Precipitation of amorphous ferromagnetic semiconductor phase in epitaxially grown Mn-doped Ge thin films

TL;DR

This study demonstrates that ferromagnetism in epitaxially grown Mn-doped Ge thin films originates from the precipitation of amorphous Ge1-xMnx clusters, rather than from exchange interactions, revealing a new mechanism for ferromagnetic semiconductor behavior.

Contribution

It identifies the phase separation of amorphous Ge1-xMnx clusters as the source of ferromagnetism in Mn-doped Ge films, challenging previous assumptions about exchange interactions.

Findings

Ferromagnetism arises from amorphous Ge1-xMnx clusters.

Epitaxial growth avoids ferromagnetic intermetallic compounds.

Magnetic behavior is linked to phase-separated clusters.

Abstract

We investigated the origin of ferromagnetism in epitaxially grown Mn-doped Ge thin films. Using low-temperature molecular beam epitaxy, Mn-doped Ge films were successfully grown without precipitation of ferromagnetic Ge-Mn intermetallic compounds, such as Mn5Ge3. Magnetic circular dichroism measurements revealed that the epitaxially grown Mn-doped Ge films exhibited clear ferromagnetic behavior, but the Zeeman splitting observed at the critical points was not induced by the s,p-d exchange interactions. High-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy analyses show phase separation of amorphous Ge1-xMnx clusters with high Mn content from a Mn-free monocrystalline Ge matrix. Since amorphous Ge1-xMnx was characterized as a homogeneous ferromagnetic semiconductor, the precipitation of the amorphous Ge1-xMnx clusters is the origin of the ferromagnetic semiconductor behavior of the epitaxially grown Mn-doped Ge films.