Magnetotransport properties of ultrathin GaMnAs layers

Janusz Sadowski 1,2,3R. R. Gareev 2Mathias Döppe 2Matthias Sperl 2Gunter Bayreuther 2Werner Wegscheider 2Dieter Weiss 2F. Terki 3S. Charar 3

1. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland
2. Institut für Experimentelle und Angewandte Physik Universität Regensburg (Uni. Regensb), Universitätsstraße 31, Regensburg 93040, Germany
3. Groupe d'Etude des Semiconducteurs CC074, Universite Montpellier II, Montpellier, France


Ferromagnetic GaMnAs is currently being used to investigate prototype spintronics devices. The progress in material fabrication in recent years led to a remarkable increase of Curie temperature (Tc) and improved conductivity of GaMnAs. This made it possible, e.g. to observe the Coulomb blockade anisotropic magnetoresistance effects in ferromagnetic GaMnAs yielding an interesting material system combining nanoelectronic and spintronic properties. Because of large carrier density, typically in the range of 1020 to 1021 cm-3 the depletion of GaMnAs via the field effect is only possible in nanoscale structures. It is therefore desirable to investigate the ferromagnetism of GaMnAs towards ultrasmall thicknesses. It was already reported that the thickness limit for ferromagnetism in single GaMnAs layers is close to 5 nm. So far it is unclear which factors cause the ferromagnetism in very thin GaMnAs layers to vanish. To address this problem we have investigated single GaMnAs layers with thicknesses between 2 and 5 nm. Samples were grown by MBE on GaAs(100) substrates. Magnetic properties of the samples were studied by SQUID magnetometry and transport experiments employing standard Hall effect measurements. Magnetisation and transport measurements revealed that the lower limit for the FM phase transition in a single Ga0.95Mn0.05As layer is close to 3 nm. Samples with thicknesses between 3 and 5 nm exhibited normal behaviour both in transport and in magnetisation measurements. This required however the insertion of suitable buffer layers which needed to be deposited prior to GaMnAs growth and a suitable post-growth annealing treatment.

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Presentation: Poster at E-MRS Fall Meeting 2006, Symposium E, by Janusz Sadowski
See On-line Journal of E-MRS Fall Meeting 2006

Submitted: 2006-05-15 19:40
Revised:   2009-06-07 00:44
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