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Here, we report the investigation of the influence of the magnetocrystalline anisotropy (MCA) in Cobalt ultrathin films grown on the vicinal surface Au(788), through the anisotropy of the orbital magnetic moment. The aim of this study was to apply the X-ray magnetic circular dichroism (XMCD) technique to probe the spin magnetic moment and the orbital magnetic moment anisotropy within the spin reorientation transition (SRT) range in the system Au/Co-Staircase/Au(788). The influence of increasing Co film thickness on SRT, from easy out-of-plane magnetization axis to in-plane magnetization was investigated by means of the magneto-optical Kerr effect (MOKE). The preparation and surface quality of the Co films were characterized using low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Analysis of XMCD measurements as a function of the film thickness for Au/Co-staircase/Au(788) reveals the anisotropic orbital magnetic moment during the SRT regime (8–12 ML range) indicating a decreasing influence of MCA with the increased thickness and nearly isotropic orbital magnetic moment above 12 ML, with a small MCA influence.

Abstract: The magnetization in a uniaxial superparamagnetic particle is modelled by spin-phonon relaxation of a giant spin. A multi-level formalism is used to simulate Mssbauer superparamagnetic relaxation spectra of spatially uniformly oriented particles. A longitudinal (parallel to anisotropy direction) external magnetic field $$\vec B$$ is admitted. Powder spectra spectra ( $$\vec B$$ =0) with log-normal volume size distribution are simulated and compared with experimental spectra. Spectra with longitudinal and transversal field are simulated in the slow and fast relaxation limit.

The Cu–S alloy is of great scientific importance due to its wide range of technological applications, including Cu–S antifluorite crystals exhibiting topological states. To gain insights into the sulfur–copper interaction, a simplified model of sulfur adsorption in copper is commonly used, particularly in surface reconstructions like the (7×7)R19.1°phase. However, determining the optimal structural model for this type of reconstruction has been a persistent challenge. Among the various models proposed to explain the reconstruction, Foss and Prince models have gained greater acceptance. In our comprehensive study, we employed a comparative approach utilizing angle-resolved photoemission spectroscopy, scanning tunneling microscopy, and density functional theory calculations. Our objective was to investigate the band structure and local density of states of this reconstruction resulting from sulfur segregation on the Cu(111) surface, with the aim of assessing the compatibility of the experimental results with the two leading models. Remarkably, our analysis unveiled intriguing localization effects within the bulk resonances and distinctive surface bands originating from the copper–sulfur cluster present in both models. Through careful examination of electronic dispersion and the local density of states, we successfully distinguished between the models and determined which one better aligned with our experimental data.

Tuning the charge carrier mobility in carbon nanotubes is a key issue for applications in novel electronic or spintronic devices. This property is directly related to the electronic density of states, which is usually modified by introduction of defects or doping with metallic atoms. Both methods can induce strong localization of electronic states, disturbing the overall nanotube conductivity and enhancing electron and spin scattering. Wrapping with organometallic nanofoils is an alternative method which preserves its charge carrier density. In this work, we have prepared single-walled carbon nanotubes (SWCNTs) wrapped with nanofoils of a cobalt-coordinated polymer (NCoDPS). Transmission electron microscopy and Raman scattering reveal that the nanotubes remain intact and are homogeneously covered by the polymer. The electronic structure of SWCNT-NCoDPS was investigated by scanning tunneling spectroscopy. This technique shows that the electronic density of states of these wrapped nanotubes increases, as compared with uncapped reference samples. We also show that the wrapping process is reversible once the carbon nanotubes are swept by the scanning tunneling microscope applying an electric potential exceeding 0.5 V.

In this work we depict schematically the use of resonant (anomalous) X-ray diffraction as a tool to directly probe strain and composition of self-assembled semiconductor islands. By employing a direct analysis at the Eu L3edge its composition gradient is quantified for EuTe:SnTe capped islands. Projection maps are proposed to visualize the results, providing an alternative capability to infer quantum dot properties. A more complex methodology is applied to the study of InP:GaAs islands, in which complementary anomalous measurements are performed. For this system the number of samples analyzed allows us to extract the activation energy for Ga adatoms diffusion from the substrate to the islands.

Abstract: In this work we depict schematically the use of resonant (anomalous) X-ray diffraction as a tool to directly probe strain and composition of self-assembled semiconductor islands. By employing a direct analysis at the Eu L3 edge its composition gradient is quantified for EuTe:SnTe capped islands. Projection maps are proposed to visualize the results, providing an alternative capability to infer quantum dot properties. A more complex methodology is applied to the study of InP:GaAs islands, in which complementary anomalous measurements are performed. For this system the number of samples analyzed allows us to extract the activation energy for Ga adatoms diffusion from the substrate to the islands.

In standard diffraction experiments, ensembles of objects are characterized yielding averaged, statistical properties (meaningful only if the ensemble is monodisperse). Focused x-ray beams are used here to localize single nanostructures, identifying and probing individual objects one by one. In a scanning mode, a 2-dimensional image of the sample is recorded, which allows the reproducible alignment of a specific nanostructure for analysis. The x-ray scattered signal is analyzed and modelled, to give access to the shape, strain and composition inside the single object with sub-micron resolution. Combination of x-ray microdiffraction technique with other micro-probe experiments on the very same individual object (simultaneous coupling of x-ray diffraction measurements with atomic force microscopy (AFM)) is also shown; we prove the possibility to interact with the objects and to address elastic properties for individual nano-structures out of an ensemble.

