One-dimensional ferromagnetic edge contacts to two-dimensional graphene/h-BN heterostructures

TL;DR

This paper investigates 1D ferromagnetic edge contacts to 2D graphene/h-BN heterostructures, revealing challenges with spurious signals caused by fringe fields and charge spreading, and discusses optimization strategies for spin injection.

Contribution

It provides the first detailed analysis of fringe field effects in 1D ferromagnetic contacts to 2D heterostructures and suggests methods to minimize these effects for improved spintronic applications.

Findings

Spurious magnetoresistance signals originate from local Hall effects.

Fringe fields from contacts can be reduced below 100 mT with geometry optimization.

Charge current spreading influences nonlocal measurement signals.

Abstract

We report the fabrication of one-dimensional (1D) ferromagnetic edge contacts to two-dimensional (2D) graphene/h-BN heterostructures. While aiming to study spin injection/detection with 1D edge contacts, a spurious magnetoresistance signal was observed, which is found to originate from the local Hall effect in graphene due to fringe fields from ferromagnetic edge contacts and in the presence of charge current spreading in the nonlocal measurement configuration. Such behavior has been confirmed by the absence of a Hanle signal and gate-dependent magnetoresistance measurements that reveal a change in sign of the signal for the electron- and hole-doped regimes, which is in contrast to the expected behavior of the spin signal. Calculations show that the contact-induced fringe fields are typically on the order of hundreds of mT, but can be reduced below 100 mT with careful optimization of the contact geometry. There may be additional contribution from magnetoresistance effects due to tunneling anisotropy in the contacts, which need to be further investigated. These studies are useful for optimization of spin injection and detection in 2D material heterostructures through 1D edge contacts.