Magnetic polarization of the americium J=0 ground state in AmFe(2)

Trivalent americium has a nonmagnetic (J=0) ground state arising from the cancellation of the orbital and spin moments. However, magnetism can be induced by a large molecular field if Am^{3+} is embedded in a ferromagnetic matrix. Using the technique of x-ray magnetic circular dichroism, we show that this is the case in AmFe_{2}. Since ⟨J_{z}⟩=0, the spin component is exactly twice as large as the orbital one, the total Am moment is opposite to that of Fe, and the magnetic dipole operator ⟨T_{z}⟩ can be determined directly; we discuss the progression of the latter across the actinide series.

Strong magneto-chiral dichroism in a paramagnetic molecular helix observed by hard X-ray

Magneto-chiral dichroism (MχD) is a non-reciprocal, i. e. directional, effect observed in magnetised chiral systems featuring an unbalanced absorption of unpolarised light depending on the direction of the magnetisation. Despite the fundamental interest in a phenomenon breaking both parity and time reversal symmetries, MχD is one of the least investigated aspects of light-matter interaction because of the weakness of the effect in most reported experiments. Here we have exploited the element selectivity of hard X-ray radiation to investigate the magneto-chiral properties of enentiopure crsytals of two isostructural molecular helicoidal chains comprising Cobalt(II) and Manganese (II) ions, respectively. A strong magneto-chiral dichroism, with Kuhn asymmetry of the order of a few percent, has been observed in the Cobalt chain system, while it is practically absent for the Manganese derivative. The spectral features of the XMχD signal differ significantly from the natural and magnetic dichroic contributions and have been here rationalized using the simple multipolar expansion of matter-radiation interaction.

[Staying and working at home or considering migrating: Survey-based study of African ophthalmologists]

BACKGROUND

The shortage of ophthalmologists is a major obstacle in the struggle of fighting preventable blindness in sub-Saharan Africa. However, to date reasons affecting migration of ophthalmologists have not been completely understood.

OBJECTIVES

Evaluation of reasons reported by ophthalmologists for staying in their current work setting/country, of potential reasons for migration as well as of effects of German-African partnerships.

MATERIAL AND METHODS

In the years 2009-2011 and 2013 participants of continuous medical education courses in Ethiopia, Cameroon and Kenya were interviewed using a standardized questionnaire.

RESULTS

A total of 106 ophthalmologists participated in this survey. In the years 2009/2010 participants were mainly board certified ophthalmologists, while the 2011/2013 surveys were answered mainly by residents. The main reasons for staying in their current region/country were good working conditions, commitment to help/patriotism, possibility of further training, good income and familial ties. Professional development elsewhere and better income abroad were named as the main reasons for considering migration followed by better technical equipment elsewhere and insecurity in the home country.

CONCLUSION

Good working conditions and the possibility of further training were named as the top reasons for staying in the current region/country apart from commitment to help and familial ties. Therefore, international cooperation programs aiming at improving training of ophthalmologists and establishing an ophthalmic infrastructure may have a role in promoting ophthalmic care in Africa.

[The relationship between the temperature increase caused by phacoemulsification and the damage to the corneal endothelium]

PURPOSE

Endothelial cell damage can be found after a phacoemulsification. The reason for this cell damage is not yet known. The temperature rise inside the anterior chamber during the emulsification of the lens is considered as a potential damage mechanism. The aim of this study was to investigate the relationship between the temperature increase and the cell damage.

MATERIALS AND METHODS

This study was performed with 86 enucleated porcine eyes, which were divided into six groups A-F. Group A served as control group. Phacoemulsification was simulated in the groups B-E with different surgically relevant system settings. The temperature change was measured simultaneously with temperature sensors inside the anterior chamber. Inside the eyes of group F, the instruments were positioned and irrigation and aspiration were activated, but no ultrasound was applied. For all 86 corneas, the endothelial cell damage was quantified with a standardised evaluation protocol using scanning electron microscopy (SEM). A potential correlation was checked between the observed cell damage and the measured temperature rise.

