The field of spintronics aims at using the spin degree of freedom of electrons to store and transport information. In this sense, achieving large-scale growth of two-dimensional (2D) ferromagnetic materials with high Curie temperature (Tc) and perpendicular magnetic anisotropy (PMA) is highly desirable for the development of ultra-compact magnetic sensors and magnetic memories. The van der Waals (vdW) ferromagnet Cr2Te3 appears as a promising candidate due to the high quality of the interfaces formed with other vdW or 2D materials as well as the possibility to tune its magnetic properties by strain or electric field. In the bulk, the Tc of this ferromagnet is 180 K and the easy axis of magnetization is out-of-plane. First, structural and magnetic characterization of vdW heterostructures of Cr2Te3 on 2D materials were carried out. Samples were grown on the semimetal graphene, the semiconductor WSe2 as well as the topological insulator Bi2Te3 . The heterostructures were characterized using a full set of tools ranging from atomic force microscopy (AFM) to study the layer morphology, Raman spectroscopy and x-ray diffraction for the crystal structure, transmission electron microscopy to image the interfaces, Rutherford back scattering (RBS) to determine accurately the stoichiometry and SQUID, MOKE and x-ray magnetic circular dichroism at synchrotron facilities for magnetic properties. The magnetic anisotropy of thin films (5 unit cell thick) is found to be dependent on the crystalline structure that is determined by the energy given to the system during growth. The choice of the 2D template for the epitaxy was found not to affect the crystal structure, due to weak vdW interaction. In a second step, the magnetic ordering temperature of the material was tuned with the help of post-growth annealing up to 700°C. An increase of the Tc up to 250 K was measured, associated to a change of the layers composition. Besides, electrical characterization of vdW heterostructures based on Cr2Te3 was carried out to study the Hall resistivity of the film as a function of the electronic band structure and charge transfer with the 2D material substrate. Spin-orbit torques induced by Bi2Te3 were finally measured for the electrical control and reversal of the magnetization of the 2D ferromagnetic layers.

Plus d'information :https://www.spintec.fr/phd-defense-molecular-beam-epitaxy-of-van-der-waals-heterostructures-based-on-ferromagnetic-cr2te3-for-spintronics/
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Lien visioconférence : ​https://webconf.cea.fr/ioan-lucian.prejbeanu/C89D5FFJ​​