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2006, Journal of Magnetism and Magnetic Materials
This report examines the current status and the future directions of the field of nanomagnetism and assesses the ability of hard X-ray synchrotron facilities to provide new capabilities for making advances in this field. The report first identifies major research challenges that lie ahead in three broadly defined subfields of nanomagnetism: confined systems, clusters and complex oxides. It then examines the relevant experimental capabilities that are currently available at hard X-ray synchrotron light sources, using the Advanced Photon Source (APS) at Argonne as an example. Finally, recommendations are made for future development in X-ray facilities that will enhance the study of nanomagnetism, including new experimental directions, modifications that would enable in situ sample preparation, and measurements at high magnetic fields and/or low temperatures. In particular, in situ sample preparation is of high priority in many experiments, especially those in the area of surface magnetism.
ChemInform, 2006
INDEX tuning the energy of the incident beam near absorption edges (or resonances) of constituent elements, one can study the magnetic contributions of individual components in heterogeneous structures.
Materials Today, 2006
Investigating magnetic properties of matter on the nanoscale is a very active area in modern solid-state physics 1-3 . Exciting phenomena, e.g. interlayer exchange coupling 4 or the giant magnetoresistance effect 5 , occur in low-dimensional systems where characteristic length scales, i.e. magnetic exchange lengths, become relevant. Magnetic exchange lengths can be derived from intrinsic material parameters such as anisotropy (K) and exchange (A) constants, giving values <10 nm for typical magnetic materials, e.g. permalloy (Ni 80 Fe 20 ) or the hard magnetic system 6,7 Nd 2 Fe 14 B. Generally, the energetic ground state of a ferromagnetic system is not a single-domain state, but exhibits a characteristic microscopic magnetic domain structure that reflects the interplay between competing energies, such as anisotropy, exchange, Zeeman, and magnetostatic energies 8 . In order to understand the origin of macroscopic magnetic properties, this microstructure is the target of experimental 9-16 and theoretical studies . Moreover, the corresponding dynamics of the magnetic microstructure on a subnanosecond time scale is an emerging field, both for scientific and applied reasons, and numerous activities are currently being developed. Nanomagnetism is of utmost importance to current technological developments. The dramatic increase in magnetic storage density over the last decade , various applications of miniaturized magnetic sensor devices based on the giant magnetoresistance effect , and the development of spintronics, a new generation of computing technology , require a thorough understanding of magnetism on the nanometer scale. Spintronics considers the spin of an electron as an additional degree of freedom, which can be manipulated to obtain particular functionalities. Recent concepts for spintronic logical elements discuss domain walls , i.e. the intermediate region of spin inhomogeneity between two domains with opposite magnetization directions in nanowired elements. The magnetic nanoscale systems that exhibit the largest activity, both in fundamental and applied research, are multilayers and oxides , nanoparticles , nanostructures , semiconductors , multiferroic heterostructures , and spintronic materials . Several key questions in these systems depend on the dynamics of the magnetization and the associated magnetic microstructure 52-55 : • How does the magnetization reverse, i.e. how does it switch its orientation on a short length and fast time scale?
Magnetochemistry
Nanomagnetism covers a broad range of research in magnetism and magnetic properties of low-dimensional systems, including both experimental methods in sample fabrication and characterization, as well as theoretical modeling and simulations [...]
Science Reviews - from the end of the world
Through representative examples, we illustrate the strategic value of synchrotron X-ray-based techniques for nanomaterial characterization, especially for inhomogeneous nanomaterials. These examples are used to describe opportunities, motivations for new questions and possible reexamination of older topics, not only due to the proven success of the scientific instrumentation, but also because the extraordinary specific advantages offered by the new X-ray micro and nanoprobes techniques.
