Clustering in a precipitate free GeMn magnetic semiconductor
D. Bougeard, S. Ahlers, A. Trampert, N. Sircar, and G. Abstreiter
TL;DR
This study investigates the structural and magnetic properties of precipitate-free GeMn films, revealing nanoclusters with superparamagnetic behavior but no overall spontaneous magnetization down to 2K.
Contribution
It is the first to relate the structural parameters of precipitate-free GeMn films to their magnetic behavior, highlighting the role of nanoclusters in magnetism.
Findings
Nanometer-sized Mn-rich clusters detected via TEM.
No spontaneous magnetization observed down to 2K.
Clusters exhibit superparamagnetic behavior with volume-dependent Curie temperatures.
Abstract
We present the first study relating structural parameters of precipitate free Ge0.95Mn0.05 films to magnetisation data. Nanometer sized clusters - areas with increased Mn content on substitutional lattice sites compared to the host matrix - are detected in transmission electron microscopy (TEM) analysis. The films show no overall spontaneous magnetisation at all down to 2K. The TEM and magnetisation results are interpreted in terms of an assembly of superparamagnetic moments developing in the dense distribution of clusters. Each cluster individually turns ferromagnetic below an ordering temperature which depends on its volume and Mn content.
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