不同尺度下金属钆的磁热效应研究

制备了微米级金属钆粉,并用氢电弧等离子装置制备了纳米级的钆粉,同时用扫描电镜(SEM)以及透射电镜(TEM)对不同粒度的金属钆进行观察分析,在振动样品磁强计(VSM)上测量了样品的磁性能,并计算了样品的磁熵变.结果表明,粒度对钆的磁热效应有较大的影响,而对居里温度基本上没有什么影响.粒度为100～154μm钆的在外场变化为1591.55kA/m的最大磁熵变为1.8813 J/kg·K,而纳米级的钆的磁热效应远小于微米粉末以及块状钆的磁热效应.     

磁流体的热力学特性和应用

介绍了磁流体的组成及其所具有的温度、磁热效应，热磙对流和蒸发等热物理性能，以及磁流体膜在强化传热和减小流阻的作用，并详述了磙流体在热力学领域的具体应用，如热管、磁热泵、太阳能系统等，以此来拓宽对磁流体热应用方面的研究和应用思路。     

基于激光位移法的大磁致伸缩测量技术研究

基于激光位移法建立了一套大磁致伸缩材料测量装置,可以实现磁致伸缩系数的无接触、整体、准确测量。仪器测量磁致伸缩系数的复现性可达到2%。使用该装置测量不具有磁致伸缩性能的材料,结果显示仪器系统误差仅为3×10~(-6);装置测量纯镍样品饱和磁致伸缩系数的结果与理论值吻合良好。     

LaFe11.17-xCo0.78Si1.05Bx合金磁热效应的研究

用工业纯原料研究了LaFe11.17-xCo0.78Si1.05Bx(x=0、0.1、0.2、0.3、0.4、0.5)合金在室温附近的磁热效应.B元素作为间隙原子进入晶胞,随着B含量的增加,磁相变点从x=0时的277K升高到x=0.3时的289K.同时,磁熵变和直接测量的绝热温变也随着B含量的增加而增大了,在低磁场具有较大的磁热效应.测量表明合金的热滞和磁滞均很小.     

TmNiIn化合物的磁性和磁致热效应

利用电弧熔炼技术得到TmNiIn稀土金属间化合物,研究其磁性和磁热效应。研究表明TmNiIn金属间化合物的晶体结构是ZrNiAl型的六方密堆积结构,是一种具有可逆磁热效应的材料。TmNiIn是反铁磁材料,其相变温度为3.5K,在液氦温度(4.2K)附近。根据等温磁化曲线并利用麦克斯韦关系式计算可以得到磁熵变与温度的关系。当磁场变化为5T时,最大磁熵变和制冷能力分别为12.1J/kg·K和138J/kg。当磁场变化为2T时,最大磁熵变5.3J/kg·K,同时在TmNiIn金属间化合物中未观察到热滞现象和磁滞损耗。大的可逆磁致热效应表明TmNiIn是一种在低温磁制冷技术中有应用前景的材料。     

低磁场条件下Gd5（Si1-xGex）4（x=0，0.2，0.3）合金磁热效应研究

用高频真空悬浮炉在氩气保护下制备了Gd5（Si1-xGex）4（x=0，0.2，0.3）系列样品，用直接测量方法测定了在永磁体提供的低磁场H=1.3T）条件下样品的磁热效应曲线（△Tad-T）．结果表明，用元素Ge分别替代Gd5Si4合金中的Si原子，不能增强合金的磁热效应，但可在333～300K范围改变材料的居里温度，且磁热效应峰值范围变宽．     

粘结Sm-Dy-Fe合金的磁致伸缩性能研究

采用粘结法制备了Sm_(1-x)Dy_xFe_2合金样品,测量了粘结合金样品的静态磁致伸缩、动态磁致伸缩系数、增量磁导率和磁-机械耦合系数,研究了磁致伸缩性能等随磁场H的变化规律。发现当x<0.12时合金的低场磁致伸缩随x的增加而增加,高场磁致伸缩随x的增加而降低。棒状Sm_(0.88)Dy_(0.12)Fe_2合金在H=200kA/m时的磁致伸缩达405×10~(-6),磁-机械耦合系数和动态磁致伸缩系数分别达到0.34和1.28nm/A,因而粘结Sm_(0.88)Dy_(0.12)Fe_2合金具有一定的实用价值。     

磁热效应的直接测量及装置

磁热效应的测量有间接测量和直接测量两种方法。本文在比较两种测量方法各自特点的基础上,重点综述了直接测量装置的种类及特点;指出直接测量装置在室温磁制冷技术研究中的重要作用。     

新型稀土磁致伸缩材料Tb0.27Dy0.73Fe1.95的各向异性参数研究

全面测量了《110》轴向取向的Tb0.27Dy0.73Fe1.95(商品名为TDT-110)超磁致伸缩材料的各向异性常数.利用超声波穿透法测量在零磁场下的各向异性弹性常数Cij,用振动样品磁强计测量了该材料的各向异性磁导率μ11和μ33,用磁致伸缩测量仪测量了该材料的各向异性微分磁致伸缩应变常数d.     

