By introducing different contents of Bi adatoms to the surface of monolayer graphene, the carrier concentration and their dynamics have been effectively modulated as probed directly by the time‐ and angle‐resolved photoemission spectroscopy technique. The Bi adatoms are found to assist acoustic phonon scattering events mediated by supercollisions as the disorder effectively relaxes the momentum conservation constraint. A reduced carrier multiplication has been observed, which is related to the shrinking Fermi sea for scattering, as confirmed by time‐dependent density functional theory simulation. This work gives insight into hot carrier dynamics in graphene, which is crucial for promoting the application of photoelectric devices.
We obtained epitaxial single-crystal Fe3O4(001)/MgO(001) thin films by magnetron sputtering. The high quality of the grown Fe3O4 films was confirmed by reflection high-energy electron diffraction and x-ray photoelectron spectroscopy. Atomic magnetic properties of Fe3O4(001)/MgO(001) were investigated using vibrating sample magnetometry and x-ray magnetic circular dichroism. The values of saturation magnetization and magnetic moment are 407 [Formula: see text] 5 emu/cm3 (3.26 [Formula: see text] 0.04 [Formula: see text]) and 3.31 [Formula: see text] 0.15 [Formula: see text], respectively, in the Fe3O4 film as thin as 5 nm, which are close to the bulk values. The spin polarization was directly measured using spin-resolved photoemission spectroscopy. The measured spin polarization has a maximum value of −42% [Formula: see text] 3%, which is comparable to the theoretical value for the ([Formula: see text] × [Formula: see text])R45° reconstructed Fe3O4(001) surface. Furthermore, the film thickness-dependent measurements indicate that the anti-phase boundaries significantly decrease the spin polarization rather than the lattice mismatch. Our results demonstrate that epitaxial Fe3O4(001)/MgO thin films grown by magnetron sputtering have desired magnetic properties, facilitating the potential application of Fe3O4-based spintronic devices.
Spin polarization and the Gilbert damping, as the two key parameters of the magnetic materials for spintronic applications, were suggested to be inversely proportional to each other in a series of Heusler alloys. Recently, large anisotropic Gilbert damping was found in Co2FeAl thin films, implying that spin polarization may be also anisotropic. Here, we report an isotropic spin polarization with a constant value of 60% in a 20-nm Co2FeAl thin film with a B2 structure, using spin- and angle-resolved photoemission spectroscopy and time-resolved magneto-optical Kerr effect. Furthermore, this result was also supported by the ab initio calculations that the difference of the spin polarization between all the orientations is less than 1% for the Co2FeAl thin film. This finding provides profound insight into the spin polarization in Co2FeAl alloys.
Investigation on the spin polarization of the magnetic CoFeB thin film is of practical importance in spintronic applications. Here, using a direct characterization technique of spinresolved photoemission spectroscopy, the surface spin polarization of amorphous Co40Fe40B20 thin films with different annealing temperatures from 100 ℃ to 500 ℃ prepared by magnetron sputtering is obtained. After high annealing temperature, a quasi-semiconductor state is gradually formed at the CoFeB surface due to the boron diffusion. While the global magnetization remains almost constant, the secondary electrons’ spin polarization, average valence band spin polarization and the spin polarization at Fermi level from spin-resolved photoemission spectroscopy show a general trend of decreasing with the increasing of the annealing temperature above 100 ℃. These distinct surface properties are attributed to the enhanced Fe-B bonding due to the boron segregation upon surface after annealing as confirmed by x-ray photoelectron spectroscopy and scanning transmission electron microscopy with energy dispersive spectroscopy. Our findings provide insight into the surface spin-resolved electronic structure of the CoFeB thin films, which should be important for the development of high-performance magnetic random-access memory.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.