Fe/Fe_(73.5)Cu_1Nb_3Si_(13.5)B_9纳米晶磁粉芯研究

采用Fe粉复合FeCuNbSiB纳米晶粉体制备了磁粉芯,并讨论了退火温度、Fe粉复合量、纳米晶粉体粒度以及绝缘剂等对磁粉芯磁性能的影响.结果表明,在200～350℃和350～400℃内退火,随着温度的升高,μ_e均呈先增大后减小,375℃时达到最佳;当复合Fe粉后,发现其软磁性能得到了明显改善, Fe粉量为40%时,μ_e达到最大,且在100kHz～1MHz内,频率稳定性良好,其中心频率在500kHz附近,并随Fe粉量的增加而向低频发生偏移.纳米晶粉体的粒度越大,磁粉芯的磁性能越好;粉体粒度为100～200目时,其μ_e达到最大.当375℃退火,由有机绝缘剂、40%(质量分数)Fe粉、100～200目纳米晶粉制备的磁粉芯,其μ_e达52.72、损耗Pu为0.01317J/m~3、Bs为3.92×10~(-3)T、Br=6.48×10~(-5)T、H_c为1.28A/m.     

Fe-Ni基纳米晶软磁粉芯磁性能研究

采用模压成型成功制备了Fe-Ni基纳米晶磁粉芯。并研究了热处理温度和时间、纳米晶粉体的粒度、成型压力等对其磁性能的影响和其温度稳定性和频率稳定性。结果表明,当100～900℃内退火,随着温度升高,μe和Q值都呈先增后减,600℃时μe达到最大值31.5,其最佳退火时间为2h。成型压力和纳米晶粉体粒度越大,μe越大,Q值越小。在100～1000kHz内,磁粉芯具有较好的频率稳定性。在25～100℃内,随着温度的升高,μe逐渐下降,其中25～40℃内,μe变化敏感,温度系数αμ为-1.95×10-3℃-1,而高于40℃时,其温度系数αμ仅为-2.48×10-4℃-1。     

粉末挤出成型法制备FeSiAl/FeCuNbSiB磁粉芯

采用粉末挤出成型法制备了FeSiAl/Fe-CuNbSiB纳米晶磁粉芯,并讨论了FeSiAl粉复合量、粉胶质量比对磁粉芯磁性能的影响。结果表明粘结剂配方为硬脂酸1%、聚丙烯20%、石蜡79%,挤出成型粉胶质量比10∶1的FeSiAl/FeCuNbSiB纳米晶磁粉芯,磁粉芯密度达到4.69g/cm3。200目FeSiAl粉与300目FeCuNbSiB纳米晶粉复合,当磁粉芯磁粉质量配比为"200目FeSiAl粉30%+300目FeCuNbSiB纳米晶粉70%"、粉胶质量比为10∶1、44℃×0.5h石油醚脱脂、热处理温度160℃×1h时,磁粉芯取得最佳的软磁性能,磁粉芯中心频率f为600kHz,有效磁导率μe达到16.48,品质因数Q值为57.5;频率及温度的变化对磁粉芯的有效磁导率的影响小。     

粉末挤出成型法制备FeCuNbSiB纳米晶磁粉芯

采用粉末挤出成型法制备了FeCuNbSiB纳米晶磁粉芯,并讨论了纳米晶粉体粒度对磁粉芯磁性能的影响。结果表明,粘结剂配方为硬脂酸1%、聚丙烯40%、石蜡59%采用粉末挤出成型法可以制备粉体与粘结剂比例为5∶1的FeCuNbSiB纳米晶磁粉芯;粉级搭配可提高磁粉芯密度,300、200与100目质量比为6∶3∶2的磁粉芯密度相对于300目FeCuNbSiB纳米晶磁粉芯提高了5%,达到了3.76g/cm2;200目FeCuNbSiB纳米晶粉为33%,180℃、1h热处理,磁粉芯有效磁导率μe为10.44、中心频率为600kHz、中心频率品质因数Q值为44。     

纳米晶软磁复合磁粉芯在中高频段性能研究

介绍了利用球磨后的FeCuNbSiB合金粉末冷压制作纳米晶复合磁粉芯的工艺.探讨了粉末粒度为80～200目,绝缘剂量为1%～8%时纳米晶复合磁粉芯的频率特性,直流叠加特性及品质因数Q.制备出的平均粒度为80目的磁粉芯有效磁导率μe在1MHz范围内恒为85,在100kHz时其峰值Q为65,在f=50kHz,Bm=50mT测试条件下其损耗为102mW/cm3.其功率损耗比传统铁粉芯,Fe-Ni粉芯小.     

Fe基纳米晶／铁氧体复合材料磁粉芯制备及其软磁性能

用Mn-Zn铁氧体溶胶对Fe73.5Cu1Nb3Si13.5B9纳米晶包覆,模压成型制备复合磁粉芯,并研究了铁氧体溶胶量、热处理工艺及测试温度等因素对复合材料磁粉芯软磁性能的影响.实验结果表明,随着铁氧体溶胶量的增加,磁粉芯的磁导率减小,而Q值却随铁氧体溶胶量的增加有微小的增大.复合材料磁粉芯在热处理工艺为2h,500℃时,测试频率为500kHz,磁导率达到最大值.复合磁粉芯的品质因数Q值在200～1000kHz频段中,具有波动性,Q值在500kHz时达到51.测试温度对复合磁粉芯的磁导率和品质因数均有影响,测试温度从30℃升高到80℃时,磁导率从60.1降低到58.4,变化率为2.8%,而品质因数从59下降到54.     

