Direct evidence for suppression of the Kondo effect due to pure spin current

We study the effect of a pure spin current on the Kondo singlet in a diluted magnetic alloy using nonlocal lateral spin valve structures with highly spin polarized ${\mathrm{Co}}_2\mathrm{FeSi}$ electrodes. Temperature dependence of the nonlocal spin signals shows a sharp reduction with decreasing temperature, followed by a plateau corresponding to the low temperature Fermi liquid regime below the Kondo temperature ($T_{\mathrm{K}}$). The spin diffusion length of the Kondo alloy is found to increase with increasing spin accumulation. The results are in agreement with the intuitive description that the Kondo singlet cannot survive any more in sufficiently large spin accumulation even below $T_{\mathrm{K}}$.

Figure 1

Schematic illustrations of the density of states in a Kondo alloy based on the Anderson model in $T<T_{\mathrm{K}}$ (a) without and (b) with spin accumulation ($\mathrm{\Delta }\mu$) in the host nonmagnetic metal.

Figure 2

(a) A scanning electron micrograph of a CFS-Cu(Fe)-CFS LSV. (b) Temperature dependent resistivity of Cu(Fe) used in this study. Nonlocal spin signals of CFS-Cu(Fe)-CFS LSVs with (c) $d=312$ nm and (d) $d=496$ nm, respectively, measured at 5 K with $I=1.0$ mA.

Figure 3

(a) Temperature dependence of $\mathrm{\Delta }{R}_{\mathrm{S}}$ for CFS-Cu(Fe)-CFS LSVs with various $d$ for $I=1.0$ mA. (b) Normalized $\mathrm{\Delta }{R}_{\mathrm{S}}$ as a function of temperature for the various LSVs. The inset shows a plot of (1-normalized $\mathrm{\Delta }{R}_{\mathrm{S}}$) versus temperature. The red lines are fits by using a function representing the logarithmic temperature variation.

Figure 4

(a) Temperature dependence of $\mathrm{\Delta }{R}_{\mathrm{S}}$ for a CFS-Cu(Fe)-CFS LSV (left axis) with $d=312$ nm recorded at every 1.0 mA. The data on the right axis shows reference data for a CFS-Cu-CFS LSV with $d=300$ nm recorded at every 1.0 mA. (b) The estimated ${\lambda }_{\mathrm{Cu}\left(\mathrm{Fe}\right)}$ as a function of $I$ at 5 K for the LSV with $d=312$ nm.