Hard magnetic properties of melt-spun Mn-Al-C alloys

Structural and magnetic characterization of Mnx−yAl100−x−yC2y (x = {50, 55}; y = {0, 1}) melt-spun ribbons is reported. To obtain the metastable ferromagnetic τ-phase, rapidly solidified alloys were annealed either in a vacuum furnace at 823 K or directly in the vibrating sample magnetometer under applied magnetic field. Optimal magnetic properties were demonstrated by Mn54Al44C2 samples proved to be single-phase with a coercivity of 0.19 T measured in both cases. For this composition the structural ε→τ phase transformation has been magnetically detected at 786 K, Curie temperature of τ-phase (Tc = 592 K, Tp = 610 K) has been determined using mean field approximations in ferromagnetic and paramagnetic regions. Rietveld refinement of X-ray diffraction spectra was employed to analyse the phase constitution of annealed alloys, lattice parameters as a function of chemical composition and mean grain size for the phases involved.