Magnetic Properties and Structure of Nanocrystalline Nd4.5Fe76Co1B18.5 Alloys

In this paper, the technology, structures and magnetic properties of Nd4.5Fe76Co1B18.5 nanocomposite magnets were investigated. The effect of crystallizing treatment temperature and time on structures and magnetic properties of Nd4.5Fe76Co1B18.5 amorphous ribbons was studied. The results show that Nd4.5Fe76Co1B18.5 containing more analogue metals is easy to form a morphous. The magnetic properties of 16 m/s quenched ribbon for 710 degrees Cx900 s crystallizing treatment reach H-i(c)=242.1 kA/m, B-r=0.9410 T and (BH)(max)=59.64 kJ/m(3). The even grain size is about D-Fe3B=34 nm and D-Nd2Fe14B=23 nm.     

Thermal expansion and magnetostriction of the ferromagnetic dense Kondo system CeSi x

The thermal expansion and magnetostriction of single crystals of normal and ferromagnetic dense Kondo systems CeSi_1.86 and CeSi_1.70 are measured. The results show very characteristic behavior. The strain-dependent Kondo effect supports the ₇-like ground doublet conjectured previously based on the analysis of the magnetic susceptibility data. It is shown that the result is similar to that in the usual nearly weak ferromagnetic system.     

非晶Pr8Fe86B6合金的晶化动力学

用差热分析（DTA），结合X射线衍射（XRD）研究了非晶Pr8Fe86B6合金的晶化动力学。结果表明：该非晶Pr8Fe86B6合金的晶化相为α-Fe固溶体、Pr2Fe23B3和Pr2Fe14B金属间化合物，通过对三相晶化激活能的分析得出：α－Fe相的激活能在晶化初期变化不大，当其体积分数大于8％时，其晶化激活能开始减小；而Pr2Fe23B3和Pr2Fe14B相的激活能随其体积分数的增加而减小，且α－Fe相较Pr2Fe23B3和Pr2Fe14B相容易晶化析出。     

Magnetic Properties of Nd8Fe83Co3B6 Nanocomposite Magnets

1. IntroductionThe remanence enhancement in isotropic meltspun Nd-Fe-B flakes was obtained[1]. The flakes consist of soft magnetic grains distributed on a nanometerscale within a skeleton of a nanocrystalline hard magnetic matrix. The exchange coupling nanostructureslead to a remanence higher than that of comparable alloysl2-71. The effect wajs observed by Coehoornet al.18] for the multiphase alloys in rapidly quenchedNd-Fe-B alloys. This flakes had NdZFe14B, Fe3B anda-Fe as hard and sof…     

On the crystallization of Fe77B16Si5Cr2 alloy

The crystallization of the Fe₇₇B₁₆Si₅Cr₂ alloy is characterized by calorimetric (DSC) and X-ray diffraction experiments. Two crystallization stages are resolved in DSC records with ΔH₁ = 3.6 ± 0.1 and ΔH₂ = 3.1 ± 0.1 kJ/mol and kinetics of the two exotherms is derived from isothermal annealing experiments in the Johnson-Mehl-Avrami approach. The precipitation of α-Fe and σ-FeCr phases in the first stage is followed by polymorphic crystallization of α-Fe and Fe₂B phases in the second stage in which the σ-FeCr phase is also transformed into α-Fe phase.     

Nd8Fe86B6合金非晶带的快速晶化与磁性能

利用高频感应加热，对熔体快淬Nd8Fe86B6非晶薄带进行了快速晶化。结果表明，快速加热可使非晶带迅速晶化，从而得到高性能的纳米双相Nd2Fe14B／α-Fe永磁体。加热速度对薄带的磁性能影响较大。不同的加热速度下，合适的加热时间可以得到较高磁学性能。最佳工艺所得Nd8Fe86B6薄带磁性能可达(BH)max=105．55kJ／m^3，Br=0．93T，Hci=258．26kA／m。     

Fe80-xCoxZr8Ge2B10 (x=0,8, 16)合金的热性能、结构和磁性能

用单辊快淬法制备Fe80-xCoxZr8Ge2B10(x=0,8,16)非晶合金,再对3种合金进行不同温度下退火处理.利用差热分析仪(DTA)、X射线衍射仪(XRD)和振动样品磁强计(VSM)等测试手段对样品的热性能、微观结构及磁性能进行研究.结果表明,Fe80-xCox Zr8 Ge2 B10(x=0,8,16)合金在快淬态时均形成非晶.Fe80 Zr8 Ge2B10和Fe72 Co8 Zr8 Ge2 B10的晶化过程类似,比较复杂;Fe64 Co16 Zr8 Ge2 B10合金的晶化过程不同于其他两种合金,相对简单.3种合金的比饱和磁化强度整体上随着Co含量的增加而增大.     

