Long-ranged magnetic proximity effects in noble metal-doped cobalt probed with spin- dependent tunnelling

TL;DR

This study investigates how noble metal layers like Au and Cu affect spin-dependent tunnelling in magnetic junctions, revealing long-range magnetic proximity effects and providing insights into spin transport mechanisms at interfaces.

Contribution

It demonstrates that spin polarization persists over several nanometers in noble metal layers and introduces a power law model to describe the decay of spin signals, advancing understanding of magnetic proximity effects.

Findings

TMR and TSP remain finite up to several nanometers of Au or Cu insertion.

A power law decay model fits the data better than exponential models.

A 0.1 nm Cu or Au layer restores TMR and TSP within <=1 nm of Co.

Abstract

We inserted non-magnetic layers of Au and Cu into sputtered AlOx-based magnetic tunnel junctions and Meservey-Tedrow junctions in order to study their effect on tunnelling magnetoresistance (TMR) and spin polarization (TSP). When either Au or Cu are inserted into a Co/AlOx interface, we find that TMR and TSP remain finite and measurable for thicknesses up to several nanometres. High-resolution transmission electron microscopy shows that the Cu and Au interface layers are fully continuous when their thickness exceeds ~3 nm, implying that spin-polarized carriers penetrate the interface noble metal to dis- tances exceeding this value. A power law model based on exchange scattering is found to fit the data better than a phenomenological exponential decay. The discrepancy between these length scales and the much shorter ones reported from x-ray magnetic circular dichroism studies of magnetic proximitization is ascribed to the fact that our tunnelling transport measurements selectively probe s-like electrons close to the Fermi level. When a 0.1 nm thick Cu or Au layer is inserted within the Co, we find that the suppression of TMR and TSP is restored on a length scale of <=1 nm, indicating that this is a sufficient quantity of Co to form a fully spin-polarized band structure at the interface with the tunnel barrier.