration can be modified by the metal–oxygen bonding character, and the “charge-transfer energy” is a crucial point for designing high-capacity positive electrodes for Li-ion battery.

We observe quasi-static incommensurate magnetic peaks in neutron scattering experiments on layered cobalt oxides La2−xSrxCoO4 with high Co oxidation states that have been reported to be paramagnetic. This enables us to measure the magnetic excitations in this highly hole-doped incommensurate regime and compare our results with those found in the low-doped incommensurate regime that exhibit hourglass magnetic spectra. The hourglass shape of magnetic excitations completely disappears given a high Sr doping. Moreover, broad low-energy excitations are found, which are not centered at the incommensurate magnetic peak positions but around the quarter-integer values that are typically exhibited by excitations in the checkerboard charge ordered phase. Our findings suggest that the strong inter-site exchange interactions in the undoped islands are critical for the emergence of hourglass spectra in the incommensurate magnetic phases of La2−xSrxCoO4.