Hybrid photostrictive-magnetic nanocomposites – HYPNOSE

Within the framework of CE 09 - "Nanomaterials and nanotechnologies for the products of the future", the HYPNOSE project proposes to follow a new path in the manipulation of the magnetization by combining the development of hybrid systems and the optical control of magnetization. Our approach is based on the development of vertically-assembled nanocomposites made of magnetic nanopillars epitaxially grown within photostrictive thin films. These systems, which couple magnetism and photostriction, will be used to control the magnetization by light. Our approach includes the study of the dynamical aspects of the manipulation of the magnetization down to ultrashort timescales. The consortium brings together teams with state-of-the-art expertise and experimental means that cover all aspects of a project addressing the production of complex, functional and self-assembled nano-objects, in which the nanometric scale plays a key role in controlling the magnetization as well as achieving ultrafast response.
First, different combinations of materials will be studied in order to obtain vertically self-assembled nanocomposites exhibiting a strong coupling between the photostrictive properties of the matrix and of the magnetic properties of the nanopillars. Photo-induced strain of the matrix combined with epitaxy of the nanopillars will induce changes in magneto-elastic anisotropy. The systems will be grown by pulsed laser deposition. The growth parameters will be adjusted in order to control the size, density, epitaxy and axial deformation of the nanopillars in the matrix. After this optimization phase, two more complex types of systems will be developed: "exchange spring" type systems and systems adapted to promote photo-induced out of plane / in the plane reorientation of the magnetization. The photostrictive and magnetic properties of these systems will be measured using a range of complementary techniques (diffraction, magnetometry and magneto-optics).
Secondly, the dynamical response of the systems to a pulsed laser excitation will be studied in detail. The implementation of a set of state-of-the-art pump-probe techniques will allow us to probe the ultra-fast dynamics of the different degrees of freedom. The dynamics of the magnetization will be studied using a combination of time-resolved magneto-optical Kerr effect and time-resolved X-ray resonant magnetic scattering (Tr-XRMS). For ultrafatst Tr-XRMS experiments (50 fs resolution), we will use a high-harmonic generation (HHG) and x-ray free-electron laser (XFEL) sources to probe the M and L edges of magnetic elements, respectively. The use of synchrotron radiation, tuned to the M and L edges of the magnetic elements, will make it possible to study the dynamics at intermediate timescales (resolution 10 ps). The ultrafast structural dynamics will be probed by time-resolved X-ray diffraction at the synchrotron and at XFEL facilities delivering hard X-ray pulses. All of these experiments will allow us to describe the dynamical processes at work in photostrictive-magnetic nanocomposites and to optimize their response time. The same techniques will be used to study the response of "exchange springs" and systems designed for out-of-plane / in-plane photo-induced magnetization reorientation.
Finally, a technique for transferring nanocomposites onto an x-ray transparent membrane will be developed within the framework of this project. This will make it possible to envisage time-resolved coherent imaging experiments in transmission and will pave the way for the study of the dynamics of single nanopillars.