Behavior of Medium-frequency Core Loss in Fe-based Nanocrystalline Soft Magnetic Alloys

The dependences of the power loss per cycle on frequency have been investigated in the ranges of 100 Hz<= f<=25000 Hz and 0.1 T< =Bm <=1.0 T for three main original magnetic states in five sorts of Fe-based nanocrystalline soft magnetic alloys. The measured and calculated results showed that the total power loss per cycle clearly exhibited a nonlinear behavior in the range below 3 kHz～5 kHz depending on both the magnetic state and the value of Dm, whereas it showed a quasi-linear behavior above this range. The total loss was decomposed into hysteresis loss, classical eddy current loss and excess loss, the obvious nonlinear behavior has been confirmed to be completely determined by the dependence of the excess loss on frequency. It has been indicated that the change rate of the excess loss per cycle with respect to frequency sharp decreases with increasing frequency in the range below about 3 kHz～5 kHz, wherease the rate of change slowly varies above this range, thus leading to the quasilinear behavior of the total loss per cycle. In this paper, some linear expressions of the total loss per cycle has been given in a wider medium-frequency segment, which can be used for roughly estimating the total loss.

General Properties of Low-frequency Power Losses in Fe-based Nanocrystalline Soft Magnetic Alloys

The dependences of the power loss per cycle on frequency f and amplitude flux density Bm have been investigated for the three main original magnetic states in five sorts of Fe-based nanocrystalline soft magnetic alloys in the ranges of 10 Hz<=f<=1000 Hz and 0.4 T<= Bm <=1.0 T. The total loss P is decomposed into the sum of the hysteresis loss Physt, the classical eddy current loss Pel and the excess loss Pexc. Physt has been found to be proportional to Bm^2 and f. The behavior of Pexc/f vs f being equivalent to P/f vs f clearly exhibits nonlinearity in the range not more than about 120 Hz, whereas the behavior of P/f vs f roughly shows linearity in the range far above 100 Hz and not more than 1000 Hz. In the range up to 1000 Hz, Physt is dominant in the original high permeability state and the state of low residual flux density, whereas Pexc in the state of high residual flux density is dominant in the wider range above about 100 Hz. The framework of the statistical theory of power loss has been used for representing the behavior of Pexc/f vs f. It has been found that the number n of the simultaneously active 'Magnetic Objects' linearly varies as n = n0 + Hexc/H0 as a function of the dynamic field Hexc in the range below about 120 Hz, whereas n approximately follows a law of the form n = n0 + (Hexc/H0)^m with 1 < m < 2 in the range far above 100 Hz and not more than 1000 Hz. The values of the field HO in principle related to the microstructure and the domain structure have been calculated for the three states.

Reduction of High-Frequency Core Loss of a Fe_(77.2)Si_(11)B_(8.5)Cu_(0.8)Nb_(2.5)Soft Magnetic Nanocrystalline Alloy by Minor Alloying

Enhancing saturation magnetic flux density(Bs)while reducing high-frequency core loss in Finemet-type nanocrystalline alloys is of great significance in achieving the miniaturization,high-frequency,and energy-saving of modern power electronic devices.In this work,we first designed a high-Bs Fe_(77.2)Si_(11)B_(8.5)Cu_(0.8)Nb_(2.5)alloy by appropriately reducing the non-magnetic elements in typical Finemet nanocrystalline alloys,and subsequently alloyed 2 at%Co,Al,and Mo,respectively.The effects of alloying elements on structure and static and high-frequency magnetic properties were studied.The results reveal that,alloying Al or Mo reduces the averageα-Fe grain size(Dα-Fe)in the nanocrystalline alloys,while Co exhibits a slight influence.The added Al or Mo results in decreases in both the Bs and coercivity(Hc)of the nanocrystalline alloys,whereas Co increases the Bs without changing Hc,and meanwhile,all alloying elements show minimal effects on effective permeability(μe).Furthermore,the addition of Co,Al,or Mo lowers the core loss(Pcv)at 0.2 T/100 kHz of the based nanocrystalline alloy with reductions of 10.9%,29.6%,and 26.8%,respectively.A Fe_(75.2)Si_(11)B_(8.5)Cu_(0.8)Nb_(2.5)Al_(2)nanocrystalline alloy exhibits outstanding soft magnetic properties with Bs,Hc,μe at 10 kHz and 100 kHz,and Pcv at 0.2 T/100 kHz of 1.34 T,0.8 A/m,27,400,18,000,and 350 kW/m3,respectively.The reduction in Pcv is primarily attributed to the decreased eddy current losses,originating from the increased electrical resistivity by elements alloying.

