Tunable Magnetism in Atomically Thin Itinerant Antiferromagnet with Room-Temperature Ferromagnetic Order.

Addressing the need for modulated spin configurations is crucial, as they serve as the foundational building blocks for next-generation spintronics, particularly in atomically thin structures and at room temperature. In this work, we realize intrinsic ferromagnetism in monolayer flakes and tunable ferro-/antiferromagnetism in (FeCo)GeTe antiferromagnets. Remarkably, the ferromagnetic ordering (≥1 L) and antiferromagnetic ordering (≥4 L) remain discernible up to room temperature.

Ferromagnetic Order in 2D Layers of Transition Metal Dichlorides.

Magnetism in two dimensions is traditionally considered an exotic phase mediated by spin fluctuations, but far from collinearly ordered in the ground state. Recently, 2D magnetic states have been discovered in layered van der Waals compounds. Their robust and tunable magnetic state by material composition, combined with reduced dimensionality, foresee a strong potential as a key element in magnetic devices.

Tracking Coordination Environment and Reaction Intermediates in Homogeneous and Heterogeneous Epoxidation Catalysts via Ti L-Edge Near-Edge X-ray Absorption Fine Structures.

Ti-based molecules and materials are ubiquitous and play a major role in both homogeneous and heterogeneous catalytic processes. Understanding the electronic structures of their active sites (oxidation state, local symmetry, and ligand environment) is key to developing molecular-level structure-property relationships. In that context, X-ray absorption spectroscopy (XAS) offers a unique combination of elemental selectivity and sensitivity to local symmetry.

Charge Transfer and Orbital Reconstruction at an Organic-Oxide Interface.

The two-dimensional electron system (2DES) located at the surface of strontium titanate (STO) and at several other STO-based interfaces has been an established platform for the study of novel physical phenomena since its discovery. Here we report how the interfacing of STO and tetracyanoquinodimethane (TCNQ) results in a charge transfer that depletes the number of free carriers at the STO surface, with a strong impact on its electronic structure. Our study paves the way for efficient tuning of the electronic properties, which promises novel applications in the framework of oxide/organic-based electronics.

Cyclooctatetraenide-based single-ion magnets featuring bulky cyclopentadienyl ligand.

We report a family of organometallic rare-earth complexes with the general formula (COT)M(Cp) (where (COT) = cyclooctatetraenide, (Cp) = 1,2,4-tri(-butyl)cyclopentadienide, M = Y(iii), Nd(iii), Dy(iii) and Er(iii)). Similarly to the prototypical Er(iii) analog featuring pentamethylcyclopentadienyl ligand (Cp*), (COT)Er(Cp) behaves as a single-ion magnet. However, the introduction of the sterically demanding (Cp) imposes geometric constraints that lead to a simplified magnetic relaxation behavior compared to the (Cp*) containing complexes.

Orienting dilute thin films of non-planar spin-1/2 vanadyl-phthalocyanine complexes.

The molecular orientation as well as the electronic and magnetic properties of vanadyl-phthalocyanine (VOPc) diluted into titanyl-phthalocyanine (TiOPc) thin films on Si(100) and polycrystalline aluminum substrates have been investigated by soft X-ray absorption spectroscopy (XAS), X-ray linear dichroism (XLD) and X-ray magnetic circular dichroism (XMCD). On the bare substrates the films grow with a standing-up geometry. By contrast, on template layers of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA), they assume a lying-down orientation.

Metamagnetic transition and a loss of magnetic hysteresis caused by electron trapping in monolayers of single-molecule magnet Tb@CN.

Realization of stable spin states in surface-supported magnetic molecules is crucial for their applications in molecular spintronics, memory storage or quantum information processing. In this work, we studied the surface magnetism of dimetallo-azafullerene Tb@CN, showing a broad magnetic hysteresis in a bulk form. Surprisingly, monolayers of Tb@CN exhibited a completely different behavior, with the prevalence of a ground state with antiferromagnetic coupling at low magnetic field and a metamagnetic transition in the magnetic field of 2.

Tailoring magnetic anisotropy by graphene-induced selective skyhook effect on 4f-metals.

From macroscopic heavy-duty permanent magnets to nanodevices, the precise control of the magnetic properties in rare-earth metals is crucial for many applications used in our daily life. Therefore, a detailed understanding and manipulation of the 4f-metals' magnetic properties are key to further boosting the functionalization and efficiency of future applications. We present a proof-of-concept approach consisting of a dysprosium-iridium surface alloy in which graphene adsorption allows us to tailor its magnetic properties.

