Role of Fe3Zr nanocrystals on the magnetic properties of Fe-Co-Zr-B nanocrystalline alloys

Full text: Nanostructured magnetic materials have received wide attention of researchers because of their unusual magnetic properties and applications in various devices. Conventional methods of improving the intrinsic and extrinsic soft magnetic properties have been focused on tailoring composition, control of microstructure with annealing, reduction of coercivity, increase of magnetic induction, and control of intergranular exchange coupling in amorphous (a-) and nanocrystalline alloys. However, the questions related to the influence of nanocrystalline microstructure on the soft magnetic properties are still open because of the complexity of the problem. Also, understanding how magnetic properties are optimized in conjunction with the microstructures would be useful for designing high-performance materials. In this study, we have investigated systematically the effect of Co substituting element on nanocrystalline microstructure and magnetic properties of a-Fe89-x-yCoyZr11Bx alloys annealed under static magnetic field applied along the longitudinal direction in order to clarify the role of Fe3Zr nanocrystals on the soft magnetic properties of Fe-Co-Zr-B nanocrystalline alloys. Amorphous Fe-Co-Zr-B alloy ribbons were prepared by melt-spun technique and annealed at different temperature (TA) under magnetic field. Microstructural variations of a-Fe84-x,CoxB5,Zr11 alloy ribbons annealed at 673 (a), 823 (b) and 923 K (c) for one hour duration. With increasing TA, the formations of α-Fe (Co) nanocrystals appear for the sample annealed at 823 K and α-Fe (Co) and Fe3Zr(B) compounds were observed for the sample annealed at 923 K. Coercivity (Hc) and saturation magnetization (Ms) of these nanocrystalline samples were measured by Coercimeter and vibrating sample magnetometer. Hc of the annealed sample increases from 0.1 to 0.6 Oe with increasing TA to 823 K. On further increasing TA to 923 K, Hc increased suddenly to 220 Oe due to the formation of Fe3Zr compounds and resulting magnetic hardness due to the structural inhomogeneities. We have also investigated temperature dependent magnetic properties of these alloys between 20 and 300 K to understand the role of Fe3Zr nanocrystals on the magnetic properties of Fe-Co-Zr-B nanocrystalline alloys