Showing papers by "Amandine Bellec published in 2018"

Molecular scale dynamics of light-induced spin crossover in a two-dimensional layer

Abstract: Spin cross-over molecules show the unique ability to switch between two spin states when submitted to external stimuli such as temperature, light or voltage. If controlled at the molecular scale, such switches would be of great interest for the development of genuine molecular devices in spintronics, sensing and for nanomechanics. Unfortunately, up to now, little is known on the behaviour of spin cross-over molecules organized in two dimensions and their ability to show cooperative transformation. Here we demonstrate that a combination of scanning tunnelling microscopy measurements and ab initio calculations allows discriminating unambiguously between both states by local vibrational spectroscopy. We also show that a single layer of spin cross-over molecules in contact with a metallic surface displays light-induced collective processes between two ordered mixed spin-state phases with two distinct timescale dynamics. These results open a way to molecular scale control of two-dimensional spin cross-over layers.

Temperature-, Light-, and Soft X-ray-Induced Spin Crossover in a Single Layer of FeII-Pyrazolylborate Molecules in Direct Contact with Gold

Abstract: Understanding the properties of spin-crossover molecules in direct contact with metals is crucial for their future integration in electronic and spintronic devices. By X-ray absorption spectroscopy, we investigate the properties of FeII((3,5-(CH3)2Pz)3BH)2 molecules in the form of monolayer islands on a metallic substrate, namely, Au(111). We demonstrate that the spin-crossover transition can be thermally induced from the high spin state to a mixed spin state phase containing one-third of high-spin-state and two-thirds of low-spin-state molecules in agreement with previous work by scanning tunneling microscopy. In addition, at 4.4 K, the spin crossover from the low spin state to the high spin state can also be induced by X-ray and by light excitations.

Iconography : Molecular electronics: Scanning tunneling microscopy and single-molecule devices

Abstract: Comptes Rendus Chimie - In Press.Proof corrected by the author Available online since jeudi 19 juillet 2018

Experimental and theoretical investigations of magnetic anisotropy and magnetic hardening at molecule/ferromagnet interfaces

Abstract: We measure by means of in situ magneto-optical Kerr effect the magnetism of ultrathin magnetic films supported on gold and platinum during the capping with molecular layers We observe both for ${\mathrm{C}}_{60}$ and ${\mathrm{Alq}}_{3}$ molecules deposited on Co films an enhancement of the out-of-plane magnetic anisotropy, leading to a magnetic hardening for out-of-plane magnetization Surprisingly, the amplitude of this hardening depends strongly on the underlying substrate While we find an increase of the coercive field around 100% for Co/Au(111), it can reach almost 600% on Co/Pt(111) Those results are discussed by using both tight-binding and ab initio calculations It is shown on the case of ${\mathrm{C}}_{60}$ that both the adsorption geometry and the strain in the magnetic layer can be key ingredients to predict the quantitative change of magnetic anisotropy induced by the interface between a magnetic material and a molecular layer On the contrary, the crystalline stacking of the Co has a minor influence