Revisiting the measurement of the spin relaxation time in graphene-based devices

Abstract

A long spin relaxation time (τ sf ) is the key for the applications of graphene to spintronics but the experimental values of τ sf have been generally much shorter than expected. We show that the usual determination by the Hanle method underestimates τ sf if proper account of the spin absorption by contacts is lacking. By revisiting series of experimental results, we find that the corrected τ sf are longer and less dispersed, which leads to a more unified picture of τ sf derived from experiments. We also discuss how the correction depends on the parameters of the graphene and contacts.

Spin transport in two-layer-CVD-hBN/graphene/hBN heterostructures

“…To study the influence of the LR contacts on spin transport [24,[35][36][37], we calculate the values of (R c /R s , L/λ s ) parameters. Here R s = R sq λ s /W is the spin resistance of the graphene with λ s = √ D s τ s , the spin-relaxation length, and the ratio R c /R s quantifies the back-flow of injected spins into the contacts [24].…”

Nanosecond spin relaxation times in single layer graphene spin valves with hexagonal boron nitride tunnel barriers

“…8 , high quality tunnel barriers are critical for obtaining higher spin relaxation times (τ s ) in graphene because barriers with pinholes or rough surface morphology can cause additional contact-induced spin relaxation, which has received a great deal of interest recently. [10][11][12][13][14] As opposed to growing oxide tunnel barriers on graphene, a thin insulating twodimensional (2D) van der Waals material can also be used as a tunnel barrier. A particular material of interest is single (or few) layer h-BN because of its various suitable properties 15 : large energy band gap ~5.97 eV, high crystallinity, spin filtering 16 , absence of pinholes and dangling bonds, atomic lattice similar to graphene, and chemical stability at ambient conditions.…”

Long Spin Diffusion Length in Few-Layer Graphene Flakes

“…By fitting Hanle curves [2] that describe the precession of transport spins in an out-of-plane magnetic field, a wide range of values for l G sf was reported, from 1 μm [15] up to 30 μm [17] at room temperature. The origin of the spin relaxation that limits l G sf is still debated and may be associated with impurities [18], ripples [6], substrates [19], and spin absorption in ferromagnetic electrodes [12,20,21].…”

“…This problem can be avoided by inserting an insulating barrier between the two materials [23], e.g., with resistances in the range of a few MΩ for graphene with metallic electrodes [20]. By exploiting this approach, Ref.…”

“…Therefore, we may directly compare our low-temperature values with the smaller experimental values of ≤30 μm, for graphitic flakes [13][14][15] and graphene [17] at various temperatures, including room temperature. Although high interfacial resistance is required to limit spin absorption [12,20,21] in our LSMO electrodes, our interfacial resistance is so high that MR is suppressed. This is seen for the aforementioned choice of γ ¼ 0.8, where reducing the interfacial resistance to obtain R P ¼ 12.5 kΩ would increase MR to 170% (Fig.…”