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 一阶回转曲线（first order reversal curve 简称FORC）图谱法被视为研究滞后效应领域中的“指纹鉴定”，受到了地质学界和物理学界的科学家极大的关注。在磁滞后系统中，FORC图谱可以相当敏感地表征磁性颗粒间的交换作用和矫顽力的分布情况，并且能够对磁化过程中的动态问题如不同的磁场变化速率等情况做出精确的分析。FORC图谱法也可应用到其它有滞后效应的领域如铁电滞后、热滞后、弹性滞后等。文章将从磁性领域入手，通过比较Preisach模型引入FORC图谱法，利用Takacs模型验证FORC图谱的计算过程，并列举出FORC图谱在纳米双相磁性材料的应用。     

Temperature Dependence of Permeability of Co66Fe4Mo2Si16B12 Alloy

At different annealing temperatures, the saturation magnetostrictions and the correlation between the permeability μi and the temperature T (μi-T curves) of the Co66Fe4Mo2Si16B12 alloy were investigated using a small-angle magnetization tester and core tester. The experimental results showed that the μi-T curves had different shapes at different ranges of annealing temperature;the permeability μi of the alloy improved with the increase of the annealing temperatures below 460℃; when the alloy was annealed above 480℃, the poor magnetic properties were considered to be caused by larger saturation magnetostriction.     

Structural characteristics and magnetic properties of bulk nanocrystalline Fe_(84)Zr_2Nb_4B_(10) alloy prepared by mechanical alloying and spark plasma sintering consolidation

Magnetic properties of Fe84Zr2Nb4B10 sample were investigated. The sample was produced from nanocrystalline powders made by the mechanical alloying (MA) and consolidation using the spark plasma sintering (SPS) technique. Effects of milling time on phase transformation, structural characteristics, and magnetic properties of powders were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and physical property measure system (PPMS), respectively. Results show that nanostructured α-Fe supersaturated solid solution is obtained in the final MAed products. The saturation magnetization (Ms) increased with increasing milling time and became constant at 130 h, but the coercivity (Hc) increased firstly and then decreased. The consolidated bulk sample exhibited a high density of 6.893 g·cm-3, there was no phase change during SPS process, and the saturation magnetization and susceptibility of the SPSed bulk sample improved in comparison with the milled powders. The variation of magnetic parameters can be explained by nano-scale effect and Herzer model.     

Crystallization process and soft magnetic properties of nanocrystalline (Fe0.5 Co0.5 ) 86 Hf7 B6 Cu1 alloy used in elevated temperature applications

Nanocrystalline (Fe0.5 Co0.5 )86 Hf7 B6 Cu1 HITPERM alloy was investigated as the candidate of soft magnetic material for high temperature applications, compared with Fe86 Hf7B6 Cu1 NANOPERM alloy. Amorphous alloy ribbons were prepared by single-roller melt-spinning technology. Crystallization process of as-quenched ribbon was investigated using differential scanning calorimeter at different heating rates. The coercivity was determined from quasi-static hysteresis loop measured at room temperature using a computerized hysteresis loop tracer. X-ray diffraction with Cu Kα radiation was used to determine the structure. The vibrating sample magnetometer was usedto measure the magnetization as a function of temperature of the nanocrystllized alloys. That Co substitution for Fein alloy enhances the Curie temperature of amorphous alloy and the magnetization of nanocrystalline alloy at hightemperature. After annealing amorphous precursor, the optimum nanocrystalline alloy obtained shows the local minimum coercivity. The coercivity increases with the increasing annealing temperature corresponding to the formation of ferromagnetic phase in the secondary crystallization.     

