Search results for "Magnetic circular dichroism"
showing 10 items of 86 documents
Element-Selective Magnetic Imaging in Exchange-Coupled Systems by Magnetic Photoemission Microscopy
1998
We have used a photoemission microscope to obtain element-resolved magnetic contrast in stacked magnetic thin film systems. Magnetic information is thereby provided by X-ray magnetic circular dichroism. Elemental sensitivity, which is crucial for studying magnetic coupling phenomena in systems with several different layers, is achieved by tuning the energy of the illuminating photons to atomic absorption edges. We present measurements of a Ni-coated Co micropattern on Cu(001), and a wedged Co/Cr/Fe(001) sample. In the former sample the Ni magnetization is seen to follow the magnetization of the Co pattern, thereby changing from an out-of-plane easy axis in areas without underlying Co to in…
Giant magnetic anisotropy energy and coercivity in Fe island and atomic wire on W(110)
2012
We have directly investigated the giant magnetic anisotropy energy and coercivity of monolayer (ML) Fe islands and stripes on flat and stepped W(110) surfaces using x-ray magnetic circular dichroism. Both for islands and stripes, the magnetic anisotropy energy is $\ensuremath{\sim}$1.0 meV/atom, independent of the coverage below 0.5 ML. On the contrary, the coercive field of the islands rapidly drops from 4.3 T at 0.25 ML to 1.9 T at 0.50 ML, while that of the stripes moderately degrades from 3.5 T at 0.15 ML ($\ensuremath{\sim}$3 atom rows) to 3.0 T at 0.50 ML. We explain the contrastive behavior for the islands and stripes by different nucleation and remagnetization processes. Considering…
Half-metallic ferromagnetism with high magnetic moment and high Curie temperature in Co$_2$FeSi
2006
Co$_2$FeSi crystallizes in the ordered L2$_1$ structure as proved by X-ray diffraction and M\"o\ss bauer spectroscopy. The magnetic moment of Co$_2$FeSi was measured to be about $6\mu_B$ at 5K. Magnetic circular dichroism spectra excited by soft X-rays (XMCD) were taken to determine the element specific magnetic moments of Co and Fe. The Curie temperature was measured with different methods to be ($1100\pm20$)K. Co$_2$FeSi was found to be the Heusler compound as well as the half-metallic ferromagnet with the highest magnetic moment and Curie temperature.
RbBr and CsBr doped with Eu2+ as new competitive X-ray storage phosphors
2001
Abstract After X-irradiation of the alkali halides RbBr and CsBr doped with divalent Eu a significant photostimulated luminescence (PSL) effect was found. In both systems the electron trap centre is an F centre, the hole trap centre is still unknown. The Eu 2+ aggregation with cation vacancies plays an important role. Although all of the different Eu 2+ aggregates seem to show PSL effects, they have different PSL efficiencies, decay times and spectral characteristics. In the case of RbBr:Eu 2+ it was possible to investigate the different Eu 2+ -cation vacancy aggregate states by magnetic circular dichroism of the optical absorption (MCDA) and MCDA-detected electron paramagnetic resonance. I…
Magnetization dynamics in microscopic spin-valve elements: Shortcomings of the macrospin picture
2007
We have studied ultrafast magnetodynamics in micropatterned spin-valve structures using time-resolved x-ray photoemission electron microscopy combined with x-ray magnetic circular dichroism. Exciting the system with ultrafast field pulses of $250\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ width, we find the dynamic response of the free layer to fall into two distinctly different contributions. On the one hand, it exhibits localized spin wave modes that strongly depend on the shape of the micropattern. A field pulse applied perpendicular to the exchange bias field along the diagonal of a square pattern leads to the excitation of a standing spin wave mode with two nodes along the field direction.…
Compositional dependence of element-specific magnetic moments in Ni2MnGa films
2009
Element-specific magnetic moments were investigated for epitaxial Ni2Mn1+xGa1−x and (Ni2MnGa)1−x(Co2FeSi)x Heusler films using x-ray absorption spectroscopy and x-ray circular magnetic dichroism in transmission. The epitaxial films of the Ni2MnGa-derived compositions were prepared by dc-sputtering on Al2O3 substrates at 773 K. X-ray diffraction confirms a (1 1 0) oriented growth. An increase in the Mn concentration reduces the magnetic spin moment of both Mn and Ni. An increase in the content of Co2FeSi in the Ni2MnGa compound leads to an increase in the Mn and Ni spin moments and to a decrease in Tm for 5% Co2FeSi and finally to a suppression of the phase transition for 20% Co2FeSi. The or…
Direct observation of temperature dependent magnetic domain structure of the multiferroic La0.66Sr0.34MnO3/BiFeO3 bilayer system by x-ray linear dich…
2014
Low-thickness La0.66Sr0.34MnO3 (LSMO)/BiFeO3 (BFO) thin film samples deposited on SrTiO3 were imaged by high resolution x-ray microscopy at different temperatures. The ultra-thin thickness of the top layer allows to image both the ferromagnetic domain structure of LSMO and the multiferroic domain structure of the buried BFO layer, opening a path to a direct observation of coupling at the interface on a microscopic level. By comparing the domain size and structure of the BFO and LSMO, we observed that, in contrast to LSMO single layers, LSMO/BFO multilayers show a strong temperature dependence of the ferromagnetic domain structure of the LSMO. Particularly, at 40 K, a similar domain size for…
ODMR of cd impurity centers in gg irradiated BaF2crystals
1995
Abstract The magnetic circular dichroism of the optical absorption (MCD), optically detected magnetic resonance (ODMR) as well as ESR and luminescence in Cd- doped BaF2 crystals γ-irradiated at RT were investigated. MCD signals centered at 295 nm, 290 nm and 365 nm are observed, together with corresponding radiation induced optical absorption bands in the same wavelength regions. The ODMR detected in all these bands is caused by hyperfine (hf) interaction of unpaired spin with Cd− nucleus. Three types of different Cd− related defects have been separated: 1) Cd+ c, represented by the MCD of derivative type centered at 295 nm and hf constant ACd = 480 mT, 2) Cd++c -center having lowered symme…
Quantitative measurements of magnetic stray field dynamics of Permalloy particles in a photoemission electron microscopy
2010
By example of a Permalloy particle (40 × 40 μm(2) size, 30 nm thickness) we demonstrate a procedure to quantitatively investigate the dynamics of magnetic stray fields during ultrafast magnetization reversal. The measurements have been performed in a time-resolving photoemission electron microscope using the X-ray magnetic circular dichroism. In the particle under investigation, we have observed a flux-closure-dominated magnetic ground structure, minimizing the magnetic stray field outside the sample. A fast magnetic field pulse introduced changes in the micromagnetic structure accompanied with an incomplete flux closure. As a result, stray fields arise along the edges of domains, which cau…
Recent progress in photoemission microscopy with emphasis on chemical and magnetic sensitivity
1997
Abstract With the improved access to synchrotron radiation sources photoemission electron microscopy is developing into a versatile analytical tool in surface and materials science. The broad spectral range and the well-defined polarization characteristics of synchrotron light permit a unique combination of topographic, chemical, and even magnetic investigations down to a mesoscopic scale. The potentiality of photoemission electron microscopy is demonstrated by several experiments on surfaces and microstructured thin film systems, which have been carried out with a newly designed instrument. We discuss its different modes of operation with respect to both microscopy and spectroscopy. A comb…