NEW FERRIMAGNETIC QUASI-CRYSTALS IN AL-PD-MN-B AND AL-CU-MN-B SYSTEMS

An icosahedral (1) quasicrystal with ferrimagnetism at room temperature was found for rapidly solidified Al-Pd-Mn-B and Al-Cu-Mn-B alloys in the composition ranges from 5 to 20 at% Pd or Cu, 10 to 35 at% Mn and 0 to 30 at% B. The lattice parameter of the I-phase decreases linearly with increasing B content. These alloys exhibited significant magnetization when the structure consisted of the I-phase and the magnetization disappeared by the annealing-induced phase transition from I to crystalline phase. From the thermomagnetic data, the ferromagnetic Curie temperature (THETA(f)) and the asymptotic Curie temperature (THETA(a)) were determined to be 473 to 508 K and 130 to 420 K, respectively, for I-Al32.5-57.5Pd7.5-17.5Mn15-30B10-20 alloys. The difference between THETA(f) and THETA(a) decreases with an increase in Mn content, and this change was interpreted to result from the increase in the ferromagnetic interaction. The largest magnetization at 293 K in the I-Al-Pd-Mn-B alloys attained to 6.1 x 10(-7) Hm2/kg for Al42.5Pd7.5Mn30B20 and the residual magnetization was 3.2 x 10(-9) Hm2/kg. The appearance of the ferrimagnetism is presumed to be attributed to the enhancement of magnetic Mn-Mn interaction through the decrease in the atomic distance by the dissolution of B.