Matrix effect in soft metal-bonded samarium-cobalt (SmCo5) permanent magnets

This paper discusses the preparation of samarium-cobalt (SmCo₅) alloy powders by reduction-diffusion process. These powders were blended with equal weight percentages of soft metal/alloy powders, such as indium, tin and solder alloy (Pb-17Sn), to prepare bonded magnets. Important magnetic properties such as remanence, coercivity and energy product of these magnets were measured. Effect of matrix metal/alloy on the magnetic properties of processed magnets is outlined.     

放电等离子烧结制备块状纳米晶SmCo5烧结磁体

采用放电等离子烧结（SPS）技术制备了致密纳米晶SmCo5烧结磁体，研究了磁体的结构和磁性能。X衍射结果表明，烧结磁体具有CaCu5结构，说明SPS过程可以获得稳定的1：5相。TEM观察显示，磁体由平均晶粒尺寸约为30nm的1：5相构成。室温时磁体的矫顽力高达2208kA/m，而剩磁比高达0，7，说明在纳米晶之间存在强烈的晶间交换耦合作用。烧结磁体具有良好的高温性能，773K时的矫顽力为456kA/m，矫顽力温度系数β为-0．212％/K。     

车载永磁传感器件中NdFeB烧结永磁的稳定性分析

研究了电磁干扰、振动和温度等环境因素对NdFeB永磁性能的影响。研究结果表明:(1)场强或频率越高,失效越大,而交变磁场比稳恒磁场更为严重;(2)交变场下因涡流的趋肤效应,导致永磁出现不可逆的热退磁现象,当外场为30kA/m、500Hz干扰时,其失效瞬间即超过15%;(3)振动和高温的共同作用干扰,使得退磁失效情况加剧。     

防氧化剂对烧结NdFeB永磁性能的影响

研究了防氧化剂的添加对Nd13.6Dy0.39Tb0.14FecalAl0.8B625的烧结永磁体的微观结构与磁性能的影响规律.结果表明,添加一定量防氧化剂后的主相晶粒尺寸较小且较为均匀,晶界清晰,空隙及缺陷较少.由于磁体微结构的改善,磁体的性能得到了较大的提高.同时发现防氧化剂复合添加的方式对磁性能的效果优于球磨或气流磨时单独添加防氧化剂时的效果.     

Room-temperature magnetic refrigerator using permanent magnets

A magnetic refrigerator device based on adiabatic magnetic refrigeration is described. The magnetic material is cyclically magnetized and demagnetized by permanent magnets in an adiabatic process. A temperature difference of 1.6 K between the hot and cold regions was obtained under a low magnetic field (0.3 T). Gadolinium was the magnetic material used in experiments at room temperature. The range of working temperatures is between 70 and 300 K for a variety of active magnetic materials. The optimized experimental setup increased the device efficiency by achieving a temperature difference between hot and cold sources up to 5 K     

The structure of Ni-Co-Al-Ti-Cu-Fe permanent magnets

A technique has been developed for extracting one of the phases present in Ni-Co-Al-Ti-Cu-Fe permanent magnet alloys heat-treated to give optimum magnetic properties. Examination of such extracts by electron microscopy and electron-probe microanalysis has confirmed previously held theories that the precipitate is strongly magnetic (50 percent Fe and 50 percent Co) in a virtually nonmagnetic matrix. The results show that for permanent magnets containing 5-percent Ti the matrix has the same structure (L2_{1}) as a range of materials known as Heusler alloys.     