Giant magneto-impedance effects in nanocrystalline soft magnetic alloy ribbons

SINCE the discovery of the giant magneto-impedance (GMI) effects in amorphous wire (or rib-bon) of CoFeSiB and nanocrystalline wire (or film) of FeCuNbSiB, it has attracted greatattention due to its promising potential applications in industry. Amorphous (and nanocrys-talline) soft magnetic alloys have very large magnetic permeability, when an ac driving currentand an external magnetic field (EMF) are applied, the EMF will damp the magnetic fluxchange caused by the ac driving current, thus the magnetic permeability will decrease; as a re-

Formation and crystallization behavior of Fe-based amorphous precursors with pre-existingα-Fe nanoparticles-Structure and magnetic properties of high-Cu-content Fe-Si-B-Cu-Nb nanocrystalline alloys

Structure,crystallization behavior,and magnetic properties of as-quenched and annealed Fe_(81.3)Si_(4)O_(13)Cu_(1.7)(Cu1.7)alloy ribbons and effects of Nb alloying have been studied.Three-dimensional atom probe and transmission electron microscopy analyses reveal that high-number-density Cu-clusters and Pre-existing Nano-sized a-Fe Particles(PN-a-Fe)are coexistence in the melt-spun Cu1.7 amorphous matrix,and the PN-α-Fe form by manners of one-direction adjoining and enveloping the Cu-clusters.Two-step crystallization behavior associated with growth of the PN-a-Fe and subsequent nucleation and growth of newly-formedα-Fe is found in the primary crystallization stage of the Cu1.7 alloy.The number densities of the Cu-clusters and PN-a-Fe in melt-spun Fe8_(1.3-x)Si_(4)B_(13)Cu_(1.7)Nb_(x)alloys are gradually reduced with enriching of Nb,and a fully amorphous structure forms at 4 at.%Nb,although smaller Cu-clusters still exist.After annealing,2 at.%Nb coarsens the average size(D_(α-F)e)of theα-Fe grains from 14.0 nm of the Nb-free alloy to 21.6 nm,and 4 at.%Nb refines the D_(α-Fe)to 8.9 nm.The mechanisms of theα-Fe nucleation and growth during quenching and annealing for the alloys with large quantities of PN-α-Fe as well as after Nb alloying have been discussed,and an annealing-induced oc-Fe growth mechanism in term of the barrier co-contributed by competitive growth among the PN-a-Fe and diffusion-suppression effect of Nb atoms has been proposed.A coercivity(HC)αDα-Fe^(3)correlation has been found for the nanocrystalline alloys,and the permeability is inverse with the H_(C).

Effects of Ribbon Thickness on Structure and Soft Magnetic Properties of a High-Cu-Content FeBCuNb Nanocrystalline Alloy

The effects of ribbon thickness(t)on the structure and magnetic properties of a Fe_(82.3)B_(13)Cu_(1.7)Nb_(3) alloy in melt-spun and annealed states have been investigated.Increasing the t from 15 to 23μm changes the structure of the melt-spun ribbons from a single amorphous phase to a composite with denseα-Fe nanograins embedded in the amorphous matrix.The grain size(D_(α-Fe))of theα-Fe near the free surface of the ribbon is about 6.7 nm,and it gradually decreases along the cross section toward the wheel-contacted surface.Further increasing the t to 32μm coarsens the D_(α-Fe) near the free surface to 15.2 nm and aggravates the D_(α-Fe) ramp along the cross section.After annealing,the ribbon with t=15μm has relatively largeα-Fe grains with D_(α-Fe)>30 nm,while the thicker ribbons possessing the pre-existing nanograins form a finer nanostructure with D_(α-Fe)<16 nm.The structural uniformity of the ribbon with t=23μm is better than that of the ribbon with t=32μm.The annealed ribbons with t=23 and 32μm possess superior soft magnetic properties to the ribbon with t=15μm.The ribbon with t=23μm exhibits a high saturation magnetic flux density of 1.68 T,low coercivity of 9.6 A/m,and high effective permeability at 1 kHz of 15,000.The ribbon with t=32μm has a slightly larger coercivity due to the lower structural uniformity.The formation mechanism of the fine nanostructure for the ribbons with suitable t has been discussed in terms of the competitive growth effect among the pre-existingα-Fe nanograins.

