107 research outputs found
Prediction of the bias voltage dependent magnetic contrast in spin-polarized scanning tunneling microscopy
This work is concerned with the theoretical description of the contrast,
i.e., the apparent height difference between two lateral surface positions on
constant current spin-polarized scanning tunneling microscopy (SP-STM) images.
We propose a method to predict the bias voltage dependent magnetic contrast
from single point tunneling current or differential conductance measurements,
without the need of scanning large areas of the surface. Depending on the
number of single point measurements, the bias positions of magnetic contrast
reversals and of the maximally achievable magnetic contrast can be determined.
We validate this proposal by simulating SP-STM images on a complex magnetic
surface employing a recently developed approach based on atomic superposition.
Furthermore, we show evidence that the tip electronic structure and magnetic
orientation have a major effect on the magnetic contrast. Our theoretical
prediction is expected to inspire experimentalists to considerably reduce
measurement efforts for determining the bias dependent magnetic contrast on
magnetic surfaces.Comment: 28 pages manuscript, 1 table, 6 figure
Effect of Pt impurities on the magnetocrystalline anisotropy of hcp Co: a first-principles study
In terms of the fully relativistic screened Korringa-Kohn-Rostoker method we
investigate the variation in the magnetocrystalline anisotropy energy (MAE) of
hexagonal close-packed cobalt with the addition of platinum impurities. In
particular, we perform calculations on a bulk cobalt system in which one of the
atomic layers contains a fractional, substitutional platinum impurity. Our
calculations show that at small concentrations of platinum the MAE is reduced,
while at larger concentrations the MAE is enhanced. This change of the MAE can
be attributed to an interplay between on-site Pt MAE contributions and induced
MAE contributions on the Co sites. The latter ones are subject to pronounced,
long-ranged Friedel-oscillations that can lead to significant size effects in
the experimental determination of the MAE of nano-sized samples.Comment: 16 page
Spin-correlations and magnetic structure in an Fe monolayer on 5d transition metal surfaces
We present a detailed first principles study on the magnetic structure of an
Fe monolayer on different surfaces of 5d transition metals. We use the
spin-cluster expansion technique to obtain parameters of a spin model, and
predict the possible magnetic ground state of the studied systems by employing
the mean field approach and in certain cases by spin dynamics calculations. We
point out that the number of shells considered for the isotropic exchange
interactions plays a crucial role in the determination of the magnetic ground
state. In the case of Ta substrate we demonstrate that the out-of-plane
relaxation of the Fe monolayer causes a transition from ferromagnetic to
antiferromagnetic ground state. We examine the relative magnitude of nearest
neighbour Dzyaloshinskii-Moriya (D) and isotropic (J) exchange interactions in
order to get insight into the nature of magnetic pattern formations. For the
Fe/Os(0001) system we calculate a very large D/J ratio, correspondingly, a spin
spiral ground state. We find that, mainly through the leading isotropic
exchange and Dzyaloshinskii-Moriya interactions, the inward layer relaxation
substantially influences the magnetic ordering of the Fe monolayer. For the
Fe/Re(0001) system characterized by large antiferromagnetic interactions we
also determine the chirality of the N\'eel-type ground state.Comment: 15 pages, 8 figures, 2 table
Considerations and strategies in L2 vocabulary acquisition among Japanese 1st year university students.
This article proposes a framework of strategies1) for L2 vocabulary acquisition among low-to-mid level L2 learners in their first year at Kansai University. The framework relies upon considerations posited by Kudo (1999), as well as, Hunt and Beglar’s (2005) model for developing EFL reading vocabulary, although the objective for our target learners is tofacilitate vocabulary acquisition in a learner-centered communicative context, where possible. This paper firstly underlines the critical role of vocabulary in second language acquisition, while raising awareness of the surrounding pedagogic climate in Japanese secondary education.ç ”ç©¶ãƒŽãƒ¼
Formation and destabilization of Ga interstitials in GaAsN: Experiment and theory
Using first-principles total energy calculations we have found complex defects induced by N incorporation in GaAsN. The formation energy of the Ga interstitial atom is very significantly decreased due to local effects within the defect complex. The stability of the Ga interstitials is further increased at surfaces. The present results suggest that the energetically favorable Ga interstitial atoms are much more abundant in GaAsN than the previously considered N defects, which have relatively large formation energies. Our synchrotron radiation core-level photoemission measurements support the computational results. The formation of harmful Ga interstitials should be reduced by incorporating large group IV B atoms in GaAsN
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