Exchange bias in GeMn nanocolumns: the role of surface oxidation

TL;DR

This paper investigates how surface oxidation induces exchange bias in GeMn nanocolumns, revealing the role of MnO-like caps in magnetic coupling and demonstrating enhancement via MnO layer deposition.

Contribution

It demonstrates the occurrence of exchange bias in GeMn nanocolumns due to surface oxidation and shows how depositing MnO layers enhances this effect.

Findings

Exchange bias shift of ~100 Oe observed.

Coercivity increased by about 70 Oe.

Surface oxidation leads to MnO-like caps causing magnetic coupling.

Abstract

We report on the exchange biasing of self-assembled ferromagnetic GeMn nanocolumns by GeMn-oxide caps. The x-ray absorption spectroscopy analysis of this surface oxide shows a multiplet fine structure that is typical of the Mn2+ valence state in MnO. A magnetization hysteresis shift |HE|~100 Oe and a coercivity enhancement of about 70 Oe have been obtained upon cooling (300-5 K) in a magnetic field as low as 0.25 T. This exchange bias is attributed to the interface coupling between the ferromagnetic nanocolumns and the antiferromagnetic MnO-like caps. The effect enhancement is achieved by depositing a MnO layer on the GeMn nanocolumns.