Observation of the Orbital Rashba-Edelstein Magnetoresistance

TL;DR

This paper reports the discovery of a novel orbital Rashba-Edelstein magnetoresistance in Py/Cu* heterostructures, demonstrating orbital angular momentum transport's role in magnetoresistance without heavy elements, and revealing larger spin diffusion lengths than in conventional systems.

Contribution

It provides the first experimental evidence of orbital Rashba-Edelstein magnetoresistance driven by OAM transport in a system without heavy elements, advancing understanding of orbital effects in spintronics.

Findings

Sizable MR ratio observed without heavy elements.

Interface responsible for the MR, confirmed by thickness variation.

Py's spin diffusion and dephasing lengths are larger than in Pt-based systems.

Abstract

We report the observation of magnetoresistance (MR) originating from the orbital angular momentum transport (OAM) in a Permalloy (Py) / oxidized Cu (Cu*) heterostructure: the orbital Rashba-Edelstein magnetoresistance. The angular dependence of the MR depends on the relative angle between the induced OAM and the magnetization in a similar fashion as the spin Hall magnetoresistance (SMR). Despite the absence of elements with large spin-orbit coupling, we find a sizable MR ratio, which is in contrast to the conventional SMR which requires heavy elements. By varying the thickness of the Cu* layer, we confirm that the interface is responsible for the MR, suggesting that the orbital Rashba-Edelstein effect is responsible for the generation of the OAM. Through Py thickness-dependence studies, we find that the effective values for the spin diffusion and spin dephasing lengths of Py are significantly larger than the values measured in Py / Pt bilayers, approximately by the factor of 2 and 4, respectively. This implies that another mechanism beyond the conventional spin-based scenario is responsible for the MR observed in Py / Cu* structures originated in a sizeable transport of OAM. Our findings not only unambiguously demonstrate the current-induced torque without using any heavy element via the OAM channel but also provide an important clue towards the microscopic understanding of the role that OAM transport can play for magnetization dynamics.