Spin relaxation through Kondo scattering in Cu/Py lateral spin valves

Abstract

The temperature dependence of the spin diffusion length typically reflects the scattering mechanism responsible for spin relaxation. Within nonmagnetic metals it is reasonable to expect the Elliot-Yafet mechanism to play a role and thus the temperature dependence of the spin diffusion length might be inversely proportional to resistivity. In lateral spin valves, measurements have found that at low temperatures the spin diffusion length unexpectedly decreases. By measuring the transport properties of lateral Py/Cu/Py spin valves, fabricated from Cu with magnetic impurities of <1 ppm and ∼ 4 ppm, we extract a spin diffusion length which shows this suppression below 30 K only in the presence of the Kondo effect. We have calculated the spin-relaxation rate and isolated the contribution from magnetic impurities. We find the spin-flip probability of a magnetic impurity to be 34%. Our analysis demonstrates the dominant role of Kondo scattering in spin relaxation, even in low concentrations of order 1 ppm, and hence illustrates its importance to the reduction in spin diffusion length observed by ourselves and others.

Interdiffusion-controlled Kondo suppression of injection efficiency in metallic nonlocal spin valves

“…As the magnetic impurity density in the bulk of the channel increases, Kondo effects should become visible also in . 21 There may be some evidence of this at = 500 °C in Fig. 1(e), although the error bars are significant in that case due to the increased fitting error when Δ departs from the form of Eq.…”

Room temperature spin Kondo effect and intermixing in Co/Cu non-local spin valves

“…A long-standing puzzle in metallic NLSVs has been the widely observed suppression of the spin accumulation signal DR NL ¼ DV NL =I at low temperatures (T) for common FM/N pairings, i.e., non-monotonic DR NL ðTÞ. [6][7][8][9][10][11][12][13][14][15][16][17][18] This is in apparent contrast to predictions based on Elliott-Yafet (EY) spin relaxation in pure N metals with low spin-orbit coupling, [19][20][21] where the spin relaxation time, and hence DR NL , should increase monotonically on cooling.…”

“…Most significantly, at T A ¼ 300 C, we find no clear saturation or peak in a eff ðTÞ, even up to 275 K. This indicates that the spin Kondo effect in Co/Cu NLSVs can be active even at room temperature. In contrast, previous studies of Kondo effects in NLSVs focused on FM/N pairings with T K well below 300 K, such as Fe or Fe-based alloys with Cu (T K ¼ 30 K) 6,[8][9][10][11][12][13]15 or Ag (T K % 5 K). 7,36,37 As already noted, the low T suppression of a eff T ð Þ at T A ¼ 500 C is similar to that at T A ¼ 300 C, even evidencing a non-monotonic T A dependence.…”

“…This manifestation of the Kondo effect has now been observed in NLSVs in which the Kondo impurities diffuse into the N from the FM contacts, 11,13 as well as those in which the magnetic impurities are introduced throughout the N channel. 12,16 In the former case, local moments near the interface reduce the polarization a of the injected current. This can be quantitatively described by an extension of the Valet-Fert model accounting for spin relaxation at local moments.…”

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

“…This many-body effect, so-called Kondo effect, is currently being researched extensively due to its rich physics in condensed matter [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]; a logarithmic increase in the resistivity of diluted magnetic alloys below the characteristic temperature, i.e., the Kondo temperature (T K ), is a representative aspect of the Kondo effect. Among them, the effect of spin polarized electrons on the Kondo singlet is now receiving great interest from both theoretical [13,14,18,24] and experimental [15,17,20,22,25] points of view.…”