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 $S=1/2$ 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

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