BeCu/绝缘层/NiCoP复合结构丝巨磁阻抗效应的研究

利用化学镀方法制备了BeCu/绝缘层/NiCoP复合丝,对细丝在200℃进行热处理以改善铁磁层的磁性,并首次研究了巨磁阻抗效应.结果表明该复合丝在较低频率下有较大的巨磁阻抗效应,在1kHz时磁阻抗比为-3.32%,300kHz时磁阻抗比获得最大值108%.研究了样品退火前后的巨磁阻抗效应和镀层厚度对巨磁阻抗效应的影响.研究表明磁阻抗比不仅取决于△R/R和△X/X,还和R与X的比值相关.     

化学镀带绝缘层LC共振型复合结构丝的巨磁阻抗效应

研究了LC共振型复合结构丝的巨磁阻抗效应并作了机理分析.用化学镀的方法制备了BeCu/绝缘层/NiCoP复合结构丝,由其自身构成串联LCR共振回路.该LC共振型复合结构丝的巨磁阻抗效应比一般型大幅度增加,长度为11cm的复合结构丝在频率f=24MHz时由一般型的54.7%增加到254.3%,增加了4.65倍.共振频率随复合结构丝长度的增加而减小.巨磁阻抗效应在共振频率附近迅速增强,而远离该频率则明显减小,具有很好的频率选择性.     

磁控溅射制备Cu/FeNi复合丝的巨磁阻抗效应

采用磁控溅射法制备了Cu/FeNi复合结构丝,并对其结构及巨磁阻抗(GMI)效应进行了研究.结果表明,Cu/FeNi复合结构丝具有良好的GMI效应,在较低频率下观察到的最大磁阻抗变化可达247.4%,同时发现FeNi铁磁层厚度对复合结构丝的软磁性能有重要影响,找到了复合结构丝铁磁层最佳厚度的范围,当厚度达到一定值时铁磁层内磁矩方向由环向分布转向复合丝长轴方向,表现出不同的GMI行为.     

高磷含量CoP-Cu复合丝巨磁阻抗效应的频谱特性

控制电化学工艺条件在直径为200μm的铜丝表面合成CoP磁性镀层成功地制备出高磷含量CoP—Cu复合丝巨磁阻抗效应材料。当磷含量为20%（原子分数）时,复合丝巨磁阻抗效应非常显著,达80%以上。本文详细研究了复合丝材料的频谱及巨磁阻抗效应频谱,指出复合丝巨磁阻抗具有较低的特征频率及较宽的频率使用范围与此新型结构有关,本文还发现,随频率的增加,最大负巨磁阻抗比对应的外加直流磁场也在增加,并且在高频与低频时,巨磁阻抗效应随磁场的响应曲线明显不同。     

化学镀CoP/Insulator/BeCu复合结构丝的巨磁阻抗效应研究

采用含复合络合剂的碱性镀液,改变镀液配方组分和工艺条件在绝缘层上合成软磁性良好的CoP合金镀层,制备出CoP/Insulator/BeCu复合结构的巨磁阻抗效应材料.样品采用电流退火进行焦耳热处理.电流退火后,在较低频率下观察到显著的磁阻抗效应,在97kHz时最大磁阻抗效应为991%,磁场灵敏度高达2.78%/(A·m-1);在3kHz～30MHz的频率范围内,磁阻抗比率都在50%以上,具有很宽的频率应用范围.利用复数磁导率探讨材料的磁化特性,发现有效磁导率实部和虚部的频率特性在退火后发生了很大变化.     

电流退火NiFeCoP/BeCu复合结构丝的巨磁阻抗效应和磁化特性

用化学镀的方法制备了镀NiFeCoP膜的复合结构丝,这种复合结构丝在较低频率下就有较好的磁阻抗效应.对样品进行电流退火处理,不同电流密度退火对复合结构丝磁阻抗效应特性的影响不同.利用复数磁导率探讨了该复合丝在不同电流密度退火后的磁化过程和磁化频率特性,较大电流密度退火后复合结构丝的畴壁运动被抑制,减弱了动态磁化过程,降低了相应的磁阻抗效应.     