In this work, different multilayer conformations of a linear amphiphilic molecule, octadecylphosphonic acid (OPA), were investigated by atomic force microscopy (AFM), X-ray reflectivity, and X-ray diffraction. It was found that these molecules spontaneously pack into well-organized self-assembled bilayers (SABs) when the structures are formed inside concentrated solutions and/or after slow solvent evaporation. The molecular structure of an OPA SAB was observed to be dependent on its position along a stack of bilayers:  when the SAB is at, or close to, the stack surface, OPA molecules are vertically aligned and form 5 nm thick bilayers; when it is in the middle of a stack of hundreds, or thousands, of bilayers, OPA molecules are tilted and form 3.4 nm thick bilayers. The van der Waals interactions among the long OPA alkyl chains were used to explain and also predict some features of the molecular arrangement inside both bilayer types. Using the AFM technique, which also enabled the application of pressure onto a bilayer surface, oblique and hexagonal molecular packings were observed, probably corresponding to both 5 and 3.4 nm thick bilayers, respectively.

We present results obtained by different analysis methods as scanning tunneling microscopy (STM), atomic force microscopy (AFM), grazing incidence small angle X-ray scattering (GISAXS), and elastic recoil detection (ERD) on two similar semiconductor structures grown by molecular beam epitaxy (1) Si(111) substrate/Si buffer layer/B layer with σB=(2.6±δ)×1014cm−2/Ge cap layer and (2) Si(111) substrate/Si buffer layer/B layer with σB=(2.6±δ)×1014cm−2/Si cap layer. It will be shown that the deposition of B with concentrations up to 2.6×1014cm−2leads to a breakdown of the 7×7 reconstructed Si surface of the buffer layer and the formation of a Si(111)-√3×√3-R30°B surface phase (BSP) located on T4-sites. Furthermore it is shown that this BSP acts as a ‘lubricant’ for additional deposited adatoms (Si and Ge) at deposition temperatures <800°C due to the saturation of all Si dangling bonds. This leads to the formation of triangular, nearly relaxed, and well ordered Ge dots in the special case of Ge deposited at 400°C onto a BSP. For higher deposition temperatures it is shown that this ‘lubricant effect’ vanishes due to the B migration from the T4-site via S5into the substrate.

Abstract: Single crystal LiNbO3:57Fe(III) Mssbauer absorption spectra at 3 Tesla and 120...300K can be fitted using a dynamical spin Hamiltonian according to spin-lattice relaxation. At high fields (0.9...7 Tesla) and 4.2K the spectra can be fitted using an electronuclear spin Hamiltonian. The area of the subspectra due to each electronic state is not in accordance with a Boltzmann distribution at the bath temperature. From the population we calculate spin temperatures which depend linearly on the external magnetic field.

Abstract: From Mssbauer spectra of57Fe with elliptically polarized radiation we fit the coefficients of the spin (or electric field gradient) texture function expanded in real spherical harmonics up to 1=2. We determine, and show in perspective graphs, the spin texture of the surface of a transformer metal sheet (Fe−Si), of magnetic videotapes (demagnetized and magnetized) and the electric field gradient texture of a powder of an organometallic compound. We calculate some averages that have an important physical significance.

The stochastic and ab initio (resolvent) methods for the calculation of Mössbauer relaxation spectra are shortly reviewed. The relaxation matrix based on a first order dynamical Hamiltonian is calculated and corresponding simulations are presented. The spin-phonon interaction spectral bath densities are calculated in the Debye approximation for the direct one and two phonon processes. Some least squares fits are presented.

Mössbauer spectra of polycrystalline samples of Fe(Ox)3, Fe(BPHA)3 and K3[Fe(malonate)3] · 3H2O exhibit fast relaxation patterns in the temperature range 4.2–300 K. The magnetic hyperfine splitting has nearly completely collapsed due to rapid electronic spin-spin relaxation of the Fe ions. We use a static Hamiltonian and describe the spin-spin interaction by an effective field Hamiltonian . From this the relaxation supermatrix and the Mössbauer spectra are calculated. The random texture of the samples is taken into account by averaging the radiation dipole operators over the whole sphere. Least-squares fits of the spectra for longitudinal, isotropic and transverse spin relaxation are presented. From the fits the temperature dependence of the relaxation is obtained. We conclude that in these materials the iron is present as high-spin Fe(III) and that the crystal field splitting constantD is greater than zero. The sign ofVzz is found to be positive.

From Mössbauer spectra of LiNbO3∶57Fe(III) single crystals under external fields of 4.92 and 6.2 T, the crystal field and hyperfine parameters are determined. Transmission integral fits indicate a Boltzmann population of the Fe(III) electronic levels with a spin temperature equal to the sample temperature. Spectra at external fields of 0 T and 19 mT can be satisfactorily simulated using an effective spin 1/2,g-factors calculated from spin-expectation values and an internal averaged dipole field of 5.5 mT inclined 20‡ to thec-axis. The simulations indicate cross-relaxation between Nb and Li nuclear spins and the Fe(III) electronic spin.

The theory of calculating Mössbauer spectra by anab initiomethod is shortly reviewed. The relaxation supermatrix is calculated in an electronic basis and its dimension is reduced. Spectra are fitted using a dynamical spin-Hamiltonian. A procedure for fitting the spectra in the whole temperature range is suggested.

The expressions for line intensities in spectra recorded with polarized γ-rays are reviewed. A density matrix formalism is used. The texture function is expanded in sphericals harmonics and the intensities are calculated for a rotated thin absorber and polarized source. A corresponding expeimental setup was developed. From measurements with videotapes the texture function was determined for demagnetized and magnetized tapes.

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