成型压强对FeSiB磁粉芯磁性能的影响

磁粉芯作为软磁材料的新兴发展成果相较于传统软磁材料在电力电子方面有着巨大的应用潜力。本文以气雾化FeSiB磁粉末为原料,经过预处理、包覆、成型压制和退火处理等过程制备了FeSiB磁粉芯,并研究了不同成型压强对磁粉芯磁性能的影响。结果表明,经钝化处理后的FeSiB粉末相比于未钝化粉末具有更稳定、致密的表面包覆层,提高了磁粉芯的电阻率、降低了磁损耗。对比不同成型压强下磁粉芯的磁性能,得出随着压强的增加,磁粉芯的磁导率先增加后减小,且在较宽频率范围内有着稳定的频率特性,当成型压强为1 400 MPa,f为100 kHz,B_m为50 mT时,磁粉芯表现出良好的软磁性能,其中磁导率为17.66,磁损耗为103.04 W/kg,Q值为64.34。     

Fe78Si13B9/铁氧体复合材料磁粉芯制备及其软磁性能

用Mn-Zn铁氧体溶胶对非晶Fe78Si13B9粉体包覆,模压成型制备了复合磁粉芯,并研究了复合材料磁粉芯的软磁性能.实验结果表明,铁氧体粉体在500℃×2h的热处理条件下逐渐生成,并在非晶Fe78Si13B9颗粒表面较好包覆;铁氧体溶胶的加入,大大提高了非晶Fe78Si13B9磁粉芯的品质因数Q值.当铁氧体溶胶量为7%、30℃的测试温度时,Fe78Si13B9/铁氧体复合材料磁粉芯的磁导率在1MHz时达到最大值32,Q值高达23.     

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.     

多角形非晶粉/硅橡胶复合薄膜压磁性能研究

分别以FeCuNbSiB和FeSiB非晶粉为粉体与硅橡胶复合,制成具有压磁效应的复合薄膜。利用4284A阻抗分析仪对两种薄膜的压磁特性进行了研究。研究表明,非晶FeCuNbSiB粉体/硅橡胶和FeSiB粉体/硅橡胶复合薄膜均具有良好的压磁性能,对于FeCuNbSiB粉体/硅橡胶复合薄膜,在压应力<0.6MPa,频率低于200kHz的条件下,压磁效应敏感;对于FeSiB粉体/硅橡胶复合薄膜在0～1.45MPa内,薄膜的压磁效应变化幅度比较均匀;薄膜中粉体含量越高,复合薄膜的压磁效应越大,当含量为83.3%(质量分数)时,压磁性能最好;相同条件下,以FeCuNb-SiB为粉体制成的复合薄膜的压磁性能优于以FeSiB为粉体制成的薄膜的压磁性能。     

Inhomogeneous magnetic structure in clean magnetic superconductors

Clean magnetic superconductors are considered in which the phase transition into the ferromagnetic state takes place at a temperature ? in the absence of superconductivity, with ??T _c1, whereT _c1 is the superconducting critical temperature. The exchange and electromagnetic interactions of electrons and localized magnetic moments are taken into account, as well as magnetic anisotropy. We show that below the temperatureT _M≈? in the superconducting state the inhomogeneous magnetic structure of transverse one-dimensional domain type (DS phase) should occur at real values of the exchange interaction and anisotropy. In the DS phase gapless superconductivity is realized at temperatures sufficiently far fromT _M. Here the equilibrium direction of the magnetic structure wave vectorQ can be changed by applying a supercurrent across the sample. The behavior of this DS phase in an external magnetic field is also considered.     

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.     

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.     

Structural transformation-induced magnetic ordering in degenerate magnetic semiconductors

Electrical properties and molar specific heats have been measured in the temperature range 2–300 K of Bridgman-grown Sn_1–x Cr _x Te crystals. In addition to the paramagnetic-to-ferro or ferrimagnetic transition temperatureT _c (= 150–300 K), in this magnetic system there is another characteristic temperatureT _AHE (= 4–5 K), above which the anomalous Hall effects vanish and around which the specific heats show a small peak, indicating an extra magnetic transition. The low-temperature transition is considered as induced by a cubic-to-rhombohedral structural phase transition of the host SnTe crystal occurring at a critical temperature ofT _s (= 80–100 K). Data on the isothermal annealing of these crystals are also presented.     

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。     

The microfluxgate magnetic sensor having closed magnetic path

This paper presents a microfluxgate magnetic sensor in printed circuit board (PCB). In order to observe the effect of the closed magnetic path, the magnetic cores of rectangular ring and two bars were each fabricated. Each fluxgate sensor consists of five PCB stack layers including one layer magnetic core and four layers of excitation and pickup coils. The center layer as a magnetic core is made of a Co-based amorphous magnetic ribbon with extremely high dc permeability of /spl sim/100,000. Four outer layers as excitation and pickup coils have a planar solenoid structure and are made of copper foil. In the case of the fluxgate sensor having the rectangular ring-shaped core, excellent linear response over the range of -100 to +100 /spl mu/T is obtained with 780-V/T sensitivity at an excitation sine wave of 3 V/sub P-P/ and 360 kHz. The chip size of the fabricated sensing element is 7.3/spl times/5.7 mm/sup 2/. The very low power consumption of /spl sim/8 mW was measured.     

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。     

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.     

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.