Atomic-scale spin sensing with a single molecule at the apex of a scanning tunneling microscope.

Recent advances in scanning probe techniques rely on the chemical functionalization of the probe-tip termination by a single molecule. The success of this approach opens the prospect of introducing spin sensitivity through functionalization by a magnetic molecule. We used a nickelocene-terminated tip (Nc-tip), which offered the possibility of producing spin excitations on the tip apex of a scanning tunneling microscope (STM). When the Nc-tip was 100 picometers away from point contact with a surface-supported object, magnetic effects could be probed through changes in the spin excitation spectrum of nickelocene. We used this detection scheme to simultaneously determine the exchange field and the spin polarization of iron atoms and cobalt films on a copper surface with atomic-scale resolution.

Tailoring the chiral magnetic interaction between two individual atoms.

Chiral magnets are a promising route towards dense magnetic storage technology due to their inherent nano-scale dimensions and energy efficient properties. Engineering chiral magnets requires atomic-level control of the magnetic exchange interactions, including the Dzyaloshinskii-Moriya interaction, which defines a rotational sense for the magnetization of two coupled magnetic moments. Here we show that the indirect conduction electron-mediated Dzyaloshinskii-Moriya interaction between two individual magnetic atoms on a metallic surface can be manipulated by changing the interatomic distance with the tip of a scanning tunnelling microscope. We quantify this interaction by comparing our measurements to a quantum magnetic model and ab-initio calculations yielding a map of the chiral ground states of pairs of atoms depending on the interatomic separation. The map enables tailoring the chirality of the magnetization in dilute atomic-scale magnets.

Exploring the phase diagram of the two-impurity Kondo problem.

A system of two exchange-coupled Kondo impurities in a magnetic field gives rise to a rich phase space hosting a multitude of correlated phenomena. Magnetic atoms on surfaces probed through scanning tunnelling microscopy provide an excellent platform to investigate coupled impurities, but typical high Kondo temperatures prevent field-dependent studies from being performed, rendering large parts of the phase space inaccessible. We present a study of pairs of Co atoms on insulating Cu2N/Cu(100), which each have a Kondo temperature of only 2.6 K. The pairs are designed to have interaction strengths similar to the Kondo temperature. By applying a sufficiently strong magnetic field, we are able to access a new phase in which the two coupled impurities are simultaneously screened. Comparison of differential conductance spectra taken on the atoms to simulated curves, calculated using a third-order transport model, allows us to independently determine the degree of Kondo screening in each phase.

A diamond-based scanning probe spin sensor operating at low temperature in ultra-high vacuum.

We present the design and performance of an ultra-high vacuum (UHV) low temperature scanning probe microscope employing the nitrogen-vacancy color center in diamond as an ultrasensitive magnetic field sensor. Using this center as an atomic-size scanning probe has enabled imaging of nanoscale magnetic fields and single spins under ambient conditions. In this article we describe an experimental setup to operate this sensor in a cryogenic UHV environment. This will extend the applicability to a variety of molecular systems due to the enhanced target spin lifetimes at low temperature and the controlled sample preparation under UHV conditions. The instrument combines a tuning-fork based atomic force microscope (AFM) with a high numeric aperture confocal microscope and the facilities for application of radio-frequency (RF) fields for spin manipulation. We verify a sample temperature of <50 K even for strong laser and RF excitation and demonstrate magnetic resonance imaging with a magnetic AFM tip.

Spin excitations of a Kondo-screened atom coupled to a second magnetic atom.

Screening the electron spin of a magnetic atom via spin coupling to conduction electrons results in a strong resonant peak in the density of states at the Fermi energy, the Kondo resonance. We show that magnetic coupling of a Kondo atom to another unscreened magnetic atom can split the Kondo resonance into two peaks. Inelastic spin excitation spectroscopy with scanning tunneling microscopy is used to probe the Kondo effect of a Co atom, supported on a thin insulating layer on a Cu substrate, that is weakly coupled to a nearby Fe atom to form an inhomogeneous dimer. The Kondo peak is split by interaction with the non-Kondo atom, but can be reconstituted with a magnetic field of suitable magnitude and direction. Quantitative modeling shows that this magnetic field results in a spin-level degeneracy in the dimer, which enables the Kondo effect to occur.

Melting of two-dimensional adatom superlattices stabilized by long-range electronic interactions.

The melting transition of Ce adatom superlattices stabilized by long-range substrate-mediated electronic interactions on Cu(111) and Ag(111) noble metal surfaces has been investigated by low-temperature scanning tunneling microscopy, density functional theory calculations, and kinetic Monte Carlo simulations. Intriguingly, owing to the interaction between Ce adatoms and substrate, these superlattices undergo two-dimensional melting to a liquid without transition through the hexatic phase. The crucial parameters for this direct solid to liquid transition are identified.

Effects of temperature on the toxicity of m-parathion, chlorpyrifos, and pentachlorobenzene to Chironomus tentans.

This study examined the influence of temperature (10, 20, and 30 degrees C) on the acute toxicity and accumulation of two organophosphate (OP) insecticides and a narcotic chemical to the midge (Chironomus tentans). OP insecticides used in this study included chlorpyrifos and m-parathion, and pentachlorobenzene was the chosen narcotic. Chlorpyrifos was the most toxic chemical tested, followed by m-parathion and then pentachlorobenzene. A positive correlation was found between temperature and toxicity for each of the chemicals tested. A reverse trend was noted for total OP insecticide body residues with decreased concentrations found at the higher temperatures. Pentachlorobenzene body residues remained constant at all temperatures. All three chemicals showed increased uptake rates at 20 and 30 degrees C in comparison to 10 degrees C. The noted decrease in midge body residues at the higher temperatures for the OP insecticides was contributed to increased biotransformation and elimination rates at the higher temperatures. Overall, temperature had a greater influence on OP toxicity than for pentachlorobenzene, and this may be due to accelerated biotransformation of the OPs to more toxic o-analog metabolites at the higher temperatures.http://link.springer-ny. com/link/service/journals/00244/bibs/37n4p542.html

[Health status and vaccination status of 4th grade students in the Rhine-Lahn district]. / Gesundheitszustand und Impfstatus von Viertklässlern im Rhein-Lahn-Kreis.

Within the framework of the school examination of fourth-formes in 1988, 997 children of the primary schools in the Rhein-Lahn district were examined by the Board of Health of Lahnstein. Nearly every 5th child had to be referred to established specialists because of suspicious diagnoses. Primarily this was a matter of pathological skeleton findings. About 20% of the children were overweight. About 75% of the pupils complied with our request to show us their vaccination certificates. After a part of them had been revaccinated, complete vaccination status was available in three quarter of the children. The significance of medical examination in school is underlined by the great number of children with medical problems. First of the area of the spinal column is alarmingly high. The health-political significance results from the possibility of an early prevention of degenerative diseases of the spinal column.