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A surfactant-assisted ball milling technique was employed to synthesize NdFeB nanoparticles and nanoflakes from melt-spun nanocrystalline powders. The microstructure evolution during ball milling and the particle size dependent magnetic properties were investigated. The formation mechanism of submicrometre flakes and textured nanoflakes were discussed. The surfactant and ball-to-powder weight ratio played a crucial role in the formation of nanoflakes. The coercivity of the particles decreased with decreasing particle size. Significant room temperature coercivity HC higher than 300 kA m-1 was obtained in the nanoparticles with a mean size of ~20 nm. The spin reorientation temperature was found to decrease with reducing particle size, which may be related to the change in magnetocrystalline anisotropy caused by the induced strain during ball milling. [ABSTRACT FROM AUTHOR]

Bi(Fe1-xMgx)O3-x/2 (x = 0-10%) ceramics were synthesized by high-energy ball milling and solid-state reaction. It was found that a small amount of Mg doping leads to a dramatic enhancement in dielectric permittivity (~two orders of magnitude), along with an apparent improvement in ferromagnetism. The observed significant enhanced dielectric properties may be interpreted by the Maxwell-Wagner relaxation in association with internal barrier layer capacitance. The ferromagnetism can be ascribed to the creation of unbalanced Fe3+ spins and relative long-range coupling mediated by the oxygen vacancies trapped localized electrons [ABSTRACT FROM AUTHOR]

FeTaN thin films with uniaxial anisotropy were fabricated by sputtering and patterned into strips with width of 21 µm, separation gap of 10 µm and angular displacement of 0° to 90° from the magnetic easy axis of the unpatterned films. The effective magnetic anisotropy field was effectively modified in both value and direction dependent on the displacement angle. The unpatterned thin films had a maximum permeability of m'[?]700, m''[?]1000 and a ferromagnetic resonance frequency of [?]1.1 GHz. After patterning, the ferromagnetic resonance frequency was found to be ranging from 1 to 1.8 GHz as the angular displacement was varied, indicating that this method is a viable way of tuning the ferromagnetic resonance frequency. These results were well explained according to the well-known Kittel's formula assuming two fold anisotropies in the patterned films. [ABSTRACT FROM AUTHOR]

The thermal stability of nanocrystalline melt-spun Nd/Pr-(Dy)-Fe/Co-B alloy ribbons, defined in terms of the long-term and short-time irreversible losses in remanence and coercivity, has been investigated. Cobalt substitution for iron improves the thermal stability of nanocrystalline (Nd/Pr)-(Fe/Co)-B alloys through reducing both long-term and short-time irreversible losses. Nanocomposite alloys manifest lower long-term irreversible losses than single phase alloys. Dysprosium substitution for (Nd/Pr) also decreases the irreversible losses. It is demonstrated that the magnitudes of the Curie temperature, coercivity, saturation magnetization and the degree of inter-crystalline exchange coupling have important effects on the irreversible losses. [ABSTRACT FROM AUTHOR]

In situ multiphase structure Gd65Mn25Si10 alloys were fabricated by melt spinning and subsequent crystallization treatment. In the process of crystallization, the α-Gd, GdMn2 and Gd5Si3 phases precipitate in the amorphous matrix in turn. The Curie temperature (TC) values for the α-Gd crystallization phase and amorphous matrix can be tailored by tuning the crystallization treatment time. All three multiphase alloys obtained by crystallization treatment at 637 K for 20, 30 and 40 min, respectively, undergo multiple successive magnetic phase transitions. A table-like magnetic entropy change over a wide temperature range (~90–120 K) and a large full width at half maximum (ΔTFWHM) magnetic entropy change (~230 K) were achieved in the above-mentioned crystallized alloys, resulting in large refrigerant capacities (RCs). The enhanced RCs of the three crystallized alloys for a magnetic field change of 0–5 T are in the range of 541–614 J kg−1. Large ΔTFWHM and RC values and a table-like (−ΔSM)max feature obtained in in situ multiphase Gd65Mn25Si10 crystallized alloys make them suitable for potential application in efficient Ericsson-cycle magnetic refrigeration working in a temperature range from 74 to 310 K. [ABSTRACT FROM AUTHOR]

Metal oxide nanowires (NWs) can be easily grown by the thermal oxidation method, but the low adhesion between the NWs and the substrate restricts their practical applications in functional devices. In this work, the conventional hotplate technique is simply modified by introducing one or two stainless steel plates to supply a more stable oxidation environment, which is found to be beneficial to the growth and adhesion of CuO NWs on the Cu substrate. In detail, the Cu foils were heated on the hotplate directly, on one plate over the hotplate, and between two plates over the hotplate at 400 °C in ambient condition. It is found that the NWs obtained between two plates exhibit large length and diameter with moderate density. The sufficient activated oxygen, stable temperature, and proper temperature gradient configuration caused by the two plates accelerate the formation of CuO NWs, and result in the longest NWs with enhanced adhesion. The grain-boundary diffusion and Kirkendall effect are proposed to explain the mechanism of NWs growth and the formation of cracks. The NWs obtained between two plates also showed the best field emission properties, with lowest turn-on field (5.31 V μm−1) and threshold field (9.8 V μm−1). Excellent field emission properties and enhanced NW-substrate adhesion indicate that these NW arrays could be potentially used as the cathode of field emission displays. [ABSTRACT FROM AUTHOR]

