Conduction electron scattering and spin-flipping at sputtered Al/Cu Interfaces

A. Sharma, N. Theodoropoulou, R. Loloee, W. P. Pratt, J. Bass, J. M. Zhang, M. A. Crimp, D. A. Cullen, David J. Smith, Kai Liu, Shuai Wang, Ke Xia

Research output: Contribution to journalArticle

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Abstract

We use two different techniques to derive the two parameters describing conduction electron scattering and spin-flipping at sputtered Al/Cu interfaces in the current-perpendicular-to-plane (CPP) geometry. These parameters are: 2ARAl/Cu, twice the interface specific resistance, where A is the area through which the CPP current flows; and δAl/Cu, which gives the probability P of spin-flipping from P = 1 - exp(δ-). A technique involving simple multilayers, and sample temperature not exceeding room temperature, gives 2ARAl/Cu = 2.3 ± 0.2 fΩm2. A technique involving exchange-biased spin-valves (EBSVs), where the sample is annealed briefly to 453 K, gives 2ARAl/Cu = 2.0 ± 0.15 fΩm2. Averaging the two values, but increasing the uncertainty for reasons explained, gives the best estimate of 2ARAl/Cu 2.15 ± 0.4 fΩm2. This average is comparable to, but smaller than, the published value of 2ARAl/Cu 3.6 ± 1 fΩm 2 derived from thermal conductance measurements, and larger than our calculated values for interface thicknesses up to 6 monolayers (ML). However, it is similar to our calculated values for an interface thickness of 8 ML. Combining extrapolation of higher temperature bulk diffusion data for Al in Cu and vice-versa, with x-ray and transmission electron microscope (TEM) studies of similarly sputtered multilayers, indicates that such interface thicknesses are possible, especially for annealed multilayers. CPP-magnetoresistance (MR) measurements of the EBSV samples give only very small spin-flipping at the Al/Cu interface-δAl/Cu 0.05-0.05+0.02. Such a small value is consistent with expected small spin-orbit interactions in both Al and Cu. Supplementary studies of CPP-MR of Permalloy (Py)-based EBSVs containing [Cu/Al/Cu] trilayers, show unusual behavior when the central Al layer is at least 10 nm thick, giving a CPP-MR like that for Py/Al, independent of Cu layer thicknesses from 0 to 10 nm. MR, x-ray, and TEM results give some clues as to the origins of this behavior, but a completely satisfactory explanation is not yet available.

LanguageEnglish (US)
Article number053903
JournalJournal of Applied Physics
Volume109
Issue number5
DOIs
StatePublished - Mar 1 2011

Profile

electron spin
conduction electrons
electron scattering
spin exchange
Permalloys (trademark)
electron microscopes
spin-orbit interactions
extrapolation
x rays
room temperature
estimates
geometry
temperature

ASJC Scopus subject areas

  • Physics and Astronomy(all)

Cite this

Sharma, A., Theodoropoulou, N., Loloee, R., Pratt, W. P., Bass, J., Zhang, J. M., ... Xia, K. (2011). Conduction electron scattering and spin-flipping at sputtered Al/Cu Interfaces. Journal of Applied Physics, 109(5), [053903]. DOI: 10.1063/1.3549688

Conduction electron scattering and spin-flipping at sputtered Al/Cu Interfaces. / Sharma, A.; Theodoropoulou, N.; Loloee, R.; Pratt, W. P.; Bass, J.; Zhang, J. M.; Crimp, M. A.; Cullen, D. A.; Smith, David J.; Liu, Kai; Wang, Shuai; Xia, Ke.

In: Journal of Applied Physics, Vol. 109, No. 5, 053903, 01.03.2011.

Research output: Contribution to journalArticle

Sharma, A, Theodoropoulou, N, Loloee, R, Pratt, WP, Bass, J, Zhang, JM, Crimp, MA, Cullen, DA, Smith, DJ, Liu, K, Wang, S & Xia, K 2011, 'Conduction electron scattering and spin-flipping at sputtered Al/Cu Interfaces' Journal of Applied Physics, vol. 109, no. 5, 053903. DOI: 10.1063/1.3549688
Sharma A, Theodoropoulou N, Loloee R, Pratt WP, Bass J, Zhang JM et al. Conduction electron scattering and spin-flipping at sputtered Al/Cu Interfaces. Journal of Applied Physics. 2011 Mar 1;109(5). 053903. Available from, DOI: 10.1063/1.3549688
Sharma, A. ; Theodoropoulou, N. ; Loloee, R. ; Pratt, W. P. ; Bass, J. ; Zhang, J. M. ; Crimp, M. A. ; Cullen, D. A. ; Smith, David J. ; Liu, Kai ; Wang, Shuai ; Xia, Ke. / Conduction electron scattering and spin-flipping at sputtered Al/Cu Interfaces. In: Journal of Applied Physics. 2011 ; Vol. 109, No. 5.
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N2 - We use two different techniques to derive the two parameters describing conduction electron scattering and spin-flipping at sputtered Al/Cu interfaces in the current-perpendicular-to-plane (CPP) geometry. These parameters are: 2ARAl/Cu, twice the interface specific resistance, where A is the area through which the CPP current flows; and δAl/Cu, which gives the probability P of spin-flipping from P = 1 - exp(δ-). A technique involving simple multilayers, and sample temperature not exceeding room temperature, gives 2ARAl/Cu = 2.3 ± 0.2 fΩm2. A technique involving exchange-biased spin-valves (EBSVs), where the sample is annealed briefly to 453 K, gives 2ARAl/Cu = 2.0 ± 0.15 fΩm2. Averaging the two values, but increasing the uncertainty for reasons explained, gives the best estimate of 2ARAl/Cu 2.15 ± 0.4 fΩm2. This average is comparable to, but smaller than, the published value of 2ARAl/Cu 3.6 ± 1 fΩm 2 derived from thermal conductance measurements, and larger than our calculated values for interface thicknesses up to 6 monolayers (ML). However, it is similar to our calculated values for an interface thickness of 8 ML. Combining extrapolation of higher temperature bulk diffusion data for Al in Cu and vice-versa, with x-ray and transmission electron microscope (TEM) studies of similarly sputtered multilayers, indicates that such interface thicknesses are possible, especially for annealed multilayers. CPP-magnetoresistance (MR) measurements of the EBSV samples give only very small spin-flipping at the Al/Cu interface-δAl/Cu 0.05-0.05+0.02. Such a small value is consistent with expected small spin-orbit interactions in both Al and Cu. Supplementary studies of CPP-MR of Permalloy (Py)-based EBSVs containing [Cu/Al/Cu] trilayers, show unusual behavior when the central Al layer is at least 10 nm thick, giving a CPP-MR like that for Py/Al, independent of Cu layer thicknesses from 0 to 10 nm. MR, x-ray, and TEM results give some clues as to the origins of this behavior, but a completely satisfactory explanation is not yet available.

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