Natural circular dichroism (NCD) provides fundamental insight into molecular chirality and stereochemical environments. Extending this concept into the hard-x-ray regime enables element-specific and site-selective chiral sensitivity inaccessible to optical wavelengths. Here, we demonstrate that 1s2p resonant inelastic x-ray scattering (RIXS) can be used to probe NCD in the enantiomeric model compound [Co(en)3](NO3)2. Using high-resolution detection of Co K alpha emission under circularly polarized excitation at the cobalt 1s pre-edge, we observe pronounced dichroic behavior directly linked to the Co-centered chirality. The RIXS-NCD signal reaches approximate to 23% of the pre-edge maximum-more than twice the amplitude of the previously reported x-ray NCD signal for the same compound-and exhibits the expected angular dependence for the crystal's P6322 symmetry. Two-dimensional RIXS-NCD maps further reveal strong helicity-dependent features across both excitation and emission energies, providing a richer description of the chiral electronic structure. These results establish RIXS-NCD as a photon-in-photon-out methodology for investigating natural optical activity with elemental and orbital specificity, paving the way for future applications to complex chiral and bioinspired materials.

We study binary ferrofluids composed of multicore "nanoflowers" of magnetically hard CoFe2O4 and magnetically soft MnFe2O4, as a way to optimise heat dissipation while suppressing aggregation-properties essential for biomedical applications. Bulk magnetometry and molecular dynamics simulations were combined to elucidate their behaviour. Experiments show wasp-waisted hysteresis, composition-dependent coercivity, and strong protocol dependence (field cooling). Simulations reproduce these trends and reveal the underlying structure-property coupling: (i) in an applied magnetic field, CoFe2O4 forms chains that dominate collective switching; (ii) adding MnFe2O4 "poisons" these chains-shortening and de-branching clusters-thereby lowering coercivity and loop area relative to a weighted superposition of the individual component responses without interactions; (iii) dipolar coupling reciprocally hardens the magnetically soft phase and softens the magnetically hard phase even without large-scale aggregation; and (iv) at higher total volume fraction (ϕ = 0.1) magnetically soft particles still suppress chain growth, reducing mean cluster size by up to an order of magnitude while keeping heating-relevant hysteresis close to Stoner-Wohlfarth expectations. These results establish composition-controlled microstructure as a means to decouple thermal output from aggregation: CoFe2O4 : MnFe2O4 mixtures can be tuned to enhance loss mechanisms while mitigating aggregation, offering a route to binary ferrofluids optimized for magnetic hyperthermia and drug delivery.

While natural optical activity in crystals belonging to specific achiral point groups has been predicted by symmetry arguments, birefringence hampers its measurement in the UV-vis energy ranges. Here we use X-rays to reveal natural circular dichroism at the K-edges of copper and iron coordination salts crystallizing in the achiral point groups 4̅2m and 4̅ respectively. The experimental signals follow the angular dependence exactly as predicted by the symmetry of the point groups. In addition, an angular phase shift was observed for 4̅, which is explained by the crystalline a and b axes not being determined by the crystal point group but by the translation operations of the space group.

Maghemite nanoparticles functionalised with Co(II) coordination complexes at their surface show a significant increase of their magnetic anisotropy, leading to a doubling of the blocking temperature and a sixfold increase of the coercive field. Magnetometric studies suggest an enhancement that is not related to surface disordering, and point to a molecular effect involving magnetic exchange interactions mediated by the oxygen atoms at the interface as its source. Field- and temperature-dependent X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) studies show that the magnetic anisotropy enhancement is not limited to surface atoms and involves the core of the nanoparticle. These studies also point to a mechanism driven by anisotropic exchange and confirm the strength of the magnetic exchange interactions. The coupling between the complex and the nanoparticle persists at room temperature. Simulations based on the XMCD data give an effective exchange field value through the oxido coordination bridge between the Co(II) complex and the nanoparticle that is comparable to the exchange field between iron ions in bulk maghemite. Further evidence of the effectiveness of the oxido coordination bridge in mediating the magnetic interaction at the interface is given with the Ni(II) analog to the Co(II) surface-functionalised nanoparticles. A substrate-induced magnetic response is observed for the Ni(II) complexes, up to room temperature.

