RESUMEN
We investigate the spin relaxation of Ho single atom magnets on MgO/Ag(100) as a function of temperature and magnetic field. We find that the spin relaxation is thermally activated at low field, while it remains larger than 1000 s up to 30 K and 8 T. This behavior contrasts with that of single molecule magnets and bulk paramagnetic impurities, which relax faster at high field. Combining our results with density functional theory, we rationalize this unconventional behavior by showing that local vibrations activate a two-phonon Raman process with a relaxation rate that peaks near zero field and is suppressed at high field. Our work shows the importance of these excitations in the relaxation of axially coordinated magnetic atoms.
RESUMEN
Fullerene single molecule magnets (SMMs) DySc2N@C80 and Dy2ScN@C80 are functionalized via a 1,3-dipolar cycloaddition with surface-anchoring thioether groups. The SMM properties of Dy-fullerenes are substantially affected by the cycloaddition. Submonolayers of the physisorbed derivatives exhibit magnetic hysteresis on an Au(111) surface at 2 K as revealed by X-ray magnetic circular dichroism.
RESUMEN
A permanent magnet retains a substantial fraction of its saturation magnetization in the absence of an external magnetic field. Realizing magnetic remanence in a single atom allows for storing and processing information in the smallest unit of matter. We show that individual holmium (Ho) atoms adsorbed on ultrathin MgO(100) layers on Ag(100) exhibit magnetic remanence up to a temperature of 30 kelvin and a relaxation time of 1500 seconds at 10 kelvin. This extraordinary stability is achieved by the realization of a symmetry-protected magnetic ground state and by decoupling the Ho spin from the underlying metal by a tunnel barrier.
RESUMEN
We report on the magnetic properties of individual Fe atoms deposited on MgO(100) thin films probed by x-ray magnetic circular dichroism and scanning tunneling spectroscopy. We show that the Fe atoms have strong perpendicular magnetic anisotropy with a zero-field splitting of 14.0±0.3 meV/atom. This is a factor of 10 larger than the interface anisotropy of epitaxial Fe layers on MgO and the largest value reported for Fe atoms adsorbed on surfaces. The interplay between the ligand field at the O adsorption sites and spin-orbit coupling is analyzed by density functional theory and multiplet calculations, providing a comprehensive model of the magnetic properties of Fe atoms in a low-symmetry bonding environment.
RESUMEN
Single-ion magnets (SIMs) are mononuclear molecular complexes exhibiting slow relaxation of magnetization. They are currently attracting a lot of interest because of potential applications in spintronics and quantum information processing. However, exploiting SIMs in, e.g. molecule-inorganic hybrid devices requires a fundamental understanding of the effects of molecule-substrate interactions on the SIM magnetic properties. In this review the properties of lanthanide SIMs in the bulk crystalline phase and deposited on surfaces in the (sub)monolayer regime are discussed. As a starting point trivalent lanthanide ions in a ligand field will be described, and the challenges in characterizing the ligand field are illustrated with a focus on several spectroscopic techniques which are able to give direct information on the ligand-field split energy levels. Moreover, the dominant mechanisms of magnetization relaxation in the bulk phase are discussed followed by an overview of SIMs relevant for surface deposition. Further, a short introduction will be given on x-ray absorption spectroscopy, x-ray magnetic circular dichroism and scanning tunneling microscopy. Finally, the recent experiments on surface-deposited SIMs will be reviewed, along with a discussion of future perspectives.
RESUMEN
We investigated the magnetic properties of individual Ho atoms adsorbed on the (111) surface of Pt, which have been recently claimed to display single ion magnetic behavior. By combining x-ray absorption spectroscopy and magnetic dichroism measurements with ligand field multiplet calculations, we reveal a ground state which is incompatible with long spin relaxation times, in disagreement with former findings. A comparative study of the ground state and magnetic anisotropy of Ho and Er on Pt(111) and Cu(111) emphasizes the different interaction of the 4f orbitals with localized and delocalized substrate states. In particular, we find a striking rotation of the magnetization easy axis for Er, which changes from out of plane on Pt(111) to in plane on Cu(111).
RESUMEN
We determine the magnetic properties of individual Co atoms adsorbed on graphene (G) with x-ray absorption spectroscopy and magnetic circular dichroism. The magnetic ground state of Co adatoms strongly depends on the choice of the metal substrate on which graphene is grown. Cobalt atoms on G/Ru(0001) feature exceptionally large orbital and spin moments, as well as an out-of-plane easy axis with large magnetic anisotropy. Conversely, the magnetic moments are strongly reduced for Co/G/Ir(111), and the magnetization is of the easy-plane type. We demonstrate how the Co magnetic properties, which ultimately depend on the degree of hybridization between the Co 3d orbitals and graphene π bands, can be tailored through the strength of the graphene-substrate coupling.
RESUMEN
The paramagnetic NMR study of HoM2N@C80-Ih and Ho2MN@C80-Ih nitride cluster fullerenes (M = Sc, Lu, Y) reveals strong dependence of Ho-induced paramagnetic shifts (δ(para)) in (13)C NMR spectra on the size of the diamagnetic metal in the cluster. In particular, the δ(para) value in HoY2N@C80 is almost doubled in comparison to that in HoSc2N@C80. X-ray magnetic circular dichroism studies show that all Ho-nitride cluster fullerenes have the same magnetic ground state of Ho(3+). Point-charge ligand-field splitting calculations show that the increase of the M(3+) radius in going from Sc to Y results in a considerable increase of the energy splitting between different Jz states. This leads to a 19% higher magnetic anisotropy of Ho(3+) in HoY2N@C80 than in HoSc2N@C80 at 300 K. Variations of the molecular geometry and cluster dynamics with the size of the cluster are found to have even greater influence on δ(para) values. This work shows that the magnetic properties of the species confined inside the fullerene cages can be tuned using the geometrical factors such as the cluster and the cage size.
RESUMEN
In sharp contrast to previous studies on FeRh bulk, thin films, and nanoparticles, we report the persistence of ferromagnetic order down to 3 K for size-selected 3.3 nm diameter nanocrystals embedded into an amorphous carbon matrix. The annealed nanoparticles have a B2 structure with alternating atomic Fe and Rh layers. X-ray magnetic dichroism and superconducting quantum interference device measurements demonstrate ferromagnetic alignment of the Fe and Rh magnetic moments of 3 and 1µ(B), respectively. The ferromagnetic order is ascribed to the finite-size induced structural relaxation observed in extended x-ray absorption spectroscopy.
RESUMEN
Through the utilization of index-matched GaAs immersion lens techniques, we demonstrate a record extinction (12%) of a far-field focused laser beam by a single InAs/GaAs quantum dot. This contrast level enables us to report for the first time resonant laser transmission spectroscopy on a single InAs/GaAs quantum dot without the need for phase-sensitive lock-in detection.