哈斯勒合金Ni50Mn36Sn14的马氏体相变和反磁热效应

通过磁性测量手段，研究了哈斯勒合金Ni50Mn36Sn14的马氏体相变和反磁热效应。研究结果表明样品在奥氏体相和马氏体相的磁性有较大的差异。同时，通过理论计算获得该舍金样品在磁场改变△H4．776MA/m时，获得其马氏体相变温度附近的最大正磁熵变为20．8J/Kg·K，而其制冷量（RC）更是达到了152J/kg，这说明Ni．Mn．Sn合金作为一种磁工质具有较好的应用前景。     

Method for estimation of magnetic viscosity of ferromagnetics

A method providing quantitative estimation of the degree of magnetic viscosity of ferromagnetic materials by measurement of the phase of the signal from the measuring coil at field excitation by a sinusoidal signal in longitudinally extended samples with constant cross section is described. It is demonstrated that, in estimation of magnetic viscosity, it is necessary to take into account the sample size and shape, as well as the frequency of measurement. Additional information obtained by determination of the decrement of the signal from the measuring coil can be used together with the magnetic viscosity for determination of steel grade. Corresponding plots are presented.     

Gd_5Ge_4中磁场温度诱导的磁结构相变研究

最近的研究表明,在低温低场时,Gd_5Ge_4的一级磁结构相变被阻止而进入一种磁玻璃态,即在反铁磁母体中随机分布着铁磁团簇.结合这一最新研究结果,通过对Gd_5Ge_4样品不同低温的磁场诱导的磁化强度进行两次循环测量,研究发现在不同条件下Gd_5Ge_4的磁结构相变存在可逆性与不可逆性,并结合磁玻璃态进行了分析讨论.验证了Gd_5Ge_4的等温磁化行为和结构变化的一致性,这为证明在磁和晶格之间存在耦合作用提供了直接的实验证据,揭示了一级磁结构相变对巨磁热效应的产生起了重要作用.     

Indirectly coupled films

A positive coupling has been observed between magnetic films separated by a thin metallic layer. Five methods which have been developed for measuring this coupling and the variation of the coupling with evaporation temperature, measuring temperature, and thickness of the intermediate layer are described. Three mechanisms are proposed for the observed coupling : bulk diffusion of ferromagnetic atoms into the intermediate layer, diffusion of magnetic atoms along grain boundaries, and polarization of conduction electrons. The effect of this coupling on slow switching, pulse switching, and creep is discussed.     

The influence of magnetic field on the fracture toughness of soft ferromagnetic materials

This paper studies the effect of magnetic fields on the fracture toughness in nickel iron soft ferromagnetic materials. Tensile tests were conducted on single-edge cracked plate specimens in the bore of a superconducting magnet at room temperature, and the critical load was determined. The magnetoelastic analysis of a soft ferromagnetic strip with a single-edge crack was also performed, and the magnetic stress intensity factor was calculated. Based on the magnetic stress intensity factor, the fracture toughness was then obtained.     

Application of ferromagnetic resonance probes to the characterization of flaws in metals

This article presents some results obtained in the characterization of surface flaws by means of probes using ferromagnetic resonance of yttrium iron garnets (FMR probes). These experiments on artificial flaws show that FMR probes operate like eddy current probes for nonmagnetic materials and like magnetic field sensors for magnetic ones. Consequently, the working distance is larger for magnetic materials (1000–1500 µm) than for nonmagnetic ones (100–300 µm). FMR probes have good sensitivity to narrow flaws, good spatial discrimination, and are sensitive to flaw width and depth. Vector analysis allows the separation of distance and flaw effect by phase analysis on nonmagnetic materials. On magnetic materials this phase separation does not exist and another procedure is suggested. These results, and in particular those obtained on ferromagnetic materials, point to the possibility of replacing some eddy current or magnetic particle inspections by tests with ferromagnetic resonance probes.     

