Abstract
In our previous work, we succeeded in fabricating ferrite/Sm2Fe17N3 composite magnets from explosive-consolidating Sm2Fe17N3 powders (2μm size) which were coated with a continuous iron ferrite layer (50nm thick) in an aqueous solution. The magnetization curves had no inflection, which suggests that the soft magnetic ferrite layer is exchange-coupled with the hard ferromagnetic Sm2Fe17N3 particles. In this paper, we provide evidence of exchange coupling in ferrite/Sm2Fe17N3 composites by the following means: 1) measurements of recoil permeability, 2) detailed microstructural observation and 3) calculations of the reduction in remanence due to the introduction of a ferrite layer in the Sm2Fe17N3 magnets. Our ferrite/Sm2Fe17N3 composite magnets are a novel type of spring magnet in which an insulating soft magnetic phase is exchange-coupled with hard magnetic phase.
Highlights
Sm2Fe17N3 compounds are good candidates for high performance magnets because of their high saturation magnetization and strong uniaxial anisotropy.[1,2] Since Sm2Fe17N3 compounds decompose into SmN and α-Fe when heated above 873K, it is fairly difficult to obtain fully dense magnets
The magnetization curves had no inflection, which suggests that the soft magnetic ferrite layer is exchange-coupled with the hard ferromagnetic Sm2Fe17N3 particles
We provide evidence of exchange coupling in ferrite/Sm2Fe17N3 composites by the following means: 1) measurements of recoil permeability, 2) detailed microstructural observation and 3) calculations of the reduction in remanence due to the introduction of a ferrite layer in the Sm2Fe17N3 magnets
Summary
Sm2Fe17N3 compounds are good candidates for high performance magnets because of their high saturation magnetization and strong uniaxial anisotropy.[1,2] Since Sm2Fe17N3 compounds decompose into SmN and α-Fe when heated above 873K, it is fairly difficult to obtain fully dense magnets. Several researchers have attempted to prepare fully dense magnets by using shock compression, aerosol deposition, hot-isostatic pressure, compression shearing, cylindrical explosive consolidation and high-pressure current sintering,[3,4,5,6,7,8] the Sm2Fe17N3 magnets produced by those methods have not yet achieved practical application because, other than oxidation resistance, Sm2Fe17N3 magnets do not provide any overwhelming advantages, such as high resistivity or low cost processing, over existing sintered rare-earth magnets At present, their application is limited to resin bonded magnets. These designs are in principle very difficult to realize due to the thin 2δs and the fine critical diameter d0 for a single domain particle of the soft magnetic phase
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