arXiv subjects

David Serrate

Publications and source records attributed to David Serrate.

8 recordsLinked to original sources

arXiv2026

Atomic scale demonstration of ferromagnetism in a single layer FeCl2 on Au(111)

FeCl2 is a promising single-layer material with sizeable magnetic susceptibility and insulating character that can be easily grown by molecular beam epitaxy on various surfaces. In order to include it into the select palette of van der Waals materials used to engineer functional heterostructures, it is necessary to confirm its magnetic and electronic ground states, and understand the influence of the supporting substrate. In this work, we unambiguously demonstrate ferromagnetic ordering in a single-layer FeCl2 on Au(111) by means of spin-polarized scanning tunnelling microscopy. The material features a relatively wide insulating gap of 3.3 eV and a strongly spin-polarized conduction band that emerges at 1.5 eV above the Fermi level. Atomic scale defects with triangular shape play a primary role in the electronic gap and spin density distribution. Specifically, in a region of 1.6 nm around each defect, the conduction band is locally suppressed and the tunnelling magneto-conductance is reduced a factor of four. By tracking the spin-dependent tunnelling conductance as a function of the applied magnetic field, we record atomically resolved hysteresis loops, revealing a soft ferromagnetic ground state with pronounced out-of-plane anisotropy and coercive fields in the range of 15-50 mT.

cond-mat.mtrl-sci↗

arXiv2024

Systematic Modulation of Charge and Spin in Graphene Nanoribbons on MgO

Graphene nanostructures can be engineered with atomic precision to display customized electronic states with application in spintronics or quantum technologies. In order to take advantage of their full potential, their charge and spin state must be precisely controlled. Graphene systems exchange charge to reach thermodynamic equilibrium with their environment, requiring external gating potentials to tune their ground state. Alternative strategies like intrinsic doping or substrate modifications provided small variations of their equilibrium charge and poor control over their spin. Here, we show systematic manipulation of the electron occupation in graphene nanoribbons (GNRs) laying on MgO layers grown on Ag(001). Owing to the extraordinary decoupling properties of MgO, and the electropositive character of the substrate, GNRs are found to host an integer number of electron charges that depend on their length and shape. This results in the alternation between a non-magnetic closed-shell state and an open-shell paramagnetic system for even and odd electron occupations respectively. For the odd case, we found the spectral fingerprint of a narrow Coulomb correlation gap, which is the smoking gun of its spin 1/2 paramagnetic state. Comparisons of scanning tunnelling microscopy (STM) data with mean-field Hubbard (MFH) simulations confirm the practical discretization of the GNR electronic states and point to charge excess of up to 19 electrons in a single ribbon. We anticipate that GNRs supported by MgO ultra-thin insulating films can open the door to customized devices for quantum sensing and quantum processing applications..

cond-mat.mes-hall↗

arXiv2023

Bistable electric field control of single-atom magnetocrystalline anisotropy

We reversibly switch the polar environment of an individual magnetic atom with an electric field to control the energy barrier for reversal of magnetization. By applying an electric field in the gap between the tip and sample of a scanning tunneling microscope, we induce bistable changes in the polarization of the region surrounding a chlorine vacancy in a monolayer of sodium chloride on copper terminated by a monolayer of copper nitride. The displacement of the sodium chloride ions alters the local electric polarization and modifies the magnetocrystalline anisotropy experienced by a single cobalt atom. When a cobalt atom is near a chlorine vacancy, spin-sensitive inelastic electron tunneling spectroscopy measurements can reveal the change in anisotropy. The demonstration of atomic-scale control of magnetic properties with electric fields opens new possibilities for probing the origins of magnetoelectric coupling and will stimulate the development of model artificial mutliferroic systems.

cond-mat.mes-hall↗

arXiv2023

Detecting the spin-polarization of edge states in graphene nanoribbons

Low dimensional carbon-based materials are interesting because they can show intrinsic $\pi$-magnetism associated to p-electrons residing in specific open-shell configurations. Consequently, during the last years there have been impressive advances in the field combining indirect experimental fingerprints of localized magnetic moments with theoretical models. In spite of that, a characterization of their spatial- and energy-resolved spin-moment has so far remained elusive. To obtain this information, we present an approach based on the stabilization of the magnetization of $\pi$-orbitals by virtue of a supporting substrate with ferromagnetic ground state. Remarkably, we go beyond localized magnetic moments in radical or faulty carbon sites: In our study, energy-dependent spin-moment distributions have been extracted from spatially extended one-dimensional edge states of chiral graphene nanoribbons. This method can be generalized to other nanographene structures, representing an essential validation of these materials for their use in spintronics and quantum technologies.

