Giant forced-volume and saturation magnetostrictions of amorphous La(FexAl1-x)13 alloys composed of icosahedral clusters

Abstract

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.