Island formation of Er(trensal) single-ion magnets on graphene observed on the micrometer scale.

We have studied the morphology of Er(trensal) single-ion molecular magnets adsorbed on graphene/Ru(0001) using X-ray photoemission electron microscopy (X-PEEM). By exploiting the elemental contrast at the erbium M edge we observe the formation of molecular islands of homogeneous height with a lateral size of several micrometers. The graphene/Ru(0001) substrate exhibits two different signal levels in bright-field low-energy electron microscopy (LEEM) and in X-PEEM, which are ascribed to the presence of small-angle rotational domains of the graphene lattice.

Amyloid-beta-copper interaction studied by simultaneous nitrogen K and copper L edge soft X-ray absorption spectroscopy.

We study the interaction between amyloid β (Aβ) peptides and Cu and Zn metal ions by using soft X-ray absorption spectroscopy. The spectral features of the peptides and Cu are simultaneously characterized by recording spectra at the N K-edge and at the Cu L edges. In the presence of the peptides, the Cu L edge shows a fingerprint of monovalent Cu(I), caused by the interaction with the peptides.

Correlation between Electronic Configuration and Magnetic Stability in Dysprosium Single Atom Magnets.

Single atom magnets offer the possibility of magnetic information storage in the most fundamental unit of matter. Identifying the parameters that control the stability of their magnetic states is crucial to design novel quantum magnets with tailored properties. Here, we use X-ray absorption spectroscopy to show that the electronic configuration of dysprosium atoms on MgO(100) thin films can be tuned by the proximity of the metal Ag(100) substrate onto which the MgO films are grown.

Noncollinear Magnetic Order in Two-Dimensional NiBr Films Grown on Au(111).

Metal halides are a class of layered materials with promising electronic and magnetic properties persisting down to the two-dimensional limit. While most recent studies focused on the trihalide components of this family, the rather unexplored metal dihalides are also van der Waals layered systems with distinctive magnetic properties. Here we show that the dihalide NiBr grows epitaxially on a Au(111) substrate and exhibits semiconducting and magnetic behavior starting from a single layer.

Exceptionally High Blocking Temperature of 17 K in a Surface-Supported Molecular Magnet.

Single-molecule magnets (SMMs) are among the most promising building blocks for future magnetic data storage or quantum computing applications, owing to magnetic bistability and long magnetic relaxation times. The practical device integration requires realization of 2D surface assemblies of SMMs, where each magnetic unit shows magnetic relaxation being sufficiently slow at application-relevant temperatures. Using X-ray absorption spectroscopy and X-ray magnetic circular dichroism, it is shown that sub-monolayers of Dy @C (CH Ph) dimetallofullerenes prepared on graphene by electrospray deposition exhibit magnetic behavior fully comparable to that of the bulk.

Heterometallic Co-Dy SMMs grafted on iron oxide nanoparticles.

Heterometallic 3d-4f SMM [Co4Dy(OH)2(SALOH)5(chp)4(MeCN)(H2O)2] (1) has been deposited onto iron oxide nanoparticles (NPs) with an oleate self-assembled monolayer (SAM) as a surfactant. The obtained hybrid molecular-inorganic system 1-NP has been thoroughly characterized. The oleate SAM separates SMM 1 from the magnetic substrate to avoid the strong-coupling between the surface and molecule to ensure that 1 retains its magnetic properties in 1-NP.

Magnetic Hysteresis at 10 K in Single Molecule Magnet Self-Assembled on Gold.

Tremendous progress in the development of single molecule magnets (SMMs) raises the question of their device integration. On this route, understanding the properties of low-dimensional assemblies of SMMs, in particular in contact with electrodes, is a necessary but difficult step. Here, it is shown that fullerene SMM self-assembled on metal substrate from solution retains magnetic hysteresis up to 10 K.

Substrate-Independent Magnetic Bistability in Monolayers of the Single-Molecule Magnet Dy ScN@C on Metals and Insulators.

Magnetic hysteresis is demonstrated for monolayers of the single-molecule magnet (SMM) Dy ScN@C deposited on Au(111), Ag(100), and MgO|Ag(100) surfaces by vacuum sublimation. The topography and electronic structure of Dy ScN@C adsorbed on Au(111) were studied by STM. X-ray magnetic CD studies show that the Dy ScN@C monolayers exhibit similarly broad magnetic hysteresis independent on the substrate used, but the orientation of the Dy ScN cluster depends strongly on the surface.