ANISOTROPY IN Nd_(12)Fe_(77)Co_5B_6 MELT SPUN FLAKES

１．ＩｎｔｒｏｄｕｃｔｉｏｎＯｎｅｏｆｔｈｅｍｅｔｈｏｄｓｔｏｉｍｐｒｏｖｅｔｈｅｐｅｒｆｏｒｍａｎｃｅｏｆｂｏｎｄｅｄＮｄＦｅＢｍａｇｎｅｔｓｉｓｔｏｆａｂｒｉｃａｔｅｐｏｗｄｅｒｓｗｉｔｈｈｉｇｈａｎｉｓｏｔｒｏｐｙ〔１〕．ＴｈｅｅｎｅｒｇｙｐｒｏｄｕｃｔｓｏｆＮｄＦｅＢｂｏｎｄｅｄｍａｇｎｅｔｓｍａｄｅｆｒｏｍｉｓｏｔｒｏｐｉｃｍｅｌｔｓｐｕｎｐｏｗｄｅｒｓａｒｅ９～１０ＭＧＯｅ〔２３〕．Ｉｔｉｓｌｏｗｅｒｔｈａｎｔｈａｔｏｆｔｈｅｍａｇｎｅｔｓｍａｄｅｆｒｏｍａｎｉｓｏｔｒｏｐｉｃ…     

化学镀Fe—TM—B（TM=Sn,W,Mo—W）合金的磁性研究

利用化学镀方法首次成功地制备了Ｆｅ－ＴＭ－Ｂ（ＴＭ＝Ｓｎ,Ｗ,Ｍｏ－Ｗ）合金,采用ＶＳＭ研究了合金施镀态和热处理后的磁性。结果表明：随镀层中Ｆｅ含量的增加和热处理温度的降低,镀层饱和磁化强度出现增加趋势,在Ｂ含量分别为１４．９ａｔ％和９．３ａｔ％时,Ｆｅ－Ｓｎ－Ｂ和Ｆｅ－Ｗ－Ｂ镀层的矫顽力出现极小值;Ｆｅ－Ｍｏ－Ｗ－Ｂ镀层矫顽力随退火温度的提高而连续增加。Ｆｅ－Ｓｎ－Ｂ和Ｆｅ－Ｗ－Ｂ镀层的剩磁比不     

Experimental studies of the magneto-mechanical memory (MMM) technique using permanently installed magnetic sensor arrays

The magneto-mechanical memory (MMM) method, that is often referred to as the metal magnetic memory method, has been reported to be a non-destructive testing technique capable of quantifying stress concentrations and detecting defects in ferromagnetic materials. The underlying mechanism behind MMM has been explained in the literature, but the sensitivity to stress concentration has not been satisfactorily investigated. In this paper, both the normal and tangential components of the stress-induced MMM signal were measured by permanently installed magnetic sensor arrays on specimens made from three grades of L80 alloy steel and 20 other structural steels; tests were also carried out on a pipe made from the 4140-L80 steel. As expected, the stress history affects the MMM signal, but the experimental results show that significant irreversible change of magnetization always occurs only in the first cycle of loading regardless whether the deformation is purely elastic or partially plastic. If the peak stress level is increased at a given point during cycling, the immediately following next cycle acts as a new “first” cycle at that peak stress level and causes additional significant irreversible change of magnetization, but there is no evidence that plastic deformation might build up a cumulative magnetization. The MMM effect is very small in the steel samples tested, indicating that it will not be useful in field applications. In un-notched specimens the irreversible change in magnetization caused a proportional change in the measured external magnetic field on the order of only 5–10 A/m, while in the case of notched specimens the leakage field was on the order of 30–60 A/m.     

Effect of Dy2O3 intergranular addition on thermal stability and corrosion resistance of Nd–Fe–B magnets

Sintered Nd–Fe–B magnets with and without Dy₂O₃ were prepared by powder blending method. The temperature-dependent magnetic properties, thermal stability, microstructure and corrosion resistance of sintered magnets were investigated. The temperature-dependent magnetic properties revealed that with intergranular addition of Dy₂O₃, the reversible temperature coefficients β and α in the range of 293–373 K were both lowered, indicating that the thermal stability was effectively improved. This was also verified by the decreased irreversible flux loss (h_irr) and the increased maximum operating temperature (MOT). Moreover, the electrochemical and accelerated corrosion results clearly evidenced that the corrosion resistance of Nd–Fe–B magnet was also modified by addition of Dy₂O₃. Furthermore, the related mechanisms on improved thermal stability and corrosion resistance were systematically discussed.     

