颗粒形貌对Fe-35%Co合金吸收剂磁性能的影响

采用高能球磨的方法处理水雾化Fe-35%(质量分数)Co软磁合金粉末,运用SEM、VSM和矢量网络分析仪分析测试不同球磨时间下合金粉末的微观形貌和静磁参数及其1~18 GHz频率范围的复磁导率(μ=μ'-jμ″)。结果表明,球磨处理可以使合金粉末颗粒扁平化,使得其复磁导率实部和虚部均明显提高;随着球磨时间增加,合金粉末的饱和磁化强度逐渐减小、矫顽力逐渐增大、扁平率以及复磁导率实部和虚部均先增大后减小,过度球磨会使合金粉末软磁性能恶化,不利于其微波磁导率的提高。     

BST掺杂对M/Z型六角铁氧体复磁导率(1MHz～1GHz)的影响

摘　要: 　采用陶瓷工艺制备 Co2Z ( Ba3 ( Co0.4Zn0.6)2Fe23.4O41)和BaM(BaFi1.4Co1.4Fe9.2O19)六角铁氧体,二次球磨时掺杂少量 BST(BaSrTiO3 )铁电材料,对比研究了 BST 掺杂对 Z 型和 M 型铁氧体在1MHz~ 1GHz 频率范围内相对复磁导率(μr =μr′ iμr″)的影响。BST的掺杂使Z型铁氧体μr 增大,共振频率点移向低频;使M型铁氧体的μr 减小,共振频率点移向高频。通过对其微观结构和磁参数的测试分析,讨论了 BST掺杂对 Z型和 M型铁氧体复磁导率不同影响的作用机理。     

应用于NFC的FeSiAl磁粉-POE弹性体柔性电磁屏蔽片制备

选用高能球磨扁平化处理工艺制备的片状Fe84Si6Al10合金粉体为磁性填料,与热塑性弹性体POE混合,通过压延工艺制成柔性软磁合金电磁屏蔽片,研究了磁性合金填料的形貌、粒径以及填充量对电磁屏蔽片磁谱和电磁屏蔽性能的影响规律。结果表明,高能球磨处理能获得高扁平率Fe84Si6Al10合金片状粉末,扁平率达100;厚度1μm的不同粒径片状磁粉对电磁屏蔽片的磁谱影响不显著;随片状Fe84Si6-Al10粉体填充量增加,电磁屏蔽片磁导率实部明显提高,磁导率虚部略有增大;当磁粉与基体的质量比为9∶1时,电磁屏蔽片在13.56 MHz的磁导率实部μ'达35.1,读写距离达33 mm,能应用于NFC系统的抗电磁干扰。     

Fe基合金的微结构与频率特性

用高能球磨的方法制备铁基纳米晶铁钴和铁镍合金,研究材料的结构与频率特性.结果表明:具有体心立方晶体结构样品的颗粒尺寸在0.5~5μm之间,尺寸分布较宽;而具有体心立方和面心立方混合晶体结构样品的在5~20μm之间,尺寸分布较窄.含钴样品的钴含量有提高样品截止频率的作用;样品的磁导率实部在掺杂量为7.69%(原子分数)时均出现极大值.Co掺杂的样品显示出弛豫型磁谱特征,而Ni掺杂样品则显示出共振型磁谱特征.Fe-Co样品在高频区域磁导率虚部随着掺杂量的增大而减小,同时随着掺杂量的增加,磁导率虚部最小值向高频区域移动.Fe-Ni样品的磁导率虚部最小值也随着掺杂量的增加向高频区域移动.纯铁样品则在高频区域磁导率虚部小于掺杂样品.     

片状Fe-Cr-Si-Al 磁粉/Co2Z铁氧体粉末混合组分的电磁特性

采用机械球磨的方法扁平化处理气雾化Fe-Cr-Si-Al软磁合金（SMSS）粉末，并以柠檬酸溶胶-凝胶法合成六角铁氧体Ba3Co2Fe24O41（C02Z）粉末．运用SEM、XRD表征粉末的表面形貌和晶体结构，并测试不同质量比的片状SMSS磁粉与Co2Z粉末混合组分在2．0-8．2GHz范围的复介电常数和复磁导率．结果表明，随着Co2Z粉末质量分数的增加，样品的复介电常数和复磁导率减小；同时计算得到的反射系数曲线显示样品的匹配频率移向高频，当SMSS磁粉与Co2Z粉末的质量比为4／1时，样品具有最小的反射系数峰值．     

粉末冶金法制备Fe-Si-Ni磁粉芯及其磁性能

采用熔炼-铸锭-球磨的方法制备了Fe-Si-Ni粉末,经过预退火热处理、绝缘包覆后将粉末压制成磁粉芯,并对成型后的磁粉芯进行去应力退火处理。对Fe-Si-Ni粉末及磁粉芯的性能系统地进行了检测分析。结果显示:经过预退火处理后的Fe-Si-Ni粉末具有较高的饱和磁化强度(Ms)。Fe-Si-Ni磁粉芯的有效磁导率(μe)在10~1000kHz的频率范围内变化很小,且随着Ni含量和退火温度的升高而增大。Fe-Si-Ni磁粉芯有着良好的直流叠加特性(dc-bias),当Ni≥5wt.%时,尽管磁导率百分比随着退火温度的升高逐渐减小,然而在外加直流磁场强度为50Oe时,磁粉芯的磁导率百分比均在70%以上。品质因数(Q)随着Ni含量和退火温度的升高逐渐增大,磁芯损耗随着Ni含量和退火温度的升高而减小。当Ni=8wt.%,退火温度为750℃时,磁粉芯在50kHz,50mT下的磁芯损耗有最小值312mW/cm3。     

