Recoil hysteresis and temperature dependence of coercivity of Nd 4Fe73.5Co3Hf0.5Ga 0.5B18.5

Abstract

Recoil hysteresis and temperature dependence of coercivity of have been measured for the sample of composition Nd4Fe73.5Co 3Hf0.5Ga0.5B18.5 prepared by rapid quenching method with a wheel speed of 25 m/s and after subsequent annealing in an evacuated quartz tube under a pressure of 10-5 mbar at different temperatures and times. In the optimum and over-annealed condition, recoil hysteresis loops have been measured by the application of progressively increasing negative field and successive withdrawal to the remanence and found to have steep recoil loop and small recoil area, which is characterisitic to exchange-biased system. Temperature dependence of coercivity in the range of 5 K to 380 K has been measured for the sample of composition Nd4Fe 73.5Co3Hf0.5Ga0.5B18.5. Variation in the shape of the hysteresis loop has been observed in this temperature range. In the low temperature region i.e. below 150 K hysteresis loops are constricted due to spin reorientation of Nd2Fe 14B at 135 K while above this temperature the hysteresis loops are characterized by convex M(H) curve similar to single-phase permanent magnet. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.