Investigation of structure and magnetization reversal in mechanically alloyed SmCo6.8Zr0.2 magnets

Nanocrystalline SmCo_6.8Zr_0.2 permanent magnets are prepared by intensive milling and subsequent annealing. XRD patterns of the samples annealed at 600 °C and 700 °C show a single SmCo₇ phase with TbCu₇ structure, while the SmCo₇ phase decomposes into a mixture of Sm₂Co₁₇ and Co₂₃Zr₆ phase at higher annealing temperatures. The highest coercivity and energy product of about 2.06 T and 9.5MGOe are obtained in the sample annealed at 700 °C for 10 min. Further analysis reveals that a very strong inter-grain exchange coupling is observed in samples annealed at 700 °C for 3 (SZ-3) and 10 (SZ-10) min, indicating by the high remanence ratio and positive δm in henkel-plot. It was supposed that the magnetization reversal process is controlled by domain wall pinning.     

Comparative study on the characteristics of network and continuous Ni films

Ni films were deposited on anodic aluminum oxide (AAO) and SiO₂/Si(100) substrates at 300 K by direct current magnetron sputtering with the oblique target. The film thickness was 80 nm, 160 nm and 260 nm. The films grown on AAO substrates have a network structure while those deposited on SiO₂/Si(100) substrates are continuous. The network film consists of granules and is formed by granule connection. The granule consists of many fine grains. The granule size increases with increasing film thickness. The 80 nm-thick network film has a honeycomb-like structure. The continuous films grow with a columnar structure and the transverse size of columnar grains increases with increasing film thickness. All the network films show a Ni(111) diffraction peak while the 160 nm- and 260 nm-thick continuous films exhibit the Ni(111) and Ni(200) diffraction peaks. The network films have higher coercivity and residual magnetization ratio compared with the continuous films. The coercivity and the residual magnetization ratio increase with increasing film thickness for the network films while they are almost independent of the film thickness for the continuous films. A temperature dependence of the resistance within 5-200 K reveals that the 80 nm-thick network Ni film exhibits markedly a minimal resistance at about 40 K. A logarithmic temperature dependence of the conductance is verified at temperatures below 40 K. The temperature coefficient of resistance is smallest for the 80 nm-thick network film and is largest for the 260 nm-thick continuous film.     

Synthesis of sphere-like Co3O4 nanocrystals via a simple polyol route

A simple polyol method was developed to synthesize uniform sphere-like Co₃O₄ nanocrystals in ethylene glycol. Powder X-ray diffraction (XRD) and electron diffraction (ED) showed that the as-prepared sample was indexed as the cubic spinel structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the Co₃O₄ nanocrystals were spherical with the crystallite size in the range of 90-110 nm. Infrared spectra and Raman spectra confirmed the formation of the Co₃O₄ nanocrystals. The magnetic properties of the Co₃O₄ nanocrystals were measured by using a superconducting quantum interference device (SQUID) magnetometer, which showed that the as-prepared sample exhibited a tiny hysteresis loop with the magnetization value of 2.4 emu/g and the coercivity of 110 Oe.     

Anomalous exchange bias in Gd/Cr bilayer and Cr/Gd/Cr trilayers

Exchange bias has been observed in Gd/Cr bilayers and Cr/Gd/Cr trilayers systems in which the Curie temperature (T_C) of ferromagnetic Gd is less than the Néel temperature (T_N) of antiferromagnetic Cr. The exchange bias field H_E and coercivity H_C of the samples exhibit anomalous temperature dependence behavior in comparison with the conventional ferromagnet/antiferromagnet bilayers with T_C > T_N. As temperature increases, H_E increases monotonically until T_C, whereas H_C drops first and then goes up; finally, it disappears at T_C, which is attributed to the noncollinear interfacial exchange coupling between Gd and Cr. The results show that the exchange bias may exist in the AFM/FM bilayers regardless of the condition of T_C > T_N.     

NC型多元磁化肥的生产技术

ＮＣ型多元磁化肥以尿素、普钙、氯化钾等为原料，粉煤灰、硫铁矿灰、黄磷炉渣等作磁性载体。其生产过程与复混肥生产过程基本相同，只需增设一台磁化机。原料配方及剩磁强度可灵活掌握。对油菜、小麦、玉米及水稻的增产幅度分别为５％￣８％、５％￣１０％、１０％￣１８％和５％，经济效益十分明显。     

水玻璃磁化改性的工艺参数研究

系统地研究了水玻璃模数、流速和磁场强度等诸因素对水玻璃砂粘结强度的影响，通过优化设计，确定了水玻璃磁化改性的最佳工艺参数。研究表明，磁化处理可提高水玻璃的粘结强度３０％～４０％，从而可相应减少型砂中水玻璃的加入量，改善水玻璃砂的溃散性。磁化处理可以在输送水玻璃的管道中进行。     

Magnetic properties of Al–Gd–Ni orthorhombic compounds

The magnetic properties of the Al₄GdNi, Al₂GdNi and AlGd₂Ni₂ compounds have been investigated using magnetic measurements in the temperature range 4–800 K and magnetic fields up to 9 T and X-ray photoelectron spectroscopy at room temperature. The compounds Al₄GdNi and AlGd₂Ni₂ order antiferromagnetically at T_N = 20 and 25 K, respectively, and Al₂GdNi orders ferromagnetically at T_C = 39 K. The results are discussed in terms of the Ruderman–Kittel–Kasuya–Yosida theory, the polarization of 5d electrons by the local exchange interaction 4f–5d and the spin fluctuations on Ni sites.     

Structure and magnetic properties of Gd3(Fe1−xTix)29 (x=0.011–0.034)

Single-phase compounds Gd₃(Fe_1−xTi_x)₂₉ (x=0.0110.034) have been synthesized. Gd₃(Fe_1−xTi_x)₂₉ crystallises in a monoclinic lattice with space group P2₁/c, and the crystal structure is refined by the Rietveld technique based on X-ray powder diffraction data. Thermomagnetic analysis indicates that the Curie temperature of the compounds ranges from 517 K to 538 K. The saturation magnetizations of the Gd₃(Fe_1−xTi_x)₂₉ (x=0.011, 0.022, 0.034) at 1.5 K are 103.6, 102.0 and 94.3 Am²/kg, and the anisotropy fields at 1.5 K are 6.0, 6.2 and 6.4T, respectively.     

NiFeNb薄膜的磁特性及磁阻效应研究

研究了射频磁控溅射膜（Ｎｉ８１Ｆｅ１９）１００－Ｎｂｘ的各向异性磁阻效应ＡＭＲ、矫顽力Ｈｃ、饱和磁化强度４ｘｍｓ和饱和磁化场Ｈ。研究其作为磁阻磁头材料和低磁场高灵敏度材料的可能性。我们发现Ｎｂ的含量对（Ｎｉ８１Ｆｅ１９）１００－ｘＮｂｘ的各向异性磁阻效应ＡＭＲ＝２％、矫顽力Ｈｃ＝１１９Ａ／ｍ和饱和磁化场Ｈｘ＝４４５Ａ／ｍ，适宜于低磁场高灵敏度检测材料。     

磁处理对粘土颗粒表面电性的影响

用对比法研究了磁处理前后钻井液中粘土胶粒表面电性的变化规律,并用胶粒表面阳离子释放量来进行验证。结果表明,磁处理后粘土胶粒表面ζ电位升高;粘土胶粒相互碰撞时易分开而不易聚结,提高了体系的聚结稳定性,使钻井液网状结构变弱,内部摩擦变小,从而使钻井液的粘度和切力降低。