The decoration of technologically relevant surfaces, such as metal oxides, with Single-Molecule Magnets (SMMs) constitutes a persistent challenge for the integration of these molecular systems into novel technologies and, in particular, for the development of spintronic and quantum devices. We used UHV thermal sublimation to deposit tetrairon(iii) propeller-shaped SMMs (Fe-4) as a single layer on a TiO2 ultrathin film grown on Cu(001). The properties of the molecular deposit were studied using a multi-technique approach based on standard topographic and spectroscopic measurements, which demonstrated that molecules remain largely intact upon deposition. Ultralow temperature X-ray Absorption Spectroscopy (XAS) with linearly and circularly polarized light was further employed to evaluate both the molecular organization and the magnetic properties of the Fe-4 monolayer. X-ray Natural Linear Dichroism (XNLD) and X-ray Magnetic Circular Dichroism (XMCD) showed that molecules in a monolayer display a preferential orientation and an open magnetic hysteresis with pronounced quantum tunnelling steps up to 900 mK. However, unexpected extra features in the XAS and XMCD spectra disclosed a minority fraction of altered molecules, suggesting that the TiO2 film may be chemically non-innocent. The observed persistence of SMM behaviour on a metal oxide thin film opens new possibilities for the development of SMM-based hybrid systems.

Conglomerate formation, where enantiomers within a racemic mixture self-segregate upon crystallization, is an advantageous property for obtaining chirally pure crystals and allows large-scale chiral resolution. However, the prevalence of conglomerates is low and difficult to predict. In this report, we describe our attempts to engineer conglomerates from racemate-forming compounds by integrating them into a conglomerate-forming matrix. In this regard, we found that Ni(II) and Fe(II) form molecular alloys with Zn(II) in [MxZn(1−x)(bpy)3](PF6)2 (where bpy = 2,2′-bipyridyl). Powder X-ray Diffraction (PXRD) and Energy-Dispersive X-ray spectroscopy (EDX) evidenced conglomerate crystallization with Ni(II) concentrations up to about 25%, while it was observed only for much lower concentrations of Fe(II). This can be attributed to the ability of [Ni(bpy)3](PF6)2 to access a metastable conglomerate phase, while no such phase has been detected in [Fe(bpy)3](PF6)2. Furthermore, the chiral phase appears to be favored in fast-growing precipitates, while the racemic phase is favored in slow re-crystallizations for both Ni(II) and Fe(II) molecular alloys. X-ray natural circular dichroism (XNCD) measurements on [Ni0.13Zn0.87(bpy)3](PF6)2 demonstrate the chirality of the nickel molecules within the zinc molecular matrix.

The potassium hexacyanoferrate(III), K3[FeIII(CN)6], is known for its exceptional magnetic anisotropy among the 3d transition metal series. The Fe(III) ions are in the S = 1/2 low spin state imposed by the strong crystal field of the cyanido ligands. A large orbital magnetic moment is expected from previous publications. In the present work, X-ray magnetic circular dichroism was recorded for a powder sample, allowing direct measurement of the Fe(III) orbital magnetic moment. A combination of molecular multiconfigurational ab initio and atomic ligand field multiplets calculations provides the spin and orbital magnetic moments for the [FeIII(CN)6]3- isolated cluster, the crystallographic unit cell, and the powder sample. The calculations of the angular dependencies of the spin and orbital magnetic moments with the external magnetic induction direction reveal easy magnetization axes for each S = 1/2 molecular entity and the crystal. It also shows that the orbital magnetic moment dominates the spin magnetic moment for all directions. Our measurements confirm that the orbital magnetic moment contributes to 60% of the total magnetization for the powder, which is in excellent agreement with our theoretical predictions. An orbital magnetic moment greater than the spin magnetic moment is exceptional for 3d transition metal ions. The impact of crystal field strength and distortion, π back-bonding, spin-orbit coupling, and external magnetic induction was analyzed, leading to a deeper understanding of the spin and orbital magnetic anisotropies.

