Atomic Structures, Magnetovolume and Pressure Effects in Amorphous La(Fe_xAl_(1-x))_(13) Alloys Consisting of Icosahedral Clusters

摘要

The atomic structures of amorphous La(Fe_xAl_(1-x))_(13) alloys have been investigated by x-ray diffraction, and the local ordering characterized by the icosahedral clusters has been confirmed. From the ~(57)Fe Mossbauer spectra, it has been revealed that the local environment around Fe atoms in the amorphous La(Fe_(0.09Al_(0.10))_(13) alloy is very similar to that in the crystalline counterpart. Re- entrant spin-glass behavior has been observed in the concentration range where the antiferromagnetic order occurs in the crystalline state. The Curie temperature in the amorphous state decreases with increasing x and it is higher than the Neel and Curie temperatures in the crystalline state. The spin-wave stiffness constant in the amorphous state is extremely small, suggesting a magnetic instability. The amorphous RE(Fe_xAl_(1-x))_(13) alloys also exhibit re-entrant spin-glass behavior and the spin freezing temperature is hardly changed by replacing RE because there is no change in the Fe-Fe distance in the icosahedral clusters. A large thermal expansion anomaly has been observed in a wide temperature range. This anomaly is retained, even at high temperatures well above T_c. A significant DELTA E effect has also been found in the temperature and field dependences of Young's modulus. The temperature dependence of the forced-volume magnetostriction partial deriv omega/partial deriv H exhibits a broad peak at the spin freezing temperature T_f and its divergent behavior at T_f is accounted for by the variable amplitude of the local magnetic moment in the itinerant spin glasses. The temperature dependence of the saturation magnetostriction lambds_S of the ferromagnetic alloys is explained by the two-ion model, reflecting the peculiar amorphous structure consisting of icosahedral clusters. Poisson's ratio determined from the surface phase velocities of the Rayleigh and Sezawa waves is very close lo 1/3. The compressibility kappa obtained from Brillouin scattering is significantly large. Various magnetovolume and pressure effects become remarkable with increasing Fe content.