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Single lanthanide atoms and molecules are promising candidates for atomic data storage and quantum logic due to the long lifetime of their magnetic quantum states. Accessing and controlling these states through electrical transport requires precise knowledge of their electronic configuration at the level of individual atomic orbitals, especially of the outer shells involved in transport. However, no experimental techniques have so far shown the required sensitivity to probe single atoms with orbital selectivity. Here we resolve the magnetism of individual orbitals in Gd and Ho single atoms on MgO/Ag(100) by combining X-ray magnetic circular dichroism with multiplet calculations and density functional theory. In contrast to the usual assumption of bulk-like occupation of the different electronic shells, we establish a charge transfer mechanism leading to an unconventional singly ionized configuration. Our work identifies the role of the valence electrons in determining the quantum level structure and spin-dependent transport properties of lanthanide-based nanomagnets.

Single spins are considered as a versatile candidate for miniaturizing information devices down to the nanoscale. To engineer the spin's properties, metal-organic frameworks provide a promising route which in turn requires thorough understanding of the metal-molecule interaction. Here, we investigate the magnetic robustness of a single iron (Fe) atom in artificially built Fe-tetracyanoethylene (TCNE) complexes by using low-temperature scanning tunneling microscopy (STM). We find that the magnetic anisotropy and spin relaxation dynamics of the Fe atom within the complexes remain unperturbed in comparison to well-isolated Fe atoms. Density functional theory (DFT) calculations support our experimental findings, suggesting that the 3d orbitals of the Fe atom remain largely undisturbed while the 4s and 4p orbitals are rearranged in the process of forming a complex. To precisely determine the location of the spin center within the complex, we utilize STM-based spin relaxometry, mapping out the spatial dependence of spin relaxation with subnanometer resolution. Our work suggests that the magnetic properties of atoms can remain unchanged while being embedded in a weakly bound molecular framework.

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. Increasing the MgO thickness from 2.5 to 9 monolayers induces a change in the dysprosium electronic configuration from 4f(9) to 4f(10). Hysteresis loops indicate long magnetic lifetimes for both configurations, however, with a different field-dependent magnetic stability. Combining these measurements with scanning tunneling microscopy, density functional theory, and multiplet calculations unveils the role of the adsorption site and charge transfer to the substrate in determining the stability of quantum states in dysprosium single atom magnets.

Spin resonance of single spin centers bears great potential for chemical structure analysis, quantum sensing, and quantum coherent manipulation. Essential for these experiments is the presence of a two-level spin system whose energy splitting can be chosen by applying a magnetic field. In recent years, a combination of electron spin resonance (ESR) and scanning tunneling microscopy (STM) has been demonstrated as a technique to detect magnetic properties of single atoms on surfaces and to achieve sub-microelectronvolts energy resolution. Nevertheless, up to now the role of the required magnetic fields has not been elucidated. Here, we perform single-atom ESR on individual Fe atoms adsorbed on magnesium oxide (MgO) using a two-dimensional vector magnetic field as well as the local field of the magnetic STM tip in a commercially available STM. We show how the ESR amplitude can be greatly improved by optimizing the magnetic fields, revealing in particular an enhanced signal at large in-plane magnetic fields. Moreover, we demonstrate that the stray field from the magnetic STM tip is a versatile tool. We use it here to drive the electron spin more efficiently and to perform ESR measurements at constant frequency by employing tip-field sweeps. Lastly, we show that it is possible to perform ESR using only the tip field, under zero external magnetic field, which promises to make this technique available in many existing STM systems.

Microscopic studies on thin film superconductors play an important role for probing non-equilibrium phase transitions and revealing dynamics at the nanoscale. However, magnetic sensors with nanometer scale spatial and picosecond temporal resolution are essential for exploring these. Here, we present an all-optical, microwave-free method that utilizes the negatively charged nitrogen-vacancy (NV) center in diamond as a non-invasive quantum sensor and enables the spatial detection of the Meissner state in a superconducting thin film. We place an NV implanted diamond membrane on a 20 nm thick superconducting La 2 − xSr xCuO 4 (LSCO) thin film with T c of 34 K. The strong B-field dependence of the NV photoluminescence allows us to investigate the Meissner screening in LSCO under an externally applied magnetic field of 4.2 mT in a non-resonant manner. The magnetic field profile along the LSCO thin film can be reproduced using Brandt’s analytical model, revealing a critical current density j c of 1.4 × 10 8 A / c m 2. Our work can be potentially extended further with a combination of optical pump probe spectroscopy for the local detection of time-resolved dynamical phenomena in nanomagnetic materials.