RESULTS

The highest temperature increase in group E with an obstructed aspiration line and an output power setting of 50 % was 17.77 °C. The temperature increase in group D with an output power setting of 100 % and unblocked fluid flow was significantly lower (p = 0.006). The highest temperature increase in group D was 8.89 °C. In contrast, the cells in group D were rated with a significantly lower score value than the cells in group E (p < 0.001). No significant correlation between the temperature rise and the cell damage could be obtained in due consideration of all measured data. However, an increase of the output power setting was connected with a non-linear increase of the cell loss.

CONCLUSION

The temperature rise was not the main reason for the endothelial cell damage in the performed experiments. Therefore, there seems to be no causal relationship between the temperature increase inside the anterior chamber during a common phacoemulsification and the endothelial cell damage. Due to the strong dependence between the output power setting and the cell damage, the lowest output power setting should be used during surgery which ensures the emulsification of the nucleus.

X-ray Natural Circular Dichroism

Natural Circular Dichroism was only recently discovered in the x-ray range[1]. This effect stems from the interference terms which mix multipole transition moments of opposite parity: the Electric Dipole-Electric Quadrupole (E1.E2) and the Electric Dipole-Magnetic Dipole (E1.M1) exist only in structures with broken space inversion symmetry. The scalar E1.M1 term known to be responsible for Circular Dichroism at optical wavelengths is usually considered to be vanishingly small for core level spectroscopies. The E1.E2 interference term, on the contrary, can be large in the X-ray region, but it is a parity odd second rank tensor and therefore observable only in 13 non-centrosymmetric crystal classes. X-ray Natural Circular Dichroism has now been detected in the XANES region for several uniaxial and biaxial crystals. It can give access to the absolute configuration of chiral absorbing centers. On the other hand, Chiral-EXAFS, i.e. the analog of Magnetic-EXAFS for Natural Circular Dichroism has also been measured recently using a uniaxial optically active crystal of paratellurite (TeO2). Chiral-EXAFS originates from symmetry allowed multiple scattering paths. In this presentation, we wish to report on recent advances in X-ray natural circular dichroism and its applications. Determination of absolute configuration is illustrated with measurements of both E1.E2 and E1.M1 terms in chiral alpha-Ni(H2O)6·SO4 single crystals. Manifestation of X-ray optical acitivity in magnetoelectric crystals will be illustrated with various dichroisms measured at the Fe K-edge in multiferroic GaFeO3 crystal. Finally, we will review briefly the perspectives open by our experiments.

Europium nitride: a novel diluted magnetic semiconductor

Europium nitride is semiconducting and contains nonmagnetic Eu3+, but substoichiometric EuN has Eu in a mix of 2+ and 3+ charge states. We show that at Eu2+ concentrations near 15%-20% EuN is ferromagnetic with a Curie temperature as high as 120 K. The Eu3+ polarization follows that of the Eu2+, confirming that the ferromagnetism is intrinsic to the EuN which is, thus, a novel diluted magnetic semiconductor. Transport measurements shed light on the likely exchange mechanisms.

Spin-polarization transfer in colloidal magnetic-plasmonic Au/iron oxide hetero-nanocrystals

We report on the unprecedented direct observation of spin-polarization transfer across colloidal magneto-plasmonic Au@Fe-oxide core@shell nanocrystal heterostructures. A magnetic moment is induced into the Au domain when the magnetic shell contains a reduced Fe-oxide phase in direct contact with the noble metal. An increased hole density in the Au states suggested occurrence of a charge-transfer process concomitant to the magnetization transfer. The angular to spin magnetic moment ratio, m(orb)/m(spin), for the Au 5d states, which was found to be equal to 0.38, appeared to be unusually large when compared to previous findings. A mechanism relying on direct hybridization between the Au and Fe states at the core/shell interface is proposed to account for the observed transfer of the magnetic moment.

Strong paramagnetism of gold nanoparticles deposited on a Sulfolobus acidocaldarius S layer

Magnetic properties of Au nanoparticles deposited on an archaeal S layer are reported. X-ray magnetic circular dichroism and superconducting quantum interference device magnetometries demonstrate that the particles are strongly paramagnetic, without any indication of magnetic blocking down to 16 mK. The average magnetic moment per particle is M(part)=2.36(7) μ(B). This contribution originates at the particle's Au 5d band, in which an increased number of holes with respect to the bulk value is observed. The magnetic moment per Au atom is 25 times larger than any measured in other Au nanoparticles or any other configurations up to date.

