BiMn: Synthesis, separation by centrifugation, and characterization

Abstract

Several Mn-based compounds have been identified as promising materials to replace permanent magnetic alloys based on rare earth elements. Amongst them is the compound BiMn, in particular the low temperature modification α-BiMn (hP4, AsNi-type, B81), which has been shown to exhibit interesting magnetic properties. In the present study, it was attempted to synthesize phase-pure α-BiMn by annealing samples at 320 °C and centrifuging them at this temperature. In this way, it was possible to obtain a distinct phase separation with the intermetallic compound on top and the liquid Bi, which is always present after the high-temperature syntheses, at the bottom. After solidification, α-BiMn with a purity of up to 87%, though not phase-pure, could be recovered. Thermal analyses as well as the temperature dependence of the magnetization indicated a peritectic decomposition at 355 ± 2 °C whereas the phase re-formed on cooling at 341 ± 2 °C. High-temperature X-ray diffraction led to a complete oxidation of the sample even in a rather pure He atmosphere. Magnetic measurements showed an increase of the coercivity of α-BiMn with increasing temperature, in general agreement with earlier literature reports. The Curie temperature could not be determined experimentally as it is apparently higher than the temperature of the peritectic decomposition.