电流对Ni80Fe20/Cu复合结构丝磁性能的影响

利用磁控溅射方法制备了Ni80Fe20/Cu复合结构丝,过程中给基底Cu丝施加电流,研究了电流对复合结构丝的形貌、磁结构及磁阻抗(Magnetoimpedance,MI)的影响。实验结果表明,施加电流后样品表面形貌趋于平整致密。适当的诱导电流大小和时间能够诱导磁性层产生环向磁结构,降低其等效各向异性场,进而提高样品的MI效应。溅射时间为40min,电流大小为125mA、通电时间30min时,样品的磁阻抗效应最明显。当诱导电流继续增大或电流时间进一步增加时,铁磁层磁结构转为纵向,矫顽力相应增加,阻抗效应降低。利用电流的热效应和磁效应对实验结果进行了有益的分析和讨论。     

CoP／Insulator／BeCu混联共振型巨磁阻抗效应的研究

采用化学镀的方法制备了CoP/insulator/BeCu复合结构丝,对样品进行电流退火热处理.通过自构建一定的回路,样品分别在频率为60.0MHz时出现了80.0%的LCR类并联共振和79.6MHz时出现了793.1%的LCR类串联共振.根据混联共振样品的特征建立了等效回路模型,利用模型对样品的混联共振型巨磁阻抗效应机理以及共振频率点的位置进行分析,理论与实验值吻合得较好.     

同轴电缆结构复合丝巨磁阻抗效应的研究

采用脉冲电沉积工艺在直径为200μm的铜丝表面沉积铁镍合金镀层,形成具有同轴电缆结构的巨磁阻抗复合丝材料。分别改变复合丝磁性外壳厚度与铜丝直径,研究复合丝结构对巨磁阻抗效应的影响。发现巨磁阻抗比值随磁性外壳厚度的增大及铜丝直径的增大而增大,特征频率则向低频端移动。本文还发现在外加直流磁场低于5．57kA／m时,驱动交流电幅值增大,巨磁阻抗效应增大;高于5．57kA／m时,驱动交流电幅值的大小几乎不再影响复合丝的巨磁阻抗效应。在驱动电流上叠加20mA以下的直流偏置对巨磁阻抗效应没有影响。     

巨磁阻抗增强效应及其应用

结合实验室工作,介绍近年来GMI增强效应研究的最新结果以及理论解释,并对其应用做简单介绍。取得的主要进展有:在基础研究方面,不仅在Co基非晶材料和多种磁晶各向异性常数K小、磁致伸缩常数λ_s小的均质和异质软磁材料中观察到GMI效应,而且对均质材料的GMI机理也进行了深入研究,认为其在不同频率涉及到电感效应、趋肤效应和铁磁共振效应等,利用等效电路方法也分析了均质材料的磁参数和阻抗关系;在应用研究方面,GMI效应在高灵敏度磁传感器、磁记录读头、磁编码器、生物传感器、汽车自动导向以及薄钢板无损检测等诸多领域已取得突破,并朝着器件小型化和集成化方向发展。近年来,科学家们还对复合材料巨磁阻抗效应进行了深入的研究。三明治薄膜和复合结构丝的巨磁阻抗效应相对于单质材料表现出两个明显的特点,一是巨磁阻抗效应显著增强,另外就是起始和最佳频率向低频移动。在复合材料中,在铁磁层和导电层中间再加适当厚度绝缘层,则其GMI效应会进一步增强。最近还发现利用材料的LC共振和磁机械振动可以大大增强GMI效应,并可以根据应用调解使用频率。     

Fabrication of 6-filament MgB2 wires enhanced by high strength 91-filament Cu–Nb composite

We chose high strength and high conductive Cu–Nb composite as strengthening core to improve the mechanical properties of 6-filament MgB₂ wires. The Cu–Nb core become partially dispersion strengthened during the fabrications of the MgB₂ wires. It has been found that this Cu–Nb composite offers good promise of increased strength while maintaining the superconducting properties of the MgB₂ wire. The Young’s modulus of the best wire samples increased significantly to about 130 GPa, which is comparable to those of high strength ferromagnetic materials sheathed wires but without negative ferromagnetic effects. Those mechanical properties were enough to satisfy the low field application needs. The critical current I _c also achieves 200 A (engineering critical current density, J _ce above 1.30 × 10⁴ A/cm²) at 20 K 1 T field. The 91-filament Cu–Nb composite core reinforced wires were fabricated by in situ Powder In Tube method.     

