Enhanced magnetic properties of cobalt nanoparticles on FeMn films

Monodisperse cobalt nanoparticles are synthesized by the thermal decomposition of Co₂(CO)₈ in phenyl ether and subsequently deposited on antiferromagnetic (AFM) FeMn films and glass substrates, respectively. Magnetic measurement shows that the as-prepared Co nanoparticles are superparamagnetic and can be transformed into ferromagnetic (FM) through thermal treatment. While keeping monodisperse, the annealed FM Co nanoparticles on AFM FeMn films show a much larger coercivity than the ones on glass substrates due to FM/AFM exchange coupling. Accordingly, we propose a convenient method to enhance magnetic properties of nanoparticles.     

Facile synthesis of prickly CoNi microwires

Novel prickly CoNi microwires have been successfully synthesized via a hydrothermal synthetic route. The samples prepared at 120 °C for 6 h were made up of large-scale wire-like assemblies with the diameter of about 3 μm and length up to several dozens microns. These wires exhibited hierarchical structure, which was constructed by thornlike crystals with the length of 300-500 nm. The morphology of the wires could be adjusted by the NaOH contents in the system. The magnetic hysteresis measurement revealed that the CoNi microwires displayed ferromagnetic behaviors with a saturation magnetization (Ms) of 83.90 emu/g and a coercivity (Hc) of 119.1 Oe.     

Microstructure, martensitic transformation and superelasticity of Ti49.6Ni45.1Cu5Cr0.3 shape memory alloy

The aim of this study is to investigate the microstructure, martensitic transformation behavior, shape memory effect and superelastic property of Ti_49.6Ni_45.1Cu₅Cr_0.3 alloy, with Cu and Cr substituting for Ni. After annealing, the alloy showed single step A-M/M-A transformations within the whole annealing temperature range of 623 K to 1273 K even in the presence and Ti₂(Ni, Cu) precipitates. With the increase of the annealing temperature, the transformation temperatures exhibited three stages: increasing from 623 K to 873 K, decreasing from 873 K to 1023 K and unchanging from 1023 K to 1273 K. Meanwhile, the critical stress for stress induced martensitic (SIM) transformation decreased to a minimum value and increased after that, exhibiting a V shape curve. The alloy annealed at 623, 773 and 923 K exhibited shape recovery ratio more than 90% when the deformation strain was below 20%.     

Solution assisted laser ablation synthesis of discrete aluminum nanoparticles

Discrete aluminum nanoparticles with an average particle size of 21 nm have been prepared by laser ablation of a metallic aluminum target submerged in dry tetrahydrofuran in the presence of 0.001 M oleic acid as a stabilizing ligand. The particles display high solubility and minimal aggregation while the absence of oleic acid leads to highly aggregated particles and a broader particle size distribution. O/Al ratios obtained from EDS analysis suggest that the particles produced are primarily metallic aluminum with minimal oxide content.     

Microwave-assisted synthesis and magnetic studies of cobalt oxide nanoparticles

An efficient microwave-assisted route has been used to synthesize nanoparticles of cobalt oxide. The particles were well characterized by transmission electron microscopy (TEM) which showed that the average diameter of the particles is around 6 nm. X-ray diffraction (XRD) studies further confirmed the formation of the spinel Co₃O₄. Purity of the products was detected by Fourier transform infrared spectroscopy (FTIR) combined with thermal gravimetric analysis (TG/DTG). The magnetic measurements revealed a small hysteresis loop at room temperature indicating a weak ferromagnetic nature of the synthesized Co₃O₄ nanoparticles. The magnetic moment of the particles was measured to be 4.27 μ_eff.     

