Boosting the Curie temperature in carbon-doped Mn5Ge3/Ge heterostructures
Résumé
We have combined structural and magnetic characterisations to
investigate the effect of carbon incorporation in epitaxial Mn 5 Ge 3 C x films
grown on Ge(111) by Molecular Beam Epitaxy (MBE). It is shown that up to a
carbon content of saturation of ~0.6, most of carbon can be incorporated into
the interstitial sites of the Mn 5 Ge 3 lattice. Such a process results in a linear
increase in the Curie temperature (T C ) of the alloy, which can reach a value as
high as ~430 K. Above this carbon content, T C is found to decrease. Structural
characterisations reveal that Mn 5 Ge 3 C x films are in perfect epitaxy when x ≤0.6
whereas cluster formation in the grown layers is detected above that threshold.
The clusters can be attributed to manganese carbide (MnC) compounds, which
are formed when the carbon content exceeds the saturation value of 0.6 by
consuming previously deposited carbon. In addition, we also show that after
post-thermal annealing, the carbon-doped Mn 5 Ge 3 C x alloys remain
magnetically and structurally stable up to a temperature as high as 1123 K. The
obtained results are very promising for integrating Mn 5 Ge 3 C x into
ferromagnetic/semiconductor heterostructures, the ultimate goal being the
realisation of spintronics devices.