Publications (2)2.17 Total impact
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Article: Phase-separated alloys for bulk exchange-biased permanent magnets
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ABSTRACT: Explorations in the metallurgical synthesis from the melt of bulk permanent magnets with coercivity conferred by the exchange bias mechanism were carried out in a two-phase materials system composed of ferromagnetic FeCo and antiferromagnetic, nominally equiatomic AuMn . Rapid solidification synthesis of composite alloys of nominal composition ( Fe <sub>65</sub> Co <sub>35</sub>)<sub>100-x</sub>( AuMn )<sub>x</sub> ( x=5 , 10, and 15) was carried out. The ribbons possess AuMn and Au <sub>2</sub> Mn spherical phases in a bcc (Fe,Co) matrix with a bimodal size distribution of nanoscaled and micron sizes. Magnetization measurements of the composite confirm an exchange bias effect correlated with a coercivity increase over that of the (Fe,Co) melt-spun base alloy. While the exchange bias effect is small, the enhanced coercivity and shifted hysteresis loop observed in a single sample create a strong argument for coercivity enhancement conferred by the exchange bias interaction between antiferromagnetic and ferromagnetic phases in a bulk melt-spun nanocomposite material.Journal of Applied Physics 05/2006; · 2.17 Impact Factor -
Article: Exchange coupling and recoil loop area in Nd2Fe14B nanocrystalline alloys
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ABSTRACT: The recoil behavior of nanocrystalline materials based on Nd2Fe14B has been investigated in melt-spun alloys with the stoichiometric composition Nd2Fe14B and in the nanocomposite Nd9Fe86B5. The onset of recoil hysteresis, or attainment of appreciable area of the recoil loop, was determined and followed as a function of the reverse applied magnetic field. Its behavior was correlated with that of two other independent parameters: the reversible portion of the recoil susceptibility and the recoil remanence, which both provide information on the ease of remagnetization of the materials. The simultaneous appearance of extrema in a restricted internal field range in all three parameters strongly suggests that the area of the recoil loops in these materials may be taken as a measure of the extent of the intergranular exchange. The temperature dependence of the results provides information about the thermal evolution of the interphase exchange coupling; this information is not evident in major loop measurements. Preliminary results indicate that the off-stoichiometric Nd9Fe86B5 maintains a higher degree of interphase exchange coupling but only at low reverse fields; the stoichiometric Nd2Fe14B maintains a lower degree of magnetic reversibility but sustains it to higher reverse fields. Comparison of the results obtained from different forms of the Nd2Fe14B-based nanocrystalline alloys highlights the origins of the differences in their technical magnetic behavior and suggests structural modification pathways to improve their properties.Journal of Magnetism and Magnetic Materials.
