Abstract Typical exchange spring magnets are composed of two phases, a rare-earth hard magnetic material and a metallic soft magnetic material, whose magnetization value is higher than those of hard magnetic phases, such as α-Fe, Fe-B, or Fe-Co. A novel high-electrical-resistance composite magnet was fabricated by consolidating micron-sized ferromagnetic nitride Sm2Fe17N3 powder particles coated with a continuous nano-sized soft magnetic ferrite oxide layer, which suppressed intergrain conductivity but sustained the magnetic exchange interactions between grains [21] . A non-magnetic resin or ceramic insulator may suffice for the coated layer but gives rise to high electrical resistance of the magnet with large deterioration of magnetization. The soft magnetic ferrite oxide layer not only suppressed intergrain conductivity, but also only slightly reduced the magnetization of the magnet. At present, the only exchange spring magnet having a combination of a soft magnetic oxide and hard magnetic nitride is the ferrite/Sm2Fe17N3 composite magnet. Sm2Fe17N3 powder particles with a size of 2 μm were coated with an “iron ferrite” layer with a grain size of about 10 nm by ferrite plating, which is an aqueous process, following which the samples were consolidated by the explosive consolidation (EC) technique. The coercivity and rectangularity of the ferrite/Sm2Fe17N3 composite magnet decreased slightly compared to those of a Sm2Fe17N3 magnet. The fully dense ferrite/Sm2Fe17N3 magnet exhibited a resistivity of about 4000 μΩ cm, which is ten times larger than that of a fully dense Sm2Fe17N3 magnet. Thus, the soft magnetic ferrite layer in the composite magnet maintained the magnetic exchange coupling between ferromagnetic Sm2Fe17N3 grains and simultaneously suppressed intergrain electrical coupling to increase the resistivity. This decreased the eddy current loss and improved the high-frequency characteristics of the composite magnets. Therefore, ferrite/Sm2Fe17N3 composites are promising materials for magnets that are operated at high frequencies in advanced applications, such as electric vehicle magnets.

中文翻译：

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基于 Sm2Fe17N3 微粉铁氧体镀层的绝缘纳米复合材料研究进展

摘要 典型的交换弹簧磁体由稀土硬磁材料和金属软磁材料两相组成，其磁化值高于α-Fe、Fe-B或Fe-等硬磁相。公司 通过将微米级铁磁性氮化物 Sm2Fe17N3 粉末颗粒包覆连续的纳米级软磁性铁氧体氧化物层固结，制备了一种新型高电阻复合磁体，其抑制了晶粒间的电导率，但维持了晶粒之间的磁交换相互作用 [21] 。非磁性树脂或陶瓷绝缘体对于涂层可能就足够了，但会导致磁体的高电阻和磁化的严重劣化。软磁性铁氧体氧化物层不仅抑制晶间导电性，但也只是略微降低了磁铁的磁化强度。目前，唯一具有软磁氧化物和硬磁氮化物组合的交换弹簧磁体是铁氧体/Sm2Fe17N3复合磁体。Sm2Fe17N3 粉末颗粒尺寸为 2 μm，通过铁氧体电镀包覆颗粒尺寸约为 10 nm 的“铁氧体”层，这是一种水性工艺，然后通过爆炸固结（EC）技术对样品进行固结. 与 Sm2Fe17N3 磁铁相比，铁氧体/Sm2Fe17N3 复合磁铁的矫顽力和矩形度略有下降。全致密铁氧体/Sm2Fe17N3 磁体的电阻率约为 4000 μΩ cm，是全致密 Sm2Fe17N3 磁体电阻率的十倍。因此，复合磁体中的软磁性铁氧体层保持了铁磁性 Sm2Fe17N3 晶粒之间的磁交换耦合，同时抑制了晶粒间的电耦合以增加电阻率。这降低了涡流损耗并改善了复合磁体的高频特性。因此，铁氧体/Sm2Fe17N3 复合材料是用于在高级应用中以高频运行的磁体的有前途的材料，例如电动汽车磁体。