346 research outputs found
Magnetism of epitaxial Tb films on W(110) studied by spin-polarized low-energy electron microscopy
Thin epitaxial films of Tb metal were grown on a clean W(110) substrate in ultrahigh vacuum and studied in situ by low-energy electron microscopy. Annealed films present magnetic contrast in spin-polarized low-energy electron microscopy. The energy dependence of the electron reflectivity was determined and a maximum value of its spin asymmetry of about 1% was measured. The magnetization direction of the Tb films is in-plane. Upon raising the temperature, no change in the domain distribution is observed, while the asymmetry in the electron reflectivity decreases when approaching the critical temperature, following a power law ∼(1-T/TC)β with a critical exponent β of 0.39.This research was partly supported by Spain under Projects
No.MAT2014-52477-C5-5-P, No.MAT2015-64110-C02-1-P
(MINECO), and No. FIS2008-01431 (MICINN). Experiments
were performed at the National Center for Electron Microscopy,
Lawrence Berkeley National Laboratory, supported
by the Office of Science, Office of Basic Energy Sciences,
Scientific User Facilities Division, of the U.S. Department of
Energy under Contract No. DE-AC02-05CH11231.Peer Reviewe
Stable and Metastable Structures of Cobalt on Cu(001): An ab initio Study
We report results of density-functional theory calculations on the
structural, magnetic, and electronic properties of (1x1)-structures of Co on
Cu(001) for coverages up to two monolayers. In particular we discuss the
tendency towards phase separation in Co islands and the possibility of
segregation of Cu on top of the Co-film. A sandwich structure consisting of a
bilayer Co-film covered by 1ML of Cu is found to be the lowest-energy
configuration. We also discuss a bilayer c(2x2)-alloy which may form due to
kinetic reasons, or be stabilized at strained surface regions. Furthermore, we
study the influence of magnetism on the various structures and, e.g., find that
Co adlayers induce a weak spin-density wave in the copper substrate.Comment: 11 pages including 4 figures. Related publications can be found at
http://www.fhi-berlin.mpg.de/th/paper.htm
Spin reorientation transition of magnetite (001)
We have imaged the rearrangement of the magnetic domains on magnetite (001) when crossing the spin reorientation transition and the Verwey transition with nanometer resolution. By means of spin-polarized low-energy electron microscopy we have monitored the change in the easy axes lowering the temperature through both transitions in remanence. The spin reorientation transition occurs in two steps: initial nucleation and growth of domains with a new surface magnetic orientation is followed by a smooth evolution.We thank Dr. A. T. N'Diaye for his support with the scripts for the color representation of the magnetization. This research was partly supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under Projects No. MAT2011-52477-C5-2-P, No. MAT2012-38045-C04-01, and No. MAT2015-64110-C2-1-P. G.S.P. and R.B. acknowledge funding from the Austrian Science Fund START prize Y 847-N20 and Project No. P24925-N20. Experiments were performed at the Molecular Foundry, Lawrence Berkeley National Laboratory, supported by the Office of Science, Office of Basic Energy Sciences, Scientific User Facilities Division, of the U. S. Department of Energy under Contract No. DE-AC02-05CH11231. L.M.-G. thanks the MINECO for an FPI contract with reference Contract No. BES-2013-063396. R.B. acknowledges a stipend from the TU Wien and Austrian Science Fund doctoral college Solids4Fun (Project No. W1243). A.M. thanks the support of the Spanish Ministry of Education through Project No. PRX14/00307.Peer Reviewe
Phase Diagram of a Spin Ladder with Cyclic Four Spin Exchange
We present the phase diagram of the Heisenberg model on the two leg
ladder with cyclic four spin exchange, determined by a combination of Exact
Diagonalization and Density Matrix Renormalization Group techniques. We find
six different phases and regimes: the rung singlet phase, a ferromagnetic
phase, two symmetry broken phases with staggered dimers and staggered scalar
chiralities, and a gapped region with dominant vector chirality or collinear
spin correlations. We localize the phase transitions and investigate their
nature.Comment: 4 pages, 6 figures, REVTeX 4, published versio
Fluctuating diamagnetism in underdoped high temperature superconductors
The fluctuation induced diamagnetism of underdoped high temperature
superconductors is studied in the framework of the Lawrence-Doniach model. By