Femtosecond laser synthesis of bimetallic Pt-Au nanoparticles

Bimetallic Pt-Au nanoparticles were successfully synthesized by irradiating the metal precursor solution with high intensity femtosecond laser. The intense optical field created by femtosecond laser pulse induced the production of highly charged ions and molecules due to the optical decomposition of metal precursor molecules. Further collisions with molecules result in subsequent growth of the nuclei and codeposition of Pt and Au atoms on the nuclei to form the larger ones. The method is a simple, easy-to-control and environmentally benign process. The average size and morphology of bimetallic nanoparticles were examined by transmission electron microscope. The compositional distributions of Pt and Au of individual Pt-Au nanoparticles were examined by X-ray energy dispersive spectroscopy (EDS).     

High-temperature strength-coercivity balance in a FeCo-based soft magnetic alloy via magnetic nanoprecipitates

Precipitation strengthening is an effective approach to enhance the strength of soft magnetic alloys for applications at high temperatures,while inevitably results in deterioration in coercivity due to the pinning effect on the domain wall movement.Here,we realize a good combination of high-temperature strength and ductility (ultimate tensile strength of 564 MPa and elongation of ～ 20 ％,respectively) as well as low coercivity (6.97 Oe) of FeCo-2V-0.3Cr-0.2Mo soft magnetic alloy through introducing high-density magnetic nanoprecipitates.The magnetic nanoprecipitates are characterized by FeCo-based phase with disordered body-centered cubic structure,whichenables the alloy to have a low coercivity.In addition,these nanoprecipitates can impede the dislocation motion and suppress the brittle fracture,which lead to a high tensile strength and ductility.This work provides a guideline to enhance strength and ductility while maintaining low coercivity in soft magnetic alloys via magnetic nanoprecipitates.     

End-closed NiCoFe-B nanotube arrays by electroless method

A novel approach is obtained during the fabrication of NiCoFe-B nanotube arrays via electroless method. Porous anodic aluminum oxide (AAO) templates fabricated by anodization of aluminum foil were sensitized using PdCl₂ solution and immersed into electroless plating baths at room temperature to produce nanotube arrays. Compositional and morphological properties of the nanotube arrays are characterized. Results indicates the formation of end-closed nanotubes with the dimension of 100-130 nm in outside diameter, which is determined by the pore size of the AAO template, and about 15 nm in thickness of tube walls. The possible formation mechanism of end-closed metallic nanotube arrays is discussed.     

Viscous feature of Sb-Bi alloy under magnetic field

Viscosity of SbBi melts under different magnetic induction intensity was investigated by using RHEOTRONI C VIII torsional oscillation viscometer with 0-0.27 T horizontal magnetic field. The viscosity of all melts measured decreased with increasing temperature under different magnetic intensity. Furthermore, the viscosity increased as horizontal magnetic intensity enhanced. The effect of magnetic induction intensity on the viscosity of melts increased with the content of Sb in the melts. The viscosity-temperature curves can be well fitted with Equation η = η₀ + AB².     

Template electrodeposition to cobalt-based alloys nanotube arrays

Parallel uniform arrays of amorphous ferromagnetic Co₈₁Ni₁₉ and Co₃₇Fe₆₃ alloy nanotubes with outer diameter around 325-365 nm, wall thickness of 30-60 nm and length of over 40 μm were prepared by a direct current electrodeposition with mercury cathode using porous anodic aluminum oxide membrane as template. The morphology, structure, composition and magnetic property were studied. The results showed that mercury cathode is the key factor to form amorphous alloy nanotubes, and the as-prepared nanotube arrays exhibit obvious uniaxial magnetic anisotropy and the easy magnetization direction is perpendicular to the nanotubes axis. The mechanism of formation of Co based alloy nanotubes was also discussed.     

Algorithm for the calculation of the coefficient of thermal expansion of multicomponent metallic alloys

An algorithm for the calculation of temperature dependent bulk properties of multicomponent systems is introduced and illustrated with the calculation of the coefficient of thermal expansion, equilibrium volume, energy of formation and compressibility of Ni-Ti-Nb shape memory alloys.     

