Rapid diffusion of electrons in GaMnAs

We report ultrafast transient-grating measurements, above and below the Curie temperature, of the dilute ferromagnetic semiconductor (Ga,Mn)As containing 6% Mn. At 80 K (15 K), we observe that photoexcited electrons in the conduction band have a lifetime of 8 ps (5 ps) and diffuse at about 70 cm2/s (60 cm2/s). Such rapid diffusion requires either an electronic mobility exceeding 7,700 cm2/Vs or a conduction-band effective mass less than half the GaAs value. Our data suggest that neither the scattering rate nor the effective mass of the (Ga,Mn)As conduction band differs significantly from that of GaAs.Comment: 5 pages, 3 figures. Differs from the previous version in incorporating additional data and changes made during the review process. Differs from the published version in including section headings and in omitting AIP copy-edits. No substantial differences in scientific conclusions from either versio

Professional boundaries: crossing a line or entering the shadows?

This article explores the professional boundaries guidance for social workers. It presents research findings from the formal literature, from agency codes of practice, from telephone interviews with regulatory and professional bodies and from an exercise using ‘snowballing techniques’ in which informants responded to brief scenarios illustrating boundary dilemmas. The findings suggest that formal research plays little part in the guidance that individuals use to help them determine professional boundaries. Similarly, only 10–15 per cent of informants made regular reference to regulatory and professional codes of practice, with an even smaller percentage quoting specific sections from these codes. A slightly larger group (15–20 per cent) made fairly regular reference to their agency's policy documents. However, a clear majority relied on their own sense of what is appropriate or inappropriate, and made their judgements with no reference to any formal guidance. Agency guidance tended to ignore the ambiguous areas of practice and seemed to act as an insurance policy, brought out and dusted off when something goes awry. The authors caution against ever-increasing bullet points of advice and prescription, and advance a notion of ethical engagement in which professionals exercise their ethical senses through regular discussion of professional boundary dilemmas

Wine of Cool-climate Areas in South Poland

A number of new vinery production regions, especially in the southern parts of Poland, have appearedin the last ten-odd years. This study was aimed at completing the chemical characterisation of wineproduced from ten Polish grape cultivars planted near Krakow. The wine was analysed to determineorganic acid concentrations, total polyphenols and extract content, antioxidant activity, alcohol content,total acidity and pH. Moreover, a sensory analysis was performed on the wine. Significant differenceswere recorded between red and white wine. The total acidity expressed as tartaric acid, and tartaric andmalic acid concentrations, were significantly higher in white and red wines, whereas antioxidant activityand phenolic content were significantly higher in the red wines. Similarities and relationships betweenvarious parameters and specific wine brands were further examined with cluster analysis. Our resultsshow that, under Polish climatic conditions, it is possible to produce wine with quality comparable towine from established wine denomination regions. Selected wine brands showed high antioxidantactivity (FRAP – ferric reducing antioxidant power) and a high level of polyphenols. This study alsoprovides confirmation that wines from colder climates frequently reveal unique and desirable properties

External control of the direction of magnetization in ferromagnetic InMnAs/GaSb heterostructures

In this paper, we demonstrate external control over the magnetization direction in ferromagnetic (FM) In_{1-x}Mn_{x}As/GaSb heterostructures. FM ordering with T_C as high as 50 K is confirmed by SQUID magnetization, anomalous Hall effect (AHE), and magneto-optical Kerr effect (MOKE) measurements. Even though tensile strain is known to favor an easy axis normal to the layer plane, at low temperatures we observe that the magnetization direction in several samples is intermediate between the normal and in-plane axes. As the temperature increases, however, the easy axis rotates to the direction normal to the plane. We further demonstrate that the easy magnetization axis can be controlled by incident light through a bolometric effect, which induces a pronounced increase in the amplitude of the AHE. A mean-field-theory model for the carrier-mediated ferromagnetism reproduces the tendency for dramatic reorientations of the magnetization axis, but not the specific sensitivity to small temperature variations.Comment: 11 pages, 3 figures, submitted to NGS-1

