LaFe_(11.4)Si_(1.6)B_y系列化合物的磁性和磁熵变

LaFe11.4Si1.6By(y=0、0.1、0.2、0.3、0.4和0.5)系列化合物,通过添加少量的B后,可以明显的缩短退火时间。晶格常数随着B含量的增加先减小后增大。该系列化合物的热滞很小,B的添加对其热滞几乎没有影响。在外加磁场变化为0～1.5T时,等温磁熵变的最大值从19.1J/(kg.K)(y=0)逐渐下降到7.1J/(kg.K)(y=0.5)。该系列化合物在B含量较低时,处于居里温度(Tc)之上,存在比较明显的场致变磁转变特性。随着B含量增加到0.5时,场致变磁转变特性明显减弱。     

Excellent mechanical properties and large magnetocaloric effect of spark plasma sintered Ni-Mn-In-Co alloy

The Ni43.75Mn37.5In12.5Co6.25 alloy was obtained by using the spark plasma sintering (SPS) technique.The martensitic transformation,magnetic and mechanical properties of the SPS alloy were investigated.Key findings demonstrate that the martensitic transformation temperature of this alloy is about 10 K lower than that of the as-cast one.Both SPS and as-cast alloys show a 7 layered modulated martensite (7M) at room temperature.The compressive fracture strength and strain of the SPS alloy increase by 176.92％ and 33.33％ compared with the as-cast alloy,achieving 1440 MPa and 14％,respectively.The maximum magnetic entropy change △Sm is 17.1 J kg-1 K-1 for the SPS alloy at the magnetic field of 5 T.     

Magnetic properties and magnetocaloric effects of Gd65(Cu,Co,Mn)35 amorphous ribbons

The magnetic phase transition and magnetocaloric effects of Gd₆₅(Cu,Co,Mn)₃₅ amorphous ribbons were investigated. The increased Mn substitution for Co or Mn substitution for Cu led into a higher second-order magnetic phase transformation temperature, near 200 K in all ribbons. Under the field change of 7 T, a maximum entropy change (ΔS_m^max) of 6 J kg⁻¹ K⁻¹ was achieved in Gd₆₅Cu₁₀Co₂₀Mn₅ ribbon and slightly dependent on the compositions. With varied composition, a full width at half of ΔS_m^max was greatly widened to be over than 180 K for Gd₆₅Cu₁₅Co₁₀Mn₁₀ ribbon. The refrigeration capacity was also greatly enhanced to 1000 J kg⁻¹ for Gd₆₅Cu₂₀Co₁₀Mn₅ ribbon, which was even excellent compared with other Gd-based amorphous systems.     

Gd2Co2Al合金的磁相变及磁热效应

电弧炉熔炼的Gd2Co2Al合金在铸态条件下即为W2Co2B型单相正交结构。变温磁化曲线表明,当外加磁场为0.01和0.1T时,可以在40、77和215K附近观察到磁相变;而外加磁场增加到1T以上时,40和215K温度处的磁相变消失。在排除第二相相变的前提下,推测215和77K处的相变对应Gd2Co2Al合金中Co和Gd次晶格的磁有序相变,而40K处的相变可能是由于自旋重取向产生。在0～5T磁场变化下,Gd2Co2Al合金在77K附近的最大磁熵变(-ΔSMmax)为10.7J/kgK,相对制冷量的值为5.4×102J/kg,表明该合金适合作为工作在液氮温区附近的磁致冷工质。     

Interdiffusion phenomena in Au/Cu and Cu/Au bilayers

The microstructures of epitaxial deposits of (111) Cu/(111) Au and (111) Au/(111) Cu at various stages of interdiffusion are described. The most prominent microstructural features of Au/Cu films (where gold deposition occurred at temperatures less than 400 °C) were (Matthews) coincidence lattice misfit dislocations lying along < 1$\text{1}$0 > directions in the film plane with $\text{|b| =}\text{a}\text{2}\text{< 110 >}$ directed out of the film plane. Their spacings, transmission electron microscopy (TEM) hot stage behavior and generation mechanisms are discussed. For more severe diffusion anneals, the coincidence dislocation density decreased and hexagonal networks identified as ( van der Merwe) natural lattice misfit dislocations became resolvable. They are edge type (lying along <11$\text{2}$> directions in the film plane) with $\text{|b| =}\text{a}\text{2}\text{< 1}\text{1}\text{0 >}$. For the case of Cu/(111) Au bilayers, copper deposited at and below 315 °C with a 20 min anneal again showed coincidence misfit networks. Higher temperature deposition of copper (or hot stage annealing) resulted in natural lattice misfit dislocations in the microstructure. The densities of both types of dislocations were determined and their TEM hot stage behavior was investigated. The method by which the two networks contribute to the relief of misfit strain in both bilayers is discussed.     