Spin fluctuations of paramagnetic Rh clusters revealed by x-ray magnetic circular dichroism

The magnetic moment induced on Rh atoms, forming 1.6 nm average diameter clusters, embedded in an Al(2)O(3) matrix, has been determined using x-ray magnetic circular dichroism measurements. The magnetic moment varies linearly with the applied magnetic field. At 2.3 K and under 17 T, the spin magnetic moment amounts to 0.067(2) μ(B)/Rh atom. The orbital moment does not exceed 2% of the spin moment. The susceptibility is highly temperature dependent. This is in agreement with a prediction due to Moriya and Kawabata, that in itinerant electron systems, close to the onset of magnetism, the renormalization of the magnetic susceptibility by electron correlations, leads to a Curie-like behavior.

Magnetic properties of textured CoPd nanocrystalline thin films

CoPd is an important nanomaterial for magnetic and magneto-optic storage of information. In this work, CoPd alloyed thin films are grown via radio frequency magnetron sputtering on silicon, glass and polyimide substrates in a vacuum chamber with base pressure of 5 x 10(-8) mbar. The films are nanocrystalline with grain size between 4 and 80 nm. The magnetic properties of thoroughly textured CoPd alloyed thin films are compared to random polycrystalline ones. Magnetization hysteresis loops recorded under fields up to 12 kOe via a home-made magneto-optic Kerr-effect magnetometer reveal strong tendency for perpendicular magnetic anisotropy for the textured film. This anisotropy leads to the formation of well-defined stripe or labyrinthine ferromagnetic domains with the local spins oriented perpendicular to the film plane. The domain patterns and the hysteresis loops are simulated with micromagnetic calculations. Finally, an induced magnetic moment of 0.44 microB/atom is measured for Pd via X-ray magnetic circular dichroism and it is separated into spin and orbital magnetic moment contributions.

X-ray detected magnetic resonance: a unique probe of the precession dynamics of orbital magnetization components

X-ray Detected Magnetic Resonance (XDMR) is a novel spectroscopy in which X-ray Magnetic Circular Dichroism (XMCD) is used to probe the resonant precession of local magnetization components in a strong microwave pump field. We review the conceptual bases of XDMR and recast them in the general framework of the linear and nonlinear theories of ferromagnetic resonance (FMR). Emphasis is laid on the information content of XDMR spectra which offer a unique opportunity to disentangle the precession dynamics of spin and orbital magnetization components at given absorbing sites. For the sake of illustration, we focus on selected examples in which marked differences were found between FMR and XDMR spectra simultaneously recorded on ferrimagnetically ordered iron garnets. With pumping capabilities extended up to sub-THz frequencies, high-field XDMR should allow us to probe the precession of orbital magnetization components in paramagnetic organometallic complexes with large zero-field splitting. Even more challenging, we suggest that XDMR spectra might be recorded on selected antiferromagnetic crystals for which orbital magnetism is most often ignored in the absence of any supporting experimental evidence.

Co-doped ZnO epitaxial films: from a Brillouin-like paramagnet to a phase-separated superparamagnetic ensemble

Co-doped ZnO films are epitaxially grown on sapphire by reactive magnetron sputtering. The preparation conditions such as temperature and the composition of the sputtering gas are systematically varied. For optimized growth conditions virtually all Co dopant atoms are located on substitutional Zn lattice sites as revealed by X-ray linear dichroism (XLD). The material behaves as a Brillouin-like paramagnet with S = 3/2 and L = 1 as revealed by integral and element specific magnetometry. Reducing the oxygen content during preparation leads to the onset of phase separation as revealed by X-ray diffraction, and more clearly by a strong reduction of the XLD signal. Such samples behave like a blocked superparamagnetic ensemble. In the entire range of preparation conditions no signs of intrinsic ferromagnetism are found.