The dependences of saturation magnetostriction lambda s and forced-volume magnetostriction delta omega / delta H on the concentration and temperature have been investigated for amorphous La(FexAl1-x)13 alloys prepared by high-rate DC sputtering. The magnetic phase diagram obtained from the differential magnetic susceptibility dM/dH has been correlated with these magnetostrictions. The spin freezing temperature Tf is drastically decreased but the Curie temperature TC is slightly increased on application of a magnetic field. The temperature dependences of lambda s and delta omega / delta H exhibit a broad peak at the spin freezing temperature Tf. The temperature dependence of lambda s for the ferromagnetic alloys is explained by the two-ion model, reflecting the peculiar amorphous structure consisting of icosahedral clusters. The peak of delta omega / delta H at the Curie temperature becomes indistinct with increasing ferromagnetic state in contrast with the peak at the spin freezing temperature. The giant values of delta omega / delta H and its divergent behaviour at the spin freezing temperature are accounted for by the variable amplitude of the local magnetic moment in the itinerant spin glasses. The significant large delta omega / delta H is connected with the pronounced large magnetovolume and magnetoelastic effects such as the spontaneous volume magnetostriction omega s, compressibility kappa and high-field susceptibility chi hf which bring about various Invar anomalies.
Atomic structures of amorphous La(FexAl1-x)13 alloys (x=0.80, 0.85, 0.90 and 0.95) were studied by X-ray diffraction. The distance between the icosahedral cluster and the La atom is slightly reduced with the increase in x. This indicates a slight change in arrangements of the icosahedral clusters around the La atom without changing the basic structure of the icosahedral clusters. On the other hand, the concentration dependence of coordination numbers for Fe-Fe pairs in the amorphous state resembles that in the crystalline From the 57Fe Mossbauer spectra, it was revealed that local environment around Fe atoms in the La(Fe0.9Al0.1)13 alloy is very similar to that in the crystalline counterpart. The magnetic properties of the amorphous and crystalline alloys have been closely correlated with their characteristic atomic strictures.
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