Engineering the interlayer exchange coupling in magnetic trilayers

TL;DR

This paper investigates how quantum well states in nanoscale metal films influence magnetic interlayer exchange coupling in Fe/Ag/Fe trilayers, revealing tunable oscillatory behaviors useful for device engineering.

Contribution

It demonstrates how boundary conditions and crystal structures affect quantum well states and enables control of IEC periods in magnetic trilayers.

Findings

QWSs form at zone center and edge, causing oscillatory IEC.

Changing Fe-layer thickness switches IEC oscillation periods.

Features are applicable to other noble-metal spacer trilayers.

Abstract

When the thickness of metal film approaches the nanoscale, itinerant carriers resonate between its boundaries and form quantum well states (QWSs), which are crucial to account for the film electrical, transport and magnetic properties. Besides the classic origin of particle-in-a-box, the QWSs are also susceptible to the crystal structures that affect the quantum resonance. Here we investigate the QWSs and the magnetic interlayer exchange coupling (IEC) in the Fe/Ag/Fe (001) trilayer from first-principles calculations. We find that the carriers at the Brillouin-zone center (belly) and edge (neck) separately form electron- and hole-like QWSs that give rise to an oscillatory feature for the IEC as a function of the Ag-layer thickness with long and short periods. Since the QWS formation sensitively depends on boundary conditions, one can switch between these two IEC periods by changing the Fe-layer thickness. These features, which also occur in the magnetic trilayers with other noble-metal spacers, open a new degree of freedom to engineer the IEC in magnetoresistance devices.