Spin Dynamics and Spin Transport

Spin-orbit (SO) interaction critically influences electron spin dynamics and spin transport in bulk semiconductors and semiconductor microstructures. This interaction couples electron spin to dc and ac electric fields. Spin coupling to ac electric fields allows efficient spin manipulating by the electric component of electromagnetic field through the electric dipole spin resonance (EDSR) mechanism. Usually, it is much more efficient than the magnetic manipulation due to a larger coupling constant and the easier access to spins at a nanometer scale. The dependence of the EDSR intensity on the magnetic field direction allows measuring the relative strengths of the competing SO coupling mechanisms in quantum wells. Spin coupling to an in-plane electric field is much stronger than to a perpendicular field. Because electron bands in microstructures are spin split by SO interaction, electron spin is not conserved and spin transport in them is controlled by a number of competing parameters, hence, it is rather nontrivial. The relation between spin transport, spin currents, and spin populations is critically discussed. Importance of transients and sharp gradients for generating spin magnetization by electric fields and for ballistic spin transport is clarified.Comment: Invited talk at the 3rd Intern. Conf. on Physics and Applications of Spin-Related Phenomena in Semiconductors, Santa Barbara (CA), July 21 - 23. To be published in the Journal of Superconductivity. 7 pages, 2 figure

Controlling Curie temperature in (Ga,Ms)As through location of the Fermi level within the impurity band

The ferromagnetic semiconductor (Ga,Mn)As has emerged as the most studied material for prototype applications in semiconductor spintronics. Because ferromagnetism in (Ga,Mn)As is hole-mediated, the nature of the hole states has direct and crucial bearing on its Curie temperature TC. It is vigorously debated, however, whether holes in (Ga,Mn)As reside in the valence band or in an impurity band. In this paper we combine results of channeling experiments, which measure the concentrations both of Mn ions and of holes relevant to the ferromagnetic order, with magnetization, transport, and magneto-optical data to address this issue. Taken together, these measurements provide strong evidence that it is the location of the Fermi level within the impurity band that determines TC through determining the degree of hole localization. This finding differs drastically from the often accepted view that TC is controlled by valence band holes, thus opening new avenues for achieving higher values of TC.Comment: 5 figures, supplementary material include

Knowledge, opinions and attitudes of Polish women towards banking and donation of human breast milk

Objectives: The aim of the study was to obtain information on the knowledge, opinions and attitudes of Polish women in terms of functioning of human milk banks, as well as the possibility to be a donor. Specific objectives included consideration of responses in the sociodemographic aspect and identification of factors influencing donation decisions.Material and methods: A cross-sectional survey was conducted, obtaining 871 responses. Women were asked to provide basic sociodemographic data, information related to pregnancy and lactation. Knowledge and opinion about breast milk banks as well as the impact of various factors on a potential donation decision were investigated.Results: Of all women participating in the study, 604 (69%) were aware of the breast milk banks existence. 69% of respondents indicated the Internet, 10% — a nurse or midwife, while only 4% — a doctor as source of knowledge about human breast milk donation. Among women who had children (n = 453), only 9 (2%) donated breast milk in the past. The indicated reasons for not donating were no milk excess (38%), insufficient knowledge about the procedure or unawareness of its existence (33% and 25%, respectively), long distance to affiliated facility (17%).Conclusions: The awareness of breast milk banks existence, possibilities and terms of donation in the studied group is not satisfactory. Widely sharing reliable information on banking and promoting the idea of donating human breast milk in society can lead to impressive results. There is a need for further development of human breast milk banks and continuous improvement of their availability in Poland

Magnetic and chemical nonuniformity in Ga[1-x]Mn[x]As films as probed by polarized neutron and x-ray reflectometry

We have used complementary neutron and x-ray reflectivity techniques to examine the depth profiles of a series of as-grown and annealed Ga[1-x]Mn[x]As thin films. A magnetization gradient is observed for two as-grown films and originates from a nonuniformity of Mn at interstitial sites, and not from local variations in Mn at Ga sites. Furthermore, we see that the depth-dependent magnetization can vary drastically among as-grown Ga[1-x]Mn[x]As films despite being deposited under seemingly similar conditions. These results imply that the depth profile of interstitial Mn is dependent not only on annealing, but is also extremely sensitive to initial growth conditions. We observe that annealing improves the magnetization by producing a surface layer that is rich in Mn and O, indicating that the interstitial Mn migrates to the surface. Finally, we expand upon our previous neutron reflectivity study of Ga[1-x]Mn[x]As, by showing how the depth profile of the chemical composition at the surface and through the film thickness is directly responsible for the complex magnetization profiles observed in both as-grown and annealed films.Comment: Now Published in Physical Review