Coercivity of titanium-substituted high-temperature permanent magnets

Authors

Jian Zhou, University of Nebraska - Lincoln
Ralph Skomski, University of Nebraska-LincolnFollow
David J. Sellmyer, University of Nebraska-LincolnFollow

Date of this Version

July 2001

Comments

Published by IEEE; IEEE-Trans. Mag. 37, 2518 (2001). ©2001 IEEE. Permission to use. http://ieeexplore.ieee.org/

Abstract

The temperature dependence of the coercivity of Sm–Co based magnets is investigated by magnetization measurements and model calculations. The Zr-free titanium-substituted Sm–Co material exhibits a positive temperature coefficient dH_{c/dT of the coercivity (TCC) above room temperature, a reasonable hysteresis-loop shape, and an appreciable coercivity of 12.3 kOe at 500 C for the nominal composition Sm(Co6.2Cu0.8Ti0.3). The samples were produced by heat-treating the disordered 1 : 5 alloy commonly referred to as the TbCu7 (or 1 : 7) phase. X-ray diffraction analysis shows that, upon annealing at 1165 C, the starting material segregates into more-or-less stoichiometric 1 : 5 and 2 : 17 phases. The TCC is explained by taking into account that two-phase Sm–Co magnets are of the pinning type, that is the coercivity is realized by capturing (or repelling) domain walls at 1 : 5/2 : 17 phase boundaries. Starting from a planar-defect approach, the TCC is modeled as a function of the anisotropy constants of the involved phases. The present approach yields a fair agreement between theory and experiment, and explains the existence of a coercivity maximum in terms of the Cu concentration.}