By Ne ion sputtering on the single-crystalline MoS2 surface, we demonstrate that the S layers sandwiching Mo in the top layer are sequentially removed by top-down desulfurization, but the intermediate Mo layer is maintained. Selective desulfurization can be used to control the bandgap of MoS2 by switching the polarity from n-type to p-type conductivity and further inducing metallization. Furthermore, the polarity of the MoS2 surface can also be switched by controlling the hydrogen bonding at/around various sulfur vacancy defects. More importantly, we reveal that such desulfurization weakens the hydrogen interaction on the cleaved MoS2 surface by removing the mono-sulfur vacancies (VS). This finding elucidates the important role of the VS defect for high catalytic activity.
The electronic structure, magnetic moments, effective exchange interaction parameter and the magnetic anisotropy energy of [monolayer Co]/Ir(1 1 1) and Co intercalated graphene on Ir(1 1 1) are studied making use of the first-principles density functional theory calculations. A large positive magnetic anisotropy of 1.24 meV/Co is found for [monolayer Co]/Ir(1 1 1), and a high Curie temperature of 1190 K is estimated. These findings show the Co/Ir(1 1 1) system is a promising candidate for perpendicular ultra-high density magnetic recording applications. The magnetic moments, exchange interactions and the magnetic anisotropy are strongly affected by graphene. Reduction of the magnetic anisotropy and the Curie temperature are found for graphene/[monolayer Co]/Ir(1 1 1). It is shown that for graphene placed in the hollow-hexagonal positions over the monolayer Co, the magnetic anisotropy remains positive, while for the placements with one of the C atoms on the top of Co it becomes negative. These findings may be important for assessing the use of graphene for magnetic recording and magnetoelectronic applications.
Spin-orbit torque manifested as an accumulated spin-polarized moment at nonmagnetic normal metal, and ferromagnet interfaces is a promising magnetization switching mechanism for spintronic devices. To fully exploit this in practice, materials with a high spin Hall angle, i.e., a charge-to-spin conversion efficiency, are indispensable. To date, very few approaches have been made to devise new nonmagnetic metal alloys. Moreover, new materials need to be compatible with semiconductor processing. Here we introduce W-Ta and W-V alloys and deploy them at the interface between $\beta$-W/CoFeB layers. First, spin Hall conductivities of W-Ta and W-V structures with various compositions are carried out by first-principles band calculations, which predict the spin Hall conductivity of the W-V alloy is improved from $-0.82 \times 10^3$ S/cm that of W to $-1.98 \times 10^3$ S/cm. Subsequently, heterostructure fabrication and spin-orbit torque properties are characterized experimentally. By alloying $\beta$-W with V at a concentration of 20 at%, we observe a large enhancement of the absolute value of spin Hall conductivity of up to $-(2.77 \pm 0.31) \times 10^3$ S/cm. By employing X-ray diffraction and scanning transmission electron microscopy, we further explain the enhancement of spin-orbit torque efficiency is stemmed from W-V alloy between W and CoFeB.
Simultaneously enhancing the uniaxial magnetic anisotropy ([Formula: see text]) and thermal stability of [Formula: see text]-phase Fe[Formula: see text]N[Formula: see text] without inclusion of heavy-metal or rare-earth (RE) elements has been a challenge over the years. Herein, through first-principles calculations and rigid-band analysis, significant enhancement of [Formula: see text] is proposed to be achievable through excess valence electrons in the Fe[Formula: see text]N[Formula: see text] unit cell. We demonstrate a persistent increase in [Formula: see text] up to 1.8 MJ m[Formula: see text], a value three times that of 0.6 MJ m[Formula: see text] in [Formula: see text]-Fe[Formula: see text]N[Formula: see text], by simply replacing Fe with metal elements with more valence electrons (Co to Ga in the periodic table). A similar rigid-band argument is further adopted to reveal an extremely large [Formula: see text] up to 2.4 MJ m[Formula: see text] in (Fe[Formula: see text]Co[Formula: see text])[Formula: see text]N[Formula: see text] obtained by replacing Co with Ni to Ga. Such a strong [Formula: see text] can also be achieved with the replacement by Al, which is isoelectronic to Ga, with simultaneous improvement of the phase stability. These results provide an instructive guideline for simultaneous manipulation of [Formula: see text] and the thermal stability in 3d-only metals for RE-free permanent magnet applications.
We report results of an angle-resolved photoemission study to elucidate the driving mechanism of the Mo(001) surface reconstruction. We find, for the first time, a remarkable change of the shapes of Fermi contours upon cooling, which reveals a significant nesting at ${\mathit{k}}_{\mathrm{\ensuremath{\parallel}}}$=0.65 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$, extended 0.30 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$ perpendicular to the \ensuremath{\Sigma}\ifmmode\bar\else\textasciimacron\fi{} axis. The results suggest that the reconstruction should occur essentially by Peierls-type 2${\mathit{k}}_{\mathit{F}}$ instabilities with significant matrix-element effects.
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