B掺杂对SmFe_(10)Mo_2合金的结构及磁性的影响

用电弧熔炼法制备Sm Fe10Mo2及Sm Fe10Mo1.5B0.5母合金锭,将其均匀化退火后用球磨法制备Sm Fe10Mo1.5B0.5纳米晶合金粉末,研究了B掺杂对Sm Fe10Mo2块体合金和球磨对Sm Fe10Mo1.5B0.5纳米粉末的相结构和磁性的影响。结果表明,B掺杂后合金的Th Mn12相结构不变,居里温度由270℃提高到334℃;合金成分不均匀导致热磁曲线出现两个相变点。Sm Fe10Mo1.5B0.5合金经球磨处理0.5 h后Mo大量析出,1∶12相明显减少;随着球磨时间的增加α-Fe析出并形成非磁性的Mo2Fe B2相,使内禀矫顽力明显减小,且其饱和磁化强度随着球磨时间的增加呈现先增大后减小的趋势。球磨0.5 h的纳米合金粉末永磁磁性能最佳:Ms=55Am2/kg,iHc=0.2T。     

环氧树脂包裹超微铁磁性复合粒子电磁参数的研究

用反相微乳液方法制备了环氧树脂(EP)包裹超微铁磁性复合粒子。用SEM、XRD进行了微观结构的表征,进行了复介电常数(ε=ε′-jε″)和复磁导率(μ=μ′-jμ″)的测试。结果表明复合粒子呈EP包裹α Fe结构;它能有效阻止超微铁粒子的氧化。随着复合时ATPU用量的增加,复合粒子的密度减小。ε和μ均随ATPU用量的增大而减小。ε′、μ′和μ″均随频率的增大而减小;当ATPU用量<2.32%时,ε″随频率的增大而减小,但当ATPU用量增大,ε″随频率的变化不明显。     

Ni_(1-X)Zn_XFe_2O_4铁氧体纳米粉末在GHz波段的吸波性能

利用溶胶-凝胶自蔓延燃烧反应制备了Ni1-XZnXFe2O4(x=0.5,0.65和0.8)铁氧体纳米粉末,将粉末分别在室温、550、800和1050℃下退火2小时,研究了退火样品的晶体结构及其在0.1~1.5GHz波段的电磁性质。实验表明,选择合适的退火温度和适当的Zn2+掺杂量有助于提高纳米Ni-Zn铁氧体粉末的复介电常数和复磁导率,改善其阻抗匹配性,提高其吸波性能;而随着退火温度的升高,Zn2+掺杂量过多的样品的介电损耗虽略有增加,但磁损耗却随之减小,且试样的饱和磁化强度、剩磁及矫顽力均大幅下降。     

Fe73．5Cu1Nb3Si13．5B9纳米晶磁粉芯磁性能研究

用Fe73.5Cu1Nb3Si13.5B9纳米晶粉体,加入一定量的塑化剂,通过模压成型方法制备磁粉芯.实验结果表明,在一定粒度范围内,磁导率μ随粉体粒度增大而增大,品质因数Q,随着粒度的增大而减小,且在一定频率范围内,μ呈现良好的频率稳定性;塑化剂质量百分含量α越大,μ越小.当α=6.5%时,μ达到最大值31.8.0～300kHz范围内,α与Q成反比;300～1000kHz范围内,α与Q成正比例关系;磁导率μ随着成型压力的增加而提高,相反,压力越大,Q值越小;磁导率随着磁粉芯测试温度的提高逐渐减小,0≤f≤700kHz范围内,温度升高,Q降低,700kHz≤f≤1000kHz范围内时,温度升高,Q值升高;随退火温度的增加,μ和Q均呈现先增大后减小的趋势.     

Quantitative measurement of the magnetic moment of individual magnetic nanoparticles by magnetic force microscopy

The quantitative measurement of the magnetization of individual magnetic nanoparticles (MNPs) using magnetic force microscopy (MFM) is described. Quantitative measurement is realized by calibration of the MFM signal using an MNP reference sample with traceably determined magnetization. A resolution of the magnetic moment of the order of 10(-18) A m(2) under ambient conditions is demonstrated, which is presently limited by the tip's magnetic moment and the noise level of the instrument. The calibration scheme can be applied to practically any magnetic force microscope and tip, thus allowing a wide range of future applications, for example in nanomagnetism and biotechnology.     

