Room-temperature ferromagnetic organic magnets derived from fluoro-graphite via facile halide exchange

Room-temperature ferromagnetic organic magnet is developed via a facile halide exchange process using fluoro-graphite (FG) as a starting material. Structural and chemical analysis reveals that heterogeneous C–F bond cleavage in the defect sites of FG is essentially related to the formation of ferromagnetic hydroxyl-graphene (HG). Pyrolysis of FG in a polar solvent with iodine ions induces a formation of metastable C–I bond and subsequent replacement of the I sites with the hydroxyl groups. Specifically, defective sites can be formed in FG due to nucleophile attack where the OH groups can be easily generated. As a result, the FG can be transformed into the HG with a network of sp²-conjugated carbon motifs in a sp³-based graphene matrix. Hence, the paramagnetic centers in the π-electron system of FG can be transformed to the long-range ordered ferromagnetic centers in the sp²-conjugated system of HG. Electron paramagnetic resonance data demonstrate the weak ferromagnetic property of HG stable at room temperature.     

Microstructure,optical and magnetic properties of TiO2/CuO nanocomposites synthesized by a two-step method

TiO₂/CuO composites in different ratios were prepared via a two-step method. X-ray diffraction and transmission electron microscopy results indicated that part of Cu²⁺ substituted Ti⁴⁺ in the TiO₂ lattice in the composite, leading to Cu²⁺-substituted sites in the TiO₂ lattice as well as Cu²⁺ species located in the CuO lattice. Scanning electron microscopy revealed a morphology change in the sample from a three-dimensional structure to a two-dimensional structure while forming an interface between TiO₂ and CuO. X-ray photoelectron spectroscopy and Raman spectra showed that there are oxygen vacancies (V_O) and Ti³⁺ in the lattice. UV–vis absorption spectra exhibited a widening of the absorption range and a decrease in the bandgap with increasing amount of CuO in the TiO₂/CuO composites. Additionally, the composites exhibited room-temperature ferromagnetism (RTFM), as can be explained by the indirect double-exchange model, which is related to V_O and the exchange interaction between the 3d orbitals of Ti³⁺ and Ti⁴⁺ at the interface.     

反置结构ZnO微米级圆晶的制备和性能研究

利用全自动化功能磁控溅射技术在硅/PS(聚苯乙烯)胶体球模板上制备了具有室温铁磁性和紫外发光特性的两种ZnO微米级圆晶。采用SEM、XRD、PL和VSM对样品进行了表征。结果表明:在PS胶体球去除方法上采用略有不同工艺制备的六边形和反置六边形结构ZnO微米级圆晶均具有(002)择优取向,晶粒大小分别为21.7nm和26.5nm,应力分别为3.26×109 Pa和-1.21×109 Pa,均出现361nm和444nm两个发光峰。两种结构ZnO阵列的铁磁性有所不同,可能是缺陷不同引起的。     

Robust Room Temperature Ferromagnetism In Cobalt Doped Graphene by Precision Control of Metal Ion Hybridization

Graphene-based magnetic materials exhibit novel properties and promising applications in the development of next-generation spintronic devices. Modern synthesis techniques have paved the way to design precisely the local environments of metal atoms anchored onto a nitrogen-doped graphene matrix. Herein, it is demonstrated that grafting cobalt (Co) into the graphene lattice induces robust and stable room-temperature ferromagnetism. These comprehensive experiments and first-principles calculations unambiguously identify that the mechanism for this unusual ferromagnetism is π-d orbital hybridization between Co d_xz and graphene p_z orbitals. Here, it is found that the magnetic interactions of Co–carbon ions are mediated by the spin-polarized graphene p_z orbitals, and room temperature ferromagnetism can be stabilized by electron doping. It is also found that the electronic structure near the Fermi level, which sets the nature of spin polarization of graphene p_z bands, strongly depends on the local environment of the Co moiety. This is the crucial, previously missing, ingredient that enables control of the magnetism. Overall, these observations unambiguously reveal that engineering the atomic structure of metal-embedded graphene lattices through careful d to p orbital interactions opens a new window of opportunities for developing graphene-based spintronics devices.     

Proximity Coupling of Graphene to a Submonolayer 2D Magnet

Imprinting magnetism into graphene may lead to unconventional electron states and enable the design of spin logic devices with low power consumption. The ongoing active development of 2D magnets suggests their coupling with graphene to induce spin-dependent properties via proximity effects. In particular, the recent discovery of submonolayer 2D magnets on surfaces of industrial semiconductors provides an opportunity to magnetize graphene coupled with silicon. Here, synthesis and characterization of large-area graphene/Eu/Si(001) heterostructures combining graphene with a submonolayer magnetic superstructure of Eu on silicon are reported. Eu intercalation at the interface of the graphene/Si(001) system results in a Eu superstructure different from those formed on pristine Si in terms of symmetry. The resulting system graphene/Eu/Si(001) exhibits 2D magnetism with the transition temperature controlled by low magnetic fields. Negative magnetoresistance and the anomalous Hall effect in the graphene layer provide evidence for spin polarization of the carriers. Most importantly, the graphene/Eu/Si system seeds a class of graphene heterostructures based on submonolayer magnets aiming at applications in graphene spintronics.     

Mechanism-based tuning of room-temperature ferromagnetism in Mn-doped β-Ga2O3 by annealing atmosphere

Mn-doped β-Ga₂O₃ (GMO) films with room-temperature ferromagnetism (RTFM) are synthesized by polymer-assisted deposition, and the effects of annealing atmosphere (air or pure O₂ gas) on their structures and physical properties are investigated. The characterizations show that the concentrations of vacancy defects and Mn dopants in various valence states and lattice constants of the samples are all modulated by the annealing atmosphere. Notably, the samples annealed in air (GMO–air) exhibit a saturation magnetization as strong as 170% times that of the samples annealed in pure O₂ gas (GMO–O₂), which can be quantitatively explained by oxygen vacancy (V_O)-controlled ferromagnetism due to bound magnetic polarons established between delocalized hydrogenic electrons of V_Os and local magnetic moments of Mn²⁺, Mn³⁺, and Mn⁴⁺ ions in the samples. Our results provide insights into mechanism-based tuning of RTFM in Ga₂O₃ and may be useful for design, fabrication, and application of related spintronic materials.     

γ-irradiation hardness investigations of (PANI)1−x(Bi2Te3)x composites for thermistor applications

The (PANI)_1−x(Bi₂Te₃)_x composites were successfully synthesized. These composites have a simple physical combination of intrinsic conducting polymer and nanocrystal topological insulator materials which are promising new materials for unusual applications. The influence of γ-irradiation (100 kGy doses) on the performance of the (PANI)_1−x(Bi₂Te₃)_x composites was described by atypical techniques to assess the radiation hardness of the samples. X-ray diffraction and Raman spectroscopy measurements show the semi-crystalline phases, the other structural parameters, and the phonon modes. The compositional analysis and the morphological properties were investigated by energy-dispersive X-ray, while transmission electron microscopy imaging confirmed the morphology of the dopants of Bi₂Te₃ nanoparticles into the polyaniline (PANI) matrix, which shows the accumulation of the particles. Thermogravimetric analysis figured out the degradation behavior of the compositions. The representative electron spin resonance (ESR) signal exhibits a narrow single-line ESR spectrum for PANI/Bi₂Te₃ nanoparticle concentrations. (PANI)_1−x(Bi₂Te₃)_x illustrates unexpected ferromagnetic behavior that confirms the magnetic performance of the samples without introducing any magnetic dopants. The obtained materials showed promising performance for using such hybrid materials as a positive temperature coefficient thermistor.