Kondo physics in non-local metallic spin transport devices

Abstract

The non-local spin-valve is pivotal in spintronics, enabling separation of charge and spin currents, disruptive potential applications and the study of pressing problems in the physics of spin injection and relaxation. Primary among these problems is the perplexing nonmonotonicity in the temperature-dependent spin accumulation in non-local ferromagnetic/ non-magnetic metal structures, where the spin signal decreases at low temperatures. Here we show that this effect is strongly correlated with the ability of the ferromagnetic to form dilute local magnetic moments in the NM. This we achieve by studying a significantly expanded range of ferromagnetic/non-magnetic combinations. We argue that local moments, formed by ferromagnetic/non-magnetic interdiffusion, suppress the injected spin polarization and diffusion length via a manifestation of the Kondo effect, thus explaining all observations. We further show that this suppression can be completely quenched, even at interfaces that are highly susceptible to the effect, by insertion of a thin non-moment-supporting interlayer.

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

“…A pivotal aspect here is the fabrication of the LSVs, and in particular, whether both FM and NM were deposited within the same vacuum cycle. These techniques alter the process by which MIs enter the structure, either during the deposition [12,15] or through the source material [13]. In this Rapid Communication we show direct evidence linking the presence of the Kondo effect to the low temperature reduction in the spin diffusion length and provide a semiquantitative explanation for this.…”

“…The reduction of spin accumulation in LSVs fabricated through shadow deposition was shown by O'Brien et al to be a consequence of the diffusion of FM material into the NM at their interface [15]. Through measurements of LSVs fabricated with different FM/NM pairings, the reduction in R s is correlated to material combinations that exhibit a Kondo effect.…”

“…Arguments for the peaked behavior of the nonlocal spin signal relating to transport in the NM require the addition of surface scattering from nonmagnetic [11,16,17] and magnetic sources [12,15] which cause a reduction in λ NM below 50 K. The appearance of a thickness dependence of the temperature where the maximum spin signal occurs [11] has been attributed to the temperature where the electronic mean free path is comparable to the thickness, increasing spin flipping events through surface scattering. However, experiments by Villamor et al [13], performed with two step lithography, show no thickness dependence of the peak position in λ NM and as a result they introduced the possibility of magnetic impurities (MIs) as the origin of the low temperature reduction in λ NM .…”

“…Both sets of LSVs have a reduction in α below 70 K due to the intermixing of Py and Cu at the interface [15].…”

“…The nonmonotonic behavior of R s has prompted many theories focusing on either changes in the spin polarization of the FM/NM interface α [15] or scattering effects altering the spin diffusion length of the NM (λ NM ) [ 11,12,[15][16][17]. Arguments for the peaked behavior of the nonlocal spin signal relating to transport in the NM require the addition of surface scattering from nonmagnetic [11,16,17] and magnetic sources [12,15] which cause a reduction in λ NM below 50 K. The appearance of a thickness dependence of the temperature where the maximum spin signal occurs [11] has been attributed to the temperature where the electronic mean free path is comparable to the thickness, increasing spin flipping events through surface scattering.…”