Philippe Sainctavit

Bio: Philippe Sainctavit is an academic researcher from Pierre-and-Marie-Curie University. The author has contributed to research in topics: Magnetic circular dichroism & X-ray magnetic circular dichroism. The author has an hindex of 30, co-authored 56 publications receiving 3603 citations. Previous affiliations of Philippe Sainctavit include Soleil Synchrotron & Institut de recherche pour le développement.

Magnetic memory of a single-molecule quantum magnet wired to a gold surface.

Abstract: In the field of molecular spintronics, the use of magnetic molecules for information technology is a main target and the observation of magnetic hysteresis on individual molecules organized on surfaces is a necessary step to develop molecular memory arrays. Although simple paramagnetic molecules can show surface-induced magnetic ordering and hysteresis when deposited on ferromagnetic surfaces, information storage at the molecular level requires molecules exhibiting an intrinsic remnant magnetization, like the so-called single-molecule magnets (SMMs). These have been intensively investigated for their rich quantum behaviour but no magnetic hysteresis has been so far reported for monolayers of SMMs on various non-magnetic substrates, most probably owing to the chemical instability of clusters on surfaces. Using X-ray absorption spectroscopy and X-ray magnetic circular dichroism synchrotron-based techniques, pushed to the limits in sensitivity and operated at sub-kelvin temperatures, we have now found that robust, tailor-made Fe(4) complexes retain magnetic hysteresis at gold surfaces. Our results demonstrate that isolated SMMs can be used for storing information. The road is now open to address individual molecules wired to a conducting surface in their blocked magnetization state, thereby enabling investigation of the elementary interactions between electron transport and magnetism degrees of freedom at the molecular scale.

Quantum tunnelling of the magnetization in a monolayer of oriented single-molecule magnets

Abstract: Single-molecule magnets are molecular complexes with magnetic bistability, and recently it was shown that such a magnetic memory effect is retained for Fe4 clusters when they are wired to a gold surface. These authors have tailored the clusters to have a preferential orientation and form a self-assembled monolayer on the surface. It then becomes possible to observe quantum tunnelling of the magnetization, which shows up as steps in the magnetic hysteresis loop.

Chemical strategies and characterization tools for the organization of single molecule magnets on surfaces

Abstract: Addressing individual bistable magnetic molecules, known as Single Molecule Magnets (SMMs), is a fascinating goal at the borderline between molecular magnetism and spin electronics. This tutorial review focuses on the first step towards single-molecule experiments, namely the organization of SMMs on surfaces. Both preparation and characterization of surface-supported SMMs prove to be quite demanding and a multidisciplinary approach is necessary, which is described here using selected examples. We first illustrate the chemical strategies devised to assemble SMMs and to control their orientation on surfaces. Then, we present characterization tools, which have been selected on the basis of their relevance to address specific points, i.e. the chemical composition of the deposited SMM films, the organization of the molecules on the surface, the intramolecular arrangement of the spins, the magnetic anisotropy of SMMs, and eventually the dynamics of their magnetization on surfaces. Particular attention is devoted to techniques exploiting synchrotron light.

Photoinduced Ferrimagnetic Systems in Prussian Blue Analogues CIxCo4[Fe(CN)6]y (CI = Alkali Cation). 2. X-ray Absorption Spectroscopy of the Metastable State

Abstract: A CoFe Prussian blue analogue Rb1.8Co4[Fe(CN)6]3.3·13H2O was synthesized, which presents an important photomagnetic effect. The electronic structure and the local structure of the ground and of the excited states have been investigated. X-ray absorption spectroscopy measurements at the Co and Fe L2,3 edges and cobalt K-edge (XANES and EXAFS) evidence the local electronic transfer and the spin change of the cobalt ions induced by irradiation. We observed a 0.19 A increase of the Co−N bond length, associated with the transformation of CoIII low spin to CoII high spin. The CoII/CoIII ratio has been evaluated as a function of the irradiation time and revealed as an important parameter to understanding the bulk magnetic properties. The combined role of the diamagnetic FeII−CoIII pairs and hexacyanoferrate(III) vacancies is locally evidenced. This work is a new step in the understanding of the photoinduced electron transfer.

Temperature- and Light-Induced Spin Crossover Observed by X-ray Spectroscopy on Isolated Fe(II) Complexes on Gold.

Abstract: Using X-ray absorption techniques, we show that temperature- and light-induced spin crossover properties are conserved for a submonolayer of the [Fe(H2B(pz)2)2(2,2′-bipy)] complex evaporated onto a Au(111) surface. For a significant fraction of the molecules, we see changes in the absorption at the L2,3 edges that are consistent with those observed in bulk and thick film references. Assignment of these changes to spin crossover is further supported by multiplet calculations to simulate the X-ray absorption spectra. As others have observed in experiments on monolayer coverages, we find that many molecules in our submonolayer system remain pinned in one of the two spin states. Our results clearly demonstrate that temperature- and light-induced spin crossover is possible for isolated molecules on surfaces but that interactions with the surface may play a key role in determining when this can occur.

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Exploiting single-ion anisotropy in the design of f-element single-molecule magnets

Abstract: Scientists have long employed lanthanide elements in the design of materials with extraordinary magnetic properties, including the strongest magnets known, SmCo5 and Nd2Fe14B. The properties of these materials are largely a product of fine-tuning the interaction between the lanthanide ion and the crystal lattice. Recently, synthetic chemists have begun to utilize f-elements—both lanthanides and actinides—for the construction of single-molecule magnets, resulting in a rapid expansion of the field. The desirable magnetic characteristics of the f-elements are contingent upon the interaction between the single-ion electron density and the crystal field environment in which it is placed. This interaction leads to the single-ion anisotropies requisite for strong single-molecule magnets. Therefore, it is of vital importance to understand the particular crystal field environments that could lead to maximization of the anisotropy for individual f-elements. Here, we summarize a qualitative method for predicting the ligand architectures that will generate magnetic anisotropy for a variety of f-element ions. It is hoped that this simple model will serve to guide the design of stronger single-molecule magnets incorporating the f-elements.

Molecular spin crossover phenomenon: recent achievements and prospects

Abstract: Recently we assisted a strong renewed interest in the fascinating field of molecular spin crossover complexes by (1) the emergence of nanosized spin crossover materials through direct synthesis of coordination nanoparticles and nanopatterned thin films as well as by (2) the use of novel sophisticated high spatial and temporal resolution experimental techniques and theoretical approaches for the study of spatiotemporal phenomena in cooperative spin crossover systems. Besides generating new fundamental knowledge on size-reduction effects and the dynamics of the spin crossover phenomenon, this research aims also at the development of practical applications such as sensor, display, information storage and nanophotonic devices. In this critical review, we discuss recent work in the field of molecule-based spin crossover materials with a special focus on these emerging issues, including chemical synthesis, physical properties and theoretical aspects as well (223 references).

Old materials with new tricks: multifunctional open-framework materials.

Abstract: The literature on open-framework materials has shown numerous examples of porous solids with additional structural, chemical, or physical properties. These materials show promise for applications ranging from sensing, catalysis and separation to multifunctional materials. This critical review provides an up-to-date survey to this new generation of multifunctional open-framework solids. For this, a detailed revision of the different examples so far reported will be presented, classified into five different sections: magnetic, chiral, conducting, optical, and labile open-frameworks for sensing applications. (413 references.)