Atomic scale engineering of magnetic fields is a key ingredient for miniaturizing quantum devices and precision control of quantum systems. This requires a unique combination of magnetic stability and spin-manipulation capabilities. Surface-supported single atom magnets offer such possibilities, where long temporal and thermal stability of the magnetic states can be achieved by maximizing the magnet/ic anisotropy energy (MAE) and by minimizing quantum tunnelling of the magnetization. Here, we show that dysprosium (Dy) atoms on magnesium oxide (MgO) have a giant MAE of 250 meV, currently the highest among all surface spins. Using a variety of scanning tunnelling microscopy (STM) techniques including single atom electron spin resonance (ESR), we confirm no spontaneous spin-switching in Dy over days at approximate to 1 K under low and even vanishing magnetic field. We utilize these robust Dy single atom magnets to engineer magnetic nanostructures, demonstrating unique control of magnetic fields with atomic scale tunability., Single atom magnets on surfaces offer potentially long lived and stable spin states, particular lanthanides, which can be adsorbed onto Magnesium Oxide. Here, the authors report on Dysprosium adsorbed onto Magnesium Oxide, which exhibits large magnetic anisotropy energy, and a spin life time of several days at low temperatures

We investigate the spin relaxation of Ho single atom magnets on $\mathrm{MgO}/\mathrm{Ag}(100)$ 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.

We have studied thin films of Fe(II) spin crossover complexes deposited on differently poled ferroelectric PMN-PT ([Pb(Mg1/3Nb2/3)O3]1–x[PbTiO3]x, x = 0.32) substrates by X-ray absorption spectroscopy. The X-ray spectra reveal the temperature-driven conversion between high-spin and low-spin states without any observable effect of the ferroelectric polarization on the spin state of the molecules down to 100 K. In the soft X-ray-induced excited spin-state trapping (SOXIESST) regime at 3 K, large differences occur between the two ferroelectric polarizations. The efficiency of X-rays in exciting the molecules to the high-spin state is more than an order of magnitude larger when the ferroelectric dipoles of the substrate are pointing toward the surface compared to the opposite polarization. We explain our findings by a modulation of the polarization-dependent efficiency of the scattering of X-ray-generated secondary electrons at the molecules. Our results provide a deep insight into the SOXIESST mechanism and ...

Atomic spins for quantum technologies need to be individually addressed and positioned with nanoscale precision. C60 fullerene cages offer a robust packaging for atomic spins, while allowing in-situ physical positioning at the nanoscale. However, achieving single-spin level readout and control of endofullerenes has so far remained elusive. In this work, we demonstrate electron paramagnetic resonance on an encapsulated nitrogen spin (14N@C60) within a C60 matrix using a single near-surface nitrogen vacancy (NV) center in diamond at 4.7 K. Exploiting the strong magnetic dipolar interaction between the NV and endofullerene electronic spins, we demonstrate radio-frequency pulse controlled Rabi oscillations and measure spin-echos on an encapsulated spin. Modeling the results using second-order perturbation theory reveals an enhanced hyperfine interaction and zero-field splitting, possibly caused by surface adsorption on diamond. These results demonstrate the first step towards controlling single endofullerenes, and possibly building large-scale endofullerene quantum machines, which can be scaled using standard positioning or self-assembly methods., European Union’s Horizon 2020 research and innovation programme, Volkswagen Stiftung, Projekt DEAL

We combine x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD) and x-ray magnetic linear dichroism (XMLD) data with first principles density functional theory (DFT) calculations and a multiorbital many body Hamiltonian approach to understand the electronic and magnetic properties of Co atoms adsorbed on h-BN/Ru(0001) and h-BN/Ir(111). The XAS line shape reveals, for both substrates, an electronic configuration close to $3d^8$, corresponding to a spin $S = 1$. Magnetic field dependent XMCD data show large (14 meV) out-of-plane anisotropy on h-BN/Ru(0001), while it is almost isotropic (tens of $\mu$eV) on h-BN/Ir(111). XMLD data together with both DFT calculations and the results of the multiorbital Hubbard model suggest that the dissimilar magnetic anisotropy originates from different Co adsorption sites, namely atop N on h-BN/Ru(0001) and 6-fold hollow on h-BN/Ir(111)., Comment: 18 pages, 5 figures

We perform on-surface synthesis of single-ion molecular magnets on an Ag(111) surface and characterize their morphology, chemistry, and magnetism. The first molecule we synthesize is TbPc2 to enable comparison with chemically synthesized and subsequently surface adsorbed species. We demonstrate the formation of TbPc2 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. Moreover, exposure of the surface adsorbed TbPc2 molecules to air does not modify their magnetic and morphological properties. To demonstrate the versatility of our approach, we synthesize novel Tb double deckers using tert-butyl-substituted phthalocyanine (tbu-2H-Pc). The Tb(tbu-Pc)(2) molecules exhibit magnetic hysteresis and therefore are the first purely on-surface synthesized single ion magnet.