Understanding the Superior Stability of Single-Molecule Magnets on an Oxide Film.

The stability of magnetic information stored in surface adsorbed single-molecule magnets is of critical interest for applications in nanoscale data storage or quantum computing. The present study combines X-ray magnetic circular dichroism, density functional theory and magnetization dynamics calculations to gain deep insight into the substrate dependent relevant magnetization relaxation mechanisms. X-ray magnetic circular dichroism reveals the opening of a butterfly-shaped magnetic hysteresis of DyPc molecules on magnesium oxide and a closed loop on the bare silver substrate, while density functional theory shows that the molecules are only weakly adsorbed in both cases of magnesium oxide and silver.

Magnetic properties of on-surface synthesized single-ion molecular magnets.

We perform synthesis of single-ion molecular magnets on an Ag(111) surface and characterize their morphology, chemistry, and magnetism. The first molecule we synthesize is TbPc to enable comparison with chemically synthesized and subsequently surface adsorbed species. We demonstrate the formation of TbPc with a yield close to 100% and show that on-surface synthesis leads to identical magnetic and morphological properties compared to the previously studied chemically synthesized species.

Multimodeling Approach to Ferromagnetic Spin-Wave Excitations in the High-Spin Cluster MnSr Observed by Inelastic Neutron Scattering.

The magnetism of the mixed-valence high-spin cluster [MnSrO(N)Cl(MedhmpH)(MeCN)]Cl () exhibiting intramolecular ferromagnetic interactions was studied using inelastic neutron scattering (INS), and reliable values for the exchange coupling constants were determined based on the quality of simultaneous fits to the INS and magnetic data. The challenge of the huge size of the Hilbert space (3 375 000) and many exchange coupling constants (7 assuming a symmetry) generally encountered in large spin clusters was resolved as follows: (a) The results of the restricted Hilbert space ferromagnetic cluster spin wave theory were compared to the experimental spectroscopic data. The observed INS transitions were thus assigned to spin wave excitations in a bounded ferromagnetic spin cluster and moreover could be visualized in a straightforward way based on this theory.

Direct Observation of Charge Transfer and Magnetism in FeCo Cyanide-Bridged Molecular Cubes.

We have studied the zero-dimensional cubane molecular correspondent of a Prussian blue analogue Cs-FeCo at low temperature and high magnetic field by means of L-edge X-ray absorption spectroscopy and X-ray magnetic circular dichroism. We probe the magnetic and electronic structures of Fe and Co separately upon light irradiation, which allows us to observe directly the electron transfer coupled to a spin transition phenomenon within the molecular cubes and to investigate the nature of the metastable photoexcited state. The magnetic moments in the photoexcited state are found to be M = 1.

Non-empirical calculation of X-ray magnetic circular dichroism in lanthanide compounds.

Affordable calculations of X-ray magnetic circular dichroism and X-ray linear dichroism spectra of lanthanide ions purely based on structural input are difficult to achieve. Here we report on the successful application of ligand-field density-functional theory to obtain an exquisite reproduction of experimental spectra. As a testbed we use TbPc2 single-molecule magnets on a flat substrate.

Stability of metallo-porphyrin networks under oxygen reduction and evolution conditions in alkaline media.

Transition metal atoms stabilised by organic ligands or as oxides exhibit promising catalytic activity for the electrocatalytic reduction and evolution of oxygen. Built-up from earth-abundant elements, they offer affordable alternatives to precious-metal based catalysts for application in fuel cells and electrolysers. For the understanding of a catalyst's activity, insight into its structure on the atomic scale is of highest importance, yet commonly challenging to experimentally access.

On-surface transmetalation of metalloporphyrins.

Increasing the complexity of 2D metal-organic networks has led to the fabrication of structures with interesting magnetic and catalytic properties. However, increasing complexity by providing different coordination environments for different metal types imposes limitations on their synthesis if the controlled placement of one metal type into one coordination environment is desired. Whereas metal insertion into free-base porphyrins at the vacuum/solid interface has been thoroughly studied, providing detailed insight into the mechanisms at play, the chemical interaction of a metal atom with a metallated porphyrin is rarely investigated.