674 research outputs found
Co atoms on BiSe revealing a coverage dependent spin reorientation transition
We investigate Co nanostructures on BiSe by means of scanning
tunneling microscopy and spectroscopy [STM/STS], X-ray absorption spectroscopy
[XAS], X-ray magnetic dichroism [XMCD] and calculations using the density
functional theory [DFT]. In the single adatom regime we find two different
adsorption sites by STM. Our calculations reveal these to be the fcc and hcp
hollow sites of the substrate. STS shows a pronounced peak for only one species
of the Co adatoms indicating different electronic properties of both types.
These are explained on the basis of our DFT calculations by different
hybridizations with the substrate. Using XMCD we find a coverage dependent spin
reorientation transition from easy-plane toward out-of-plane. We suggest
clustering to be the predominant cause for this observation.Comment: 10 pages, 4 figure
Magnetic properties of substitutional Mn in (110) GaAs surface and subsurface layers
Motivated by recent STM experiments, we present a theoretical study of the
electronic and magnetic properties of the Mn-induced acceptor level obtained by
substituting a single Ga atom in the (110) surface layer of GaAs or in one of
the atoms layers below the surface. We employ a kinetic-exchange tight-binding
model in which the relaxation of the (110) surface is taken into account. The
acceptor wave function is strongly anisotropic in space and its detailed
features depend on the depth of the sublayer in which the Mn atom is located.
The local-density-of-states (LDOS) on the (110) surface associated with the
acceptor level is more sensitive to the direction of the Mn magnetic moment
when the Mn atom is located further below the surface. We show that the total
magnetic anisotropy energy of the system is due almost entirely to the
dependence of the acceptor level energy on Mn spin orientation, and that this
quantity is strongly dependent on the depth of the Mn atom.Comment: 14 pages, 13 figure
Magnetic Scanning Tunneling Microscopy with a Two-Terminal Non-Magnetic Tip: Quantitative Results
We report numerical simulation result of a recently proposed \{P. Bruno,
Phys. Rev. Lett {\bf 79}, 4593, (1997)\} approach to perform magnetic scanning
tunneling microscopy with a two terminal non-magnetic tip. It is based upon the
spin asymmetry effect of the tunneling current between a ferromagnetic surface
and a two-terminal non-magnetic tip. The spin asymmetry effect is due to the
spin-orbit scattering in the tip. The effect can be viewed as a Mott scattering
of tunneling electrons within the tip. To obtain quantitative results we
perform numerical simulation within the single band tight binding model, using
recursive Green function method and Landauer-B\"uttiker formula for
conductance. A new model has been developed to take into account the spin-orbit
scattering off the impurities within the single-band tight-binding model. We
show that the spin-asymmetry effect is most prominent when the device is in
quasi-ballistic regime and the typical value of spin asymmetry is about 5%.Comment: 5 pages, Late
Strong out-of-plane magnetic anisotropy of Fe adatoms on BiTe
The electronic and magnetic properties of individual Fe atoms adsorbed on the
surface of the topological insulator BiTe(111) are investigated.
Scanning tunneling microscopy and spectroscopy prove the existence of two
distinct types of Fe species, while our first-principles calculations assign
them to Fe adatoms in the hcp and fcc hollow sites. The combination of x-ray
magnetic circular dichroism measurements and angular dependent magnetization
curves reveals out-of-plane anisotropies for both species with anisotropy
constants of meV/atom and meV/atom. These values are well in line with the results of
calculations.Comment: 6 pages, 3 figure
Direct comparison between potential landscape and local density of states in a disordered two-dimensional electron system
The local density of states (LDOS) of the adsorbate induced two-dimensional
electron system (2DES) on n-InAs(110) is studied by low-temperature scanning
tunneling spectroscopy. The LDOS exhibits irregular structures with fluctuation
lengths decreasing with increasing energy. Fourier transformation reveals that
the k-values of the unperturbed 2DES dominate the LDOS, but additional lower
k-values contribute significantly. To clarify the origin of the additional
k-space intensity, we measure the potential landscape of the same 2DES area
with the help of the tip induced quantum dot. This allows to calculate the
expected LDOS from the single particle Schroedinger equation and to directly
compare it with the measured one. Reasonable correspondance between calculated
and measured LDOS is found.Comment: 7 pages, 4 figures, submitted to PR
Correction of systematic errors in scanning tunnelling spectra on semiconductor surfaces: the energy gap of Si(111)-7x7 at 0.3 K
The investigation of the electronic properties of semiconductor surfaces
using scanning tunnelling spectroscopy (STS) is often hindered by
non-equilibrium transport of the injected charge carriers. We propose a
correction method for the resulting systematic errors in STS data, which is
demonstrated for the well known Si(111)-(7x7) surface. The surface has an odd
number of electrons per surface unit cell and is metallic above 20 K. We
observe an energy gap in the ground state of this surface by STS at 0.3 K.
After correction, the measured width of the gap is (70 +- 15) meV which is
compatible with previous less precise estimates. No sharp peak of the density
of states at the Fermi level is observed, in contrast to proposed models for
the Si(111)-(7x7) surface.Comment: 10 pages, 4 figure
Spin-sensitive shape asymmetry of adatoms on noncollinear magnetic substrates
The spin-resolved density of states of Co atoms on a noncollinear magnetic support displays a distinct shape contrast, which is superimposed on the regular height contrast in spin-polarized scanning tunneling microscopy. The apparent atom height follows the well-known cosine dependence on the angle formed by the tip and adatom local magnetization directions, whereas the shape contrast exhibits a sine dependence. We explain this effect in terms of a noncollinear spin density induced by the substrate, which in our case is the spin spiral of the Mn monolayer on W(110). The two independent contrast channels, apparent height and shape, are identified with the Co magnetization projections onto two orthogonal axes. As a result, all components of the overall atom magnetic moment vector can be determined with a single spin-sensitive tip in the absence of an external magnetic field. This result should be general for any atom deposited on noncollinear magnetic layers
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