Ferromagnetic Mn-based decagonal alloys at room temperature

A decagonal (D) phase was observed in rapidly solidified Mn-based Mn-Al-Ge-B alloys. The composition range for formation of the D-phase is 22 to 28% Al, 12 to 24% Ge and 7 to 17% B for Mn₄₅Al_55-x-yGe_xB_y alloys. The D-phase has fine grains 50 to 200 nm in diameter and the periodic lattice spacing along the c axis determined from the electron diffraction pattern is 1.2 nm. The D-phase changes to a crystalline phase after annealing for 60s at 950 K. The D-alloys exhibit ferromagnetism at room temperature and the saturation magnetization under a field of 18 kOe (J₁₈), remanence (B_r) and intrinsic coercive force (_iH_c) are 21 emu/g. 8 emu/g and 300 Oe, respectively, for Mn₄₅Al₂₅Ge₁₅B₁₅. The ferromagnetic D-alloys have a Curie temperature of 590 K in the as-quenched state and the annealing for 60s at 950K causes a decrease in Tc of about 40K. The occurrence of a ferromagnetic D-phase in Mn-based alloys is important in the future development of ferromagnetic quasicrystalline alloys with high coercive forces which result from the D-structure with strong anisotropy.