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Séminaire nanostructures et systèmes quantiques

Magnetic Properties fo Fe Ultrathin Layers in Fe/GaMnAS Bilayers

Khashayar Khazen

A crucial aspect of magneto-electronics, or as it is frequently called spintronics is to manipulate the spins of the charge carriers in an electronic device via an externally controllable parameter, in order to be able to benefit from the basic phenomena of the field such as GMR, TMR, etc. We have previously studied and shown the possibility of modifying the magnetization in a diluted ferromagnetic semiconductor (the particular case of GaMnAs) via numerous possible external controls such as gate voltage, magnetic field, strain and even in many published works are dedicated to optical control of the magnetic properties of such systems.

Very recently, Fe/GaMnAs bilayers have attracted a considerable interest as it has been reported that the coupling between the Fe layer and GaMnAs in the interface is able to enhance locally its Tc up to room temperature. In order to elucidate the controversial physics of this system, we have studied the exchange coupling between the two layers. This coupling, which can be described in an exchange spring model and controls the alignment of the soft GaMnAs layer, is compared to other types of coupled systems, studied previously in our group. Moreover, very recently, an experimental work supported by different modelisations has shown that it is possible to modify the magnetic anisotropy of ultrathin Fe layers by application of an external gate voltage which adds another degree of the control in this system.

In this frame, studies concerning the structural and magnetic properties of the Fe/GaMnAs bilayers as well as the individual components will be presented which have led to fully understand the physics of such systems. On such well characterized samples, the application of magnetometry, magnetic resonance, XMCD and neutron reflectivity enabled us to analyze the magnetic energies of the layers as well as the exchange coupling between the layers, as well as their thickness dependence.

The presentation also includes the magnetic properties of the Fe ultrathin layers, the dominating processes involving in the relaxation of the magnetization in such systems, as well as the device made for studying the possibility of modifying the magnetic anisotropy in such layers