MAGNETIC, ELECTRONIC AND STRUCTURAL-PROPERTIES OF ICOSAHEDRAL QUASI-CRYSTALS

Fe-57 transmission Mossbauer spectroscopy and X-ray diffraction measurements are performed on icosahedral quasicrystals. Magnetic and electronic properties including lattice vibrational states are studied and compared for Al-Cu-Fe- and Fe-doped Al-Cu-Ge-Mn-type quasicrystalline alloys. In the latter, magnetic long-range order features, most probably ferromagnetism, are revealed below 30 K. Even though a small amount of AlGeMn ferromagnet is found by X-ray diffraction, it is concluded that the presence of magnetic hyperfine interactions at low temperatures is an intrinsic property of the Al-Cu-Ge-Mn icosahedral system and does not depend on the amount of crystalline inclusions. Al-Cu-Fe quasicrystal depicts a non-magnetic behavior in the whole temperature range studied. Absolute values of quadrupole splitting and isomer shifts point out different electronic states of the probe atoms in both icosahedral quasicrystals. Their vibrational states are characterized by the Debye temperatures of 475 and 437 K for Al65Cu20Fe15 and (Al40Cu9.9Ge25Mn25Fe0.1)-Fe-57, respectively. Low energy mechanical activation in a ball mill is investigated for Al65Cu20Fe15 icosahedral alloy. Originally quasicrystalline structure is continuously being changed into an amorphous one in the course of mechanical grinding. Amorphous regions appear already in the early stage of ball milling and after 200 h the structural transformation is completed.