Superconductors and magnetic materials, including molecules, are key ingredients for quantum computing and spintronics. However, only a little is known about how these materials interact in multilayer nanostructures like the hybrid architectures nowadays under development for such advanced applications. Here, we show that a single layer of magnetic molecules, Terbium(III) bis-phthalocyaninato (TbPc2) complexes, deposited under controlled UHV conditions on a superconducting Pb(111) surface is sensitive to the topology of the intermediate state of the superconductor, namely to the presence and evolution of superconducting and normal domains due to screening and penetration of an external magnetic field. The topological hysteresis of the superconducting substrate imprints a local evolution of the magnetisation of the TbPc2 molecules in the monolayer. Element and surface selective detection is achieved by recording the X-ray magnetic circular dichroism of the Tb atoms. This study reveals the impressive potential of magnetic molecules for sensing local magnetic field variations in molecular/superconductor hybrid devices, including spin resonators or spin injecting and spin filtering components for spintronics applications.

Ultrathin ${\mathrm{Co}}_{x}{\mathrm{Ni}}_{1\ensuremath{-}x}$ alloy nanowires vertically embedded in ${\mathrm{SrTiO}}_{3}/{\mathrm{SrTiO}}_{3}\phantom{\rule{0.16em}{0ex}}(001)$ thin films were grown using a self-assembly approach based on sequential pulsed laser deposition. Due to vertical epitaxial coupling of the metallic and oxide phases, a large average tensile strain of up to 4% arises within the nanowires, which is evidenced using a combination of x-ray diffraction and transmission electron microscopy. Macroscopic magnetometry experiments are used to demonstrate that this huge deformation allows us to enhance the uniaxial anisotropy of the nanowires, leading to saturation field in excess of 1 T in the hard direction, large coercive field at low temperature along the easy axis, and to a blocking temperature exceeding 600 K in the case of nanowires with a diameter of 5 nm and 78% Co content. These data are complemented with angular dependent x-ray magnetic circular dichroism measurements at the Co and Ni ${L}_{2,3}$ edges. The value of the magnetic moment was extracted from these measurements by applying sum rules and the anisotropy of the orbital moment was investigated.

The spin crossover (SCO) transition is investigated in two molecular Co2+bis-imide compounds, Co(dpzca)2and Co(pypzca)2(where Hdpzca=N-(2-pyrazylcarbonyl)-2-pyrazinecarboxamide and Hpypzca=N-(2-pyrazylcarbonyl)-2-pyridinecarboxamide). They crystallize solvent-free with similar crystal structures but have been reported to exhibit different temperature-dependent magnetic behaviors. Using temperature- and pressure-dependent elements elective X-ray absorption spectroscopy (XAS and XMCD) measurements, it is revealed hereinthat although Co(pypzca)2does not afford a temperature-induced SCO, it undergoes a reversiblepressure-induced SCO transition that is less abrupt, and is complete at a higher pressure(3.5 GPa), than for Co(dpzca)2(0.5 GPa). Wave function-based calculations performed onisolated complexes confirm the LS state nature of Co(dpzca)2at low temperatures, and the valuesof spin and orbital magnetic moments are determined. Calculations show the similarity of ground-state properties for HS Co(dpzca)2and HS Co(pypzca)2and the existence of a double-well HS-LSin the potential energy surface for both compounds. It is concluded that the observed, significant differences in pressure- and temperature-induced SCO transitions of Co(dpzca)2versusCo(pypzca)2are probably due to different intermolecular interactions between Co(dpzca)2andCo(pypzca)2, which would hamper the temperature-induced SCO in Co(pypzca)2

