Searching for single-atom systems with large magnetic anisotropy energies and tunable magnetic states is of vital importance for both fundamental research of magnetism at the atomic scale and realization of future spin-based quantum computation or information storage schemes. Single $5f$ electron based actinide atoms are potential candidates for inducing large magnetic anisotropy energies (MAEs), yet they have been much less studied as compared with $3d$ or $4f$ single-atom systems. Here we present the adsorptive, electronic, and magnetic properties of a single $5f$ electron based uranium atom on two-monolayer MgO/Ag(001) by combining scanning tunneling microscopy/spectroscopy (STM/STS) and density functional theory. Our results reveal that single U atoms spontaneously adsorb at the hollow sites of the MgO/Ag(001) surface and they can be controllably switched between the hollow and the O-top sites of MgO/Ag(001) via STM atom manipulation. Most importantly, single U atoms at the O-top sites reveal complex tunneling spectral features, including a symmetric dip at the Fermi energy, which is the manifestation of the existence of a relatively large $5f$-driven magnetic anisotropy energy, whereas single U atoms at the hollow sites exhibit a two-lobe subatomic structure stemming from the valence electron orbitals of U itself and show no signs related with magnetic anisotropy. This work proves that single $5f$ electron based U atoms can possess a considerable uniaxial magnetic anisotropy via adsorbing at the appropriate sites on the carefully chosen supporting surface, and their magnetic states can be tuned by atom manipulation techniques.
An experimental research on the reduction of vibration of ball bearings is provided in this paper. The waviness of inner race and outer race are decreased by superfinishing process, and their excitation frequencies are obtained. After the bearings’ vibration is tested, the powers of vibration distributed in different frequency regions are computed. The results reveal that the waviness excitations have a considerable influence on vibration of ball bearings in medium-frequency ranges, and the vibration can be reduced greatly by superfinishing process.
The physical mechanism driving the $γ$-$α$ phase transition of face-centre-cubic (fcc) cerium (Ce) remains controversial until now. In this work, high quality single crystalline fcc-Ce thin films were grown on Graphene/6$H$-SiC(0001) substrate, and explored by XRD and ARPES measurement. XRD spectra showed a clear $γ$-$α$ phase transition at $T_{γ-α}\approx$ 50 K, which is retarded by strain effect from substrate comparing with $T_{γ-α}$ (about 140 K) of the bulk Ce metal. However, APRES spectra did not show any signature of $α$-phase emerging in the surface-layer from 300 K to 17 K, which implied that $α$-phase might form at the bulk-layer of our Ce thin films. Besides, an evident Kondo dip near Fermi energy was observed in the APRES spectrum at 80 K, indicting the formation of Kondo singlet states in $γ$-Ce. Furthermore, the DFT+DMFT calculations were performed to simulate the electronic structures and the theoretical spectral functions agreed well with the experimental ARPES spectra. In $γ$-Ce, the behavior of the self-energy's imaginary part at low frequency not only confirmed that the Kondo singlet states emerged at $T_{\rm KS} \geq 80$ K, but also implied that they became coherent states at a lower characteristic temperature ($T_{\rm coh}\sim 40$ K) due to the indirect RKKY interaction among $f$-$f$ electrons. Besides, $T_{\rm coh}$ from the theoretical simulation was close to $T_{γ-α}$ from the XRD spectra. These issues suggested that the Kondo scenario might play an important role in the $γ$-$α$ phase transition of cerium thin films.
In $f$-electron heavy fermion systems, a wide variety of fascinating magnetic and electronic properties arise, and they are often thought to be related to a crossover behavior between localized and itinerant regimes for $f$ electrons. Uranium-based compounds with partially occupied $5f$ orbitals provide an ideal platform to elucidate the outstanding issue of the competition between magnetic order and Kondo entanglement. Using angle-resolved photoemission spectroscopy, complemented by density functional theory simulations, we probe the temperature-dependent evolution of the low-energy electronic structure of ${\mathrm{UAs}}_{2}$ and observe two nearly flat bands of different origin in the antiferromagnetic (AFM) state. A nearly flat band which behaves with quasi-two-dimensional character has been observed and contributed to the heavy spectral weight at the \cyrchar\CYRG{} point around ${E}_{\mathrm{F}}$. This flat band reveals typical Kondo hybridization. Another flat band around the $M$ point is closely related to paramagnetic (PM)-AFM phase transition, which opens an energy gap below the transition temperature \ensuremath{\sim}273 K. Our results provide direct spectral demonstration of the electronic structure evolution across the $f\text{\ensuremath{-}}c$ hybridization and PM-AFM transition in ${\mathrm{UAs}}_{2}$.
A straightforward methodology to facilely synthesize optically active polymers has been successfully developed through a one-pot combination of enzymatic resolution reaction and living radical polymerization.
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