Physical properties of microwave and solid state synthesized La0.7Na0.3MnO3

We report the structural, magnetic, electrical and broadband microwave absorption in La_0.7Na_0.3MnO₃ sample synthesized by microwave (MW) irradiation (Na_0.3LMO_MW) and compare them to the sample synthesized by solid-state (SS) reaction method (Na_0.3LMO_SS). Single phase Na_0.3LMO_MW was synthesized at 800 °C in 30 min, whereas, Na_0.3LMO_SS sample was obtained by sintering at 1200 °C for 48 h. Although both these samples show ferromagnetic transition at T_C ～324.8 K, the MW-synthesized sample shows distinct physical properties: broad ferromagnetic transition, smaller saturation magnetization, a large difference between the magnetic ordering and metal-insulator transition temperatures, a large high-field magnetoresistance, a table top-like magnetocaloric effect, and a large low-field microwave absorption compared to the solid state synthesized sample. These differences are suggested to arise from magnetic heterogeneity induced by smaller grain size and surface spin disorder in the MW synthesized La_0.7Na_0.3MnO₃.     

铁磁谐振的防止与加装消谐PT的接线分析

电磁式电压互感器由于铁芯的非线性特点,在饱和时激磁电流增加,励磁电抗急剧下降,存在着与系统分布容抗产生铁磁谐振的可能。这里分析了产生铁磁谐振的条件及其防止铁磁谐振的办法,介绍了加装消谐电压互感器的办法和相应的接线形式。     

Magnetic and structural properties of ion beam sputtered Fe-Zr-Nb-B-Cu thin films

Magnetic and structural properties of Fe-Zr-Nb-B-Cu thin films, prepared by ion beam sputtering on silicon substrates by using a target made up of amorphous ribbons of nominal composition Fe₈₄Zr_3.5Nb_3.5B₈Cu₁, are reported. As-deposited thin film samples exhibit an in-plane uniaxial anisotropy, which can be ascribed to the preparation technique and the coupling of quenched-in internal stresses. Structural measurements indicate no significant variation of the grain size with thickness and with the annealing temperature. Increase in surface irregularities with annealing temperature and oxidation results in aggregates that would act as pinning centers, affecting the magnetic properties leading to magnetic hardening of the specimens. The role of the magnetic anisotropy is thoroughly discussed with the help of magnetic and ferromagnetic resonance measurements.     

Solution- and air-recoverable photocatalytic nanofibers by facile and cost-effective electrospinning and co-precipitation processes

While nanostructured materials are of particular academic and practical interest, their recoverability and recyclability have been of paramount industrial and environmental concerns. In the present contribution, co-precipitation was demonstrated as a facile and cost-effective approach to incorporate magnetic sensitivity and enhance the recoverability of nanofibrous materials which were frequently utilized in catalysis, energy and medical applications, etc. In particular, reusable magnetic and photocatalytic hybrid nanofibers were generated by electrospinning and co-precipitation method. First, TiO₂ nanofibers were prepared through sol-gel reaction and electrospinning process. To improve their recoverability, CoFe₂O₄ nanoparticles were decorated onto the nanofibers' surfaces via co-precipitation of cobalt and iron ions in the presence of the nanofibers suspension. Furthermore, the resulting CoFe₂O₄-decorated TiO₂ nanofibers maintained their photocatalytic activity after the modification. When suspended in a solution or spread on a dried surfaces, these nanofibers could be recollected with a magnet. These findings suggested that incorporation of ferromagnetic into the nanofibers maintained their photocatalytic performance and reduced production cost as well as the risk of human and environmental exposure through solution and air.     

金属磁记忆检测技术的研究现状及发展

介绍金属磁记忆检测技术对铁磁构件疲劳失效和早期诊断的重要意义。通过分析比较,描述了金属磁记忆检测技术的独到优点、金属磁记忆检测机理以及检测仪器。重点介绍了目前金属磁记忆机理研究现状和国内外该技术的应用现状并给出了两个实例分析。最后,总结了金属磁记忆检测技术目前存在的问题和未来的发展方向。     

Synthesis and ferromagnetic property of new binary copper iron pyrophosphate CuFeP2O7

The pyrophosphate of CuFeP₂O₇ was synthesized through one step-thermal synthesis at 500 °C using the mixing of copper carbonate, iron metals and phosphoric acid. FTIR and XRD results indicate the dominant feature of pyrophosphate (P₂O₇⁴⁻) anion and a pure monoclinic phase with space group C_2h⁶ (Z = 4), respectively. The crystallite size of 25 ± 9 nm for the CuFeP₂O₇ was estimated by X-ray line broadening. Room temperature magnetization result shows ferromagnetic behavior of the CuFeP₂O₇ powder, having hysteresis loop in the range of ± 10,000 Oe with the specific magnetization value of 1.57 emu g^− 1. This property is important for specific application and is presented for the first time.     

Magneto-Mechanical Finite Element Analysis of Single Crystalline Ni2MnGa Ferromagnetic Shape Memory Alloy

Based on an existing micromechanical constitutive model for Ni2MnGa ferromagnetic shape memory alloy single crystals, a three-dimensional quasi-static isothermal incremental constitutive model that is suitable for finite element analysis is derived by using Hamilton's variational principle. This equation sets up the coupling relation between the magnetic vector potential and the mechanical displacement. By using the incremental equation and ANSYS software, the mechanical behaviors of martensitic variant reorientation for Ni2MnGa single crystals are analyzed under magneto-mechanical coupling action. And the finite element results agree well with the experimental data. The methods used in the paper can well describe the mechanical behaviors of the material in complex fields.     

Structural and magnetic characterization of cobalt implanted GaN films

Cobalt ions were implanted into GaN films with multiple energies between 50 keV and 380 keV with two total fluences, 1.25 × 10¹⁶ and 1.25 × 10¹⁷ cm⁻², followed by annealing at temperatures between 600 and 850 °C. The crystal quality and surface morphology of as-implanted and subsequently annealed films were investigated by X-ray diffraction (XRD) 2θ scans, ω-rocking curve measurements and atomic force microscopy (AFM). The profiles of impurities and defects were analyzed by Rutherford backscattering spectrometry (RBS) in random and channeling configurations. The virgin GaN films have an excellent crystal quantity (χ_min = 1.4%) and in the implanted samples 60% disorder induced by ion implantation was recovered after annealing. The annealed sample become ferromagnetic, with a spontaneous magnetization of 0.1 emu/g and a coercive magnetic field of 100 Oe at 10 K, and the Curie point was found to be higher than room temperature.     

Characterization and properties of ferromagnetic shape memory alloys

Ni–Mn–Ga shape memory alloys are employed for applications in actuators and sensing devices. These alloys exhibit ferromagnetic shape memory effect with large reproducible strains in moderate magnetic fields. This work presents a study of the effect of composition and annealing treatment on the microstructure and magnetic properties in Mn-rich off-stoichiometric Ni–Mn–Ga alloys. Modulated martensitic structure (c/a < 1) with hierarchical twins was found at room temperature in alloys with Mn ≥ 28 at.% whereas the alloy containing higher Ga (> 22 at.%) revealed austenitic structure at room temperature. Ferromagnetic nature of the alloys was confirmed by the magnetization curves. It is demonstrated that a maximum of 400 parts per million strain was measured in the alloy with 7 M martensitic structure at room temperature.