Exchange Interaction of Soft and Hard Magnetic Phases in Exchange-Spring Magnet of Nd3Tb1Fe76Cu0.5Nb1B18.5

Abstract

This thesis describes the experimental investigation ofan ingot of composition Nd3Tb1Fe76Cu0.5Nb1B18.5 was prepared by arc melting the constituent elements in an argon atmosphere. The purity and origin 01 the materials were more than above 99.99% from Johnson Mathev (Alfa Aesar ). Amorphous ribbons were prepared Iron the ingot using a melt spin machine with a wheel speed of 25 m/s in an Ar atmosphere. The resulting ribbons were heat treated in an evacuated quartz tube of 10-5 mbar pressure at different temperature and times to observe the effect of annealing condition on the magnetic properties. Differential Scanning Calorimetry was used to determine the crystallization temperature and X-ray diffraction (CuKa) was used to identify the phases present in the samples at different stages of the crystallization process. The magnet i/at IOU measurements were made by Quantum Design MPMSXLS Superconducting Quantum Interference Devices (SQUID) magnetometer. Hard Nanocomposite samples of the composition Nd3 Tb1 Fe76Cuo 5Nb1 18.5 exhibited exchange spring behavior for a wide range of annealing temperature and time. Amorphous flakes have been synthesized by melt spinning system and annealed in the quartz tube under a vacuum of l05 mbar pressure to observe the variation of magnetic properties with annealing condition. Highest value of coercivity around 4.76 kOe has been obtained for the ample annealed at 923 K for 5 minutes. Recoil hysteresis loops have been measured along the major demagnetization curve to observe the extent of springness of the sample annealed at 923 K for 3 minutes. Recoil loops are small having high recoil permeability. Irreversible component of magnetization was found to have very small value below the critical field. Nd - deficient Nd2Fe14B/Fe3B based nanocomposite alloys are characterized by their exchange-spring behavior resulting in remanent ratio greater than 0.5, which is highly desirable for permanent magnetic materials. Magnetic properties of exchange spring magnets arc governed by the soft and hard magnetic phases that develop under appropriate annealing condition. High reduced remanence characteristics to these materials arise from exchange coupling of magnetic moments across the interface between two phases. Besides high reduced remanence such systems possess high energy product (BH)max and a reversible demagnetization curve, which has been called as exchange-spring behavior.