Anisotropic magnetoresistance of bulk carbon nanotube sheets

TL;DR

This study investigates the anisotropic magnetoresistance of bulk carbon nanotube sheets under various temperatures and magnetic fields, revealing significant orientation-dependent effects and potential magnetically-induced strain.

Contribution

It provides new insights into the anisotropic magnetoresistance behavior of carbon nanotube sheets and explores the influence of alignment and chemical treatment on this phenomenon.

Findings

Large magnetoresistance differences based on field orientation.

Nitric acid treatment modifies the anisotropic response.

Evidence suggests possible magnetically-induced mechanical strain.

Abstract

We have measured the magnetoresistance of stretched sheets of carbon nanotubes in temperatures ranging from 2 K to 300 K and in magnetic fields up to 9 T, oriented either perpendicular or parallel to the plane of the sheets. The samples have been partially aligned by post-fabrication stretching, such that the direction of stretching was either parallel or perpendicular to the direction of applied electric current. We have observed large differences between the magnetoresistance measured under the two field orientations, most pronounced at the lowest temperatures, highest fields, and for the laterally-aligned sample. Treatment of the sheets with nitric acid affects this anisotropy. We analyzed the results within the theoretical framework of weak and strong localization and concluded that the anisotropy bears the mark of a more unusual phenomenon, possibly magnetically-induced mechanical strain.