A general expression of magnetic force for soft ferromagnetic plates in complex magnetic fields

The experiments of ferromagnetic plates in different magnetic environments exhibit two distinct phenomena, i.e. the magnetoelastic instability of a ferromagnetic plate in transverse magnetic fields, and the increase of natural frequency of a ferromagnetic plate with low susceptibility in an inplane magnetic field. Although these two typical phenomena can be predicted separately by two kinds of theoretical models in which the magnetic forces are formulated by totally different expressions, no theoretical model has been found to commonly describe them. This makes it difficult to predict theoretically magnetoelastic interaction of a ferromagnetic structure in complex magnetic environment. A variational principle, here, is proposed to establish the governing equations of magnetoelastic interaction for soft ferromagnetic thin plate structures under complex magnetic fields. The functional is chosen as the summation of the magnetic energy and the strain energy as well as the external work from applied magnetic fields. From manipulations of the variational principle, the governing equations of the magnetic field and mechanical deformation together with an expression of equivalent magnetic force exerted on the ferromagnetic plates are obtained. It is shown that this theoretical model can commonly characterize the experimental phenomena of the magnetoelastic interaction aforementioned.     

横向常磁场中铁磁圆板的主共振特性与静载效应

针对横向常磁场中铁磁圆板的主共振问题进行研究。基于电磁基本理论,得到薄板在常磁场中所受的磁体力和洛伦兹力,应用哈密顿变分原理,推导出磁场中铁磁圆板磁弹性耦合横向振动微分方程。常磁场中铁磁圆板受到的磁体力为静载荷,根据伽辽金法得到周边夹支边界条件下铁磁圆板在静载荷作用下的初挠度,进一步应用多尺度法对周期载荷作用下的非线性方程进行一阶和二阶近似求解,得到主共振下系统幅频响应方程。通过算例,给出了系统幅频特性曲线图、振幅随磁场强度和激励力变化的曲线图,分析了板厚、磁场强度、激励力对系统共振振幅的影响,并对比了一阶近似和二阶近似计算结果的不同。结果表明,共振区域内振幅显著增加,磁场强度较小时一阶近似与二阶近似计算结果相近,而磁场强度较大时,二阶近似计算结果更加准确。     

Structural and magnetic behaviour of soft magnetic Finemet-type ribbons

Different kinds of magnetic anisotropies have been induced during the nanocrystallization process of Co- and Ni-rich amorphous ferromagnetic (Finemet) ribbons by the application of a constant stress or an axial magnetic field during the annealing process. Magnetization measurements have evidenced the presence od macroscopic anisotropy in the treated samples. The main goal of this work has been, after a careful DSC study, the structural analysis of the treated ribbons using X-ray Diffraction and Atomic Force Microscopy (AFM), detecting substantial differences in the crystallization state and grain size of the samples depending on the thermal treatment that was carried out. Moreover, AFM measurements revealed in all the treated samples a strong nanocrystallisation of the surface without evidences of amorphous matrix, which contrast with XRD measurements that have shown a high content of amorphous phase in the bulk of the ribbons. Magneto-optical Kerr effect measurements have been performed with the aim to elucidate the complex magnetic behaviour that is expected for the surface of the ribbons, measuring surface hysteresis loops that showed much higher coercive field values than that obtained in the bulk material.     

回热损失对磁斯特林制冷循环制冷率的影响

从铁磁质的磁化强度一般表示式出发，探讨热阻和回热损失对磁斯特林制冷循环性能的影响，导出最大制冷率及其它性能参数。得到了结果适用于以顺磁质为工质的磁斯特林制冷循环。并指出在理想回热条件下的结论也适用于磁卡诺制冷循环。     

Application of the differential calorimeter in magnetic measurements

Conclusions The calorimetric method of measuring losses in ferromagnetic materials can be used as a control method for checking the accuracy of measuring devices and for checking magnetic characteristics of materials at high frequencies under laboratory conditions (at plants producing magnetic materials) and in research institutes. This method is the most reliable when the voltage or current waveform are distorted, since the measurement results are almost completely independent of frequency.The differential calorimetric system provides measurements of small losses in ferromagnetic materials at high frequencies with great precision. Measurements of a power greater than 5 mw in a stable state condition and a completely balanced system can be made with an accuracy of the order of ± 1%. The sensitivity at the same time can be sufficiently high (the threshold of sensitivity in our case amounts to approximately 0.005 mv).