Thermal annealing dependence of high-frequency magnetoimpedance in amorphous and nanocrystalline FeSiBCuNb ribbons

The magnetoimpedance (MI) effect in Fe73.5Si13.5B9Nb3Cu1 melt-spun amorphous ribbons has been studied in the frequency range (1-500 MHz). Isothermal heating treatments in a furnace have been employed to nanocrystallize the ribbons (1 h at 565 degrees C in a vacuum of 10(-3) mbar), while other samples were annealed at lower temperatures (400 and 475 degrees C during 1 h), in order to evaluate the influence of the annealing temperature on the MI effect. The high-frequency impedance was measured using a technique based on the reflection coefficient measurements of a specific transmission line by using a network analyzer. Frequency dependence of the MI ratio, DeltaZ/Z, and both resistive, DeltaR/R, and reactive, DeltaX/X, components of magnetoimpedance were measured in the amorphous and annealed states, at different temperatures. A maximum value of the MI ratio of about 50% at a driving frequency of 18 MHz is obtained in the nanocrystalline (annealed at 565 degrees C) ribbon. Maxima for DeltaR/R of about 81% at 85 MHz and DeltaX/X around 140% at 5 MHz were also achieved. It is revealed that the microstructural evolution in the nanocrystalline sample leads to a magnetic softening, an optimum domain structure and a permeability which is sensitive to frequency and applied magnetic field, generating a large MI response.     

Magnetoelectric properties of CoFe2O4–Pb(Zr0.52Ti0.48)O3 multilayered composite film via sol–gel method

CoFe₂O₄–Pb(Zr_0.52Ti_0.48)O₃ (CFO–PZT) multilayered composite film was prepared on Pt/Ti/SiO₂/Si substrate via a sol–gel method and spin-coating technique. Results show that PZT and CFO phases exist in the composite film, calcined at 700 °C, besides substrate phase, and no obvious impurity phases can be detected. The composite film exhibits layered structure with obvious boundary between CFO and PZT films. Ferroelectric and ferromagnetic properties were simultaneously observed in the composite film, evidencing the ferroelectric and ferromagnetic properties in the composite film. The composite film exhibits both good magnetic and electric properties, as well as, magnetoelectric (ME) effect. The saturation magnetization value of the composite film is lower than that of the pure CFO film derived by the same processing as a result of the effect of the nonferromagnetic PZT layers. Ferroelectric hysteresis loops reveal that saturated polarization and remanent polarization of the composite film are lower than those of the pure PZT films. The composite film exhibits a very large ME effect, which makes the composite film attractive for technological applications as devices.     

Magnetoelectric properties of Ba0.8Sr0.2TiO3–CoFe2O4 multilayered composite film via sol–gel method

Ba_0.8Sr_0.2TiO₃–CoFe₂O₄ (BST–CFO) multilayered composite films were prepared on Pt/Ti/SiO₂/Si substrates via a sol–gel method and spin-coating technique. Microstructures, electric property, magnetic property and magnetoelectric (ME) property of the composites were studied. Results show that the composite films calcined at 750 °C have BST and CFO phases and no obvious impurity phases were detected. Further, the composite films exhibit layered structures and a transition layer which is composed of interfacial delamination exists at the interface between BST and CFO layers. Ferroelectric and ferromagnetic properties were simultaneously observed in the films, evidencing the coexistence of the ferroelectric and ferromagnetic properties. Furthermore, the saturation magnetization value of the composite film is lower than that of the pure CFO film derived by the same processing as a result of the effect of the nonferromagnetic BST layers. Also, ferroelectric hysteresis loops reveal that the saturated polarization and remanent polarization of the composite film are lower than those of the pure BST films. In addition, the composite film exhibits a strong ME effect, which makes the composite film attractive for technological applications as devices.     