SC铸片微结构对烧结NdFeB结构与磁性能的影响

研究了铸片工艺SC(StripCasting)制备的合金铸片的微结构对烧结钕铁硼磁体微结构与磁性能的影响。结果表明:冷却速度过高时铸片厚度变薄,同时在急冷面产生细小的等轴晶,使烧结磁体容易出现固固烧结现象和主相晶粒的反常长大,降低了磁体的永磁性能;采用合适的冷却速度制备的铸片几乎全部由厚度3～5μm片状晶组成,且被富钕相薄层均匀隔开,采用该类铸片可以获得高永磁性能的烧结磁体,其永磁性能达到:Br=1.44T,jHc=877KA/m,(BH)max=398kJ/m3(50MGOe)。     

Influence of cerium content on the structure and magnetic behavior of Co-Fe-Cu-Ce permanent magnets

As part of a continuing program to understand and optimize the magnetic behavior of Co-Fe-Cu-Ce permanent magnet alloys, we have made studies on the alloy system Co3.5Fe0.5CuCexwith x in the range 0.8 to 1.2. An alloy of x = 1 had previously been studied in detail and found to have good permanent magnet properties. In the present work, it was found that when x > 1, the coercive force was increased while both the Curie temperature and saturation magnetization were decreased. However when x < 1, the coercive force tends to decrease while the Curie temperature and saturation magnetization increase. The increase in coercive force with increase in cerium content can be accounted for largely by the decrease in saturation magnetization. These results are in accord with a domain wall pinning mechanism. Scanning electron microscopy studies have shown that a major second phase in the low cerium alloys is low in copper as compared with the matrix. On the contrary, the copper content of the second phase in the high cerium alloys is larger than that in the matrix.     

Self-nanoscaling of the soft magnetic phase in bulk SmCo/Fe nanocomposite magnets

Fabrication of bulk nanocomposite materials, which contain a magnetically hard phase and a magnetically soft phase with desired nanoscale morphology and composition distribution has proven to be challenging. Here we demonstrate that SmCo/Fe(Co) hard/soft nanocomposite materials can be produced by distributing the soft magnetic α-Fe(Co) phase particles homogenously in a hard magnetic SmCo phase matrix through a combination of high-energy ball milling and a warm compaction. Severe plastic deformation during the ball milling results in nanoscaling of the soft phase with size reduction from micrometers to ~15 nm. Up to 35% of the soft phase can be incorporated into the composites without coarsening. This process produces fully dense bulk isotropic nanocomposite materials with remarkable energy-product enhancement (up to 300%) owing to effective inter-phase exchange coupling.     

SmCo6.6Nb0．4块状纳米晶烧结磁体的结构和磁性能

采用SPS技术制备了纳米晶SmCo6．6Nb0.4烧结磁体，研究了磁体的结构和磁性能．X衍射结果表．4明烧结磁体具有TbCu7结构，说明SPS过程可以获得稳定的1：7相．TEM观察显示，磁体由平均晶粒尺寸约为30nm的1：7相构成．室温时磁体的矫顽力高达2．8T，而剩磁比高达0．74，说明在纳米晶之间存在强烈的晶间交换耦合作用．烧结磁体具有良好的高温性能，矫顽力温度系数β为-0.169％/K。     

Measurement of magnetic properties of cobalt-rare earth permanent magnets

Co-rare earth permanent magnets generally display a high intrinsic coercive force. In order to make magnetic measurements with such materials fully saturated, we have found it necessary to use magnetizing fields in excess of 50 kOe. The superconducting solenoid is ideally suited for generating such fields. In this study, we have used a 100 kOe Nb3-Sn superconducting solenoid for magnetizing samples and for measuring saturation magnetization. Demagnetization properties of long cylindrical samples have been measured in the superconducting solenoid, and also with a conventional hysteresigraph after the samples have been saturated with the superconducting solenoid or in some cases with a pulsed field solenoid. Short disk samples or ring magnets such as are used in traveling wave tube (TWT) designs are difficult to measure by these techniques. We have found torque magnetometry to be useful for such shapes. Open circuit magnetization is measured in this case. Results for ring magnets will be compared with peak axial field measurements for a periodic TWT structure. Reversible and irreversible changes in magnetization with temperature are also of interest. Techniques for measuring these changes are discussed.     