Ultrathin CoxNi1-x alloy nanowires vertically embedded in SrTiO3/SrTiO3 (001) thin films were grown using a self-assembly approach based on sequential pulsed laser deposition. Due to vertical epitaxial coupling of the metallic and oxide phases, a large average tensile strain of up to 4% arises within the nanowires, which is evidenced using a combination of x-ray diffraction and transmission electron microscopy. Macroscopic magnetometry experiments are used to demonstrate that this huge deformation allows us to enhance the uniaxial anisotropy of the nanowires, leading to saturation field in excess of 1 T in the hard direction, large coercive field at low temperature along the easy axis, and to a blocking temperature exceeding 600 K in the case of nanowires with a diameter of 5 nm and 78% Co content. These data are complemented with angular dependent x-ray magnetic circular dichroism measurements at the Co and Ni L-2,L-3 edges. The value of the magnetic moment was extracted from these measurements by applying sum rules and the anisotropy of the orbital moment was investigated.

The switching properties of a cyanido-bridged Fe/Co square molecule were investigated by single-crystal X-ray diffraction and X-ray absorption spectroscopy at both Fe and Co K-edges. Combining these two techniques, a complete picture of the thermal-, light- and X-ray-induced metal-to-metal electron transfer is obtained, illustrating the concerted role played by the Fe and Co sites.

Thin inorganic films (i.e., metal oxides) are often used as decoupling layers to optimize the interactions between the molecular magnetic layers and metallic surfaces.

Thin films of a molecular spin crossover iron(II) complex featuring a photochromic diarylethene-based ligand have been grown by sublimation in ultra-high vacuum on an highly oriented pyrolytic graphite (HOPG), and investigated by X-ray and UV photoelectron spectroscopies as well as by X-ray absorption spctroscopy. Temperature-dependent studies demonstrate that the thermally induced spin crossover behaviour is preserved in a sub-monolayer coverage. The photochromic ligand ad hoc integrated into the complex allows photoswitching of the spin states of this iron(II) complex at room temperature but our evidences suggest that this photomagnetic effect is not observed in 0.7ML sublimated films. Ab initio simulations performed on the adsorbed molecules justify this behaviour as the result of geometry of the molecules iteracting with the graphite.

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.

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.

Prussian blue analogue nanocrystals of the CsINiII[CrIII(CN)6] cubic network with 6 nm size were assembled as a single monolayer on highly organized pyrolytic graphite (HOPG). X-ray magnetic circular dichroism (XMCD) studies, at the Ni and Cr L2,3 edges, reveal the presence of an easy plane of magnetization evidenced by an opening of the magnetic hysteresis loop (coercive field of ≈200 Oe) when the magnetic field, B, is at 60° relative to the normal to the substrate. The angular dependence of the X-ray natural linear dichroism (XNLD) reveals both an orientation of the nanocrystals on the substrate and an anisotropy of the electronic cloud of the NiII and CrIII coordination sphere species belonging to the nanocrystals' surface. Ligand field multiplet (LFM) calculations that reproduce the experimental data are consistent with an elongated tetragonal distortion of surface NiII coordination sphere responsible for the magnetic behavior of monolayer.

Gaining control over the grafting geometry is critically important for any application of surface-supported single-molecule magnets (SMMs) in data storage, spintronics, and quantum information science. Here, tetrairon(III) SMMs with a propeller-like structure are functionalized with thioacetyl-terminated alkyl chains to promote chemisorption on gold surfaces from solution and to evaluate differences in adsorption geometry and magnetic properties as a function of chain length. The prepared monolayers are investigated using X-ray absorption techniques with linearly and circularly polarized light to extract geometrical and magnetic information, respectively. All derivatives remain intact and form partially oriented monolayers on the gold surface. A ligand-field analysis of the observed X-ray natural linear dichroism shows that the threefold molecular axis is invariably biased toward the surface normal, in agreement with ab initio calculations. This preferential orientation is most pronounced in monolayers of the shortest-chain derivative, which are further studied with an ultralow temperature X-ray magnetic circular dichroism setup operating down to 350 mK. The isothermal field sweeps with the magnetic field at normal incidence show an open hysteresis loop below 1 K, while measurements at different incidence angles prove the magnetic anisotropy of the monolayers.