United States

Several models for explaining of the effect of grain size on the coercivity of sintered magnets are exposed and discussed. Two situations are discussed: i) grain size bellow the single domain size ii) grain size slightly above the single domain size. For the region (i), the Stoner-Wohlfarth model is the basis for the discussion, and it can sucessfully model the hysteresis of high coercivity magnets, total or partially. For the region (ii), a model based on energy balance predicts that the coercivity decreases with the inverse of the square root of the grain size. A nucleation model is able to predict the angular dependence of the coercivity. The models are general and can be applied to any magnetic material, with or without rare-earths.


REPM 2021: The 26th International Workshop on Rare-Earth and Future Permanent Magnets and their Applications

An overview on Rare-Earths market and recycling

permanent magnets

sm-co

nd-fe-b

coercivity

It is our great pleasure to invite you to attend the 26th International Workshop on Rare Earth and Future Permanent Magnets and Their Applications (REPM2021) which will be held virtually on June 7-10, 2021. Please note, this is an updated schedule due to COVID-19 travel restrictions which forced us to postpone the conference from summer of 2020. The REPM workshop takes place every two years and is the premier conference on permanent magnets covering a wide range of topics including:

* Rare earth magnets
* Rare earth-free magnets
* Raw materials, mining and recycling
* Advanced synthesis, processing and characterization techniques
* Theoretical modeling of coercivity
* Fundamental properties of advanced magnetic materials
* Thin film magnets
* Applications of permanent magnets

***Workshop***
The workshop will be chaired by Professor George C. Hadjipanayis, University of Delaware, Newark, DE and Dr. Jinfang Liu, President & COO of Electron Energy Corporation, Landisville, PA.
The objectives of the workshop are to bring together engineers and scientists who work on permanent magnets and their applications to present their latest results and exchange ideas on a wide range of relevant topics including resources, raw materials, recycling, processing, fundamental and hard magnetic properties and applications of rare earth and future magnets.

To regsiter for this event, please follow the link below.

poster

Exchange bias in bulk FeNi-NiO nanocompounds processed by severe plastic deformation

Structural refinement and magnetic properties of SmCo5-Cu nanocomposites after high pressure torsion

Heat magnetizing method for high-performance neodymium magnets (hot-deformed Nd-Fe-B magnets)

1. Background
Neodymium magnets have high magnetic flux density and coercive force. For this reason, neodymium magnets are used in permanent magnet synchronous motors (PMSMs) such as automobile drive motors and industrial motors that require miniaturization and high output. When magnetizing magnets set on a PMSM, a method of magnetizing after setting the magnet on a rotor is often used. In recent years, motors have come into practical use with a structure in which magnets are embedded in multiple layers inside a rotor. The application of hot-deformed Nd-Fe-B magnets that do not use heavy rare earth elements to automobile drive motors is increasing. With such a change in the industry, the generated magnetic field required for full magnetization tends to increase.

2. Conventional magnetization technology
In recent years, the strength of the applied magnetic field has tended to be as large as 2400 kA / m to 3200 kA / m for full magnetization. With a conventional magnetized yoke, it has become difficult to magnetize.

3.Heat magnetizing method and analysis technology
In general, it is known that when a coercive force is reduced by heating a magnet, the intensity of a magnetic field applied for magnetization can be reduced. However, it has not yet been put to practical use. It was confirmed that by magnetizing a heated magnet (hot-deformed magnets), it was possible to sufficiently magnetize with a magnetic field strength lower than the applied magnetic field at room temperature. In order to find the magnetization conditions necessary for full magnetization, it is necessary to design a process including the magnetic circuit and the magnet temperature during magnetization, and it is essential to use a magnetization analysis method. Using general-purpose magnetic field analysis software, we clarified the importance of the input data such as the magnetization rate and improved the accuracy of the magnetization analysis.

4.Heat magnetizing method experiment for practical use and results.
A rotor and a magnetization yoke were designed and manufactured, and a test was conducted at a practical heating temperature to determine whether magnetizing was possible under conventional magnetizing conditions. When the rotor was heated, it was confirmed that there was a temperature distribution at the position of the rotor, and that the applied magnetic field also had a magnetic field distribution depending on the location. Based on the temperature distribution and the magnetic field distribution, temperature setting and magnetic field strength for uniformly performing full magnetization were determined, and magnetization was performed. Heating the rotor to a practical temperature of 100 ° C confirmed that the required magnetic field strength could be reduced by about 30%.