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.     

Magneto-impedance in glass-coated CoMnSiB amorphous microwires

A magneto-impedance (MI) effect has been experimentally detected and systematically studied in Co_68.5Mn_0.5Si₁₀ B₁₅ glass-coated amorphous microwire 14 μm in diameter. The dependence of MI on a dc applied magnetic field (up to 20 Oe) for a range of values of ac current (less than 4 mA and having a frequency between 0.2 and 2.0 MHz) flowing along the microwire has been measured in as-prepared samples, as well as after heat treatments up to 400°C. A maximum relative change in MI of around 16% is observed in the optimum conditions, that is, for about 5 Oe dc axial applied field and 3 mA, 2 MHz ac current flowing along the microwire, which finally corresponds to a magnetic field sensitivity of about 0.4 V/Oe. Such modifications are interpreted considering the dependence of the skin-effect on those parameters through the induced changes in the circular permeability. MI in these ferromagnetic wires with micrometric dimension is of technological interest for local detection of magnetic fields     

Magnetoimpedance effect in FeCoB/Cu/FeCoB sandwiched films with Permalloy underlayer

We studied the magnetoimpedance (MI) effect of FeCoB(100 nm)/Cu(100 nm)/FeCoB(100 nm) sandwiched films with different thickness of Permalloy as underlayer for the FeCoB ferromagnetic layer. The maximum MI ratio of sandwiched film is 9.2% when the thickness of the Permalloy underlayer is 2-3 nm. The improvement of MI ratio of sandwiched films with Permalloy underlayer was explained by exchange induced ripple reduction mechanism.     

Large magnetocaloric effect and magnetoresistance in ErNi single crystal

The magnetic properties,magnetocaloric effect and magnetoresistance in ErNi single crystal have been investigated in detail.With decreasing temperature,ErNi single crystal undergoes two successive mag-netic transitions:a paramagnetic to ferromagnetic transition at Tc=11 K and a spin-reorientation transition at TSR=5 K.Meanwhile,a sharp field-induced metamagnetic transition is observed below the Tc along the a axis.ErNi single crystal possesses a giant magnetocaloric effect around Tc.The maximum magnetic entropy change is-36.1 J(kg K)-1 along the a axis under the field change of 0-50 kOe.In par-ticular,the rotating magnetocaloric effect in ErNi single crystal reaches its maximum under a relatively low field,and the maximum rotating entropy change with a value of 9.3 J(kg K)-1 is obtained by rotat-ing the applied field from the[011]to[100]directions under 13 kOe.These results suggest that ErNi could be a promising candidate for magnetic refrigeration working at liquid-helium temperature region.Moreover,a complicated transport behavior is uncovered in ErNi single crystal,which is attributed to the complex magnetic states and magnetic polaronic effect.Both positive and negative magnetoresistance are observed.A considerable large magnetoresistance with the value of-34.5％is acquired at 8 K under 50 kOe when the field is along the[100]direction.     

非晶态合金丝巨应力电阻效应的研究

研究了具有近零磁致伸缩系数Ｆｅ４．３５Ｃｏ６８．１５Ｓｉ１２．５Ｂ１５晶态合金丝在外加压应力作用下显示的巨应力电阻抗效应。比较了Ｆｅ４．３５Ｃｏ６８．１５Ｓｉ１２．５Ｂ１５非晶材料及具有大磁致伸缩系数的Ｆｅ７７．５Ｓｉ７．５Ｂ１５非晶材料在弯曲应力作用下显示的应力电阻抗效应的异同。仔细胞研究了结果非晶丝两端的电压信号峰峰值与外力,驱动电流Ｉｍｓ及频率ｆ的