Quantitative considerations to self-centering magnetic suspensions with permanent magnets

Center containment and simultaneous support of rotating bodies by forces between two permanent magnets has become a technical reality due to high-coercive force magnets. The Self-Centering principle is described and experimental results are reported as examples for the advantages of the new arrangement over conventional magnetic bearings. Performance tests of prototype units are described concerning the damping conditions and the centering functions. Centering forces and supporting forces can be adjusted independently to meet changing requirements by positioning of the axle by an end bearing or by ac-forces. The actual forces measured for barium ferrite units are compared with the forces measured for samarium cobalt units. Typical values show the samarium cobalt units to be up to 25 times stronger (by weight) and up to 40 times better (per unit volume) than barium ferrite bearings, forces were measured in excess of 100 times the weight of the magnets. Analytical, computerized studies for the basic forces have been made for optimization and the design for combinations of many units for high stiffness requirements.     

Selection of parameters for testing magnetic properties of permanent magnets

Conclusions The testing of the parameters B_r, H_c, B_d, and H_d does not always provide an unambiguous estimation of whether the PM whose working point lies on the regression line is suitable for utilization in a magnetic system.The evaluation of the PM efficiency by means of the induction at the working regressionline departure point and the induction at the intersection point of the working regression line with the conductance line corresponding to the condition of the magnet in an assembled product is more efficient and universal, since it is virtually independent of the working regression-line departure-point position and it serves to halve the number of tested parameters.Translated from Izmeritel'naya Tekhnika, No. 2, pp. 49–50, February, 1979.     

The magnetic and mechanical hardness of the intermetallic compounds SmCo5 and LaCo5

The magnetisation, coercivity, H _C, and remanence coercivity, H _R, have been measured for the intermetallic compounds SmCo₅ and LaCo₅. The coercivities H _C and H _R for SmCo₅ are very much greater than those for LaCo₅. The differences in these parameters are much greater than would be expected from a simple theoretical model, so that they cannot be accounted for in terms of differences in the magnetocrystalline anisotropy constants. Since the specimens used for the magnetic measurements were produced by mechanical comminution, Knoop hardness measurements were made in an attempt to account for the magnetic behaviour in terms of the crystallographic damage and plastic deformation produced during the grinding process. The hardness results show that, within experimental error, the SmCo₅ is very nearly isotropic, whereas the LaCo₅ is very anisotropic on the {10¯10} planes with a Knoop hardness of 138 in the 0001 directions and 511 in the 12¯10. It is concluded that plastic deformation will occur more easily in LaCo₅ and that this could, to some extent, explain the comparatively low coercivities.     

Hysteresis properties of sintered Sm Co5permanent magnets

The magnetic properties of individual SmCo5particles have been extensively studied in the literature. In the present work, initial magnetization curves and hysteresis loops of sintered SmCo5magnets have been drawn with a hysteresigraph. The observed properties depend on the previous magnetic treatment of the sample. After thermal demagnetization, the initial susceptibility is very high; after dc field demagnetization, it is very weak. The inner hysteresis loops are often unsymmetrical. Results are interpreted by considering the magnets as particle assemblies related together by dipolar interactions.     

Magnetizing of permanent magnets using HTS bulk magnets

A demagnetized Nd–Fe–B permanent magnet was scanned just above the magnetic pole which contains the HTS bulk magnet generating a magnetic field of 3.27 T. The magnet sample was subsequently found to be fully magnetized in the open space of the static magnetic fields. We examined the magnetic field distributions when the magnetic poles were scanned twice to activate the magnet plate inversely with various overlap distances between the tracks of the bulk magnet. The magnetic field of the “rewritten” magnet reached the values of the magnetically saturated region of the material, showing steep gradients at the border of each magnetic pole. As a replacement for conventional pulse field magnetizing methods, this technique is proposed to expand the degree of freedom in the design of electromagnetic devices, and is proposed as a novel practical method for magnetizing rare-earth magnets, which have excellent magnetic performance and require intense fields of more than 3 T to be activated.