X-ray Characterization of Nanostructured Energy Materials by Synchrotron Radiation, 2017
Journal of Electron Spectroscopy and Related Phenomena, 2013
This work reports on the measurement of magnetic dichroism in angularresolved photoelectron spectroscopy from in-plane magnetized buried thin films. The high bulk sensitivity of hard X-ray photoelectron spectroscopy (HAXPES) in combination with circularly polarized radiation enables the investigation of the magnetic properties of buried layers. Angular distributions of high kinetic energy (7 to 8 keV) photoelectrons in a range of about 60 • were recorded in parallel to the energy distribution. Depending on purpose, energy and angular resolutions of 150 to 250 meV and 0.17 • to 2 • can be accomplished simultaneously in such experiments. Experiments were performed on exchange-biased magnetic layers covered by thin oxide films. More specifically, the angular distribution of photoelectrons from the ferromagnetic layer Co 2 FeAl layer grown on MnIr exchange-biasing layer was investigated where the magnetic structure is buried beneath a MgO layer. Pronounced magnetic dichroism is found in the Co and Fe 2p states for all angles of emission. A slightly increased magnetic dichroism was observed for normal emission in agreement with theoretical considerations.
Micron, 2006
Full-field soft X-ray microscopy in combination with X-ray magnetic circular dichroism as contrast mechanism is a powerful technique to image with elemental specificity magnetic nanostructures and multilayered thin films at high lateral resolution down to 15 nm by using Fresnel zone plates as X-ray optical elements. Magnetization reversal phenomena on a microscopic level are studied by recording the images in varying external magnetic fields. Local spin dynamics at a time resolution below 100 ps can be addressed by engaging a stroboscopic pump-and-probe scheme taking into account the time pattern of synchrotron storage rings. Characteristic features of magnetic soft X-ray microscopy are reviewed and an outlook into future perspectives with regard to increased lateral and temporal resolution is given.
IEEE Transactions on Magnetics, 2000
Top panel: schematic picture of the magnetic and structural evolution of Fe/MnAs in a thermal cycle. Bottom panel: temperature dependent magnetic signal at the Fe 2p resonance for two thermal cycles with T max = 11.8 ºC (○) and T max = 16.8 ºC (•).T min is -6 ºC.
New Journal of Physics, 2010
The use of synchrotron-based spectroscopy has revolutionized the way we look at matter. X-ray absorption spectroscopy (XAS) using linear and circular polarized light offers a powerful toolbox of element-specific structural, electronic and magnetic probes that is especially well suited for complex materials containing several elements. We use the specific example of Zn 1−x Co x O (Co:ZnO) to demonstrate the usefulness of combining these XAS techniques to unravel its intrinsic properties. We demonstrate that as 2 long as phase separation or excessive defect formation is absent, Co:ZnO is paramagnetic. We can establish quantitative thresholds based on four reliable quality indicators using XAS; samples that show ferromagnet-like behaviour fail to meet these quality indicators, and complementary experimental techniques indeed prove phase separation. Careful analysis of XAS spectra is shown to provide quantitative information on the presence and type of dilute secondary phases in a highly sensitive, non-destructive manner.
Journal of Magnetism and Magnetic Materials, 1999
Current and anticipated future research frontiers in magnetism and magnetic materials are discussed from a perspective of soft X-ray synchrotron utilization. Topics covered include dimensionality (including effects of spatial dimensions and differing time scales), magneto-electronics, structure/property relationships, and exploratory materials, with an emphasis on challenges that limit the understanding and advancement of these areas. Many soft X-ray spectroscopies can be
… status solidi (b), 2010
Mass-filtered Fe, Co and FeCo nanoparticles in the size regime from 7 to 25nm have been deposited under soft-landing conditions onto ferromagnetic films, non-magnetic surfaces as well as embedded into Al matrices. In situ X-ray magnetic circular dichroism (XMCD) measurements reveal a ferromagnetic behaviour of FeCo nanoparticles (size: 10nm) on Si-substrates at room temperature whereas the respective Co nanoparticles are superparamagnetic. Besides measurements on ensembles of nanoparticles, we have also carried out in situ measurements on individual Fe nanoparticles using X-ray photoemission electron microscopy at the Fe L3,2 edges. Fe nanoparticles on Co films show a magnetic contrast depending on the direction of the underlying poly-crystalline Co domains. This technique also allows to record XMCD spectra on individual nanoparticles.
Applied Physics Letters, 2010
Spatially resolved ac susceptibility measurements on epitaxial Fe films are performed as a function of temperature using a conventional soft-x-ray photoelectron emission microscope. A magnetic contrast is observed at sample locations where the magnetic film undergoes a paralferromagnetic phase transition . Due to the wedge structure of the Fe film and the thickness dependence of the Curie temperature the spatial extend of the phase transition region and the correlation length can be estimated.
