Spin-dependent transport for armchair-edge graphene nanoribbons between ferromagnetic leads

TL;DR

This paper theoretically studies spin-dependent electron transport in armchair-edge graphene nanoribbons between ferromagnetic leads, revealing how ribbon width and exchange splitting influence magnetoresistance and spin transfer torque, with implications for spintronic device design.

Contribution

It provides a detailed analysis of how AGNR width and exchange splitting affect spin transport and magnetoresistance, offering guidance for GNR-based spintronic device development.

Findings

TMR exhibits a plateau structure near zero bias, broader in metallic AGNRs.

Exchange splitting suppresses TMR amplitude in semiconducting AGNRs.

Current-induced spin transfer torque is larger in semiconducting AGNRs.

Abstract

We theoretically investigate the spin-dependent transport for the system of an armchair-edge graphene nanoribbon (AGNR) between two ferromagnetic (FM) leads with arbitrary polarization directions at low temperatures, where a magnetic insulator is deposited on the AGNR to induce an exchange splitting between spin-up and -down carriers. By using the standard nonequilibrium Green's function (NGF) technique, it is demonstrated that, the spin-resolved transport property for the system depends sensitively on both the width of AGNR and the polarization strength of FM leads. The tunneling magnetoresistance (TMR) around zero bias voltage possesses a pronounced plateau structure for system with semiconducting 7-AGNR or metallic 8-AGNR in the absence of exchange splitting, but this plateau structure for 8-AGNR system is remarkably broader than that for 7-AGNR one. Interestingly, the increase of exchange splitting $\Delta$ suppresses the amplitude of the structure for 7-AGNR system. However, the TMR is enhanced much for 8-AGNR system under the bias amplitude comparable to splitting strength. Further, the current-induced spin transfer torque (STT) for 7-AGNR system is systematically larger than that for 8-AGNR one. The findings here suggest the design of GNR-based spintronic devices by using a metallic AGNR, but it is more favorable to fabricate a current-controlled magnetic memory element by using a semiconducting AGNR.