| 1. |
- Brondin, Carlo Alberto, et al.
(författare)
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Tailoring Magnetic Anisotropy in Ultrathin Cobalt by Surface Carbon Chemistry
- 2024
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Ingår i: Advanced Electronic Materials. - 2199-160X. ; 10:4
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Tidskriftsartikel (refereegranskat)abstract
- The ability to manipulate magnetic anisotropy is essential for magnetic sensing and storage tools. Surface carbon species offer cost-effective alternatives to metal-oxide and noble metal capping layers, inducing perpendicular magnetic anisotropy in ultrathin ferromagnetic films. Here, the different mechanisms by which the magnetism in a few-layer-thick Co thin film is modified upon adsorption of carbon monoxide (CO), dispersed carbon, and graphene are elucidated. Using X-ray microscopy with chemical and magnetic sensitivity, the in-plane to out-of-plane spin reorientation transition in cobalt is monitored during the accumulation of surface carbon up to the formation of graphene. Complementary magneto-optical measurements show weak perpendicular magnetic anisotropy (PMA) at room temperature for dispersed carbon on Co, while graphene-covered cobalt exhibits a significant out-of-plane coercive field. Density-functional theory (DFT) calculations show that going from CO/Co to C/Co and to graphene/Co, the magnetocrystalline and magnetostatic anisotropies combined promote out-of-plane magnetization. Anisotropy energies weakly depend on carbidic species coverage. Instead, the evolution of the carbon chemical state from carbidic to graphitic is accompanied by an exponential increase in the characteristic domain size, controlled by the magnetic anisotropy energy. Beyond providing a basic understanding of the carbon-ferromagnet interfaces, this study presents a sustainable approach to tailor magnetic anisotropy in ultrathin ferromagnetic films. Magnetic properties of Co ultrathin films are shown to undergo dramatic changes upon surface carbon accumulation. Chemical transformation from molecular carbon monoxide to surface carbide and to a graphene layer progressively enhances the perpendicular magnetic anisotropy of Co. Calculations reveal that magnetocrystalline and magnetostatic contributions play distinctly different roles for the different carbon species.image
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| 2. |
- Hazarika, Abhijit, et al.
(författare)
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Ultranarrow and Widely Tunable Mn2+-Induced Photoluminescence from Single Mn-Doped Nanocrystals of ZnS-CdS Alloys
- 2013
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 110:26, s. 267401-
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Tidskriftsartikel (refereegranskat)abstract
- Extensively studied Mn-doped semiconductor nanocrystals have invariably exhibited photoluminescence over a narrow energy window of width <= 150 meV in the orange-red region and a surprisingly large spectral width (>= 180 meV), contrary to its presumed atomic-like origin. Carrying out emission measurements on individual single nanocrystals and supported by ab initio calculations, we show that Mn PL emission, in fact, can (i) vary over a much wider range (similar to 370 meV) covering the deep green-deep red region and (ii) exhibit widths substantially lower (similar to 60-75 meV) than reported so far, opening newer application possibilities and requiring a fundamental shift in our perception of the emission from Mn-doped semiconductor nanocrystals.
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