TbPc2 single-molecule magnets adsorbed on a magnesium oxide tunnel barrier exhibit record magnetic remanence, record hysteresis opening, perfect out-of-plane alignment of the magnetic easy axes, and self-assembly into a well-ordered layer.

We employed x-ray absorption spectroscopy and x-ray magnetic circular dichroism to study the magnetic properties of single rare-earth (RE) atoms (Nd, Tb, Dy, Ho, and Er) adsorbed on the graphene/Ir(111) surface. The interaction of RE atoms with graphene results for Tb in a trivalent state with $4{f}^{n\ensuremath{-}1}$ occupancy, and in a divalent state with $4{f}^{n}$ occupancy for all other studied RE atoms ($n$ corresponds to the $4f$ occupancy of free atoms). Among the studied RE on graphene/Ir(111), Dy is the only one that shows magnetic hysteresis and remanence at 2.5 K. By comparing measured spectra and magnetization curves with multiplet calculations, we determine the energy diagram of the magnetic states and show for each element the magnetization reversal process that determines the timescale of its magnetic bistability.

We report x-ray absorption spectroscopy and x-ray magnetic circular dichroism measurements as well as multiplet calculations for Dy, Ho, Er, and Tm atoms adsorbed on Pt(111), Cu(111), Ag(100), and Ag(111). In the gas phase, all four elements are divalent and we label their $4f$ occupancy as $4{f}^{n}$. Upon surface adsorption, and depending on the substrate, the atoms either remain in that state or become trivalent with $4{f}^{n\ensuremath{-}1}$ configuration. The trivalent state is realized when the sum of the atomic correction energies ($4f$\ensuremath{\rightarrow}$5d$ promotion energy ${E}_{fd}\phantom{\rule{0.16em}{0ex}}+$ intershell coupling energy $\ensuremath{\delta}{E}_{c}$) is low and the surface binding energy is large. The latter correlates with a high substrate density of states at the Fermi level. The magnetocrystalline anisotropy of trivalent RE atoms is larger than the one of divalent RE atoms. We ascribe this to the significantly smaller covalent radius of the trivalent state compared to the divalent one for a given RE element. For a given valency of the RE atom, the anisotropy is determined by the overlap between the $spd$ states of the RE and the $d$ states of the surface. For all investigated systems, the magnetization curves recorded at 2.5 K show absence of hysteresis indicating that magnetic relaxation is faster than about 10 s.

Stable magnets from single atoms An important goal in molecular magnetism is to create a permanent magnet from a single atom. Metal atoms adsorbed on surfaces can develop strong magnetization in an applied field (paramagnetism). Donati et al. show that single holmium atoms adsorbed on a magnesium oxide film grown on a silver substrate show residual magnetism for temperatures up to 30 K and bistabilty that lasts for 1500 s at 10 K (see the Perspective by Khajetoorians and Heinrich). The atom avoids spin relaxation by a combination of quantum-state symmetry and by the oxide film preventing the spin from interacting with the underlying metal via tunneling. Science , this issue p. 318 ; see also p. 296

Background: Use of Facebook is a most common phenomenon in the present world. But it has been seen that gradually excessive use of Facebook often creates some psychological problems. Literature shows that there are some specific personality profiles which are responsible for excessive Facebook use. So the main objective of the study is to reveal the specific personality profile of frequent and infrequent Facebook users. Methodology: A group of 30 frequent Facebook users of Agartala were compared with a group of 30 infrequent Facebook users aged between 18-24 years in respect to their personality traits and leisure time activity preferences with the help of Cattell’s 16 Personality Questionnaire and a general information schedule. Results: The result reveals that the frequent Facebook users are enthusiastic, cheerful, talkative, frank, expressive, quick, alert, and imperturbable, they put more emphasis in concrete thinking, they are also undependable, unsteady, quitting. And the infrequent Facebook users are self sufficient, independent, resolute, and accustomed to going their own way, making decisions and taking actions by their own and they also put more emphasis in concrete thinking. Conclusion: It may be concluded from the study that there is a significant difference between personality traits of frequent and infrequent Facebook users. However, a study with a larger sample may reveal more information regarding this issue. Keywords: Personality traits, facebook users

