Electric Field Control of Spin Transport

TL;DR

This paper demonstrates a gate-controlled magneto-resistance effect in carbon nanotube spintronic devices, showing that both the magnitude and sign of MR can be tuned electrically, revealing a potentially universal phenomenon for resonant tunneling systems.

Contribution

It introduces a novel gate-tunable MR effect in carbon nanotube devices with ferromagnetic contacts, highlighting its general applicability to resonant tunneling devices.

Findings

MR amplitude and sign are controllable by gate voltage

The effect is observed in carbon nanotube devices with ferromagnetic contacts

The phenomenon is predicted to be universal in resonant tunneling devices

Abstract

Spintronics is an approach to electronics in which the spin of the electrons is exploited to control the electric resistance R of devices. One basic building block is the spin-valve, which is formed if two ferromagnetic electrodes are separated by a thin tunneling barrier. In such devices, R depends on the orientation of the magnetisation of the electrodes. It is usually larger in the antiparallel than in the parallel configuration. The relative difference of R, the so-called magneto-resistance (MR), is then positive. Common devices, such as the giant magneto-resistance sensor used in reading heads of hard disks, are based on this phenomenon. The MR may become anomalous (negative), if the transmission probability of electrons through the device is spin or energy dependent. This offers a route to the realisation of gate-tunable MR devices, because transmission probabilities can readily be tuned in many devices with an electrical gate signal. Such devices have, however, been elusive so far. We report here on a pronounced gate-field controlled MR in devices made from carbon nanotubes with ferromagnetic contacts. Both the amplitude and the sign of the MR are tunable with the gate voltage in a predictable manner. We emphasise that this spin-field effect is not restricted to carbon nanotubes but constitutes a generic effect which can in principle be exploited in all resonant tunneling devices.