Positive temperature coefficients of remanence and coercivity in precipitation-hardened Gd-Co-Fe-Cu-Zr alloys

The high-temperature magnetic properties of precipitation-hardened GdxCo(89.5-x-y)Fe(8)Cu(y)Zr(2.5) (x - 11.5-13.5 and y = 7-17) alloys have been studied systematically. X-ray diffraction and transmission electron microscopy reveal that a cellular microstructure consisting of 2:17 cells surrounded by 1:5 cell boundaries is obtained after precipitation hardening. Thermomagnetic analysis further confirms the two-phase character and indicates that Cu mainly goes into the 1:5 phase. All samples exhibit a positive temperature coefficient of remanence alpha (= dM(r)/dT) from room temperature to about 600-700 K, while positive temperature coefficient of coercivity beta (= dH(c)/dT) is only observed in the alloys with low Cu content. It is found that the coercivity mechanism of the precipitation-hardened alloys varies with temperature and Cu content. (C) 2004 Elsevier B.V. All rights reserved.