Crystalline Evolution and Large Coercivity in Exchange-Biased Nd 2 Fe 14 B / Fe 3 B Nanocomposite Magnets

Tb substituted amorphous ribbons of composition Nd4-xTbxFe71+yCo5Cu0.5Nb1B18.5-y (x=0.4; y=12.5 and 0) prepared by a melt spinning technique in an Ar atmosphere has been studied to observe the exchange coupled soft and hard magnetic phases in the nanocrystalline state. For thermal analysis of the ribbon samples differential scanning calorimeter (DSC) was used in order to determine the crystallization temperatures. Significant changes in the crystallization temperatures are observed in the DSC traces due to the difference in B (Boron) content of two batches of composition. The samples were characterized by X-ray diffractometer (XRD) with CuKα radiation and vibrating sample magnetometer (VSM) of as-quenched and annealed condition during 10 minutes. Structure and magnetic properties of the ribbons clearly depend on their composition. Glass forming ability (GFA) of the alloys is decreased with decreasing B-concentration. Coercivity (Hc) and maximum energy product (BH)max of the alloys is significantly enhanced by increasing B-concentration. The optimal annealing conditions for the best hard magnetic performance of the ribbons were obtained. The composition dependence of the structure and magnetic properties of the alloys was discussed.

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