磁粘滞行为对永磁材料磁性参数测量结果的影响研究

讨论了磁粘滞行为对永磁材料磁参数测量结果的影响,并具体分析了不同磁场强度和温度下磁粘滞系数的变化情况,结果表明,内禀矫顽力数值随磁场变化率增大而增加。磁粘滞系数与作用磁场的关系曲线呈抛物线形,且峰值出现在内禀矫顽力数值附近。随着温度的升高,磁粘滞系数的增大,样品的磁粘滞效应增强,磁场变化速率对内禀矫顽力测量结果影响增大。     

磁性材料在磁性纸中的应用

介绍了常用磁性材料及其制备方法,综述了细胞腔加填法和原位复合法制备磁性纤维和磁性纸的研究情况,进而对两种方法制备的磁性纸的印刷适应性进行分析。     

In situ observation of magnetic orientation process of feeble magnetic materials under high magnetic fields

Abstract

An in situ microscopic observation of the magnetic orientation process of feeble magnetic fibers was carried out under high magnetic fields of up to 10 T using a scanning laser microscope. In the experiment, carbon fibers and needle-like titania fibers with a length of 1 to 20 μm were used. The fibers were observed to gradually orient their axes parallel to the direction of the magnetic field. The orientation behavior of the sample fibers was evaluated on the basis of the measured duration required for a certain angular variation. As predicted from the theoretical consideration, it was confirmed that the duration required for a certain angular variation normalized by the viscosity of the fluid is described as a function of the fiber length. The results obtained here appear useful for the consideration of the magnetic orientation of materials suspended in a static fluid.     

纳米晶软磁材料的磁性能

介绍了纳米晶软磁材料所具有的独特结构和优异的磁性能。从纳米晶软磁材料的微观组织结构和宏观磁特性紧密相关的角度,探讨了铁基纳米晶合金的结构与磁性之间的依赖关系。     

Iron-based magnetic nanoparticles for magnetic resonance imaging

Magnetic resonance imaging (MRI) has been an extensive area of research owing to its depth of penetration for clinical diagnosis. Signal intensity under MRI is related to both T₁, spin-lattice relaxation, and T₂, spin-spin relaxation. To increase the contrast variability under MRI, several contrast agents are being used, i.e. T₁ contrast agents (e.g. gadolinium) and T₂ contrast agents (e.g. iron-based magnetic nanoparticles). These contrast agents are administered prior to scanning to increase contrast visibility. They reduce the T₁ and T₂ relaxation times to produce hyperintense and hypointense signals, respectively. Tunable properties of iron-based magnetic nanoparticles and several coating materials provide a platform to get superb MRI contrast in T₂ weighted images. It has been found that contrast enhancement by iron-based magnetic nanoparticles is dependent on the size, shape, composition, surface, and magnetic properties which can be tuned with the synthesis method and coating material. Therefore, understanding the synthesis method and properties of magnetic nanoparticles is vital to contribute to MR signal enhancement which is directing the scientist to design engineered iron-based magnetic nanoparticles. This paper introduces the concept of MRI contrast enhancement. We mainly discuss the synthesis of T₂ contrast agents, i.e. iron-based magnetic nanoparticles and the modification of these T₂ contrast agents by coating followed by their biomedical applications.     

Reduction of the Shoenberg magnetic interaction by magnetic feedback

It is demonstrated that the oft-times severe waveform distortion arising from the Shoenberg magnetic interaction in the de Haas-van Alphen effect can be very effectively suppressed when measurements are made on spherical samples in the presence of a uniform magnetic feedback field. A digital spectrum analyzer is used in conjunction with a large ramping modulation field (1 kG peak-to-peak) to obtain a Fourier transform of a portion of the dHvA waveform roughly every second, and the dHvA effect itself is used to provide criteria for setting the correct gain in the magnetic feedback loop. Examples drawn from a study of the [110] orientation in Pb serve to illustrate the advantages and improvements in waveform studies which accrue from the use of magnetic feedback. The improvement is particularly impressive in the three-harmonic method for determining the spin-splitting factor g _c for extremal orbits on the Fermi surface, and the value g _c = 0.704 is found for the [110] orbit in Pb ( oscillations). A careful search has been made for low-frequency dHvA oscillations in Pb corresponding to those reported in ultrasonic attenuation and magnetoresistance experiments, but no such oscillations could be found in the magnetization.This research was supported by the Natural Sciences and Engineering Research Council of Canada.     

Influence of magnetic circuit production for their magnetic properties

Punching and packing in the process of production of magnetic cores for electrical machines result in the most significant deterioration of their magnetic properties. Specific total losses increase and magnetic polarization curve steepness decreases. This article presents a method that lets measure magnetic properties of cores following different methods of core packing. The effect has been shown of some technological operations in the production process of magnetic cores for electrical machines on their magnetic properties.     

On the interaction of magnetic fields and magnetic shields

Some general mathematical expressions have been derived for the induced self and mutual inductances of the wires inside a cylindrical ferromagnetic shell. An application of these results is given. It is shown that the effect of the ferromagnetic shell on the inductances of the multiconducting wires is strongly geometry dependent; the closer the wires to the magnetic shell, the stronger the effect. For wires in the center of the cylinder, no significant result will be caused by the presence of the magnetic shell.