Konrad Güth

In situ magnetic force microscope studies of magnetization reversal of interaction domains in hot deformed Nd-Fe-B magnets

A hot-deformed Nd-Fe-B sample has been chosen for the investigation of interaction domains by means of magnetic force microscopy. During the imaging process, a magnetic field of up to 6 T was applied in situ along the easy axis of magnetization. The thermally demagnetized state presents a regular pattern of interaction domains with an average width of about 1 μm but with a much larger length scale. Starting from the thermally demagnetized state, magnetization along the initial magnetization curve occurs via sequential switching of neighboring grain columns at the peripheries of the interaction domains. Demagnetization of a saturated sample takes place through the nucleation and expansion of a patchy domain pattern with a much larger extension and a substructure in the lateral range of the underlying grain size. Reversal processes under an applied magnetic field also take place at the borders of the domains.

Properties of isolated single crystalline and textured polycrystalline nano/sub-micrometre Nd2Fe14B particles obtained from milling of HDDR powder

Textured, polycrystalline Nd2Fe14B powders, produced by dynamic hydrogenation disproportionation desorption and recombination (d-HDDR) were further processed by wet and surfactant-assisted ball milling. After 4?h of milling at 400?rpm in absolute ethanol and heptane?+?oleic acid, the polycrystalline d-HDDR particles had disintegrated, via intergranular fracture, into the individual grains i.e. isolated single crystalline particles of size 200 to 500?nm. An excellent degree of alignment was produced in the single crystalline particles using an applied magnetic field. This was reflected in the remanence of the field-aligned single crystalline powder (148.1?emu?g?1) which was far higher than that of field-aligned un-milled d-HDDR powder (119.5?emu?g?1). Milling the single crystalline powder further at 800?rpm in the same media produced polycrystalline flakes of size 0.2 to 1.0??m. The polycrystalline flakes showed (0?0?l) in-plane texture and thus oriented edge to edge in an applied field.

Local orientation analysis by electron backscatter diffraction in highly textured sintered, die-upset, and hydrogenation disproportionation desorption and recombination Nd–Fe–B magnets

Local texture in polycrystalline Nd–Fe–B powders produced by hydrogenation disproportionation desorption and recombination (HDDR) and by pulverization of hot deformed material (MQA-F) has been studied by electron backscatter diffraction and compared with the ideal case of a powder consisting of single-crystalline particles. The HDDR powder particles exhibited a biaxial {001}, 〈100〉 local texture, whereas the MQA-F particles showed a local 〈001〉 fiber texture. This was explained by differences in the texture mechanisms of the two materials. Resin bonded compacts were prepared from the two polycrystalline powders following alignment in an external magnetic field. The degree of texture on the global scale was determined from magnetic measurements of these compacts and the results were compared with those from a commercial Nd–Fe–B sintered magnet and hot deformed magnet.

Towards an Alloy Recycling of Nd–Fe–B Permanent Magnets in a Circular Economy

Rare earth permanent magnets are an integral part of many electrical and electronic devices as well as numerous other applications, including emerging technologies like wind power, electric vehicles, fully automized industrial machines, and robots. Due to their outstanding properties, magnets based on Nd–Fe–B alloys are often not substitutable by employing less critical material systems. Today, WEEE (Waste Electrical and Electronic Equipment) take-back systems for a variety of products containing Nd–Fe–B magnets are well established. They form an ideal basis for a systematic provision of scrap magnets that can be recycled. Hydrometallurgical approaches that aim at completely dissolving the material to regain elements or oxides are energy and time consuming. Thus, they are costly and come with a large environmental footprint. Recycled rare earth elements and oxides would have to compete with virgin materials from China and can hardly be processed in Europe, due to the lack of respective industries. This paper presents material-to-material recycling approaches, which would maintain the magnet alloys and use them directly for a new magnet production loop. The recycled magnets compete well with those made from primary materials, that is, in terms of magnetic properties as well as in terms of production costs. They excel by far rare earth permanent magnets made from primary materials regarding the environmental footprint. Regarding the shift towards a Green Economy, humanity will consume less fuels in combustion processes but rather exploit functional materials in renewable energy and mobility technologies in the future. This shift fundamentally depends on a circular economy of noble as well as less-noble technology metals.