Heat conductivity of amorphous PdCuSi alloys containing Fe and Mn impurities

In a search for the existence of magnetic contributions to the phonon thermal resistivity, the low-temperature heat conductivity $\kappa \mathrm{}\left(T\right)\mathrm{}$ (0.3-10 K) of an amorphous diamagnetic ${\mathrm{Pd}}_{77.5}$ ${\mathrm{Cu}}_6$ ${\mathrm{Si}}_{16.5}$ sample has been compared with $\kappa \mathrm{}\left(T\right)\mathrm{}$ of amorphous spin-glass-like (${\mathrm{Pd}}_{77.5-x}{\mathrm{Cu}}_6{\mathrm{Si}}_{16.5}$) $M_x$ alloys, containing $3d$ transition metals with $x=3\mathrm{}$ at.% Mn and $x=1\mathrm{}$ at.% Fe. The phonon thermal conductivities ${\kappa }^{\mathrm{ph}}\mathrm{}\left(T\right)\mathrm{}$ of the magnetic alloys show roughly the same temperature dependence as the PdCuSi matrix. However, ${\kappa }^{\mathrm{ph}}$ in these alloys is between 20% and 30% smaller as compared with PdCuSi. This can be explained within the tunneling-state model by an enhanced density of two-level systems (TLS) in the magnetic samples. Influences on ${\kappa }^{\mathrm{ph}}$ due to either spin freezing in the range around $T_f$ or to external magnetic fields up to 5 T could not be detected. Therefore evidence for the existence of extrinsic magnetic TLS cannot be inferred from the present experiments.