Speaker
Description
Jeroen E. SCHEERDER1 , Bart RAES2, Marius V. COSTACHE2, Frederic BONELL2, Juan F. SIERRA2, Jo CUPPENS2, Sergio O. VALENZUELA2,3 and Joris VAN DE VONDEL1
1 INPAC - Institute for Nanoscale Physics and Chemistry, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
2 Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology, Campus UAB, Bellaterra, 08193 Barcelona, Spain
3 Institució Catalana de Recerca i Estudis Avançats (ICREA), 08070 Barcelona, Spain
Identifying the main microscopic process for spin relaxation in graphene stands as one of the most fascinating puzzles for the graphene and spintronic communities. A key property to solve this puzzle is the dependence on the carrier concentration of the spin lifetime anisotropy, which is quantified by the ratio ζ between the in-plane and out-of-plane spin lifetimes [1]. However, the only reported measurements of the out-of-plane spin lifetime, and ζ, required large (>1T) magnetic fields applied perpendicular to the graphene plane [2], thereby rendering the method unusable for low carrier densities.
Here, we demonstrate a conceptually new approach that overcomes this limitation because it does not require such large out-of-plane magnetic fields, thus making it reliable for both low and high carrier densities [3]. The approach relies on spin precession measurements under perpendicular and oblique magnetic fields (~0.1T) with respect to the graphene plane (i.e. the oblique Hanle effect). This allows to generate in- and out-of-plane spin populations and to evaluate the spin lifetime anisotropy.
In our experiments we probe the spin lifetime anisotropy in graphene based non-local lateral spin valve devices on silicon oxide. We demonstrate that in our samples ζ is independent of carrier density and temperature down to 150K, and much weaker than previously reported. Indeed, ζ is equal to one within the uncertainty of our measurements, indicating scattering dominated by random magnetic impurities or defects. These results open the way for systematic anisotropy studies on graphene with a controlled number of impurities and on different substrates. Such information is crucial to find a route to increase the spin lifetime towards the theoretical limit and, therefore, has important implications for both fundamental science and technological applications.
References
[1] W. Han et al, Nature Nanotech. 9, 794 (2014)
[2] N. Tombros et al, Phys. Rev. Let. 101, 046601 (2008) and M.H.D. Guimarães et al, Phys. Rev. Lett. 113, 086602 (2014)
[3] B. Raes, J.E. Scheerder, M.V. Costache, F. Bonell, J.F. Sierra, J. Cuppens, J. Van de Vondel and S.O.Valenzuela, Determination of the spin lifetime anisotropy in graphene using oblique spin precession, accepted in Nature Communications
E-mail: jeroen.scheerder@fys.kuleuven.be