5. Summary
We predict the magnetic field conditions for full magnetization and the heating temperature of the rotor in advance. It is possible to design a rotor assembling process including a magnetizing process. We report on the method of magnetizing by heating and the method of magnetizing analysis which are clues for practical application.



Heat magnetizing method for high-performance neodymium magnets (hot-deformed Nd-Fe-B magnets)

Magnetic properties of HD NdFeB magnets with various reduction ratios (RR) of 68-72 %, made from the commercial MQU-F powder doped with R80Al20 (R= Ce and Dy) alloy powders are studied. Fine microstructure with well aligned platelet-shape grain and good (00L) texture in Nd2Fe14B (2:14:1) phase found for the magnets doped with R80Al20 leads to high remanence and energy product ((BH)max). By doping R80Al20 powders into HD NdFeB magnets at RR = 68%, a significant enhancement in iHc, from 16.0 kOe to 20.1 kOe for R = Ce and to 21.8 kOe for R = Dy, with keeping high (BH)max of 39.0-41.5 MGOe, is found. With increasing RR from 68% to 72%, (BH)max of the magnets doped with R80Al20 is increased to 45.8-46.9 MGOe due to remanence improvement related to the promotion of (00L) texture. iHc is decreased to 17.7 kOe for R = Ce due to demagnetizing field effect, but interestingly, for R = Dy, coercivity is further increased to 23.5 kOe. The magnetic isolation effect due to R-rich phase containing Nd, Ce, Al at the GB contributes to coercivity enhancement, and besides, the strengthened magnetocrystalline anisotropy field of 2:14:1 phase with Dy substitution gives rise to further enhancement of coercivity for that with R = Dy. This study provides an effective way to enhance coercivity of HD NdFeB magnets under the conservation of the rare earth resources.

Doping effect of R80Al20 (R= Ce and Dy) alloy powders on the magnetic properties of hot-deformed NdFeB magnet with various reduction ratios

There is a large gap in energy product (BHmax) between permanent magnets based on rare-earth elements (REE) and those which are REE-free. Although the need for REE-magnets in the highest performance devices is indisputable, there are many other applications with lower magnetic demand for which REE-magnets are still employed, in the absence of REE-free alternatives which can meet the requirements. Thus, providing new REE-free options with BHmax values within this gap would allow reducing the use of these critical resources. A common approach to address the mentioned issue is trying to enhance the properties of REE-free hard phases (e.g., ferrites) by combining them with soft magnetic phases in a composite material.
In the present work, the nature of the magnetic coupling of two magnetic phases (hard-soft) in atomic contact has been studied. First, the magnetic domain configuration of an isolated SrFe12O19 platelet shaped nanoparticle (hard phase) was studied by means of photoemission electron microscopy (PEEM) combined with x-ray absorption (XAS) and magnetic circular dichroism (XMCD) at the CIRCE beamline at the ALBA Synchrotron Light Facility,[1] concluding the particle was in a single-domain state with the magnetization direction perpendicular to the platelet plane. Afterwards, a 1.2 nm layer of metallic Co (soft phase) was deposited on top of the platelet by molecular beam epitaxy (MBE) and thorough characterization of the sample at the same synchrotron beamline revealed the magnetization of the soft metallic overlayer remained in-plane despite the out of plane magnetization displayed by the hard platelet. Thus, the two phases presented completely uncorrelated magnetic domain patterns.[2]
Our experiments therefore suggest that the two magnetic phases must not be exchange coupled to one another, which is somewhat unexpected for a system in which: (i) intimate contact between the phases is presumed, as the Co overlayer is directly grown onto the SrFe12O19 surface, and (ii) the soft phase dimension is clearly below the threshold size for rigid coupling. However, the dominant energy component here appears to be the shape anisotropy term, which for this specific case is calculated to overcome the Zeeman energy of the perpendicular magnetic field generated by the hard ferrite.
[1] L. Aballe, M. Foerster, E. Pellegrin, J. Nicolas, S. Ferrer, J. Synchrotron Radiat. 2015, 22, 745.
[2] G. D. Soria, C. Granados-Miralles, A. Mandziak, P. Jenuš, M. Saura-Múzquiz, M. Christensen, M. Foerster, L. Aballe, J. F. Fernández, J. de la Figuera, A. Quesada, J. Phys. D. Appl. Phys. 2021, 54, 054003.