Shape and size-controlled synthesis of Ni Zn ferrite nanoparticles by two different routes

Monodisperse Ni–Zn ferrite nanoparticles of different compositions have been synthesized using two different routes, such as sonochemical and polyol methods. In both the cases, the process was attempted in a single reaction in the absence of any surfactant and deoxygenated conditions. X-ray diffraction data on the samples confirmed formation of pure ferrite phase with spinel structure, and indicated that the sonochemical method produces highly crystalline particles compared to the polyol process. Transmission electron microscopy images reveal formation of different shapes, such as cubic, spherical, flower-like and amorphous depending on the method and composition of the ferrite. The magnetic properties of the synthesized Ni–Zn ferrite nanoparticles, measured by vibrating sample magnetometer at room temperature, show that the highest magnetization value was obtained for the composition of Ni_0.5 Zn_0.5 Fe₂O₄ in both the synthesis methods. The results of both the methods were discussed by correlating the structure to the magnetism at nanoscales.     

High-frequency induction soldering of magnesium alloy AZ31B using a Zn−Al filler metal

Magnesium alloy AZ31B plates were soldered by means of high-frequency induction soldering using a Zn−Al filler metal in argon gas shield condition. The interfacial microstructure and phase constitution of the soldered joint were investigated. The experimental results show that α-Mg solid solution and α-Mg + MgZn eutectoid structure were formed in soldering region. Moreover, the zinc solid solution and the aluminum solid solution in the original filler metal disappeared completely after the soldering process. Test results indicate that the shear strength of the soldered joint is 19 MPa. The fracture morphology of the soldered joint exhibits intergranular fracture mode and the crack originates from α-Mg + MgZn eutectoid structure.     

Microstructure and mechanical properties of Mg-Al-Zn alloy under a low-voltage pulsed magnetic field

Effect of a low-voltage pulsed magnetic field on the solidified microstructure and mechanical properties of Mg-Al-Zn alloy has been investigated. When the low-voltage pulsed magnetic field is applied during solidification, the as-cast microstructure is significantly refined and α-Mg is modified from developed dendrite to fine rosette. This morphology modification is caused by the accumulation of Joule heat on the dendrite tip. The yield strength is improved with the application of the low-voltage pulsed magnetic field under normal casting and semi-continuous casting conditions. The ultimate tensile strength is decreased slightly under normal casting condition due to the occurrence of plenty of shrinkage under the low-voltage pulsed magnetic field. The shrinkages are removed and the yield strength and ultimate tensile strength are increased under semi-continuous casting condition with low-voltage pulsed magnetic field.     

Fabrication of oriented arrays of porous gold microsheaths using aligned silver nanowires as sacrificial template

A simple one-step process for preparation of oriented arrays of porous gold microsheaths has been developed by dissolution of sacrificial templates of aligned Ag nanowires in a mixture solution of HAuCl₄ and NaCl at room temperature. The morphology and crystal structure of the product were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Its composition was estimated by energy dispersive X-ray spectroscopy (EDX). The results indicated that the gold microsheaths had generally preserved the original orientation of Ag nanowires and their orientation was robust enough to survive the centrifugal process. The gold microsheaths consist of nanoparticles (ca. 100 nm) that form nanovoids (tens to hundreds of nanometers) between them, giving them a porous nature. Such arrays of well oriented gold microsheaths are expected to show interesting anisotropic optical and electronic properties, and their hollow porous structures might find broad potential applications in surface plasma resonance (SPR), catalysis and chemical sensing.     

