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Magnetic hardening mechanism in nanocrystalline $Nd_2Fe_{14}B$ with 0.1 at. % addition of Cr, Cu, or Zr

Raviprasad, K and Ravishankar, N and Chattopadhyay, K and Umemoto, M (1998) Magnetic hardening mechanism in nanocrystalline $Nd_2Fe_{14}B$ with 0.1 at. % addition of Cr, Cu, or Zr. In: Journal of Applied Physics, 83 (02). pp. 916-920.

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The nanocrystalline hard magnetic Nd2Fe14B phase plays a crucial role in the development of exchange spring magnets. We report the hardening mechanism of nanocrystalline Nd2Fe14B, as well as the effect of small amounts of magnetic additions on the hardening behavior. It is shown that the hardening mechanism is of the pinning type in the pure Nd2Fe14B phase. Retention of pinning-type behavior, with a marginal increase in coercivity was observed for small additions of Cr or Cu. Addition of Zr changes the mechanism to nucleation type with a decrease in coercivity. Additions of Zr or Cu are thought to form precipitates at grain boundaries. The precipitates containing Cu were found to be effective in pinning the domains and enhancing the coercivity. The Zr-containing precipitates were found to be ineffective in pinning the domain walls and act as nucleation centers for reverse domains, resulting in nucleation-type hardening. The magnetic behavior of Cr-containing samples above the Neel temperature of Cr remains unaltered. This lack of change in the Cr-containing samples combined with the observed lowering of remanence indicates the presence of Cr in solution with Nd2Fe14B. Thus, we conclude that not only the magnetic nature of the impurity, but also its location is important in controlling the coercivity mechanism.

Item Type: Journal Article
Publication: Journal of Applied Physics
Publisher: American Institute of Physics
Additional Information: Copyright of this article belongs to American Institute of Physics.
Department/Centre: Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited: 22 Dec 2009 07:32
Last Modified: 19 Sep 2010 05:25
URI: http://eprints.iisc.ac.in/id/eprint/18890

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