Investigating the magnetic coupling of hard (SrFe12O19) and soft (Co) phases in atomic contact

Microstructural Defects in Hot-Deformed and As-Transformed τ-MnAl-C using TEM

Synthesis of La-Zn co substituted M-type ferrite under high oxygen pressure

Hard magnetic Sm1+xFe9.5Nb0.1Nδ (x=0, 0.05, 0.10, 0.15) powders were synthesized by melt-spinning, annealing and nitriding. The structure, magnetic properties and thermal stability have been investigated by means of powder X-ray diffraction, vibrating sample magnetometer, HRTEM and flux meter. By changing the Sm content and correspondingly adjusting the ratio of TbCu7–type structure and Th2Zn17–type structure, the magnetic properties can be tuned accordingly and a series of high performance Sm-Fe-N magnetic powders can be obtained. The maximum energy product obtained was 15.50 MGOe associated with a coercivity of 9.1 kOe for the SmFe9.5Nb0.1Nδ, and 13.50 MGOe associated with the highest intrinsic coercivity (HcJ) of 13.3 kOe for the Sm1.1Fe9.5Nb0.1Nδ. After exposed at 120℃ for 200 hours, the irreversible flux loss of Sm1.1Fe9.5Nb0.1Nδ bonded magnets is -4.5%, which have increased 40% compared with the Sm1+xFe9.5Nb0.1Nδ(x=0) sample.These properties for Sm-Fe-N magnetic powders are close to those of NdFeB commercial powders, which have never been reported in Sm based isotropic magnetic powders.

Controlled magnetic properties and thermal stability by tuning TbCu7 /Th2Zn17 phase in isotropic Sm-Fe-Nb-N compounds

Rare earth free MnAl-C permanent magnets have the potential to replace polymer bonded Nd-Fe-B magnets in applications where energy products of 40-100 kJm-3 are required. In addition to further improvements in magnetic properties, successful commercialisation of MnAl-C magnets will require detailed studies of their stability in various environments. MnAl-C permanent magnets consist mostly of the hard magnetic τ-phase, which has its origin in the high temperature ε-phase. In samples consisting of the ε-phase, it is possible to precipitate the carbide phase, Mn3AlC. The orientation relationship between the ε-phase and Mn3AlC is of interest as the presence of the carbide precipitates may influence the subsequent formation and magnetic properties of the τ-phase. Other phases which may be present in small volume fractions are βMn and γ2, which are the decomposition products of the metastable τ-phase, and the carbide Al4C3. Both Mn3AlC and Al4C3 are known to react with water vapour in the ambient air. In certain circumstances, the expansion caused by this reaction can lead to a decrepitation of the material. In the current work, Mn-Al-C alloys of various compositions have been produced and have been heat treated in different ways in order to influence the formation of the carbides. After characterisation in the electron microscope, the resulting materials were exposed to laboratory air for long periods of time at various temperatures and levels of humidity in order to assess the effect of composition on the environmental stability of the material.



Formation of Carbide Phases in MnAl-C Magnets

MnAl-C magnets, based on the tau-phase, contain no critical elements and have the potential to achieve energy products which would enable them to replace isotropic Nd-Fe-B bonded magnets, thus contributing to the long-term sustainability of rare earth magnet production. The tau-phase is thermodynamically metastable and is formed from the hexagonal precursor phase, epsilon. The phase transformation mechanism is of interest because it determines the population of defects in the product tau-phase. The various proposed transformation mechanisms will be reviewed here. The stability of the tau-phase can be greatly improved by the addition of C. The solubility of C in the relevant phases, along with the phase equilibria will be discussed. Detailed knowledge of the intrinsic magnetic properties of the tau-phase are useful both for estimating the upper limits of the extrinsic properties and as input for first principles calculations and micromagnetic models. Recent measurements of the intrinsic properties will be summarised and typical values will be given. The best extrinsic magnetic properties in MnAl-C to date were achieved more than 40 years ago in commercially produced, extruded materials. Since then, a number of alternative processing routes have been explored and these will be compared and contrasted here. The reported energy products of all MnAl-C materials fall short of the upper limits, estimated from the intrinsic properties of the tau-phase and therefore further improvements are possible. The extruded MnAl-C materials contain a range of defects, which potentially interact with magnetic domain walls. Understanding both this interaction and the formation mechanisms of the defects is the key to developing enhanced processing routes which deliver materials with higher energy product. Various insights from the characterisation of these defects on different length scales will be discussed. 


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Exchange bias in bulk FeNi-NiO nanocompounds processed by severe plastic deformation

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