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The microstructure, high performance magnetic hardness and magnetic after-effect of an α- FeCo/Pr2Fe14B nanocomposite magnet with low Pr concentration

In this paper, a systematic investigation of the microstructure, high performance magnetic hardness as well as novel magnetic memory effect of the Pr4Fe76Co10B6Nb3Cu 1 nanocomposite magnet fabricated by conventional melt-spinning followed by annealing at temperatures ranging from 600 to 700 °C in Ar gas for nanocrystallization are presented and discussed. Transmission electron microscopy (TEM) observation confirms an ultrafine structure of bcc-Fe(Co) as a magnetically soft phase and Pr2Fe14B as a hard magnetic phase with a spring-exchange coupling in order to form the nanocomposite state. Electron diffraction analysis also indicates that the Co atoms together with Fe atoms form the Fe70Co30 phase with a very high magnetic moment (2.5μB), leading to a high saturation magnetization of the system. High magnetic hardness is obtained in the optimally heat-treated specimen with coercivity Hc = 3.8kOe, remanence Br = 12.0kG, Mr/Ms = 0.81 and maximum energy product (BH) max = 17.8MGOe, which is about a 25% improvement in comparison with recent results for similar compositions. High remanence and reduced remanence are the key factors in obtaining the high performance with low rare-earth concentration (only 4at.%). High-resolution TEM analysis shows that there is a small amount of residual amorphous phase in the grain boundary, which plays a role of interphase to improve the exchange coupling. Otherwise, in terms of magnetic after-effect measurement, a magnetic memory effect was observed for the first time in an exchange-coupled hard magnet. © 2009 IOP Publishing Ltd.

 Ngo D.-T., Duong H.-G., Nguyen H.-H., Nguyen C., Basith M., Hoang D.-Q.
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  Từ khóa : Coercivity; Electron diffraction analysis; Energy products; Fe atoms; Hard magnetic phase; Hard magnets; Heat-treated specimens; High-resolution TEM analysis; High-saturation magnetizations; Key factors; Magnetic after effects; Magnetic hardness; Magnetic memories; Melt-spinning; Nanocomposite magnets; Rare-earth; Residual amorphous phase; Systematic investigations; Tem; Ultra fine structures; Atoms; Exchange coupling; Grain boundaries; Hardness; Iron compounds; Magnetic moments; Magnetic storage; Magnets; Microstructure; Nanocomposites; Nanocrystallization; Niobium; Rare earth elements; Remanence; Saturation magnetization; Sodium compounds; Transmission electron microscopy; Magnetic materials; boron; cobalt; copper; iron; nanocomposite; nanocrystal; nanomaterial; nanoparticle; nanoribbon; niobium; praseodymium; article; concentration process; electron diffraction; energy; hardness; magnet; magnetic field; magnetism; nanochemistry; nanofabrication; particle size; priority journal; temperature; transmission electron microscopy