We present a comprehensive study of Er(trensal) single ion magnets deposited in ultrahigh vacuum onto metallic surfaces. X ray photoelectron spectroscopy reveals that the molecular structure is preserved after sublimation and that the molecules are physisorbed on Au(111) while they are chemisorbed on a Ni thin film on Cu(100) single crystalline surfaces. X ray magnetic circular dichroism ({XMCD)} measurements performed on Au(111) samples covered with molecular monolayers held at temperatures down to 4 K suggest that the easy axes of the strongly anisotropic molecules are randomly oriented. Furthermore {XMCD} indicates a weak antiferromagnetic exchange coupling between the single ion magnets and the ferromagnetic {Ni/Cu(100)} substrate. For the latter case spin Hamiltonian fits to the {XMCD} M(H) suggest a significant structural distortion of the molecules. Scanning tunneling microscopy reveals that the molecules are mobile on Au(111) at room temperature whereas they are more strongly attached on {Ni/Cu(100).} X ray photoelectron spectroscopy results provide evidence for the chemical bonding between Er(trensal) molecules and the Ni substrate. Density functional theory calculations support these findings and in addition reveal the most stable adsorption configuration on {Ni/Cu(100)} as well as the {Ni?Er} exchange path. Our study suggests that the magnetic moment of Er(trensal) can be stabilized via suppression of quantum tunneling of magnetization by exchange coupling to the Ni surface atoms. Moreover it opens up pathways toward optical addressing of surface deposited single ion magnets.

In Tb(Pc)2 single-molecule magnets, where Pc is phthalocyanine, adsorbed on magnesium oxide, the fluctuations of the terbium magnetic moment are strongly suppressed in contrast to the adsorption on silver. On page 5195, J. Dreiser and co-workers investigate that the molecules are perfectly organized by self-assembly, as seen in the scanning tunnelling microscopy image (top part of the design). The molecules are probed by circularly polarized X-rays depicted as green spirals.

We report our experimental observations of variation in on-off statistics and fluorescence intensity of single Rhodamine6G molecules in presence of resonantly driven surface plasmon of silver nanoparticle. Derived lifetimes from on-off statistics of fluorophore show that interaction between the fluorophore and the subwavelength metal nanoparticle improves photostability and enhances fluorescence intensity. This enhancement follows the trend predicted by the dipole-dipole interaction model.

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).

Regular arrays of single atoms with stable magnetization represent the ultimate limit of ultrahigh density storage media. Here we report a self-assembled superlattice of individual and noninteracting Dy atoms on graphene grown on Ir(111), with magnetic hysteresis up to 5.6 T and spin lifetime of 1000 s at 2.5 K. The observed magnetic stability is a consequence of the intrinsic low electron and phonon densities of graphene and the 6-fold symmetry of the adsorption site. Our array of single atom magnets has a density of 115 Tbit/inch(2), defined by the periodicity of the graphene moire pattern.

We report magnetic hysteresis in Er clusters on Cu(111) starting from the size of three atoms. Combining X-ray magnetic circular dichroism, scanning tunneling microscopy, and mean-field nucleation theory, we determine the size-dependent magnetic properties of the Er clusters. Er atoms and dimers are paramagnetic, and their easy magnetization axes are oriented in-plane. In contrast, trimers and bigger clusters exhibit magnetic hysteresis at 2.5 K with a relaxation time of 2 min at 0.1 T and out-of-plane easy axis. This appearance of magnetic stability for trimers coincides with their enhanced structural stability.

We report on the antiferromagnetic exchange coupling between a submonolayer of Mn(II)-phthalocyanine molecules and a ferromagnetic Eu(II)-oxide thin film. The exchange energy is larger by nearly two orders of magnitude compared to previous studies involving oxidic substrates.

We report on the magnetic properties of HoCo dimers as a model system for the smallest intermetallic compound of a lanthanide and a transition metal atom. The dimers are adsorbed on ultrathin MgO(100) films grown on Ag(100). New for 4f elements, we detect inelastic excitations with scanning tunneling spectroscopy and prove their magnetic origin by applying an external magnetic field. In combination with density functional theory and spin Hamiltonian analysis, we determine the magnetic level distribution, as well as sign and magnitude of the exchange interaction between the two atoms. In contrast to typical 4f-3d bulk compounds, we find ferromagnetic coupling in the dimer. © 2018 American Physical Society.