492 research outputs found
Ferrimagnetic nanostructures for magnetic memory bits
Increasing the magnetic data recording density requires reducing the size of
the individual memory elements of a recording layer as well as employing
magnetic materials with temperature-dependent functionalities. Therefore, it is
predicted that the near future of magnetic data storage technology involves a
combination of energy-assisted recording on nanometer-scale magnetic media. We
present the potential of heat-assisted magnetic recording on a patterned
sample; a ferrimagnetic alloy composed of a rare earth and a transition metal,
DyCo, which is grown on a hexagonal-ordered nanohole array membrane. The
magnetization of the antidot array sample is out-of-plane oriented at room
temperature and rotates towards in-plane upon heating above its
spin-reorientation temperature (T) of ~350 K, just above room temperature.
Upon cooling back to room temperature (below T), we observe a well-defined
and unexpected in-plane magnetic domain configuration modulating with ~45 nm.
We discuss the underlying mechanisms giving rise to this behavior by comparing
the magnetic properties of the patterned sample with the ones of its extended
thin film counterpart. Our results pave the way for novel applications of
ferrimagnetic antidot arrays of superior functionality in magnetic nano-devices
near room temperature.Comment: 19 pages, 4 figure
Sn and Cu in melt inclusions of the Albernoa felsic volcanic centre, Iberian Pyrite Belt, Portugal : seeking for the missing (magmatic) link
About the strength of correlation effects in the electronic structure of iron
The strength of electronic correlation effects in the spin-dependent
electronic structure of ferromagnetic bcc Fe(110) has been investigated by
means of spin and angle-resolved photoemission spectroscopy. The experimental
results are compared to theoretical calculations within the three-body
scattering approximation and within the dynamical mean-field theory, together
with one-step model calculations of the photoemission process. This comparison
indicates that the present state of the art many-body calculations, although
improving the description of correlation effects in Fe, give too small mass
renormalizations and scattering rates thus demanding more refined many-body
theories including non-local fluctuations.Comment: 4 pages, 4 figure
Absence of giant spin splitting in the two-dimensional electron liquid at the surface of SrTiO3 (001)
We reinvestigate the putative giant spin splitting at the surface of SrTiO3 reported by Santander-Syro et al. [Nature Mat. 13, 1085 (2014)]. Our spin- and angle-resolved photoemission experiments on fractured (001) oriented surfaces supporting a two-dimensional electron liquid with high carrier density show no detectable spin polarization in the photocurrent. We demonstrate that this result excludes a giant spin splitting while it is consistent with the unconventional Rashba-like splitting seen in band structure calculations that reproduce the experimentally observed ladder of quantum confined subbands.PostprintPeer reviewe
Quantitative determination of spin-dependent quasiparticle lifetimes and electronic correlations in hcp cobalt
We report on a quantitative investigation of the spin-dependent quasiparticle
lifetimes and electron correlation effects in ferromagnetic hcp Co(0001) by
means of spin and angle-resolved photoemission spectroscopy. The experimental
spectra are compared in detail to state-of-the-art many-body calculations
within the dynamical mean field theory and the three-body scattering
approximation, including a full calculation of the one-step photoemission
process. From this comparison we conclude that although strong local many-body
Coulomb interactions are of major importance for the qualitative description of
correlation effects in Co, more sophisticated many-body calculations are needed
in order to improve the quantitative agreement between theory and experiment,
in particular concerning the linewidths. The quality of the overall agreement
obtained for Co indicates that the effect of non-local correlations becomes
weaker with increasing atomic number
XRD Identification of Ore Minerals during Cruises: Refinement of Extraction Procedure with Sodium Acetate Buffer
The on-board identification of ore minerals during a cruise is often postponed until long after the cruise is over. During the M127 cruise, 21 cores with deep-seafloor sediments were recovered in the Trans-Atlantic Geotraverse (TAG) field along the Mid Atlantic Ridge (MAR). Sediments were analyzed on-board for physicochemical properties such as lightness (L*), pH and Eh. Selected samples were studied for mineral composition by X-ray powder diffraction (XRD). Based on XRD data, sediment samples were separated into high-, low- and non-carbonated. Removal of carbonates is a common technique in mineralogical studies in which HCl is used as the extraction agent. In the present study, sequential extraction was performed with sodium acetate buffer (pH 5.0) to remove carbonates. The ratio between the highest calcite XRD reflection in the original samples (Iorig) vs its XRD-reflection in samples after their treatment with the buffer (Itreat) was used as a quantitative parameter of calcite removal, as well as to identify minor minerals in carbonated samples (when Iorig/Itreat > 24). It was found that the lightness parameter (L*) showed a positive correlation with calcite XRD reflection in selected TAG samples, and this could be applied to the preliminary on-board determination of extraction steps with acetate buffer (pH 5.0) in carbonated sediment samples. The most abundant minerals detected in carbonated samples were quartz and Al- and Fe-rich clays. Other silicates were also detected (e.g., calcic plagioclase, montmorillonite, nontronite). In non-carbonated samples, Fe oxides and hydroxides (goethite and hematite, respectively) were detected. Pyrite was the dominant hydrothermal mineral and Cu sulfides (chalcopyrite, covellite) and hydrothermal Mn oxides (birnessite and todorokite) were mineral phases identified in few samples, whereas paratacamite was detected in the top 20 cm of the core. The present study demonstrates that portable XRD analysis makes it possible to characterize mineralogy at cored sites, in particular in both low- and high-carbonated samples, before the end of most cruises, thus enabling the quick modification of exploration strategies in light of new information as it becomes available in near-real time
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