Perpendicular spin orientation in ultrasmall Fe islands on W(110)

Nuclear resonant scattering from 193Ir as a probe of the electronic and magnetic properties of iridates

The high brilliance of modern synchrotron radiation sources facilitates experiments with high-energy x-rays across a range of disciplines, including the study of the electronic and magnetic correlations using elastic and inelastic scattering techniques. Here we report on Nuclear Resonance Scattering at the 73 keV nuclear level in ¹⁹³Ir. The transitions between the hyperfine split levels show an untypically high E2/M1 multi-polarity mixing ratio combined with an increased sensitivity to certain changes in the hyperfine field direction compared to non-mixing transitions. The method opens a new way for probing local magnetic and electronic properties of correlated materials containing iridium and provides novel insights into anisotropic magnetism in iridates. In particular, unexpected out-of-plane components of magnetic hyperfine fields and non-zero electric field gradients in Sr₂IrO₄ have been detected and attributed to the strong spin-orbit interaction in this iridate. Due to the high, 62% natural abundance of the ¹⁹³Ir isotope, no isotopic enrichment of the samples is required, qualifying the method for a broad range of applications.

⁵⁷Fe polarization-dependent synchrotron Mössbauer spectroscopy using a diamond phase plate and an iron borate nuclear Bragg monochromator

Energy-domain (57)Fe polarization-dependent synchrotron radiation Mössbauer spectroscopy was developed by using a diamond X-ray phase plate and an iron borate nuclear Bragg monochromator. The former controls the polarization of the incident synchrotron radiation X-rays and the latter filters the (57)Fe-Mössbauer radiation with a narrow bandwidth of ∼3.4 Γ0 (Γ0 ≃ 4.7 neV: natural linewidth of the (57)Fe nucleus) from the broadband synchrotron radiation. The developed nuclear diffraction optics allowed (57)Fe-Mössbauer studies to be performed with various polarization states, i.e. linear polarization, circular polarization and non-polarization. In this paper, the spectrometer system, beam characterization, performance-test experiments and a grazing-incidence Mössbauer measurement of an isotope-enriched ((57)Fe: 95%) iron thin film are described.

Artificial neural networks applied to the analysis of synchrotron nuclear resonant scattering data

The capabilities of artificial neural networks (ANNs) have been investigated for the analysis of nuclear resonant scattering (NRS) data obtained at a synchrotron source. The major advantage of ANNs over conventional analysis methods is that, after an initial training phase, the analysis is fully automatic and practically instantaneous, which allows for a direct intervention of the experimentalist on-site. This is particularly interesting for NRS experiments, where large amounts of data are obtained in very short time intervals and where the conventional analysis method may become quite time-consuming and complicated. To test the capability of ANNs for the automation of the NRS data analysis, a neural network was trained and applied to the specific case of an Fe/Cr multilayer. It was shown how the hyperfine field parameters of the system could be extracted from the experimental NRS spectra. The reliability and accuracy of the ANN was verified by comparing the output of the network with the results obtained by conventional data analysis.

An ultrahigh vacuum system for in situ studies of thin films and nanostructures by nuclear resonance scattering of synchrotron radiation

A multifunctional ultrahigh vacuum (UHV) system has been set up at the nuclear resonance beamline ID18 of the European Synchrotron Radiation Facility (ESRF). Thin and ultrathin films, nanoislands and -wires, multilayers, and stoichiometric oxides can be prepared by molecular beam epitaxy and characterized by low-energy electron diffraction, Auger electron spectroscopy, and reflection high-energy electron diffraction. Upon characterization the sample is transferred under UHV conditions to the chamber for experiments with the synchrotron beam. Electronic and magnetic properties, vibrational dynamics, and diffusion phenomena can be investigated by several synchrotron radiation based techniques, such as nuclear forward scattering, nuclear inelastic and quasielastic scattering, synchrotron radiation based perturbed angular correlations, and nuclear and electronic reflectivity. In addition, two portable UHV chambers serve to transfer the sample to other beamlines profiting from the available experimental techniques at the ESRF.

MAGNETISM AND LATTICE DYNAMICS OF NANOSCALE STRUCTURES STUDIED BY NUCLEAR RESONANT SCATTERING OF SYNCHROTRON RADIATION

Nuclear resonant scattering of synchrotron radiation is applied to investigate the magnetic structure and the lattice dynamics of nanoscale systems. The outstanding brilliance of modern synchrotron radiation sources allows for sensitivities to smallest amounts of material. Due to the isotopic sensitivity of the scattering process, ultrathin probe layers of Mössbauer isotopes can be used to map out the magnetic and vibrational structure of thin films with sub-nm spatial resolution. Elastic nuclear resonant scattering is applied to determine the magnetic spin structure of an exchange-coupled bilayer system. Inelastic nuclear resonant scattering was used to determine the vibrational density of states in Fe islands on the W(110) surface.

Imaging the magnetic spin structure of exchange-coupled thin films

We have investigated the magnetic spin structure of a soft-magnetic film that is exchange-coupled to a hard-magnetic layer to form an exchange-spring layer system. The depth dependence of the magnetization direction was determined by nuclear resonant scattering of synchrotron radiation from ultrathin 57Fe probe layers. In an external field a magnetic spiral structure forms that can be described within a one-dimensional micromagnetical model. The experimental method allows one to image vertical spin structures in stratified media with unprecedented accuracy.