Cross-sectional surface analysis of magnetic domains, microstructures, and magnetic properties of the low-temperature phase MnBi prepared by low-temperature vacuum sintering

• Published in: Vacuum 2024-12, Vol.230, p.113685, Article 113685
• Main Authors: Borsup, Jongrak, Eknapakul, Tanachat, Yordsri, Visittapong, Thanachayanont, Chanchana, Pinitsoontorn, Supree, Saisopa, Thanit, Oo, Than Zaw, Chen, Fuming, Songsiriritthigul, Prayoon
• Format: Article
• Language: English
• ISSN: 0042-207X
• DOI: 10.1016/j.vacuum.2024.113685

In this work, the low-temperature phase MnBi prepared by a low-temperature vacuum sintering process at 325 °C was studied. We found a significant increase in the energy product from 2.63 MGOe in the 12-h sintered sample to 3.64 MGOe in the 48-h sintered sample. This improvement is attributed to the solid-liquid diffusion process. Cross-sectional scanning electron microscopy (SEM) reveals that MnBi forms at the external surface of Mn particles and along interior surfaces, notably within cracks. Transmission electron microscopy further demonstrates that the Mn ratio increases and Bi decreases with distance from the crack. The selected area diffraction showed variations in the Mn ratio with distance from cracks and identified both Bi and MnBi phases in the MnBi layer. Magnetic force microscopy (MFM) analysis exhibited large phase shifts indicating repulsive or attractive forces in single ferromagnetic domains. This provides valuable insight into magnetic domains in the MnBi regions near Mn cracks. The MnBi formation model, developed for the vicinity of single cracks with uniform MnBi content, partly explains the magnetic interactions and phase shifts observed near these cracks. These findings provide significant insights into the MnBi microstructural and magnetic properties, potentially useful in tailoring and engineering magnetic structures. •Low-temperature vacuum sintering increased (BH)max of the MnBi from 2.63 to 3.64 MGOe due to the diffusion process.•Cross-sectional SEM and TEM revealed MnBi formation near cracks, with the presence of both Bi and MnBi phases.•MFM revealed significant phase shifts, indicating magnetic interactions within ferromagnetic domains in MnBi regions.•The MnBi formation model successfully explained the observed MFM signals and magnetic interactions.