Left-handed properties dependence versus the interwire distance in Fe-based microwires metastructures

Experimental and theoretical investigations on the left-handed properties dependence versus the interwire distance of three new proposed Fe77.5Si7.5B15 glass coated microwires-based metastructures are presented. The left-handed characteristics of the metastructures were determined in the frequency range 8.2 ÷ 12 GHz and external d.c. magnetic fields ranging from 0 to 32 kA/m. The experimental results show that the electromagnetic losses of the metastructures increase with the decreasing of the interwire distance due to the increasing of the long-range dynamic dipole-dipole interaction within inter-wires in the presence of the microwave field. The numerical calculations using Nicolson–Weiss–Ross algorithm are in agreement with the experimental results. The variation of the interwire distance proves to be a useful tool to obtain metastructures with controlled left-handed characteristics

Novel Heterostructures of Noble Plasmonic Metals/Ga-Substituted Hydrotalcite for Solar Light Driven Photocatalysis toward Water Purification

Heterostructures formed by close conjunctions of plasmonic metal nanoparticles and non-plasmonic (2D) lamellar nanostructures are receiving extensive interest as solar-light-driven photocatalysts for environmental pollutant remediation. Herein, the conjunction of plasmonic Au or Ag and Ga-substituted hydrotalcite are obtained by exploiting the manifestation of the structural “memory effect” of Ga-substituted hydrotalcite in the aqueous solutions of Au(CH3COO)3 and Ag2SO4, respectively. The 2D layered matrix of MgGaAl plays a dual function; it is involved in the synthesis of the plasmonic metal nanoparticles, and further, is acting as a support. The compressive investigations using X-ray diffraction (XRD), UV-diffuse reflectance spectroscopy (UVDR), infrared spectroscopy (FT-IR), transmission electron microscopy (TEM/HRTEM), high-angle annular dark-field imaging/scanning transmittance electron microscopy (HAADF/STEM) and X-ray photoelectron spectroscopy (XPS) describe structural, composition and nano/micromorphology characteristics of the novel heterostructures, while UVDR analysis afforded to study the features of their plasmonic responses. Results reveal that the catalysts are formed by close conjunction of small nanoparticles of Au or Ag (with a mean size less than 20 nm) that are formed on the larger particles of MgGaAl and own plasmonic features within the visible range. The catalysts performances were tested towards photocatalytic degradation of p-dichlorobenzene and 4-nitrophenol under solar light irradiation. Results revealed that the degradation of the pollutants is entangled to the plasmonic response of the heterostructured catalysts that is the key functionality in promoting photocatalysis and degrading the pollutants, under solar light irradiation. MgGaAl showed a very low photocatalytic activity when irradiated by UV or solar light. Notably, the heterostructured catalysts proceeded in good to excellent yield to remove the tested pollutants, under solar light irradiation. The sustainability of the novel catalysts was assessed through the kinetic analysis of the degradation processes of the tested pollutants and their mixture

Soft ferromagnetic bulk metallic glass with potential self-healing ability

A new concept of soft ferromagnetic bulk metallic glass (BMG) with self-healing ability is proposed. The specific [Fe36Co36B19.2Si4.8Nb4]100−x(Ga)x (x = 0, 0.5, 1 and1.5) BMGs prepared by copper mold casting were investigated as a function of Ga content. The Ga-containing BMGs still hold soft magnetic properties and exhibit large plastic strain of 1.53% in compression. Local melting during shearing produces molten droplets of several µm size throughout the fracture surface. This concept of local melting during shearing can be utilized to produce BMGs with self-healing ability. The molten regions play a vital role in deflecting shear transformation zones, thereby enhancing the mechanical properties.ISSN:1996-194

Innovative Method for the Mass Preparation of α″-Fe₁₆N₂ Powders via Gas Atomization

The iron nitride materials, especially α″-Fe16N2, are considered one of the most promising candidates for future rare-earth-free magnets. However, the mass production of α″-Fe16N2 powders as a raw material for permanent magnets is still challenging. In this work, starting from iron lumps as a raw material, we have managed to prepare the α″-Fe16N2 powders via the gas atomization method, followed by subsequent nitriding in an ammonia–hydrogen gas mixture stream. The particle size was controlled by changing the gas atomization preparation conditions. X-ray diffractograms (XRD) analyses show that the prepared powders are composed of α″-Fe16N2 and α-Fe phases. The α″-Fe16N2 volume ratio increases with decreasing powder size and increasing nitriding time, reaching a maximum of 57% α″-Fe16N2 phase in powders with size below 32 ± 3 μm after 96 h nitridation. The saturation magnetization reaches the value of 237 emu/g and a reasonable coercivity value of 884 Oe. Compared to the saturation magnetization values of α-Fe powders, the α″-Fe16N2 powders prepared through our proposed approach show an increase of up to 10% in saturation and demonstrate the possibility of mass production of α″-Fe16N2 powders as precursors of permanent magnets without rare earths

Ultrathin Nanocrystalline Magnetic Wires

The magnetic characteristics of FINEMET type glass-coated nanowires and submicron wires are investigated by taking into account the structural evolution induced by specific annealing all the way from a fully amorphous state to a nanocrystalline structure. The differences between the magnetic properties of these ultrathin wires and those of the thicker glass-coated microwires and “conventional” wires with similar structures have been emphasized and explained phenomenologically. The domain wall propagation in these novel nanowires and submicron wires, featuring a combination between an amorphous and a crystalline structure, has also been studied, given the recent interest in the preparation and investigation of new materials suitable for the development of domain wall logic applications

Effect of Nonmagnetic Hf Addition on Magnetic Properties of Melt-Spun Misch Metal-Fe-B Ribbons

Misch Metal (MM)-Fe-B magnets are proposed to develop permanent magnets with a high performance/cost ratio and to balance the disproportionate use of rare earth (RE) resources. To improve the magnetic performance of (MM)-Fe-B ribbons precursors of magnets, the addition of non-magnetic hafnium (Hf) was used. MM14Fe80−xHfxB6 (x = 0–3 at. %) ribbons were fabricated by melt-spinning technique at a wheel velocity of 35 m/s and were then annealed to obtain a nanocrystalline structure. The ribbons’ magnetic properties, morphology, and structure were investigated methodically. It was found that the coercivity, Hc, of the MM14Fe80−xHfxB6 (x = 0–3 at. %) as-spun ribbons increased significantly from 5.85 kOe to 9.25 kOe with an increase in the Hf content from 0 to 2 at. %, while the remanence decreased slightly for the whole 0–3 range at. % Hf. The grain size of the RE2Fe14B phase gradually decreased as the Hf addition content increased from 0 to 3 at. %. As a result, the best combination of magnetic properties, such as Hc = 9.25 kOe, Mr = 87 emu/g, and maximum energy product (BH)max = 9.75 MGOe, was obtained in the ribbons with 2 at. % Hf addition was annealed at an optimal temperature of 650 degrees Celsius for 20 min. This work can serve as a useful reference for the further development of a new permanent magnet based on MM and Hf elements and can provide a feasible way for the efficient use of rare earth resources

A comparative study of the Co-based amorphous alloy prepared by mechanical alloying and rapid quenching

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