EFFECT OF CHROMIUM SUBSTITUTION ON STRUCTURAL AND MAGNETIC PROPERTIES OF R_2Fe_(17) COMPOUND

ＴｗｏｄｒａｗｂａｃｋｓｒｅｓｔｒｉｃｔｔｈｅａｐｐｌｉｃａｔｉｏｎｏｆｔｈｅＲ２Ｆｅ１７ｃｏｍｐｏｕｎｄｓａｓｐｅｒｍａｎｅｎｔｍａｇｎｅｔ：ｎｏｎｅｏｆｔｈｅｍｅｘｈｉｂｉｔｓａｎｅａｓｙｃａｘｉｓｍａｇｎｅｔｏｃｒｙｓｔａｌｌｉｎｅａｎｉｓｏｔｒｏｐｙａｔｒｏｏｍｔｅｍｐｅｒａｔｕｒｅａｎｄＣｕｒｉｅｔｅｍｐｅｒａｔｕｒｅＴｃｏｆｔｈｅｍｉｓｒｅｌａｔｉｖｅｌｙｌｏｗ．Ｉｎｒｅｃｅｎｔｙｅａｒｓ,ｖａｒｉｏｕｓｍａｇｎｅｔｉｃｍａｔｅｒｉａｌｓｂａｓｅｄｏｎＲ２Ｆｅ１７ｈａｖｅｂｅｅ…     

Magnetic phase transitions in ferrimagnetic DyFe5Al7 near the compensation point

The magnetization curves of single-crystal DyFe₅Al₇ have been measured along the main crystal-lographic directions in the magnetically ordered state. The temperature dependences of the magnetic moments of the Dy and Fe sublattices and the parameter of the intersublattice exchange have been determined in the model of molecular field. Upon the measurements along the easy axis, jumps of magnetization, the values and critical fields of which strongly depend on temperature, have been revealed near the temperature of magnetic compensation. A model of the magnetization of a ferrimagnet with two magnetic sublattices coupled by weak intersublattice exchange has been suggested. Using this model, analytical expressions for the magnetization curve and critical field of the spin-reorientation transition have been obtained. A magnetic phase diagram has been constructed and magnetic structures that are realized in different fields at different temperatures have been determined. The generalization of the model to the case of a noncollinear Fe sublattice has been generalized.     

放电等离子烧结制备Fe75Zr3Si13B9磁性材料

采用机械合金化技术制备Fe75Zr3Si13B9非晶合金粉体,利用SPS放电等离子烧结技术在不同烧结温度下将非晶合金粉体制备成d20 mm×7 mm的块体非晶纳米晶合金。采用XRD和DSC分析了Fe75Zr3Si13B9非晶合金粉体的相组成、玻璃转变温度Tg、开始晶化温度Tx和晶化峰温度Tp。然后利用XRD、SEM、Gleeble3500、VSM分析不同烧结温度下块体的相转变、微观形貌、力学性能和磁性能。研究表明,在500 MPa的烧结压力下,随着烧结温度的升高,非晶相开始晶化形成非晶纳米晶双相结构,同时,样品的致密度、抗压强度、微观硬度、饱和磁化强度均显著提高。最后在500 MPa的烧结压力和863.15 K的烧结温度下,获得密度6.9325 g/cm3、抗压强度1140.28 MPa、饱和磁化强度1.28 T的非晶纳米晶磁性材料。     

STRUCTURE AND MAGNETIC PROPERTIES OF Fe/Pd COMPOSITIONALLY MODULATED FILMS

Metal Fe/Pd compositionally modulated films(CMFs) were prepared by vapour depo-sition from two sources onto glass substrate under vacuum.The modulation and crystalstructures of the films were examined by X-ray diffraction.The magnetic properties weredetermined by vibrating sample magnetometer.The Pd layers in the Fe/Pd CMFs areof fcc structure,and the Fe layer structure transits from bcc into amorphous,state withdecreasing thickness of Fe layer.The dependence of specific saturation magnetizationon thickness of Fe layers has also been discussed.     

