Melt extracted MnAl and MnAlC

Crystallographically isotropic fibers of ferromagnetic τ-phase in the Mn-Al and Mn-Al-C alloy systems have been prepared by rapid quenching from the liquid state by melt extraction and subsequent heat treatment. The permanent magnet parameters for the fibers are greatly improved as compared to the values previously reported for isotropic alloys. The values of the remanence, coercive force and energy product are Br= 3180G,IHc= 2140 Oe and BHmax= 1.6 MGO for Mn55Al45and Br= 3400G,IHc= 1700 Oe and BHmax= 1.5 MGO for Mn53.3Al45.0C1.73. The advantage previously reported for isotropic Mn-Al alloys with carbon additions no longer exists. The remanence is probably as high as can be achieved for isotropic alloys of this composition as it represents the limit for a uniaxial material where demagnetization from saturation is by domain retation only. Transforming Mn55Al45from the nonmagnetic ε-phase to the magnetic τ-phase at 360°C in a magnetic field failed to induce any detectable anisotropy in the material.