2D synthetic ferrimagnets by magnetic proximity coupling

TL;DR

This paper investigates magnetic proximity effects in Fe/EuO and Co/EuO bilayers, revealing that interface coupling enhances EuO's magnetic order, creating a 2D synthetic ferrimagnet with potential for spintronic devices.

Contribution

It demonstrates that EuO's magnetic order can be significantly increased via interface proximity coupling, forming a strong 2D synthetic ferrimagnet, with insights into the spatial range of this effect.

Findings

Antiferromagnetic proximity coupling is a short-range, interface-specific phenomenon.

EuO's magnetic order is enhanced in the 2D limit due to proximity effects.

The bilayer acts as a synthetic ferrimagnet with potential for spintronic applications.

Abstract

Proximity effects allow for the adjustment of magnetic properties in a physically elegant way. If two thin ferromagnetic (FM) films are brought into contact, electronic coupling alters their magnetic exchange interaction at their interface. For a low-TC rare-earth FM coupled to a 3d transition metal FM, even room temperature magnetism is within reach. In addition, magnetic proximity coupling is particularly promising for increasing the magnetic order of metastable materials such as europium monoxide (EuO) beyond their bulk TC, since neither the stoichiometry nor the insulating properties are modified. We investigate the magnetic proximity effect at Fe/EuO and Co/EuO interfaces using hard X-ray photoelectron spectroscopy. By exciting the FM layers with circularly polarized light, magnetic dichroism is observed in angular dependence on the photoemission geometry. In this way, the depth-dependence of the magnetic signal is determined element-specifically for the EuO and 3d FM parts of the bilayers. In connection with atomistic spin dynamics simulations, the thickness of EuO layer is found to be crucial, indicating that the observed antiferromagnetic proximity coupling is a short-ranged and genuine interface phenomenon. This fact turns the bilayer into a strong synthetic ferrimagnet. The increase in magnetic order in EuO occurs in a finite spatial range and is therefore particularly strong in the 2D limit-a counterintuitive but very useful phenomenon for spin-based device applications.