Magnetic properties of Cu substituted Co-ferrite

Copper substituted Co-Cu ferrites Co_1 − xCu_xFe₂O₄ (0 ≤ x≤0.5) have been studied with Mössbauer spectroscopy, x-ray diffraction, and vibrating sample magnetometer (VSM). The Co-Cu ferrite toroidal core samples were sintered at 860-940 °C for 2 h and the initial permeability, quality factor, density and shrinkage were also measured. The crystal structure was found to be an inverse cubic spinel with the lattice constant a₀ = 8.390 Å and a₀ = 8.386 Å for Co-ferrite and Cu²⁺ substituted Co-ferrite, respectively, by Rietveld profile analysis using the FULLPROF program. Hyperfine field was decreased with increasing Cu²⁺ concentration. The saturation magnetization (Ms) of the Co-Cu ferrite annealed at 900 °C decreased drastically and the coercivity, Hc, dropped dramatically from about 1419 to 455 Oe as copper concentration x decreased from 0.0 to 0.5. This shows that Ms, Hc can be controlled using Cu content, and initial permeability and quality factor Q is nearly constant in Cu²⁺ substituted Co-ferrite. The toroidal core data showed that the density and shrinkage of Co_1 − xCu_xFe₂O₄ (0≤x ≤ 0.5) ferrites increased with increasing quantity of Cu ions.     

Magnetic properties of Sm2Fe14−xCoxAl3 compounds

Compounds in the series Sm₂Fe_14–x Co _x Al₃ (x = 0, 1,2, 3, 4 and 5) have been shown to be of the Th₂Zn₁₇ structure. The Curie temperature is found to increase monotonically from a critical temperature,T _c equal to 471 K for thex=0 sample, toT _c=681 K for thex=5 sample. X-ray diffraction measurements of magnetic field oriented powders showed that all compounds exhibit a room temperature uniaxial anisotropy. Magnetization measurements show that the magnetic anisotropy of Sm₂Fe₁₄Al₃ can be increased substantially by the substitution of even a small quantity of Co for Fe. Results are discussed in terms of possible applications of these compounds as particulate recording media.     

Magnetic properties of Ni1−x Cu x Cr2O4(0⩽x⩽1) compounds

The compounds Ni_1−x Cu _x Cr₂O₄ (0⩽x⩽1) have been synthesised by solid-state reaction between basic nickel(II) carbonate, basic copper(II) carbonate and chromium (III) carbonate in required molar ratios at 800±10°C for 20 hr. The reaction products have been characterized by chemical analyses and powder x-ray diffraction patterns. Magnetic susceptibility has been measured in the temperature range of 300–900 K at 10 kOe. All the products show ferrimagnetic behaviour with the ferrimagnetic Curie temperature (T _c) in the range of 50–150 K. The curie temperature increases when copper(II) ion is substituted for nickel(II) ion in NiCr₂O₄. The experimental values of the average effective magneton number (p-0304;) agree with theoretical values.     

Magnetic and microstructural properties of YBa2Cu3O7−x -Ag composite

The magnetic response of YBa₂Cu₃O_7−x −5 mol% Ag composite to low-frequency magnetic field and its microstructure have been studied. Microstructural analysis shows evidence of platelet-type grain growth and silver fills the intergranular regions. The granular nature of the sample is revealed from the strong decrease in a.c. response in the presence of d.c. magnetic field. The intergranular shielding current estimated from the complex response and using the Bean’s model sharply increases with temperature below transition temperature.     

Magnetic and catalytic properties of Cu0.5Zn0.5Fe2O4 nanocrystallite powders

Cu0.5Zn0.5Fe2O4 nanocrystallite powders (average size 13 nm) were synthesized from Cu-Zn spent catalyst (fertilizers) industries and ferrous sulfate wastes formed during iron and steel making. Cu-Zn catalyst (22.4% Cu and 26.4% Zn) was chemically treated with sulfuric acid at temperature 80 degrees C for 1 hr for the complete dissolving of copper and zinc into sulfate solution, then the produced solution was mixed with stoichiometric ratio of ferrous sulfate and the mixture was chemically precipitated as hydroxides followed by hydrothermal processing. The parameters affecting the magnetic properties and crystallite size of the produced ferrites powder e.g., temperature, time, and pH were systemically studied. X-ray diffraction analysis was used in order to determine the average crystallite size and phase identifications of the produced powder. The magnetic properties were studied by vibrating sample magnetometry. The results showed that the average crystallite size of the powder decreased for the ferrites powder formed at 150 degrees C and then increased by increasing the temperature to 200 degrees C. Interestingly, the saturation magnetization (Bs), remanent magnetization (Br) and coercive force (Hc) were 25.03 emu/g, 0.71 emu/g, and 4.83 Oe, respectively at hydrothermal temperature 150 degrees C for 24 hr and changed to 16.38 emu/g, 0.3864 emu/g, and 5.2 Oe at 150 degrees C and 72 hr. The produced nanoferrite powders are used for studying the catalytic activity of CO conversion to CO2 at different temperatures, pH and times. The maximum conversion (82%) is obtained at temperature 150 degrees C for 24 hrs and pH 12.     

