185 research outputs found
Real-space study of the growth of magnesium on ruthenium
The growth of magnesium on ruthenium has been studied by low-energy electron
microscopy (LEEM) and scanning tunneling microscopy (STM). In LEEM, a
layer-by-layer growth is observed except in the first monolayer, where the
completion of the first layer in inferred by a clear peak in electron
reflectivity. Desorption from the films is readily observable at 400 K.
Real-space STM and low-energy electron diffraction confirm that sub-monolayer
coverage presents a moir\'e pattern with a 1.2 nm periodicity, which evolves
with further Mg deposition by compressing the Mg layer to a 2.2 nm periodicity.
Layer-by-layer growth is followed in LEEM up to 10 ML. On films several ML
thick a substantial density of stacking faults are observed by dark-field
imaging on large terraces of the substrate, while screw dislocations appear in
the stepped areas. The latter are suggested to result from the mismatch in
heights of the Mg and Ru steps. Quantum size effect oscillations in the
reflected LEEM intensity are observed as a function of thickness, indicating an
abrupt Mg/Ru interface.Comment: 21 pages, 10 figure
Micromagnetism in (001) magnetite by spin-polarized low-energy electron microscopy
Spin-polarized low-energy electron microscopy was used to image a magnetite
crystal with (100) surface orientation. Sets of spin-dependent images of
magnetic domain patterns observed in this surface were used to map the
direction of the magnetization vector with high spatial and angular resolution.
We find that domains are magnetized along the surface [110] directions, and
domain wall structures include 90{\deg} and 180{\deg} walls. A type of
unusually curved domain walls are interpreted as N\'eel-capped surface
terminations of 180{\deg} Bloch walls.Comment: 17 pages, 4 figures. Presented at the LEEM-PEEM 8 conferenc
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
Galones de librea con escudos de armas de familias cubanas
The heraldic livery ribbons of Cuban colonial families acquired the category of collectibles in a short amount of time due to their high interest as decorative elements. This combined with certain nostalgia evocative of customs and characters from past times gives a distinctive rank to the sugar aristocracy that led the economic development of Cuba in the 18th and 19th century. The heraldic livery ribbons are also a testimony and a valuable source of information of a period in Cuban history.Los galones de librea heráldicos de familias coloniales cubanas, en poco tiempo adquirieron la categorÃa de objetos coleccionables por su alto interés como elementos decorativos, combinado esto con cierta nostalgia evocadora de costumbres y de personajes de tiempos pasados. Constituyen un rango distintivo de la aristocracia azucarera que lideró el desarrollo económico de Cuba en los siglos XVIII y XIX, son un testimonio y una valiosa fuente de información de una etapa de la historia cubana
Magnetism in nanometer-thick magnetite
The oldest known magnetic material, magnetite, is of current interest for use
in spintronics as a thin film. An open question is how thin can magnetite films
be and still retain the robust ferrimagnetism required for many applications.
We have grown one-nanometer-thick magnetite crystals and characterized them in
situ by electron and photoelectron microscopies including selected-area x-ray
circular dichroism. Well-defined magnetic patterns are observed in individual
nano-crystals up to at least 520 K, establishing the retention of
ferrimagnetism in magnetite two-unit-cells thick.Comment: 5 pages, 4 figure
Imaging Spin Reorientation Transitions in Consecutive Atomic Co layers
By means of spin-polarized low-energy electron microscopy (SPLEEM) we show
that the magnetic easy-axis of one to three atomic-layer thick cobalt films on
ruthenium crystals changes its orientation twice during deposition:
one-monolayer and three-monolayer thick films are magnetized in-plane, while
two-monolayer films are magnetized out-of-plane, with a Curie temperature well
above room temperature. Fully-relativistic calculations based on the Screened
Korringa-Kohn-Rostoker (SKKR) method demonstrate that only for two-monolayer
cobalt films the interplay between strain, surface and interface effects leads
to perpendicular magnetization.Comment: 5 pages, 4 figures. Presented at the 2005 ECOSS conference in Berlin,
and at the 2005 Fall meeting of the MRS. Accepted for publication at Phys.
Rev. Lett., after minor change
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