cond-mat.mes-hall↗

arXiv2022

Ferromagnetism on an atom-thick and extended 2D-metal-organic framework

Ferromagnetism (FM) is the cornerstone of permanent magnets, data storage and other technologies that directly impact our everyday life by their implementation in standard applications and devices. When downscaling bulk materials into their two-dimensional (2D) magnetic isotropic form, the Mermin-Wagner theorem precludes this collective state mediated by short-range exchange interactions at finite temperatures. Interestingly, this prediction fails when significant magnetic anisotropy is present in the material, as recently demonstrated in single layered van der Waals crystals. Before the latter, single layer metal-organic frameworks (MOFs) grown on metallic supports were one of the earliest candidates for achieving 2D-FM. Such high expectations were based on the chemical and spacing control of the 2D-MOF magnetic centers, the tunability of the organic linkers and the rich self-assembled architectures displayed. However, despite many attempts, extended FM in 2D-MOFs has been experimentally elusive. In this work, we demonstrate that extended, cooperative FM takes place in an atom thick 2D-MOF consisting of 9,10-dicyanoanthracene (DCA) molecules and Fe adatoms grown on Au(111). We show this by means of an experimental multitechnique approach that is endorsed by state-of-the art first-principles calculations. Particularly, this 2D ferromagnet follows a first order transition with TC ~ 35 K, which is driven by exchange interactions mainly through the molecular linkers (J=2 meV) and exhibits an out-of-plane square-like hysteresis loop. The strict periodicity of our 2D-MOF allows us to envision the fabrication of ultra-dense single atom magnetic memories and opens the way to explore periodic magnetic 2D-models that could considerably increase the fundamental superparamagnetic limit.

cond-mat.mtrl-sci↗

arXiv2020

Chemical sensing with atomically-thin metals templated by a two-dimensional insulator

Boosting the sensitivity of solid-state gas sensors by incorporating nanostructured materials as the active sensing element can be complicated by interfacial effects. Interfaces at nanoparticles, grains, or contacts may result in non-linear current-voltage response, high electrical resistance, and ultimately, electric noise that limits the sensor read-out. Here we report the possibility to prepare nominally one atom thin, electrically continuous metals, by straightforward physical vapor deposition on the carbon zero-layer grown epitaxially on silicon carbide. With platinum as the metal, its electrical conductivity is strongly modulated when interacting with chemical analytes, due to charges being transferred to/from Pt. This, together with the scalability of the material, allows us to microfabricate chemiresistor devices for electrical read-out of chemical species with sub part-per-billion detection limits. The two-dimensional system formed by atomically-thin metals open up a route for resilient and high sensitivity chemical detection, and could be the path for designing new heterogeneous catalysts with superior activity and selectivity.

cond-mat.mtrl-sci↗

arXiv2018

Reversible magnetic switching of high-spin molecules on a giant Rashba surface

The quantum mechanical screening of a spin via conduction electrons depends sensitively on the environment seen by the magnetic impurity. A high degree of responsiveness can be obtained with metal complexes, as the embedding of a metal ion into an organic molecule prevents intercalation or alloying and allows for a good control by an appropriate choice of the ligands. There are therefore hopes to reach an "on demand" control of the spin state of single molecules adsorbed on substrates. Hitherto one route was to rely on "switchable" molecules with intrinsic bistabilities triggered by external stimuli, such as temperature or light, or on the controlled dosing of chemicals to form reversible bonds. However, these methods constrain the functionality to switchable molecules or depend on access to atoms or molecules. Here, we present a way to induce bistability also in a planar molecule by making use of the environment. We found that the particular "habitat" offered by an antiphase boundary of the Rashba system BiAg$_2$ stabilizes a second structure for manganese phthalocyanine molecules, in which the central Mn ion moves out of the molecular plane. This corresponds to the formation of a large magnetic moment and a concomitant change of the ground state with respect to the conventional adsorption site. The reversible spin switch found here shows how we can not only rearrange electronic levels or lift orbital degeneracies via the substrate, but even sway the effects of many-body interactions in single molecules by acting on their surrounding.

cond-mat.str-el↗

arXiv2014

Control of single-spin magnetic anisotropy by exchange coupling

The properties of quantum systems interacting with their environment, commonly called open quantum systems, can be strongly affected by this interaction. While this can lead to unwanted consequences, such as causing decoherence in qubits used for quantum computation, it can also be exploited as a probe of the environment. For example, magnetic resonance imaging is based on the dependence of the spin relaxation times of protons in water molecules in a host's tissue. Here we show that the excitation energy of a single spin, which is determined by magnetocrystalline anisotropy and controls its stability and suitability for use in magnetic data storage devices, can be modified by varying the exchange coupling of the spin to a nearby conductive electrode. Using scanning tunnelling microscopy and spectroscopy, we observe variations up to a factor of two of the spin excitation energies of individual atoms as the strength of the spin's coupling to the surrounding electronic bath changes. These observations, combined with calculations, show that exchange coupling can strongly modify the magnetic anisotropy. This system is thus one of the few open quantum systems in which the energy levels, and not just the excited-state lifetimes, can be controllably renormalized. Furthermore, we demonstrate that the magnetocrystalline anisotropy, a property normally determined by the local structure around a spin, can be electronically tuned. These effects may play a significant role in the development of spintronic devices5 in which an individual magnetic atom or molecule is coupled to conducting leads.

cond-mat.mes-hall↗