Spin relaxation mechanism in silver nanowires covered with MgO protection layer

Abstract

Spin-flip mechanism in Ag nanowires with MgO surface protection layers has been investigated by means of nonlocal spin valve measurements using Permalloy/Ag lateral spin valves. The spin flip events mediated by surface scattering are effectively suppressed by the MgO capping layer. The spin relaxation process was found to be well described in the framework of Elliott-Yafet mechanism and then the probabilities of spin-filp scattering for phonon or impurity mediated momentum scattering is precisely determined in the nanowires. The temperature dependent spin-lattice relaxation follows the Bloch-Grüneisen theory and falls on to a universal curve for the monovalent metals as in the Monod and Beuneu scaling determined from the conduction electron spin resonance data for bulk.Spin injection, transport and detection are key ingredients in spintoronics, which have drawn a great deal of attention in recent years due to possible application for magnetic memories as well as fundamental interests concerning the interplay between charge and spin transport. 1,2 Lateral spin valves (LSVs) offer an effective means to study transport properties of a pure spin current, i.e., a diffusive flow of spin angular momentum accompanying no charge currents. A large number of the spin injection experiments have been reported since the pioneering work by Johnson and Silsbee in 1985. 3 More recently non-local spin valve experiments by Jedema et al. 4 brought renewed interests in LSVs in response to the timely development in both micro-fabrication technology and emergent interest in the pure spin current. Having a betterinsight into the spin transport and relaxation mechanism in nano-scaled devices is important to enhance the performance for the spintronic application.The spin relaxation mechanism in nonmagnetic metals (NM) has originally been discussed by Elliott and Yafet. 5,6 According to their theory, the spin-orbit interaction (SOI) in NM lifts the spin degeneracy of Bloch electrons, and results in two different energy states for up or down spin.The spin relaxation, i.e., the transition between the opposite spin states, can therefore be caused by the spin independent momentum scatterings due to impurities, grain boundaries, surfaces and phonon. [5][6][7] The earlier experimental works on the spin relaxation mechanism were mainly performed by conduction electron spin resonance (CESR) measurements and the results were

Kondo physics in non-local metallic spin transport devices

“…For Co in Cu, we observe only a weak downturn, with T max ¼ 130 K. The limited solubility in this case limits the strength of Kondo effects, whereas the 130 K T max is consistent with the 23 KoT K o500 K bound from known limits for surface and bulk Co impurities in Cu (refs 44,47). This Kondo-suppressed spin accumulation picture is also consistent with literature observations in the heavily studied Ni 80 Fe 20 /Ag system 5,29,35,36 , including the existence of a downturn (because of local Fe moments in Ag), the relatively weak decrease in DR NL (7%, because of low miscibility) and the approximate ARTICLE correspondence between T max (o20 K) and T K (B5 K for Fe/Ag). Taken as a whole, the correlations between moment formation, T K , and the magnitude and onset temperature of the downturn in DR NL are thus remarkably strong across a wide variety of materials, revealing a simple pattern to the apparently complexity in Fig.…”

“…The 5-nm thick IL in the Fe/Al IL/Cu device almost completely restores a(T) to the monotonic form found in Fe/Al. We note that tunnel barriers between the FM and NM 5,13,14,25,36,50 could have a similar role, provided they prevent even minor NM/FM contamination.…”

“…This non-local geometry has enabled significant advances in the understanding of spin transport in metals [4][5][6][7][8][9][10][11][12][13][14][15][16]18,22,[24][25][26][27][28][29][30][31][32][33][34][35][36][37] , but has also highlighted serious discrepancies with theory. The primary example of the latter is the surprising non-monotonicity in the temperature (T) dependence of DR NL , and thus the deduced l N , in the transparent interface limit.…”

“…Remarkably, despite the maturity of metallic spintronics, there remain large gaps in our fundamental understanding of spin transport in metals, particularly with injection of spins across ferromagnet (FM)/nonmagnetic metal (NM) interfaces, and their subsequent diffusion and relaxation. Unresolved issues include the applicability of the widely employed Elliott-Yafet (E-Y) 3 spin relaxation mechanism [4][5][6][7][8][9][10] , the influence of defects, surfaces and interfaces on spin relaxation at nanoscopic dimensions 8,[11][12][13][14][15] , the importance of magnetic and spin-orbit scattering [16][17][18] and the accuracy of existing models [19][20][21][22][23] .…”

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

“…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.…”