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.

A fundamental step towards atomic- or molecular-scale spintronic devices has recently been made by demonstrating that the spin of an individual atom deposited on a surface, or of a small paramagnetic molecule embedded in a nanojunction, can be externally controlled. An appealing next step is the extension of such a capability to the field of information storage, by taking advantage of the magnetic bistability and rich quantum behaviour of single-molecule magnets (SMMs). Recently, a proof of concept that the magnetic memory effect is retained when SMMs are chemically anchored to a metallic surface was provided. However, control of the nanoscale organization of these complex systems is required for SMMs to be integrated into molecular spintronic devices. Here we show that a preferential orientation of Fe(4) complexes on a gold surface can be achieved by chemical tailoring. As a result, the most striking quantum feature of SMMs-their stepped hysteresis loop, which results from resonant quantum tunnelling of the magnetization-can be clearly detected using synchrotron-based spectroscopic techniques. With the aid of multiple theoretical approaches, we relate the angular dependence of the quantum tunnelling resonances to the adsorption geometry, and demonstrate that molecules predominantly lie with their easy axes close to the surface normal. Our findings prove that the quantum spin dynamics can be observed in SMMs chemically grafted to surfaces, and offer a tool to reveal the organization of matter at the nanoscale.

A CoFe Prussian blue analogue Rb 1.8 Co 4 [Fe(CN) 6 ] 3.3 ‚13H 2 O 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 L 2,3 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 Å increase of the Co-N bond length, associated with the transformation of Co III low spin to Co II high spin. The Co II /Co III 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 Fe II -Co III pairs and hexacyanoferrate(III) vacancies is locally evidenced. This work is a new step in the understanding of the photoinduced electron transfer.

Using X-ray absorption techniques, we show that temperature-and light-induced spin crossover properties are conserved for a sub-monolayer of the [Fe(H 2 B(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 L 2,3 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. TOC X-ray absorption techniques evidenced that temperature-and light-induced spin crossover properties were conserved for a sub-monolayer of the [Fe(H 2 B(pz) 2 ) 2 (2,2'-bipy)] complex evaporated on a Gold surface KEYWORDS: spin crossover,·UHV evaporation,·submonolayer,·X-ray absorption,·iron complexes 3 Spin Crossover (SCO) complexes are promising building blocks for spintronic 1 Using variable temperature X-ray absorption spectra, we examined a submonolayer coverage evaporated in situ under UHV conditions on Au(111), before and after irradiation with visible laser light. We compare these results to those obtained from two other samples: 1) a 5 single crystal finely scratched on gold foil, which we use as a spectroscopic bulk reference; and 2) a 300 nm thick film sublimedex situ on copper foil, to check the preservation of structure and properties of the complex. Experimental spectra were then compared to the ones obtained using multiplet calculations. 37-39The variation of the L 2,3 edge spectra for the bulk sample over the range of the thermal spin crossover (100-300 K) is reported in Figure 1a(see also Figure S1 in Supplementary Information Spectra measured on the thick film prepared ex situ are similar to the bulk, and show comparable temperature dependence (Figure 1b and Figure S1). Nevertheless, the thick film spectrum is slightly differentfrom the bulk compound: shoulders on the high-energy side (at 300 K) or at the low-energy side (at 100 K) of the L 3 absorption peak, are likely associated with a small fraction of decomposition product, which maybe caused by air exposure of this sample prepared ex situ.The analysis of the temperature-dependent spectra as weighted sums of the bulk spectra at 300 K and 100 K, chosen as representative of the HS and LS state respectively, allows for the extraction of the temperature dependence of the HS fraction (Table S2). For the thick film, the shoulder signals were found to be temperature independent, and thus do not affect the switching behavior. We extracted this spurious contribution ( Figures S3 and S4) and subtracted it from all spectra before evaluating...

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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.

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Successful attempts to deposit SMMs in UHV conditions\ud have been carried out with a tetranuclear iron(III) cluster [ 9 ]\ud and lanthanide bis-phthalocyaninato (LnPc 2 ) complexes. [ 10 , 11 ]\ud For the latter the seminal works of Ishikawa et al. [ 12 ] showed\ud that slow dynamics of the magnetization in these mononuclear\ud complexes is originated directly from their strong single ion\ud anisotropy. Very recently a structural and magnetic characterization\ud of a sub-monolayer deposit TbPc 2 based on synchrotronlight\ud techniques has confi rmed that this magnetic anisotropy is\ud retained on surface. [ 13 ] The absence of the observation of typical\ud slow dynamics of the magnetization has been attributed to the\ud long time-scale of the X-ray based experiments.\ud We report here a synchrotron-based investigation on neutral\ud TbPc 2 evaporated thick and thin fi lms evidencing that the thick\ud fi lm of TbPc 2 is characterized by slow relaxation of the magnetization\ud and opening of a butterfl y hysteresis cycle at temperatures\ud as high as 15 K but not observed for the thin fi lm. These\ud differences are accompanied with a drastic change in the orientation\ud of the TbPc 2 molecules in the two fi lm