Structure and magnetism of self-organized Ge(1-x)Mn(x) nano-columns

Abstract

We report on the structural and magnetic properties of thin Ge(1-x)Mn(x)films grown by molecular beam epitaxy (MBE) on Ge(001) substrates at temperatures (Tg) ranging from 80deg C to 200deg C, with average Mn contents between 1 % and 11 %. Their crystalline structure, morphology and composition have been investigated by transmission electron microscopy (TEM), electron energy loss spectroscopy and x-ray diffraction. In the whole range of growth temperatures and Mn concentrations, we observed the formation of manganese rich nanostructures embedded in a nearly pure germanium matrix. Growth temperature mostly determines the structural properties of Mn-rich nanostructures. For low growth temperatures (below 120deg C), we evidenced a two-dimensional spinodal decomposition resulting in the formation of vertical one-dimensional nanostructures (nanocolumns). Moreover we show in this paper the influence of growth parameters (Tg and Mn content) on this decomposition i.e. on nanocolumns size and density. For temperatures higher than 180deg C, we observed the formation of Ge3Mn5 clusters. For intermediate growth temperatures nanocolumns and nanoclusters coexist. Combining high resolution TEM and superconducting quantum interference device magnetometry, we could evidence at least four different magnetic phases in Ge(1-x)Mn(x) films: (i) paramagnetic diluted Mn atoms in the germanium matrix, (ii) superparamagnetic and ferromagnetic low-Tc nanocolumns (120 K < Tc < 170 K), (iii) high-Tc nanocolumns (Tc> 400 K) and (iv) Ge3Mn5 clusters.

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References in corpus (5)

• Ferromagnetic semiconductors
• Light and electric field control of ferromagnetism in magnetic quantum structures
• Magnetic and electronic transport percolation in epitaxial GeMn films
• Magnetic and structural properties of GeMn films: precipitation of intermetallic nanomagnets
• Precipitation of amorphous ferromagnetic semiconductor phase in epitaxially grown Mn-doped Ge thin films

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• Interface-driven phase separation in multifunctional materials: the case of GeMn ferromagnetic semiconductor
• Exchange bias in GeMn nanocolumns: the role of surface oxidation
• Strain and correlation of self-organized Ge_(1-x)Mn_x nanocolumns embedded in Ge (001)
• Mn Solid Solutions in Self-Assembled Ge/Si (001) Quantum Dot Heterostructures
• Core-shell nanostructure in a Ge_0.9Mn_0.1 film from structural and magnetic measurements
• Magnetic Mn5Ge3 nanocrystals embedded in crystalline Ge: a magnet/semiconductor hybrid synthesized by ion implantation
• Residual disorder and diffusion in thin Heusler alloy films
• Impurity band conduction in group-IV ferromagnetic semiconductor Ge1-xFex with nanoscale fluctuations in Fe concentration
• X-ray magnetic circular dichroism in (Ge,Mn) compounds: experiments and modeling