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     

Materials for permanent magnets

Until the middle 50's, both magnetically soft and hard materials were produced mostly by melting, casting and hot manipulation. Powder techniques were being applied on a pilot plant scale only, but during the last two decades these have become predominant and in the future almost all permanent magnets will be produced by this route. The development of new compositions and processes is traced, with examples of applications, with emphasis on the impact which the latest rare earth cobalt or iron super energy magnets are having in this field. They are penetrating into existing markets and expanding into new ones not possible hitherto.     

Quasi-sheet multipole permanent magnets

A Rare-Earth Permanent Magnet design system with which a desired pure multipole field can be achieved by accurately deploying REPM blocks around a working region so as to generate magnetic sheet currents which follow the profile of a magnetically soft yoke is presented here. In addition to the general Quasi-Sheet Multipole model, examples of two small operating QSM quadrupoles together with a large QSM dipole are also described.     

Modulating thickness multipole permanent magnets

The magnetic field distributions of modulating thickness permanent magnets [1,2] are discussed in this paper. The field distributions are calculated by using the program POISCR and the actual demagnetization curve of the REC permanent magnet material. The results show that the performance of the MT type magnets is about the same as or even better than that of the modulating magnetization direction type (MMD) [3] and that the MT type magnet with soft iron shield requires less REC material than MMD type magnets.     

New thin film permanent magnets

Abstract

An overview is provided of research on coupled hardsoft magnetic multilayers as model exchange-spring systems, with an emphasis on uncovering the fundamental magnetic reversal processes and the correlation between microstructure and magnetic properties. The goal is to illustrate the rich opportunities to understand and hopefully improve permanent magnets by utilising the principles of nanotechnology and the microscopic tools of the modern materials science.     

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.     

Magnetic and Thermal Properties of HTS Bulk Magnet in the Pulsed-Field Magnetizing Process

In order to enhance the field-trapping ability of high T _c superconducting melt-textured bulk materials which act as quasi-permanent magnets when they capture the external magnetic fields, it is important to enhance the mechanical toughness of the materials to stand the stress induced by the magnetic repulsive force and thermal expansion. We adopted a dense Dy123-based bulk material with reduced void concentration in the experiment. Since the heat generations due to the flux motions in the samples results in the degradation of J _c, the time evolutions of the trapped magnetic fields and the temperature rises during and after the pulsed-field magnetizing processes were precisely measured at the same time to evaluate the penetrating flux motions and the heat generations in the sample. A single and couple of the magnetic pulsed fields with various intensities were successively applied to the sample at 30 K. The single magnetic field application exhibited a peak effect in the trapped-field behavior and tended to decline due to the heat generation. In the iterative pulsed-field application, the behaviors of the trapped fields and the temperature changes were found to be inverse between the first and the second pulsed-field applications. This implies that the flux penetration behavior into the sample magnet at the second field application is strongly restricted by the presence of former trapped fields which were formed by the first field applications.     

纳米晶复合永磁材料研究进展

就近年来纳米晶双相复合永磁材料的发展状况,从该类合金的矫顽力理论和提高磁性能的方法2个方面为重点做简要的评述.     

热处理工艺对块体纳米晶Fe3B/Nd2Fe14B复合磁体性能的影响

采用放电等离子烧结技术(Spark Plasma Sintering,简称SPS技术)将快淬Nd4.5Fe77B18.5薄带制备成块状纳米晶复合磁体.着重研究了热处理工艺对磁体密度、微观结构和磁性能的影响.结果表明,通过直接烧结得到的磁体具有超细纳米晶结构,合适的热处理可以消除残余非晶,得到较好的晶体结构和磁性能.但过高的热处理温度和较长的保温时间的增大会造成晶粒长大,结果导致磁性能的恶化.在最佳热处理条件下得到的磁体的磁性能为Br=1.014T,JHc=237.21 kA/m,(BH)max=61.85 kJ/m3.     

Electrochemical corrosion resistance of Fe-Nd-B permanent magnets

The corrosion behaviour of three permanent magnets based on the Fe-R-B system, namely Fe_76.9Nd_15.1 B₈ (Vacodym 335), Fe_76.7Nd_14.3DyB₈ (Vacodym 370) and Fe₇₇Nd₁₅B₈ (Neomax 35) was investigated in 0.5 M H₂SO₄ using mass loss and electrochemical techniques. Differences in the chemical composition of the tested magnets did not affect the runs of polarization curves in the active dissolution range or in the cathodic one, but they influenced the runs of these curves in the passive state. The magnets show distinct lack of resistance to acid corrosion both in the magnetized and demagnetized state. Weak corrosion resistance appears also at strongly cathodic polarizations, and the rate of this abnormal dissolution increases with the rise of the hydrogen evolution rate on the surface of the magnets     

Separation of small nonferrous particles using an inclined drumeddy-current separator with permanent magnets

This paper presents a method for separating small metallic nonferrous particles from two-component nonferrous mixtures using, a new type of dynamic eddy-current separator with permanent magnets. The so-called inclined drum eddy-current separator (IDECS) consists of an inclined vertical rotary drum covered with permanent magnets, alternately N-S and S-N oriented, directly fixed on the axis of an electric engine. The particles to be separated are brought into the field on an oblique trajectory, hit the drum, and are deflected in the variable field under electrodynamic and mechanical interactions. The strongly conducting and poorly conducting particles assume different trajectories depending on their electrical conductivities, which lead to their separation. The paper presents the results of grade and recovery of wastes consisting of small particles (under 5 mm) derived from Cu-Pb and Cu-Al mixtures. The advantages of IDECS are that its efficiency is close to that of the usual dynamic eddy-current separator and its equipment cost is lower. A disadvantage is that the intermediate product must be passed again through a separation process     

粘结永磁体发展现状

主要分析了当前粘结永磁体产业发展的现状、最新发展动态，并叙述了粘结永磁体常用的生产方法。认为粘结水磁产业当前面临极佳的发展机遇。并对目前国内粘结永磁体现状及方向提出了一些看法和建议。     

New two-dimensional model for inhomogeneous permanent magnets

Existing solutions of the nucleation fields in inhomogeneous ferromagnets, based on the minimization of the energy equation of a soft magnetic inclusion implanted in a hard magnetic matrix, are reviewed and compared. A macroscopic two-dimensional (2-D) model based on the Preisach formalism is proposed. The properties of the model and the effect of the identification parameters on the major loop characteristics are investigated. The simulated results include major and minor loops and the rotational hysteresis loss calculation     

利用永磁体的室温磁制冷机性能研究

介绍了利用1.5 T永磁体驱动,氦气作为换热流体,采用主动式磁回热器的室温磁制冷机的实验研究情况.在现有实验装置下,通过调节气体压力与循环频率,高低温端最大达到了10.7K的温差,研究结果为室温磁制冷机的设计以及进一步发展提供了参考.     

Experimental characterization of permanent magnets used in periodicstructures

In a periodic structure, the magnetic flux density profile of a hybrid undulator depends strongly on the characteristics of its permanent magnets. A simple procedure to select the best permanent magnets for periodic magnetic structures is presented here. We used a very simple apparatus for the magnetic field measurements. We tested this by assembling periodic structure prototypes formed by brick-shaped permanent magnets