Physical Review B, 2006
We present a study of the local magnetic properties of iron/iron oxide granular nanostructures by x-ray magnetic circular dichroism ͑XMCD͒. Metallic iron ͑␣-Fe͒ nanoparticles, with average sizes ranging from 5 to 13 nm, are embedded in a nanocrystalline oxide matrix composed of both magnetite ͑Fe 3 O 4 ͒ and maghemite ͑␥-Fe 2 O 3 ͒. These granular samples were synthesized by cold compacting core-shell nanoparticles, in which a 2-3 nm-thick oxide layer surrounds the iron particles, synthesized by inert gas condensation. By exploiting the chemical selectivity and site sensitivity of XMCD, we were able to separate the magnetic contributions of the metallic core and of the two oxide phases present in the matrix and to study their behavior as a function of iron particle size and applied magnetic induction field. We detected the presence of a significant spin canting, predominantly affecting the octahedral sites of Fe in the oxide phase, and studied its dependence on the degree of structural disorder and applied magnetic induction field.
2014
The unique properties of synchrotron radiation, such as broad energy spectrum, variable light polarization, and flexible time struc-ture, have made it an enormously powerful tool in the study of magnetic phenomena and materials. The refinement of experimental techniques has led to many new research opportunities, keeping up with the challenges put up by modern magnetism research. In this contribution, we review some of the recent developments in the application of synchrotron radiation and particularly soft X-rays to current problems in magnetism, and we discuss future perspectives. Index Terms—Antiferromagnetic materials, anisotropy, biomolecules, coplanar transmission lines, electron storage rings, ferrimag-
Semiconductor Science and Technology, 2014
This review aims to introduce the x-ray emission spectroscopy (XES) and resonant inelastic x-ray scattering (RIXS) techniques to the materials scientist working with magnetic semiconductors (e.g. semiconductors doped with 3d transition metals) for applications in the field of spin-electronics. We focus our attention on the hard part of the x-ray spectrum (above 3 keV) in order to demonstrate a powerful element-and orbital-selective characterization tool in the study of bulk electronic structure. XES and RIXS are photon-in/photon-out second order optical processes described by the Kramers-Heisenberg formula. Nowadays, the availability of third generation synchrotron radiation sources permits applying such techniques also to dilute materials, opening the way for a detailed atomic characterization of impurity-driven materials. We present the Kβ XES as a tool to study the occupied valence states (directly, via valence-to-core transitions) and to probe the local spin angular momentum (indirectly, via intra-atomic exchange interaction). The spin sensitivity is employed, in turn, to study the spin-polarised unoccupied states. Finally, the combination of RIXS with magnetic circular dichroism (RIXS-MCD) extends the possibilities of standard magnetic characterization tools.
IEEE Transactions on Magnetics, 2000
The unique properties of synchrotron radiation, such as broad energy spectrum, variable light polarization, and flexible time structure, have made it an enormously powerful tool in the study of magnetic phenomena and materials. The refinement of experimental techniques has led to many new research opportunities, keeping up with the challenges put up by modern magnetism research. In this contribution, we review some of the recent developments in the application of synchrotron radiation and particularly soft X-rays to current problems in magnetism, and we discuss future perspectives.
Journal of Electron Spectroscopy and Related Phenomena, 2012
The Spin-resolved Photoelectron Emission Microscope (SPEEM) is a permanently installed set-up at Helmholtz-Zentrum Berlin (HZB). Due to its specific contrast it is mainly used for magnetic imaging and micro-spectroscopy with quantitative analysis. A crucial point in magnetic imaging is the application of magnetic fields. Many experiments require observation of magnetic responses or the preparation of a certain magnetic state during the measurement. We present a dedicated magnetic sample holder combining magnetic field during imaging with additional temperature control. This set-up enables SPEEM to measure magnetization curves of individual Fe nanocubes (18 nm) 3 in size. If additionally alternating magnetic fields are applied we can image the local magnetic AC susceptibility ( AC ) as a function of temperature. The latter is ideally suited to visualize local variations of the Curie temperature (T C ) in nanoand microstructures.