Showing papers by "Amandine Bellec published in 2021"
TL;DR: In this article, the thermal transition of the spin-crossover compound FeII((3,5-(CH3)2Pz)3BH)2 from submonolayer to multilayers on a Cu(111) substrate was studied.
Abstract: Spin-crossover molecules are very attractive compounds to realize multifunctional spintronic devices. Understanding their properties when deposited on metals is therefore crucial for their future rational implementation as ultrathin films in such devices. Using X-ray absorption spectroscopy, we study the thermal transition of the spin-crossover compound FeII((3,5-(CH3)2Pz)3BH)2 from submonolayer to multilayers on a Cu(111) substrate. We determine how the residual fraction of high spin molecules at low temperature, as well as the bistability range and the temperature of switching, depends on the layer thickness. The most spectacular effect is the clear opening of a 35 ± 9 K thermal hysteresis loop for a 3.0 ± 0.7 monolayers thick film. To better understand the role played by the substrate and the dimensionality on the thermal bistability, we have performed Monte Carlo Arrhenius simulations in the framework of a mechanoelastic model that include a molecule-substrate interaction. This model reproduces well the main features observed experimentally and can predict how the spin-crossover transition is modified by the thickness and the substrate interaction.
15 citations
TL;DR: In this paper, the voltage-induced switching of the high spin/low spin electronic states of spin-crossover molecules self-assembled in dense 2D networks on Au(111) and Cu(111), was investigated by scanning tunneling microscopy at low temperature.
Abstract: Bistable spin-crossover molecules are particularly interesting for the development of innovative electronic and spintronic devices as they present two spin states that can be controlled by external stimuli. In this paper, we report the voltage-induced switching of the high spin/low spin electronic states of spin-crossover molecules self-assembled in dense 2D networks on Au(111) and Cu(111) by scanning tunneling microscopy at low temperature. On Au(111), voltage pulses lead to the nonlocal switching of the molecules from any─high or low─spin state to the other followed by a spontaneous relaxation toward their initial state within minutes. On the other hand, on Cu(111), single molecules can be addressed at will. They retain their new electronic configuration after a voltage pulse. The memory effect demonstrated on Cu(111) is due to an interplay between long-range intermolecular interaction and molecule/substrate coupling as confirmed by mechanoelastic simulations.
9 citations
TL;DR: The tris pyrazolyl borate ligand imposes a rigid scaffold around Fe( ii ) ensuring a robust magnetic anisotropy when the molecules assembled as monolayers suffer from the dissymmetric environment of the substrate/vacuum interface.
Abstract: The tris pyrazolyl borate ligand imposes a rigid scaffold around Fe( ii ) ensuring a robust magnetic anisotropy when the molecules assembled as monolayers suffer from the dissymmetric environment of the substrate/vacuum interface.
4 citations
TL;DR: In this paper, it was shown that the magnetic anisotropy of assembled pyrazole molecules is not affected when they are present at the substrate/vacuum interface.
Abstract: The measurement of the magnetic anisotropy of [Fe{(3,5-(CH3)2Pz)3BH}2], where Pz = pyrazole, in its high spin state (S = 2) by X-ray Magnetic Circular Dichroism (XMCD) spectroscopy when assembled as an organized monolayer on Cu(111) shows the presence of a hard axis of magnetization (positive axial zero-field splitting – ZFS – parameter D). Combining magnetization and multifrequency electron paramagnetic resonance spectroscopy on a reference compound, [Fe{(3-(Ph)Pz)3BH}2], of the same family and ab initio wave function based theoretical calculations, we demonstrate that the magnetic anisotropy of the assembled molecules is not affected when they are present at the substrate/vacuum interface. Comparing our results with those of a reported complex having an almost identical FeN6 coordination sphere but an easy axis of magnetization (corresponding to a negative D value), we show that the nature of the magnetic anisotropy (easy/hard axis) is governed by the torsion angle (Ψ) defined by the relative orientation of the pyrazole five-membered rings to the pseudo three-fold axis of the molecules. The rigidity of the (Pz)3BH tridentate ligands, where the three pyrazole moieties are held by the BH group, allows only very slight changes in the torsion angle even when the molecules are in a dissymmetric environment such as an interface. This is the origin of the robust magnetic anisotropy of this family of compounds.
3 citations
TL;DR: In this article, the magnetism of a cobalt ultrathin film deposited on different two-dimensional (2D) materials, namely graphene, h-BN, and ${\mathrm{WSe}}_{2}$ by the Brillouin light scattering technique was studied.
Abstract: We have studied the magnetism of a cobalt ultrathin film deposited on different two-dimensional (2D) materials, namely graphene, h-BN, and ${\mathrm{WSe}}_{2}$ by the Brillouin light scattering technique. The studied samples are prepared by a pick-up method of large flakes deposited on ${\mathrm{SiO}}_{2}$ and the subsequent physical vapor deposition of metal layers, in a similar way to what is done to make spintronic devices out of such materials. Compared to the reference layer $(\mathrm{Co}/{\mathrm{SiO}}_{2})$, the perpendicular magnetic anisotropy is enhanced in the Co/2D systems, although less than what could be expected on single crystal samples. This result is quantitatively discussed by comparison with ab initio calculations in the case of the Co/graphene interface. We also measure an increase of the magnetic damping and a small Dzyaloshinskii-Moriya interaction in such samples which are discussed with respect to the recent literature.
2 citations