A strong pinning model for the coercivity of die-upset Pr-Fe-B magnets
- Physics Department, General Motors Research Laboratories, Warren, Michigan 48090-9055 (US)
We have measured the temperature dependence of the intrinsic coercivity {ital H}{sub {ital ci}}({ital T}) between 5 and 565 K in a die-upset Pr-Fe-B magnet. Over a very wide temperature range up to 477 K, {ital H}{sub {ital ci}}({ital T}) is in excellent agreement with a model for strong domain-wall pinning by a random array of pinning sites proposed by Gaunt (P. Gaunt, Philos. Mag. B {bold 48}, 261 (1983)). The model includes both the temperature dependence of the intrinsic magnetic properties of the Pr{sub 2}Fe{sub 14}B phase and the effects of thermal activation of domain walls over the pinning barrier. The pinning sites are modeled as nonmagnetic planar inhomogeneities at the boundaries between platelet-shaped Pr{sub 2}Fe{sub 14}B grains. We develop an expression for the maximum pinning force per site, {ital f}, and derive the model prediction that ({ital H}{sub {ital ci}}/{gamma}{ital H}{sub {ital A}}){sup 1/2} varies linearly with ({ital T}/{gamma}){sup 2/3}, where {ital H}{sub {ital A}} and {gamma} are the magnetocrystalline anisotropy field and the domain-wall energy per unit area of the Pr{sub 2}Fe{sub 14}B phase, respectively. Significant deviations from the model are observed only at high temperature, suggesting that the strong pinning model is no longer valid very close to the Curie temperature (565 K). The present result agrees with the model fit obtained for a die-upset Nd-Fe-B magnet.
- OSTI ID:
- 5594428
- Journal Information:
- Journal of Applied Physics; (USA), Vol. 69:8; ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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