This study investigates the effect of Cu doping on the magnetic properties of MnBi alloy at sub-ambient temperatures. The Curie temperatures (Tc) were observed at 175.2 and 161.6 K for Mn52Bi45Cu3 and Mn51Bi45Cu4 alloys, respectively. The Mn55Bi45 sample demonstrates a notable saturation magnetization (Ms) of 72 emu/g, reaching 90% of the theoretical value, indicating the successful synthesis of high-purity ferromagnetic low-temperature phase MnBi. Compared to Mn55Bi45, all Cu-doped samples exhibit higher coercivity (Hc) within the temperature range of 10–200 K. In particular, the sample with 4 at. % Cu exhibits an Hc of 7.4 kOe at 10 K, which is 37 times higher than that of the MnBi sample (0.2 kOe), and it remains significantly higher than that of the 0–3 at. % Cu-doped samples, even at 200 K. Further details of this investigation are presented in this paper.
