A Theoretical Study on Spin-Dependent Transport of "Ferromagnet/Carbon Nanotube Encapsulating Magnetic Atoms/Ferromagnet" Junctions with 4-Valued Conductances

TL;DR

This paper theoretically investigates spin-dependent transport in ferromagnet/carbon nanotube/ferromagnet junctions, demonstrating four-valued conductances based on nanotube resonance states, which could enable multi-level memory devices.

Contribution

It introduces a theoretical model for 4-valued conductances in FM/spin-polarized nanotube/FM junctions, considering resonance effects of encapsulated magnetic atoms.

Findings

4-valued conductances depend on nanotube resonance state

On-resonant nanotubes show opposite conductance order compared to off-resonant ones

Magnetoresistance ratio can exceed conventional parallel/anti-parallel values

Abstract

As a novel function of ferromagnet (FM)/spacer/FM junctions, we theoretically investigate multiple-valued (or multi-level) cell property, which is in principle realized by sensing conductances of four states recorded with magnetization configurations of two FMs; (up,up), (up,down), (down,up), (down,down). In order to sense all the states, 4-valued conductances corresponding to the respective states are necessary. We previously proposed that 4-valued conductances are obtained in FM1/spin-polarized spacer (SPS)/FM2 junctions, where FM1 and FM2 have different spin polarizations, and the spacer depends on spin [J. Phys.: Condens. Matter 15, 8797 (2003)]. In this paper, an ideal SPS is considered as a single-wall armchair carbon nanotube encapsulating magnetic atoms, where the nanotube shows on-resonance or off-resonance at the Fermi level according to its length. The magnitude of the obtained 4-valued conductances has an opposite order between the on-resonant nanotube and the off-resonant one, and this property can be understood by considering electronic states of the nanotube. Also, the magnetoresistance ratio between (up,up) and (down,down) can be larger than the conventional one between parallel and anti-parallel configurations.