Phonon scattering from electrons and low-energy excitations in amorphous Pd-Cu-Si containing3dtransition metals

From measurements of the thermal conductivity of amorphous ${\mathrm{Pd}}_{77.5\mathrm{-}\mathrm{x}}$ ${\mathrm{Cu}}_6$ ${\mathrm{Si}}_{16.5}$ ${\mathrm{M}}_{\mathrm{x}}$ alloys, with 3d transition metals (M) in concentrations x=0, 5, 10, 15, and 20 at. %, the contributions of phonon scattering by electrons, ${\kappa }_{\mathrm{el}}^{\mathrm{ph}}$, and by low-energy excitations (LEE’s), ${\kappa }_{\mathrm{LEE}{}^{\mathrm{ph}}}$, have been determined separately by plotting T/${\kappa }^{\mathrm{ph}}$ versus $T^{\mathrm{-}1}$. These plots are linear for T<1 K, resulting in ${\kappa }_{\mathrm{el}{}^{\mathrm{ph}\mathrm{\sim }\mathrm{T}}}$ and ${\kappa }_{\mathrm{LEE}{}^{\mathrm{ph}\mathrm{\sim }{T}^2}}$, in accordance with theoretical calculations. The changes in ${\kappa }_{\mathrm{el}{}^{\mathrm{ph}}}$ with change in transition-metal (TM) content can be explained by a variation of the electronic density of states. The observed increase of ${\kappa }_{\mathrm{LEE}{}^{\mathrm{ph}}}$ with x (for fixed TM) is due to an enhancement of the density of states ñ of the LEE’s with increasing x. For the (Pd-Cu-Si)Fe alloys we find that an increase of ñ with x is accompanied by an increase of the glass temperature $T_g$. From this we conclude that the free-volume fraction as frozen in at $T_g$ during quenching determines the density of states of LEE’s in amorphous metals.