2,940 research outputs found
Near-field spectroscopy of bimodal size distribution of InAs/AlGaAs quantum dots
We report on high-resolution photoluminescence (PL) spectroscopy of spatial
structure of InAs/AlGaAs quantum dots (QDs) by using a near-field scanning
optical microscope (NSOM). The double-peaked distribution of PL spectra is
clearly observed, which is associated with the bimodal size distribution of
single QDs. In particular, the size difference of single QDs, represented by
the doublet spectral distribution, can be directly observed by the NSOM images
of PL.Comment: 3pages, 3figue
Origin of the increased velocities of domain wall motions in soft magnetic thin-film nanostripes beyond the velocity-breakdown regime
It is known that oscillatory domain-wall (DW) motions in soft magnetic
thin-film nanostripes above the Walker critical field lead to a remarkable
reduction in the average DW velocities. In a much-higher-field region beyond
the velocity-breakdown regime, however, the DW velocities have been found to
increase in response to a further increase of the applied field. We report on
the physical origin and detailed mechanism of this unexpected behavior. We
associate the mechanism with the serial dynamic processes of the nucleation of
vortex-antivortex (V-AV) pairs inside the stripe or at its edges, the
non-linear gyrotropic motions of Vs and AVs, and their annihilation process.
The present results imply that a two-dimensional soliton model is required for
adequate interpretation of DW motions in the linear- and oscillatory-DW-motion
regimes as well as in the beyond-velocity-breakdown regime.Comment: 16 pages, 3 figure
Disorder-free sputtering method on graphene
Deposition of various materials onto graphene without causing any disorder is
highly desirable for graphene applications. Especially, sputtering is a
versatile technique to deposit various metals and insulators for spintronics,
and indium tin oxide to make transparent devices. However, the sputtering
process causes damage to graphene because of high energy sputtered atoms. By
flipping the substrate and using a high Ar pressure, we demonstrate that the
level of damage to graphene can be reduced or eliminated in dc, rf, and
reactive sputtering processes
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Controlling the Magnetic Anisotropy of the van der Waals Ferromagnet Fe3GeTe2 through Hole Doping.
Identifying material parameters affecting properties of ferromagnets is key to optimized materials that are better suited for spintronics. Magnetic anisotropy is of particular importance in van der Waals magnets, since it not only influences magnetic and spin transport properties, but also is essential to stabilizing magnetic order in the two-dimensional limit. Here, we report that hole doping effectively modulates the magnetic anisotropy of a van der Waals ferromagnet and explore the physical origin of this effect. Fe3-xGeTe2 nanoflakes show a significant suppression of the magnetic anisotropy with hole doping. Electronic structure measurements and calculations reveal that the chemical potential shift associated with hole doping is responsible for the reduced magnetic anisotropy by decreasing the energy gain from the spin-orbit induced band splitting. Our findings provide an understanding of the intricate connection between electronic structures and magnetic properties in two-dimensional magnets and propose a method to engineer magnetic properties through doping
Criterion for transformation of transverse domain wall to vortex or antivortex wall in soft magnetic thin-film nanostripes
We report on the criterion for the dynamic transformation of the internal
structure of moving domain walls (DWs) in soft magnetic thin-film nanostripes
above the Walker threshold field, Hw. In order for the process of
transformation from transverse wall (TW) to vortex wall (VW) or antivortex wall
(AVW) occurs, the edge-soliton core of the TW-type DW should grow sufficiently
to the full width at half maximum of the out-of-plane magnetizations of the
core area of the stabilized vortex (or antivortex) by moving inward along the
transverse (width) direction. Upon completion of the nucleation of the vortex
(antivortex) core, the VW (AVW) is stabilized, and then its core accompanies
the gyrotropic motion in a potential well (hill) of a given nanostripe. Field
strengths exceeding the Hw, which is the onset field of DW velocity breakdown,
are not sufficient but necessary conditions for dynamic DW transformation
Fundamental thickness limit of itinerant ferromagnetic SrRuO thin films
We report on a fundamental thickness limit of the itinerant ferromagnetic
oxide SrRuO that might arise from the orbital-selective quantum confinement
effects. Experimentally, SrRuO films remain metallic even for a thickness
of 2 unit cells (uc), but the Curie temperature, T, starts to decrease at 4
uc and becomes zero at 2 uc. Using the Stoner model, we attributed the T
decrease to a decrease in the density of states (N). Namely, in the thin
film geometry, the hybridized Ru-d orbitals are terminated by top and
bottom interfaces, resulting in quantum confinement and reduction of N.Comment: 20 pages, 4 figure
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