Optimisation of geometrical ratchets for spin-current amplification

Abstract

A two-dimensional model is used to study the geometrical effects of a nonmagnetic (NM) nanowire upon a spin-polarised electron current in a lateral spin-valve structure. We found that the implemented ratchet shapes at the centre of the NM have a crucial effect on the diffusive rate for up- and down-spin electrons along the wire, which leads to the amplification of non-local spin-current signals. By using our simple model, the geometries have been optimised. The calculated spin-current signals are in good qualitative agreement with our recent experimental results [Abdullah et al., J. Phys. D: Appl. Phys. 47, 482001(FTC) (2014)]. Our model may be very useful to evaluate such a geometrical effect on spin-polarised electron transport.

Highly Efficient Spin-Current Operation in a Cu Nano-Ring

“…For the ring device, the polarisations of the injector/detector, α , were found to be 3.6%. Over the samples that were measured in this and previous work the interfacial spin polarisation ranged by an order of magnitude from approximately 1 to 3%18. Therefore, we ignored any distributions in polarisations in our analysis.…”

Reciprocity in diffusive spin-current circuits

“…In the case of normal metal elements, reciprocity relations prove impossible "geometric spin ratchets" 19,20 that would amplify spin current or even transmit it differently in two directions.…”

“…(22) with m α 1 = m α 2 . Returning to the general expressions (20) and (21) for the currents we stress that, unlike the electric potentials µ e t , spin potentials do not have to appear only in the form of a difference µ sα 1 − µ sα 2 . In other words, the coefficients C α 1 and C α 2 are not necessarily equal in absolute value and opposite in sign.…”

“…An easy way to find the additional constraints arising from electric current conservation in a multi-terminal element is to work with the generalizations of Eqs. (20) and (21)…”

“…This naturally raises the issue of finding systems with longer spin propagation lengths. One interesting proposal 19,20 involves optimizing the geometric shape of a conductor -and a claim that, in an arrow-shaped normal wire ( Fig. 6(a)), spin transmission is enhanced as compared with a rectangular wire ( Fig.…”