Tunable magnetocaloric effect in amorphous Gd-Fe-Co-Al-Si alloys

Journal of Materials Science - A magnetocaloric effect with wide tunability was observed in melt-spun amorphous Gd65Fe15-xCo5+xAl10Si5 (x?=?0, 5, 10) alloys of different Fe/Co ratios....     

Inverse magnetocaloric effect in ferromagnetic Ni-Mn-Sn alloys

The magnetocaloric effect (MCE) in paramagnetic materials has been widely used for attaining very low temperatures by applying a magnetic field isothermally and removing it adiabatically. The effect can also be exploited for room-temperature refrigeration by using giant MCE materials. Here we report on an inverse situation in Ni-Mn-Sn alloys, whereby applying a magnetic field adiabatically, rather than removing it, causes the sample to cool. This has been known to occur in some intermetallic compounds, for which a moderate entropy increase can be induced when a field is applied, thus giving rise to an inverse magnetocaloric effect. However, the entropy change found for some ferromagnetic Ni-Mn-Sn alloys is just as large as that reported for giant MCE materials, but with opposite sign. The giant inverse MCE has its origin in a martensitic phase transformation that modifies the magnetic exchange interactions through the change in the lattice parameters.     

Large magnetocaloric effect in sintered ferromagnetic EuS

We present magnetocaloric effect measurements of the ferromagnetic semiconductor EuS in the vicinity of its ordering temperature. Single phase EuS powder was synthesized by CS₂ gas sulfurization of Eu₂O₃. A sintered compact with relative density over 95% was prepared by pulsed electric current sintering of the powder. Temperature and magnetic field dependence of the magnetization and specific heat were characteristic of a paramagnetic to ferromagnetic second order phase transition. The entropy change induced by an external magnetic field and the specific heat were both close to those of a single crystal. We obtained an entropy-temperature (S–T) diagram of the EuS sintered compact. Carnot cycle liquefaction of hydrogen using EuS was compared with several other materials, with results indicating that sintered EuS is an excellent magnetic refrigerant for hydrogen liquefaction.     

In situ TEM study of Au–Cu alloy nanoparticle migration and coalescence

The diffusion and coalescence of Au–Cu alloy nanoparticles was studied at high magnification using in situ transmission electron microscopy. The particles prepared by physical vapor deposition onto amorphous-C support films had an average composition of Cu–43 at% Au and diameters of 15–50 nm. In the case analyzed, the larger of two nanoparticles remained stationary throughout the coalescence process while a smaller nanoparticle moved toward the larger particle at a temperature of ~573 K. The surface of the small nanoparticle was observed to fluctuate while approaching the larger particle, demonstrating that collective atom process occurs along the particle periphery. The particle also decreased in size during the process, indicating that it was losing mass as well as migrating. Direct evidence of a diffusional flux between particles was observed before the coalescence process. The small nanoparticle coalesced into the large one at a highly accelerated rate compared to its prior migration.     

The effect of fast annealing treatment on the interface structure and electrical properties of Au/Hg3In2Te6 contact

The effect of fast annealing treatment on the electrical properties and interface structures of Au/Hg₃In₂Te₆ contact has been studied by means of current–voltage test and high-resolution transmission electron microscopy. The current–voltage characteristics of Au/Hg₃In₂Te₆ indicate an improvement of the Schottky barrier height (SBH) from 0.557 to 0.601 eV after proper annealing treatment. Meanwhile, the orthorhombic AuTe₂ particles with irregular morphology formed near the interface region after 200 °C annealing treatment. These particles were generated by chemical reaction between Au and Te atoms rather than the phase transformation process. Two types of crystallographic orientation relationship were confirmed between AuTe₂ particles and the Hg₃In₂Te₆ matrix owing to the orientation attachment mechanism. Based on the results, it is believed that the formation of the AuTe₂ phase is likely to introduce additional energy level in Hg₃In₂Te₆, leading to the upward of band bending and increment of SBH.