Transmission electron microscopy study of large field induced anisotropy (Co1−xFex)89Zr7B4 nanocomposite ribbons with dilute Fe-contents

Electron microscopy was employed to investigate the structure of magnetic field crystallized (Co1−xFex)89Zr7B4 alloys with only dilute Fe-contents (x=0, 0.025, 0.05, and 0.10). The x=0.025 and 0.05 alloys exhibit very large field induced anisotropies and multiple nanocrystalline phases (BCC, FCC, and HCP) surrounded by an intergranular amorphous phase. Correlation between the volume fraction crystallized and the measured value of HK suggests that the large KU values are associated with the crystalline phases that form. Multiple crystalline phases are present for the highest KU alloys and so the presence of FCC and/or HCP-type nanocrystals may be responsible for these observations. High-resolution transmission electron microscopy (HRTEM) illustrates a number of microstructural features including (1) high densities of stacking faults in many of the FCC and, in particular, the HCP-type nanocrystals, (2) infrequent BCC/FCC orientation relationships, and (3) nanocrystals with disordered or long period stacking sequences of close-packed planes. High densities of planar faults are suggested as a potential source of KU for the FCC and HCP-type nanocrystals, but the origin of the large values of KU found in dilute Fe-containing, Co-rich “nanocomposite” alloys is an area where further work is needed.