High-performance Mn-rich P2-phase Na2/3Mn0.8Fe0.1Ti0.1O2 is synthesized by a ceramic method, and its stable electrochemical performance is demonstrated. 23Na solid-state NMR confirms the substitution of Ti4+ ions in the transition metal oxide layer and very fast Na+ mobility in the interlayer space. The pristine electrode delivers a second charge/discharge capacity of 146.57/144.16 mA·h·g–1 and retains 95.09% of discharge capacity at the 50th cycle within the voltage range 4.0–2.0 V at C/10. At 1C, the reversible specific capacity still reaches 99.40 mA·h·g–1, and capacity retention of 87.70% is achieved from second to 300th cycle. In addition, the moisture-exposed electrode reaches reversible capacities of more than 130 and 80 mA·h·g–1 for C/10 and 1C, respectively, with excellent capacity retention. The correlation between overall electrochemical performance of both electrodes and crystal structural characteristics are investigated by neutron powder diffraction. The stability of pristine electrode’s crystallographic structure during the charge/discharge process has been investigated by in situ X-ray diffraction, where only a solid solution reaction occurs within the given voltage range except for a small biphasic mechanism occurring at or below 2.2 V during the discharge process. The relatively small substitution (20%) at the transition metal site leads to stable electrochemical performance, which is in part derived from the structural stability during electrochemical cycling. Therefore, the small cosubstitution (e.g., with Ti and Fe) route suggests a possible new scope for the design of sodium-ion battery electrodes that are suitable for long-term cycling.

The origin of the room-temperature ferromagnetism (RTF) in ZnO-based dilute magnetic semiconductors remains controversial. We experimentally demonstrate here that it is possible to induce RTF in ball milled (ZnO)1−x/Alx without any ferromagnetic dopant. Our work shows that RTF in (ZnO)1−x/Alx (x=0–0.5) can be realized simply by milling a mixture of high purity ZnO and Al fine powders for 8 h. The spontaneous magnetization of the milled powders is found to increase by annealing under a reduced pressure. The magnetization value depends highly on both the ratio of Al to ZnO and the annealing temperature. X-ray photoelectron spectroscopy results have revealed that the Zn2+ ions in (ZnO)1−x/Alx are partially reduced into a lower ionic state. As there are no magnetic impurities present in our samples, the origin of ferromagnetism is most likely to be due to the charge transfer between Zn and Al at the interfaces of the ball milled nanograins. Our results reinforce the significant role played by the alterations of the electronic structures in the RTF of ZnO.

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The present study reports on the origins of room temperature ferromagnetism in zinc oxide (ZnO)-Al nanoparticles using a combination of X-ray absorption near edge structure (XANES) experiments and density functional theory (DFT) simulations. Our findings reveal that the spontaneous magnetization observed in these systems originates from the adsorption of Al on surfaces of ZnO nanoparticles. Our DFT simulations have identified unique configurations for Al adsorption on ZnO surfaces that lead to a spin-polarized charge transfer to O 2p states in surface and subsurface layers. XANES spectra of the magnetic ZnO/Al nanoparticles provide the necessary experimental evidence for the charge transfer to ZnO surfaces and confirm the origin of ferromagnetic behavior. Our results illustrate a complex interplay between the atomic level interfacial structure and the resulting ferromagnetic ordering in metal-coated semiconductor oxide nanostructures.

The magnetic domains of nanocrystalline Fe84Nb6B10 annealed under static and rotating magnetic fields have been investigated by means of magneto-optical Kerr effect (MOKE) microscopy in order to clarify the origin of the dramatic magnetic softening brought about by rotating field annealing. The coercivity (Hc) values after static- and rotating-magnetic field annealings are 5.9 and 3.0A∕m, respectively. The MOKE image after static field annealing implies a highly coherent uniaxial anisotropy (Ku) in the sample whereas no sign of such a strong Ku is evident in the domain configuration after rotating field annealing. Our analytical solution of the random anisotropy model with additional Ku predicts that the fluctuating amplitude of the effective anisotropy (δK) in nanocrystalline Fe84Nb6B10 decreases from 20to11J∕m3 by removing Ku. The observed reduction of Hc may be attributed to this decrease in δK induced by rotating field annealing.