No abstract

Full insight into the dynamics of a coupled quantum system depends on the ability to follow the effect of a local excitation in real-time. Here, we trace the free coherent evolution of a pair of coupled atomic spins by means of scanning tunneling microscopy. Rather than using microwave pulses, we use a direct-current pump-probe scheme to detect the local magnetization after a current-induced excitation performed on one of the spins. By making use of magnetic interaction with the probe tip, we are able to tune the relative precession of the spins. We show that only if their Larmor frequencies match, the two spins can entangle, causing angular momentum to be swapped back and forth. These results provide insight into the locality of electron spin scattering and set the stage for controlled migration of a quantum state through an extended spin lattice.

A root bioassay was used to compare the adsorption of herbicides by activated carbon with that of muck soil, bentonite clay, a cation exchange resin, and an anion exchange resin. The effectiveness of different adsorbents was determined by comparing the concentrations of herbicide required to give 50% root inhibition of the test plant. Of eight herbicides tested, six were more strongly adsorbed by activated carbon than by any of the other adsorbents. The relative amount of adsorption by activated carbon as measured by the reduction in biological activity was as follows: isopropyl N-(3-chlorophenyl)-carbamate (CIPC) > α,α,α,trifluro-2,6-dinitro-N, N-dipropyl-p-toluidine (trifluralin) > 2,4-dichlorophenoxyacetic acid (2,4-D) > N,N-dimethyl-2,2-diphenylacetamide (diphenamid) > dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA) > 4,6-dinitro-o-sec-butylphenol (DNBP) > 3-amino-2,5-dichlorobenzoic acid (amiben). The biological activity of 1,1'-dimethyl-4,4'-bipyridinium salt (paraquat), a cationic herbicide, was not reduced by activated carbon, but was reduced by bentonite clay and the cation exchange resin. DNBP was more strongly adsorbed by the anion exchange resin than by activated carbon. Desorption from activated carbon varied greatly for the herbicides tested. The most readily desorbed herbicide was 2,4-D while CIPC and DNBP showed little or no desorption.

A rapid and sensitive method is described for the determination of phenolic acid concentrations in soil. The method consists of extraction with 0.1 M NaOH for 16 h, centrifugation, filtration, pH adjustment to reduce detector interference, and liquid chromatographic separation on a C18 column and UV detection at 280 nm. Recoveries of 6 phenolic acids (ferulic, p-coumaric, caffeic, syringic, vanillic, and p-hydroxybenzoic) were 58,100,0,66,83, and 123%, respectively. The limits of detection were 0.5 μg/g for p-hydroxybenzoic, vanillic, and syringic acids and 1.0 μg/g for ferulic and p-coumaric acids. Caffeic acid was not detectable with this method.

High-density magnetic storage or quantum computing could be achieved using small magnets with large magnetic anisotropy, a requirement that rare-earth iron alloys fulfill in bulk. This compelling property demands a thorough investigation of the magnetism in low dimensional rare-earth iron structures. Here, we report on the magnetic coupling between 4f single atoms and a 3d magnetic nanoisland. Thulium and lutetium adatoms deposited on iron monolayer islands pseudomorphically grown on W(110) have been investigated at low temperature with scanning tunneling microscopy and spectroscopy. The spin-polarized current indicates that both kind of adatoms have in-plane magnetic moments, which couple antiferromagnetically with their underlying iron islands. Our first-principles calculations explain the observed behavior, predicting an antiparallel coupling of the induced 5d electrons magnetic moment of the lanthanides with the 3d magnetic moment of iron, as well as their in-plane orientation, and pointing to a non-contribution of 4f electrons to the spin-polarized tunneling processes in rare earths.

No abstract

The orbital angular moment of magnetic atoms adsorbed on surfaces is often quenched as a result of an anisotropic crystal field. Due to spin-orbit coupling, what remains of the orbital moment typically delineates the orientation of the electron spin. These two effects limit the scope of information processing based on these atoms to essentially only one magnetic degree of freedom: the spin. In this work, we gain independent access to both the spin and orbital degrees of freedom of a single atom, inciting and probing excitations of each moment. By coordinating a single Fe atom atop the nitrogen site of the Cu 2 N lattice, we realize a singleatom system with a large zero-field splitting-the largest reported for Fe atoms on surfaces-and an unquenched uniaxial orbital moment that closely approaches the free-atom value. We demonstrate a full reversal of the orbital moment through a singleelectron tunneling event between the tip and Fe atom, a process that is mediated by a charged virtual state and leaves the spin unchanged. These results, which we corroborate using density functional theory and first-principles multiplet calculations, demonstrate independent control over the spin and orbital degrees of freedom in a single-atom system.

In this work we present a study of the structural properties of Fe 100−x Ga x (x<30) films grown by Molecular Beam Epitaxy on Mg0(100). We combine long range and local/chemically selective X-ray probes (X-ray Diffraction and X-ray absorption spectroscopy) together with real space imaging by means of Transmission Electron Microscopy and surface sensitive in situ Reflected High Energy Electron Diffraction. For substrate temperature T s below 400 o C we obtain bcc films while, for x ≈ 24 and T s ≥ 400 o C the nucleation of the fcc phase is observed. For both systems a Ga anticlustering or local range ordering phenomenon appears. The Ga/Fe composition in the first and second coordination shells of the bcc films is different from that expected for a random Ga distribution and is close to a D0 3 phase, leading to a minimization of the number Ga-Ga pairs. On the other side, a long-range D0 3 phase is not observed indicating that atomic ordering only occurs at a local scale. Overall, the epitaxial growth procedure presented in this work, first, avoids the formation of a long range ordered D0 3 phase, which is known to be detrimental for magnetostrictive properties, and second, demonstrates the possibility of growing fcc films at temperatures much lower than those required to obtain bulk fcc samples.