Phase transformation and magnetic properties of annealed Fe52.2Co46V1.8 alloy

In this work, FeCoV alloys were annealed in vacuum at various temperatures for different time, with and without applying an external magnetic field, respectively. The effect of the annealing on their magnetic properties has been investigated in regard with microstructural characterizations. X-ray diffraction analysis shows that the alloy is characterized of α-Fe bcc structure. It has been found that an order-disorder phase transformation took place locally in the surface around 993 K. In addition, α-γ phase transformation occurs at the same temperature at which the Curie point is observed in the TG curve. Coercivity is decreased with increasing annealing temperatures, and changed from about 3.2 kA/m to 78 A/m when the annealing temperatures are increased to 1173 K. Microstructural observations show that the decrease of coercivity after annealing is contributed mainly by grain growth. The coercivity of the alloy is further decreased by 32 A/m after magnetic field annealing at 1033 K. Hysteresis loops of the alloys after field annealing at 1033 K featured more rectangular shape with smaller coercivity, compared with those after vacuum annealing.     

Improved microstructure and magnetic properties of iron-cobalt nanowire via an ac electrodeposition with a multistep voltage

Highly ordered porous alumina templates prepared by a two-step anodization are widely utilized as the matrix to assemble nanowires. Usually, an ac electrodeposition with a constant voltage is employed to deposit the metal nanowires on the porous alumina template due to its simple electrodeposition process. However, the nanowires deposited under a constant voltage include many defects in the microstructure, e.g. the hole to weaken its physical properties. Recently, we used an ac electrodeposition with a multistep voltage to deposit a cobalt nanowire with less microstructure defects to enhance its magnetic properties. In this letter, we further investigate the microstructure and magnetic properties of the iron-cobalt nanowire via an ac electrodeposition with a multistep voltage on the porous alumina template. Such a FeCo nanowire has the more uniform crystalline microstructure than that of deposited under a constant voltage and thus the magnetic properties are improved. Our results indicate that an ac electrodeposition with a multistep voltage is an effective way to fabricate the nanowires on the porous alumina template.     

Size controllable synthesis of ultrafine silver particles through a one-step reaction

A simple one-step reduction method was explored to synthesize silver particles of different size. During synthesis, Polyvinylpyrrolidone (PVP) and CH₂O were used as the protective agent and the reducing agent, respectively. It is found that the reaction parameters including the concentration of PVP and AgNO₃, the amount of ammonia and the reaction temperature has great influence on the size and uniformity of silver particles. By careful tuning the reaction parameters, mono-disperse silver particles with the size of 40-2000 nm can be obtained controllably. It is considered that there were two growth modes: diffusional growth and aggregation.     

Structure, magnetic and magnetostrictive properties of Sm0.7Pr0.3Fex alloys

The structure, magnetic and magnetostrictive properties of Sm_0.7Pr_0.3Fe_x (1.45 ≤ x ≤ 1.95) alloys is investigated. X-ray diffraction analysis confirms the presence of single cubic Laves phase in Sm_0.7Pr_0.3Fe_x alloys with 1.45 ≤ x ≤ 1.85. The saturation magnetization of the alloys tends to increase with increasing Fe content. Sm_0.7Pr_0.3Fe_1.55 has the highest magnetostriction among all the Sm_0.7Pr_0.3Fe_x alloys at low fields and shows a large magnetostriction λ_// − λ_⊥ = −1008 ppm at a magnetic field of 12 kOe.     

Hollow CoNi alloy submicrospheres consisting of CoNi nanoplatelets: Facile synthesis and magnetic properties

Magnetic alloy micro/nanostructures with controllable size and morphology have drawn intensive attention due to their interesting physicochemical properties and potential applications in micro/nanodevices. In this letter, CoNi hollow submicrospheres consisting of CoNi nanoplatelets with a thickness of ca. 10 nm have been successfully synthesized via a facile wet-chemical approach free of any template or surfactant. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images indicate that the diameter and shell thickness of the as-prepared hollow submicrosphere are ca. 600 nm and 200 nm, respectively. Elemental maps demonstrate that Co and Ni elements are distributed homogeneously in the CoNi hollow submicrosphere. Magnetic measurement reveals that the hollow submicrospheres display ferromagnetic behaviour with a coercivity of 109.5 Oe.