Excellent magnetic softness-magnetization synergy and suppressed defect activation in soft magnetic amorphous alloys by magnetic field annealing

Fe-based amorphous alloys with high saturation magnetic flux density(B_(s))are increasingly attractive from both scientific and technological points of view,however,they usually suffer from the trade-off between magnetization and softness.In this work,we explore the soft magnetic properties(SMPs),magnetic and atomic structures,and defect activation during creep deformation of as-quenched and annealed Fe_(82.65-x)Co_(x)Si_(2)B_(14)Cu_(1.35)(x=0-20)amorphous alloys(AAs).Improved magnetic softness-magnetization synergy has been realized in all these alloys by field annealing.Particularly,superb SMPs with superhigh B_(s) of 1.86 T,low coercivity of 1.2 A/m and high effective permeability of 16300 are obtained in the Fe_(66.65)Co_(16)Si_(2)B_(14)Cu_(1.35) AA.The locally regularized arrangement of domains,homogenized structure with less structural/magnetic defects and suppressed crystal-like ordering by field annealing contribute synergistically to the superb SMPs.Besides,the relaxation time spectra obtained from creep deformation indicate less liquid-like and solid-like defects activated in the field-annealed AA,which is correlated with the structural homogenization and superb SMPs.This work provides new and comprehensive insight into the interplay among external field,heterogeneous structure,SMPs and defect activation of Fe-based AAs,and offers a promising pathway for softening amorphous alloys with high Bs.

The influence of Si substitution on soft magnetic properties and crystallization behavior in Fe_(83)B_(10)C_(6-x)Si_xCu_1 alloy system

In this study, the soft magnetic properties and crystallization behavior of Fes3B10C6-xSixCul （x=0-4） nanocrystalline alloys prepared by annealing the melt-spun amorphous ribbons have been investigated. It is found that in the Fe83B10C6-xSixCU1 alloy system, the coercivity （Hc） decreases slightly with increasing Si addition and exhibits a minimum value with composition of x = 2, while the effective permeability （Ue） shows an opposite variation trend. The saturation magnetic flux density （Bs） shows a slightly decreasing trend owing to the decreasing volume fraction of nanocrystalline phase. The Fe83B10CaSi2Cu1 nanocrystalline alloy exhibits excellent soft magnetic properties with a high Bs of 1.78 T, high ue of 13 600 and low Hc of 4 A/m.

FePCCu nanocrystalline alloys with excellent soft magnetic properties

The effect of Cu addition on crystallization behavior and soft magnetic properties of Fe84-xP10C6Cux （x = 0-1.15） alloys was investigated. Low-cost FePCCu nanocrystalline alloys dispersed with ct-Fe phase with an average grain size of 15-35 nm were obtained by appropriately annealing the melt-spun ribbons at 683 K for 5 min. The Fe83.25P10C6Cu0.75 nanocrystalline alloy ex- hibits a high Bs of 1.65 T, low Hc of 3.3 A/m and high μc at 1 kHz of 21 100, which is superior to the traditional FePC soft magnetic alloys. The core loss is as low as 0.32 W/kg at 1.0 T and 50 Hz, which is 60% that of nonoriented Fe 6.5 mass% Si-steel. It is encouraging to synthesize this Fe-based nanocrystalline alloy with excellent soft-magnetic properties even using commercially industry-grade raw materials, which is promising for the future industrial applications.

Microstructure and magnetic properties of Fe81.3Si4B13Cu1.7 nanocrystalline alloys with minor Nb addition

The amorphous matrix contAlning dispersive high number density （Na） α-Fe nuclei with average grAln sizes （D） of 4.3-6.2 nm was formed in the melt-spun Fe81.3-xSi4B13Cu1.7Nbx （x = 0-2） alloys, and the Nd and D values reduce with increase in the Nb content. The fine nanocrystalline structure with α-Fe grAlns of 14.0-21.6 nm in size was obtAlned for the annealed alloys, which showed high saturation magnetic flux density of 1.60-1.77 T and low coercivity （He） of 7.1-17.0 A/m. Addition of minor Nb significantly expands the optimum annealing temperature range for obtAlning good soft magnetic properties, while coarsens the α-Fe grAlns, leading to a slight increase in the Hc. The mechanism of the effect of Cu and Nb elements on the structure and magnetic properties was discussed in terms of the formation and growth of the α-Fe nuclei of the alloys.

