Magnetoresistance in multilayer fullerene spin valves: a first-principles study

TL;DR

This study uses first-principles calculations to analyze spin-dependent transport in fullerene-based spin valves, revealing that C70 layers achieve high magnetoresistance and polarization, while C60 layers do not, due to interface state differences.

Contribution

It provides a detailed first-principles analysis of spin transport in fullerene spin valves, highlighting the role of interface states and molecular layer type in magnetoresistance and polarization.

Findings

C70 layers achieve >90% current polarization and >100% magnetoresistance at small bias.

C60 layers show negligible polarization and magnetoresistance under similar conditions.

Interface states between molecules and metal surfaces critically influence spin-dependent transport.

Abstract

Carbon-based molecular semiconductors are explored for application in spintronics because their small spin-orbit coupling promises long spin life times. We calculate the electronic transport from first principles through spin valves comprising bi- and tri-layers of the fullerene molecules C60 and C70, sandwiched between two Fe electrodes. The spin polarization of the current, and the magnetoresistance depend sensitively on the interactions at the interfaces between the molecules and the metal surfaces. They are much less affected by the thickness of the molecular layers. A high current polarization (CP > 90%) and magnetoresistance (MR > 100%) at small bias can be attained using C70 layers. In contrast, the current polarization and the magnetoresistance at small bias are vanishingly small for C60 layers. Exploiting a generalized Julli`ere model we can trace the differences in spin-dependent transport between C60 and C70 layers to differences between the molecule-metal interface states. These states also allow one to interpret the current polarization and the magnetoresistance as a function of the applied bias voltage.