taking into account the fluctuations of the phase of the order parameter only,
the latter reduces to a layered XY-model describing a liquid of vortices which
can be either thermally excited or induced by the external magnetic field. The
diamagnetic response is given by a current-current correlation function which
is evaluated using the Coulomb gas analogy. Our results are then applied to
recent measurements of fluctuation diamagnetism in underdoped YBCO. They allow
to understand both the observed anomalous temperature dependence of the
zero-field susceptibility and the two distinct regimes appearing in the
magnetic field dependence of the magnetization.Comment: 12 pages, 4 figures included, accepted for publication in PR
Magnetic Response in a Zigzag Carbon Nanotube
Magnetic response of interacting electrons in a zigzag carbon nanotube
threaded by a magnetic flux is investigated within a Hartree-Fock mean field
approach. Following the description of energy spectra for both non-interacting
and interacting cases we analyze the behavior of persistent current in
individual branches of a nanotube. Our present investigation leads to a
possibility of getting a filling-dependent metal-insulator transition in a
zigzag carbon nanotube.Comment: 9 pages, 14 figure
Low-Energy Universality in Atomic and Nuclear Physics
An effective field theory developed for systems interacting through
short-range interactions can be applied to systems of cold atoms with a large
scattering length and to nucleons at low energies. It is therefore the ideal
tool to analyze the universal properties associated with the Efimov effect in
three- and four-body systems. In this "progress report", we will discuss recent
results obtained within this framework and report on progress regarding the
inclusion of higher order corrections associated with the finite range of the
underlying interaction.Comment: Commissioned article for Few-Body Systems, 47 pp, 16 fig
Origin of the energy bandgap in epitaxial graphene
We studied the effect of quantum confinement on the size of the band gap in
single layer epitaxial graphene. Samples with different graphene terrace sizes
are studied by using low energy electron microscopy (LEEM) and angle-resolved
photoemission spectroscopy (ARPES). The direct correlation between the terrace
size extracted from LEEM and the gap size extracted from ARPES shows that
quantum confinement alone cannot account for the large gap observed in
epitaxial graphene samples
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Effect of dietary vitamin D3 and 25-hydroxyvitamin D3 supplementation on plasma and milk 25-hydroxyvitamin D3 concentration in dairy cows
Milk enriched with vitamin D by supplementing dairy cow diets could provide a valuable dietary source of vitamin D, but information on the feasibility of this approach is limited. In the current study, the effects of supplementing dairy cows with either vitamin D3 or 25(OH) D3 over the transition/early lactation period on plasma and milk vitamin D concentrations were compared. Sixty dairy cows were randomly allocated to one of four dietary treatments from 14 days pre-calving to 56 days post-calving. Treatments were a control diet (Control) for both pre-calving and post-calving periods containing 0.625 mg/day vitamin D3; a pre-calving diet supplemented with 6 mg 25(OH) D3/day, but with a post-calving diet matching that of the control diet (25(OH) D3 pre-calving); the control diet pre-calving but with the post-calving diet supplemented with 2 mg vitamin D3/day (D3max), and the control diet pre-calving but with the post-calving diet supplemented with 1.5 mg 25(OH) D3/day (25(OH) D3 post-calving). No treatment effect on milk yield, composition or 25(OH) D3 concentration was observed. However there was an interaction of treatment and time for plasma 25(OH) D3 concentration; this increased within two weeks of supplementation for the 25(OH) D3 pre-calving treatment (peaking just after calving, 202 ng/ml), whereas that of the 25(OH) D3 post-calving group had a slower response following supplementation, continuing to increase at 56 days. There were correlations between plasma and milk 25(OH) D3 concentrations at days 4 and 14 of lactation, but not at later sampling times. The D3max treatment did not increase 25(OH) D3 concentration in plasma or milk. Overall, results from this study indicate that supplemental 25(OH) D3 is an effective means of enhancing dairy cow plasma 25(OH) D3 concentrations compared with vitamin D3 supplementation, but not necessarily milk concentrations
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