基于非晶带巨磁阻抗效应的新型弱磁场传感器

利用短时矩形脉冲电流对近零磁致伸缩系数钴基非晶态合金带进行退火处理,得到约114%的巨磁阻抗变化率.同时利用CMOS多谐振荡电路产生窄脉冲电流序列对前面处理过的非晶带进行激励,制作成灵敏度高、稳定性好、功耗低的弱磁场传感器.对传感器的工作原理进行了分析,并设计了信号处理电路.该传感器可应用于对弱磁场的检测.

电流退火对钴基、铁基非晶软磁合金条带有效磁导率的影响

研究了电流退火的电流密度、退火时间对钴基和铁基非晶软磁合金条带有效磁导率的影响,并与等温退火处理的结果作了比较。结果表明:电流退火可以明显提高钴基和铁基非晶软磁合金条带的有效磁导率,且存在一个最佳电流密度、退火时间值,以使有效磁导率提高最大;铁基非晶软磁合金有效磁导率的提高明显优于钴基非晶软磁合金;电流退火提高钴基和铁基非晶软磁合金有效磁导率的幅度与等温退火基本相当,具有升温和降温速度快、退火效率高的优势。

Decomposition of pre-existing Au-P clusters induced in situ a-Fe grains uniformization in Fe-P-based nanocrystalline alloys

In Fe-based amorphous-/nanocrystalline ribbons,the uniformization and refinement of a-Fe grains are key aspects for optimizing their soft magnetic and mechanical properties.Herein,the Fe-P-C-B nanocrystalline alloy system was selected for investigation.We produced as-spun ribbons with pre-existing nanocrystals through melt-quenching and then obtained a well-distributed a-Fe nanocrystalline structure through annealing below the first crystallization onset temperature(633 K)resulting in excellent magnetic properties(saturation magnetization of 1.65 T and coercivity of 1.6 A·m^(-1))ultra-wide annealing temperature window(from 613 to 733 K),and extremely high annealing stability(up to 480 min at 633 K).Furthermore,we propose a new in situ two-step mechanism for the uniformization of a-Fe nanocrystals,which is separately induced by the decomposition of the Au-P clusters and the pre-existing a-Fe nanocrystals during annealing.This work underscores the crucial significance of micro-alloying via metastable clusters primarily influenced by metal-phosphide interactions in the process of refining a-Fe nanocrystals.Furthermore,i introduces a new principle for optimizing the comprehensive properties of Fe-based amorphous/nanocrystalline alloys.

FeNi基非晶薄带的巨磁阻抗效应研究

采用甩带快淬法制备了FeNi基[(Fe50Ni50)77.5Cr0.5Si11B11]软磁非晶薄带,测试与分析了FeNi基合金薄带的微结构、静磁性能和磁阻抗.结果表明:FeNi基合金薄带在快淬态便具有良好的软磁性能和巨磁阻抗(GMI)效应,薄带的几何尺寸对其GMI效应有明显影响,尺寸为宽2 mm,长20 mm的薄带具有最佳GMI效应,在5 MHz下,最大纵向GMI比达到25.0%,最大横向GMI比达到19.7%.讨论了最佳几何尺寸样品的磁阻抗比在不同的频率下随外加直流磁场的变化规律.

非晶态软磁合金薄带的制备和磁学性能

研究了钴基和铁镍基两种非晶态软磁合金薄带的制备工艺，用示差热分析法测量了合金的起始晶化温度和居里温度，用冲击检流计法测量了合金的静态磁学性能。试验结果表明，在单辊快淬工艺条件下，钴基合金的非晶态形成能力比铁镍基合金的大，制备较容易；磁场退火处理能够显著改善两种合金的软磁性能；制备态和经磁场退火的两种合金的磁学性能均优于晶态铁镍系坡莫合金的磁学性能。

铁基软磁合金薄带高频磁导率测量方法研究

给出一种铁基软磁合金薄带高频磁导率的测量方法,详细介绍了该方法的测量原理,并利用Agilent E4991A射频阻抗/材料分析仪研究了退火温度对20μm厚铁基软磁合金薄带高频磁导率的影响。结果表明,随退火温度的提高,磁导率实部单调提高,磁导率虚部则是先升高后降低。尤其是在550℃下退火,在1MHz和10MHz下样品磁导率实部分别为2210和330;比较了不同温度退火样品的磁导率的测量结果,得知550℃是一个比较理想的退火温度。研究结果对以铁基非晶、纳米晶软磁合金薄带为磁心的高频微电感、微变压器等磁性器件的设计具有重要的指导意义。