The millimeter-sized Nd9.5Fe61.5Co10Ti2.5Nb0.5B16−xCx (x  =  0–1.25) alloy rods with various compositions were fabricated by direct casting. Nano-sized hard phase Nd2(FeCo)14B, soft phase ɑ-FeCo, and amorphous phase were observed in all alloys. An optimized amount of carbon additions improved the magnetic properties by enhancing the glass forming ability and forming near single domain-sized Nd2(FeCo)14B grains around the rod surface. Various intergranular structures were observed in the alloys with x  =  0.25–1. Micromagnetic simulation using the images obtained from the magnetic force microscope and transition electron microscope indicates that the distribution and magnetism of the intergranular phase have an important influence on the magnetic properties and demagnetization process of the alloys. A uniformly distributed nonmagnetic intergranular amorphous phase may enhance the magnetic properties, but the coercivity decreases when the amorphous phase is magnetic. It is important to modify the structure and distribution of the inter-grain amorphous phase in order to achieve high hard magnetic properties in these alloys. [ABSTRACT FROM AUTHOR]

The basic principle of the artificial periodic lattice phase analysis method on the basis of an artificial periodic lattice was thoroughly introduced in this investigation. The improved technique is intended to expand from nanoscale to micro- and macroscopic realms on the test field of experimental mechanics in combination with a submicron grid, which is produced by a focused ion beam (FIB). Phase information can be obtained from the filtered images after fast Fourier transform (FFT) and inverse FFT. Thus, the in-plane displacement fields as well as the local strain distributions related to the phase information will be evaluated. The application scope of the technique was obtained by the simulation experiment. The displacement fields as well as strain distributions of porous TiNi shape memory alloy were calculated by the technique after compressive loading in micro scale. The specimen grid was directly fabricated on the tested flat surface by employing a FIB. The evolution rule of shear zones in micro area near porous has been discovered. The obtained results indicate that the technique not only could be well applied to measuring full field deformation, but also, more significantly, is available to present mechanical properties in micro scale. [ABSTRACT FROM AUTHOR]

Partially inverse spinel CoFe2O4, which may be prepared through various heat treatments, differs remarkably from the ideal inverse spinel in many properties. The structure of partially inverse spinel CoFe2O4 as well as its electronic and magnetic properties through a systemic theoretical calculation of (Co1[?]xFex)Tet(CoxFe2[?]x)OctO4 (x = 0, 0.25, 0.5, 0.75 and 1.0) have been investigated by the generalized gradient approximation (GGA) + U approach. It is found that the Co and Fe ions prefer their high spin configurations with higher spin moments at octahedral sites in all the studied cases, in line with experimental observations. The Co ions at the octahedral sites favour being far away from each other in the partial inverse spinels, which also show half metallicity at certain inversion degrees. [ABSTRACT FROM AUTHOR]

Quantitative evaluation of the structure deformation of microfabricated electromechanical systems is of importance for the design and functional control of microsystems. In this investigation, a novel digital geometric phase technique was developed to meet the deformation evaluation requirement of microelectromechanical systems (MEMS). The technique is performed on the basis of regular artificial lattices, instead of a natural atom lattice. The regular artificial lattices with a pitch ranging from micrometer to nanometer will be directly fabricated on the measured surface of MEMS devices by using a focused ion beam (FIB). Phase information can be obtained from the Bragg filtered images after fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) of the scanning electronic microscope (SEM) images. Then the in-plane displacement field and the local strain field related to the phase information will be evaluated. The obtained results show that the technique can be well applied to deformation measurement with nanometer sensitivity and stiction force estimation of a MEMS device. [ABSTRACT FROM AUTHOR]

Double-layered Ni-Co1[?]xFex hollow microspheres with a mean size of [?]1 µm were fabricated by electroless plating of Co or Co-rich CoFe films on Ni hollow spheres (HS); the latter was synthesized by an autocatalytic reaction process. The Ni HS have a microstructure consisting of both fcc and hcp phases and have a very low coercivity. Coating a layer of Co leads to a high coercivity due to the formation of the hcp Co phase with high magnetocrystal anisotropy. Addition of 10% Fe into the Co layer decreases the coercivity from 432 to 140 Oe by transforming the hcp Co phase to the fcc CoFe phase; the latter has a low anisotropy field. Addition of 20% Fe results in a further decrease in coercivity to 69 Oe due to the formation of the bcc CoFe phase. The microwave properties of the composites consisting of HS and a polymer were investigated. Ni HS + a polymer composite have high permittivity but relatively low permeability. Co or CoFe coating decreases the permittivity but slightly increases the permeability of the composite. A reflection loss of <20 dB is obtained for the CoFe coated hollow Ni microspheres with an absorber thickness of 1.5-3.0 mm. [ABSTRACT FROM AUTHOR]