Lisa Michez

Mn segregation in Ge/Mn5Ge3 heterostructures: The role of surface carbon adsorption

Mn5Ge3 compound, with its room-temperature ferromagnetism and possibility to epitaxially grow on Ge, acts as a potential spin injector into group-IV semiconductors. However, the realization of Ge/Mn5Ge3 multilayers is highly hampered by Mn segregation toward the Ge growing surface. Here, we show that adsorption of some monolayers of carbon on top of the Mn5Ge3 surface prior to Ge deposition allows to greatly reduce Mn segregation. In addition, a fraction of deposited carbon can diffuse down to the underneath Mn5Ge3 layers, resulting in an enhancement of the Curie temperature up to ∼360 K. The obtained results will be discussed in terms of the formation of a diffusion barrier by filling interstitial sites of Mn5Ge3 by carbon.

Thermal stability of epitaxial Mn5Ge3 and carbon-doped Mn5Ge3 films

The thermal stability of epitaxial Mn5Ge3 and carbon-doped Mn5Ge3 films was investigated by combining structural and magnetic characterizations. It is shown that ferromagnetic Mn5Ge3 films transform into antiferromagnetic Mn11Ge8 upon post-annealing at 650 °C whereas carbon-doped Mn5Ge3 conserves its ferromagnetism up to 850 °C. The magnetic properties of Mn5Ge3 (Curie temperature, magnetization at saturation, and magnetic moment per Mn atom) are found to undergo a reversible transition upon carbon doping and its extraction during thermal annealing. The stability of carbon-doped Mn5Ge3 films will be discussed in terms of carbon filling of interstitial sites of Mn5Ge3, which prevents Ge diffusion from the substrate.

Epitaxial growth and magnetic properties of Mn5Ge3/Ge and Mn5Ge3Cx/Ge heterostructures for spintronic applications

The development of active spintronic devices, such as spin-transistors and spin-diodes, calls for new materials that are able to efficiently inject the spin-polarized current into group-IV semiconductors (Ge and Si). In this paper we review recent achievements of the synthesis and the magnetic properties of Mn5Ge3/Ge and carbon-doped Mn5Ge3/Ge heterostructures. We show that high crystalline quality and threading-dislocation free Mn5Ge3 films can be epitaxially grown on Ge(111) substrates despite the existence of a misfit as high as 3.7% between two materials. We have investigated the effect of carbon doping in epitaxial Mn5Ge3 films and show that incorporation of carbon into interstitial sites of Mn5Ge3 can allow not only enhancement of the magnetic properties but also an increase of the thermal stability of Mn5Ge3. Finally, toward the perspective to realize Ge/Mn5Ge3/Ge multilayers for spintronic applications, we shall show how to use carbon to prevent Mn out-diffusion from Mn5Ge3 during Ge overgrowth on top of Mn5Ge3/Ge heterostructures. The above results open the route to develop spintronic devices based on Mn5Ge3Cx/Ge heterostructures using a Schottky contact without needing an oxide tunnel barrier at the interface.

Ferromagnetic resonance and magnetic damping in C-doped Mn 5 Ge 3

Ferromagnetic resonance (FMR) was used to investigate the static and dynamic magnetic properties of carbon-doped Mn5Ge3 (C

An unusual phenomenon of surface reaction observed during Ge overgrowth on Mn5Ge3/Ge(111) heterostructures

_{0.1}

Growth competition between semiconducting Ge1−xMnx nanocolumns and metallic Mn5Ge3 clusters

and C

Mn5Ge3C0.6 /Ge(1 1 1) Schottky contacts tuned by an n-type ultra-shallow doping layer

_{0.2}

Electrical and Optical Measurements of the Bandgap Energy of a Light-Emitting Diode.

) thin films grown on Ge(111). The temperature dependence of magnetic anisotropy shows an increased perpendicular magneto-crystalline contribution at 80K with an in-plane easy axis due to the large shape contribution. We find that our samples show a small FMR linewidth (corresponding to an intrinsic magnetic damping parameter

An introduction to photocatalysis through methylene blue photodegradation

\alpha

Mn Diffusion and Reactive Diffusion in Ge: Spintronic Applications

=0.005), which is a measure of the spin relaxation and directly related with the magnetic and structural quality of the material. In the perpendicular-to-plane geometry, the FMR linewidth shows a minimum at around 200K for all the samples, which seems to be not correlated to the C-doping. The magnetic relaxation parameters have been determined and indicate the two-magnon scattering as the main extrinsic contribution. We observe a change in the main contribution from scattering centres in Mn5Ge3C0.2 at low temperatures, which could be related to the minimum in linewidth.