Giant magnetoimpedance effect of multilayered structure(F/SiO_2)_3/Ag/(SiO_2/F)_3 films deposited in a longitudinal magnetic field

The soft magnetic properties and giant magnetoimpedance(GMI) effect of the multilayered structure(F/SiO2)3/Ag/(SiO2/F)3(F≡Fe71.5Cu1Cr2.5V4Si12B9) films,which were prepared by radio frequency sputtering without and with a longitudinal magnetic field of about 72 kA/m,are studied.The results show that the GMI effect almost cannot be detected in the samples deposited without field,whereas,a longitudinal magnetic field applied during deposition process obviously optimizes the soft magnetic properties of the films,and noticeable GMI effect is obtained.The maximum values of the longitudinal and transverse GMI ratios are 45% and 44% at the frequency of 6.81 MHz,respectively.In addition,the dependence of magnetoimpedance ratio,magnetoresistance ratio,magnetoreactance ratio and effective permeability ratio on the frequency has been investigated.We found that the GMI spectrum curves in the longitudinal and transverse cases almost overlap for the field-deposited sample.The GMI effect is mainly a giant magnetoinductive effect at low frequencies.When f 】9 MHz,magnetoreactance ratio changes to a negative,i.e.,the property of reactance changes from inductive to capacitive.

退火温度对Fe_(73.5)Ni_(0.3)Cu_1Nb_3Si_(14.2)B_8合金带材软磁性能的影响

用单辊法制备的宽20 mm、厚25μm的Fe_(73.5)Ni_(0.3)Cu_1Nb_3Si_(14.2)B_8合金带材,绕制成外径为40 mm,内径为25 mm的环型磁芯。分析了合金带材的晶化行为,研究了退火温度对合金磁芯软磁性能的影响。结果表明,淬火态Fe_(73.5)Ni_(0.3)Cu_1Nb_3Si_(14.2)B_8合金带材为非晶态,一级起始晶化温度Tx1为513.2℃,二级起始晶化温度Tx2为676.9℃,当退火温度升高到550℃,在非晶基体中析出Fe(Si)软磁相,形成了非晶和纳米晶双相共存结构。当退火温度低于550℃时,随着退火温度的升高,合金磁芯的起始磁导率μ_i和饱和磁感应强度B_s增大,矫顽力Hc减小;当最大磁感应强度B_m不变时,合金磁芯的有效幅值磁导率μ_a增大,比总损耗P_s和矫顽力H_c减小;当测试频率f不变时,合金磁芯的电感L_s和品质因数Q增大。

磁致伸缩生物传感器结构优化及病菌检测研究

以铁基非晶软磁合金带材为磁致伸缩换能器,以聚乙烯醇(PVA)为功能涂层,通过加载抗体,制备出磁致伸缩生物传感器。利用阻抗分析仪研究了直流偏置磁场与交流激励磁场对磁致伸缩换能器共振特性的影响;利用电化学工作站测试对比了Au涂层和PVA涂层的耐腐蚀性能;采用尺寸为5 mm×1.4 mm×25μm的传感器检测了浓度为10^(1)-10^(8)CFU/mL大肠杆菌悬浮液,并利用扫描电子显微镜(SEM)观察病菌吸附情况。实验结果表明:厚度为347 nm的PVA涂层较2.31μm的Au涂层而言,有较大的自腐蚀电位、阻抗弧和较小的自腐蚀电流,故PVA涂层具有更好的耐腐蚀性能;随直流偏置电压增大,换能器共振信号幅值先增大后保持不变,而随交流电压增大,换能器共振信号幅值不断减小;换能器表面、PVA涂层均对大肠杆菌表现出一定的非特异性结合能力,但在相同病菌浓度下其共振频率偏移量均小于加载抗体的传感器,且随着浓度的增大,共振频率偏移量差距越大。磁致伸缩生物传感器的检测下限为102CFU/mL。扫描电子显微镜结果进一步证实了传感器共振频率偏移量由所吸附的大肠杆菌引起。