Crystallization Behavior and Magnetic Properties of （Fe0.6Co0.4）86Hf7B6Cu1 Alloy

(Fe0.6Co0.4)86HfTB6Cu1 nanocrystalline alloy obtained in isothermal annealing process from amorphous precursor was investigated as candidate of soft magnetic materials for high temperature applications. Co substitution for Fe can enhance the curie temperature of amorphous alloy (Tc = 630℃) and improve the magnetization of nanocrystalline alloy at high temperature ( ≈ 1.56T at 550℃). After annealing amorphous precursor at 550℃ for 1 hour, the optimum nanocrystalline alloy can be obtained which shows the local minimum coercivity ( ≈ 16 A/m). The coercivity increases with the increase of annealing temperature corresponding to the formation of ferromagnetic phase in the secondary crystallization. Furthermore, additions of Hf and B elements reduce the melting temperature of the alloy studied comparing with the Fe-Co binary alloy.     

Phase diagram of magnetic structures in Fe/Cr/Fe films with nanoscale geometric inhomogeneities of interfaces

Results of an analysis of magnetic structures (mutual orientations of the iron-layer magnetizations) in three-layered Fe/Cr/Fe films formed due to the exchange interactions inside the layers of iron and chromium and on the Fe/Cr interfaces are given. The analysis was performed under the following assumptions: (1) the iron layers are ferromagnetic, and the magnetic structure of chromium layers has the form of transverse linearly polarized spin-density waves; (2) the iron-chromium exchange interaction is considered as a weak disturbance as compared to the exchange interactions inside the iron and chromium layers; therefore, they were considered as first-order and second-order perturbation-theory corrections; (3) the relative value of these corrections depends on the degree of roughness of the Fe/Cr interfaces; it was assumed that the roughness has a nanometer scale. With such approximations, the mutual orientation of the magnetizations of iron layers can be parallel, antiparallel, or noncollinear. The limits of stability of these structures depending on the thickness of the chromium interlayer and on the ratio of the first-to-second-order corrections have been determined. The main attention was paid to the conditions of the loss of stability with respect to changes in the phase of the spin-density wave, which can result in jumps in the curves of magnetization and magnetization reversal of the Fe/Cr films.     

烧结(Nd,Tb)-Fe-B磁体的元素扩散、反磁化和矫顽力

采用双合金法将两种粉末混合制备烧结永磁体可提高磁体磁性能;但在烧结过程中两种粉末之间存在元素扩散,元素扩散对磁性能的影响程度需要进一步研究。本文将Nd13Fe81B6和TbHx粉末混合制备烧结磁体,Nd13Fe81B6磁体矫顽力为4.5 kOe。当TbHx混合量为3 wt.%,烧结磁体的矫顽力增加至20.0 kOe。通过热激活研究认为,磁畴壁的形核是反磁化需要经过的过程。由于热力学的原因Tb元素更容易扩散进入Nd2Fe14B主相而不是富集在晶间富稀土相。Tb元素进入主相替代Nd可形成具有更高各向异性场的(Nd,Tb)-Fe-B表层,在反磁化过程中晶粒表层磁畴壁的形核场会增加,因此矫顽力增加程度显著。但是,TbHx混合量超过5 wt.%,矫顽力增加幅度降低。对于TbHx混合量7 wt.%的磁体,元素分布显示在主相晶粒内部贫Tb区域明显增少,证实在烧结过程中更多Tb原子从晶粒表层扩散入晶粒内部,这样晶粒表层反磁化形核场的提高程度会减弱,因而磁体矫顽力增加幅度降低。本研究说明要提高双合金Nd-Fe-B磁体磁性能需进一步控制元素扩散并优化磁体的元素分布。     

