Giant forced-volume and saturation magnetostrictions of amorphous La(Fe_xAl_1-x)₁₃alloys 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.

Pressure effect on the magnetic properties of amorphous alloys composed of icosahedral clusters

“…The magnitude of ∂M/∂P increases markedly in the re-entrant spin-glass concentration regime. We should notice that the spontaneous volume magnetostriction ω s and the forced volume magnetostriction ∂ω/∂H also drastically increase with increasing x (Fukamichi et al 1995). From Maxwell's relation for the free energy, the pressure effect on the magnetization is equivalent to ∂ω/∂H , namely ∂ω/∂H = −ρ∂M/∂P , where ρ is the mass density and H is the applied magnetic field.…”

“…From Maxwell's relation for the free energy, the pressure effect on the magnetization is equivalent to ∂ω/∂H , namely ∂ω/∂H = −ρ∂M/∂P , where ρ is the mass density and H is the applied magnetic field. Therefore, the concentration dependence of the forced volume magnetostriction ∂ω/∂H (Fukamichi et al 1995) is plotted in the same figure for comparison. As is expected, both −∂M/∂P and ∂ω/∂H show a very similar trend.…”

“…The compressibility κ obtained from the data on Brillouin scattering of the amorphous La(Fe x Al 1−x ) 13 alloys is large (Yoshihara et al 1994). Furthermore, the concentration dependence of the giant forced volume magnetostriction has been demonstrated (Fukamichi et al 1995). Large pressure effects on the Curie and Néel temperatures of crystalline La(Fe 0.88−x Co x Al 0.12 ) 13 alloys have been discussed in the context of the instability of the ferromagnetic state (Medvedeva et al 1992).…”

Changes in the spin-glass state and the atomic structure on annealing the amorphous Y - Fe alloys

“…These characteristics of T C and T g may not be due to the external magnetic field but may be an intrinsic feature in the re-entrant spin-glass state for amorphous Fe-based alloys. For instance, the change corresponding to T g is very uncertain while a sharp peak appears at T f in the differential magnetic susceptibility for amorphous La(Fe 0.90 Al 0.10 ) 13 alloy, which exhibits re-entrant spin-glass behaviour in a zero magnetic field (Fukamichi et al 1995). Considering these facts, the spin freezing temperature of the annealed amorphous Y 20 Fe 80 alloy with re-entrant spin-glass behaviour is referred to as T f .…”

Formation of Icosahedral Clusters and Spin Freezing in RE(Fe<SUB>1-<i>x</i></SUB>Al<SUB><i>x</i></SUB>)<SUB>13</SUB> Amorphous Alloys

“…The ZFC and FC processes are given by the right and left direction arrows, respectively. The field dependence of the spin freezing T f and the Curie temperature T C of La(Fe 0:95 Al 0:05 ) 13 amorphous alloy obtained at various DC fields 29) is shown in the inset in Fig. 6.…”