Positron Annihilation Behaviors and Magnetic Properties of Single-phase Nd2Fe14B and Nanocomposite Nd2Fe14B／α- Fe Magnets

Positron annihilation behaviors have been studied in the single phase Nd2Fe14B magnet and the nanocomposite Nd2Fe14B/α-Fe magnet, prepared by melt spinning. The results showed that the number of vacancy-cluster at grain boundaries increases with increasing annealing temperature for the both types of magnets. The increase of this kind of defect can improve the coercivity of     

Bulk glass forming and thermal stability in Fe67.0Co9.5Nd3.0Dy0.5B20 alloy

Bulk glass forming ability (GFA) of a multicomponent alloy of Fe_67.0Co_9.5Nd_3.0Dy_0.5B₂₀ is studied by synthesizing it in shapes of thin ribbons, rods or cylinders, or pellets. The three samples are obtained with three different methods of melt spinning, copper mold casting, or mechanical attrition (of ribbons) followed by a hot compaction of derived alloy powder, respectively. A melt-spun ribbon of 50- to 100-μm thickness has a truly amorphous structure with two X-ray diffraction halos of wavevectors q₁=14.2 and q₃=33.0 nm⁻¹. A modified diffractogram consists of two halos q₁=14.5 and q₂=19.0 nm⁻¹ in the rods (3.0-mm diameter) while of three halos q₁=13.4, q₂=15.0 and q₃=24.0 nm⁻¹ in the pellets (5- to 10-mm diameter and 3- to 5-mm thickness). A small value of coercivity H_c of 7.1 kA/m in the rods or almost zero in the ribbons reveals soft magnetic behaviors characteristic of an amorphous structure of the alloy. An improved value of H_c=188.5 kA/m develops in the hot compressed pellets of the powder at ∼630 °C temperature. The pellets have some recrystallized α-Fe, Fe₃B and R₂Fe₁₄B (R=Nd or Dy) nanocrystallites in a bulk amorphous composite structure. The results are analyzed with thermal analysis and microstructures of the samples.     

Initial Magnetization Curve and Hardening Mechanism in the Nanocomposite Nd8Fe85Nb1B6 Ribbon

The melt-spun Nd8Fe85Nb1B6 ribbon was prepared by the single roller method with the tangential speed of 20 m/s. A mixture of Nd2Fe14B and α-Fe phases with the average crystalline grain size of about 20 nm was found to exist in the as-quenched ribbons. The initial magnetization curve of the nanocomposite Nd8Fe85Nb1B6 ribbon can be divided into four sections by the inflection points on it. The magnetically hardening mechanism corresponding to each section was investigated. The initial susceptibility of the Nd8Fe85Nb1B6 ribbon is higher than that of the Nd15Fe85B9 powder, which may be attributed to the reversible magnetization rotation in the central region not influenced by the exchange-coupling effect within the α-Fe grains.The above-mentioned magnetization rotation leads to the formation of equilibrium 180 deg. domain walls at the boundaries of the α-Fe grains. With the increase of applied field, these domain walls are compressed reversibly towards the Nd2Fe14B grains and eventually invade into them.The irreversible movement of the domain walls in the Nd2Fe14B grains accounts for the steepest growth of magnetization with the applied field. Finally, the magnetically inhomogeneous “core regions” are formed in the Nd2Fe14B grains, and the magnetization rotation in these“core regions”indicates the end of the whole initial saturation process.     

〈110〉轴向取向Fe83Ga17合金中原子间作用与磁致伸缩的关系

采用定向凝固的方法制备出棒状〈110〉轴向取向多晶Fe83Ga17样品,Fe83Ga17合金样品经过淬火处理后,饱和磁致伸缩应变λs可以达到2.42×10-4。实验发现样品的磁致伸缩应变与合金中的短程序密切相关。淬火处理后样品的磁性Fe原子周围的原子占位发生了改变,合金部分有序。文中采用"原子对模型"(pairmodel),从能量最小原理出发,分析讨论了Fe Ga合金中原子对间的相互作用与磁致伸缩应变的关系。     

Co64Fe11Nb5Si12B8合金磁导率与温度的关系

采用铁芯测试仪测得合金样品的初始磁导率随温度的变化曲线, 用磁化强度小角旋转法测量非晶及晶化合金条带的饱和磁致伸缩系数λs;研究了不同温度退火后Co64Fe11Nb5Si12B8合金的磁导率随温度的变化、磁性以及磁致伸缩系数;结果表明:合金在580、590℃热处理磁性变好的反常现象是由于磁致伸缩系数变小所致.