冷轧Cr16Ni14带材织构及易磁化方向的测定

无磁不锈钢Cr16Ni14冷轧带材的弱磁性能随冷变形量的增加逐渐增加。本文通过X射线衍射的正、反极图测定法,对该材料在不同变形量时的织构进行了定性、定量分析。用圆片试样进行了磁转矩的弱磁测量,得到不同方向上的弱磁性能。证明了磁性能的变化是因材料单位晶体的某一易磁化方向形成择优取向所致,确定该材料易磁化方向为[(?)12]。     

MAGNETIC PHASE DIAGRAM OF SmMn_2(Ge_(1-x)Si_x)_2 SYSTEM

1.IntroductionTheternaryRMn2X2compounds(Risrareearth,andXisGeorSi)crystallizeinthebodycenteredtetrag0nalThCr2Si2-typestructurewithspacegr0upI4/mmm,inwhichtheR,TandXatomsoccuPythe2a,4dand4csites,respectivelyl1t2].Theyexhibitillterestingmagneticpr0perties['].InSmMn2Ge2tlireedifferentmagneticorderingtypeshavebeendetermined:ferromagnetismfor153K相似文献   

PREPARATION OF Fe/Ni MULTILAYER FILMS AND THEIR MAGNETIC PROPERTIES

1. IntroductionAIllltili1},er ll1aterials attract l1lucll l1lore attelltioll[l--3I, because tlley provide a l1ewllletllod to desigll ll1aterials to lueet 1urio[[s requirelllellts. IIl additiol1, tlle developnlelltof electroll bea111 pl1}sical vapor deposi…     

MAGNETIZATION BEHAVIOUR FOR TEXTURED BULK YBaCuO POLYCRYSTALLINE SUPERCONDUCTORS

In present paper.study of magnetization behaviour was carried out for textured bulk YBaCuO polycrystalline superconductors synthesized by MTG process.Themagnetization behaviour apparently different from that of sintered samples was observed.Magnetization hysteresis measurements were performed for the texturedYBaCuO superconductors at 77K in ± 10kOe magnetic field range.Based on the results ofmagnetization hysteresis.the magnetic field dependence of critical current density(J)at77K was evaluated for the textured YBaCuO samples.The magnetic flux penetration intextured bulk YBaCuO polycrystalline superconductors was investigated at 77K throughthe magnetization hysteresis measurements under various maximum applied magnetic fields(H_M)and reasonable discussion for the phenomena was conducted in terms of Bean’s criti-cal state model.The enhancement of magnetic properties for textured bulk YBaCuOpolycrystalline superconductors is presumably attributed to the improvement ofmicrostructure in these samples.     

MAGNETIC MOMENT,CURIE TEMPERATURE AND SPIN WAVE EXCITATION FOR AMORPHOUS Fe_(90-x)Si_xZr_(10) ALLOYS

The magnetization curves at 1.5 K and thermomagnetic curves for amorphous Fe_(90-x)Si_xZr_(10)(x=0,4,7 and 10)alloys prepared by the drum spinning technique have been measured with an extracting sample magnetometer.It is obtained that the average magnetic moment,,per magnetic atom and Curie temperature,T_c,in the amorphous FeSiZr alloys increase with increasing Si content.The and T_c are found to be quite small,compared with amorphous FeSiB alloys.This unusual behavior is suggested to be due to the presence of the Fe—Fe antiferromagnetic interactions.The temperature dependence of magnetization at lower temperature is in accordance with Bloch's T~(3/2) law.Calculation shows that the spin wave stiffness constant,D,increases with increasing Si content from 0.37 meV·nm~2 for x=0 to 0.538 meV·nm~2 for x=10.The values ofindicate that the range of the exchange interaction is roughly the mean atomic distance of nearest neighbours.