Alternating magnetic anisotropy of Li2_2(Li1−xTx_{1-x}T_x)N with TT = Mn, Fe, Co, and Ni

Substantial amounts of the transition metals Mn, Fe, Co, and Ni can be substituted for Li in single crystalline Li$_2$(Li$_{1-x}T_x$)N. Isothermal and temperature-dependent magnetization measurements reveal local magnetic moments with magnitudes significantly exceeding the spin-only value. The additional contributions stem from unquenched orbital moments that lead to rare-earth-like behavior of the magnetic properties. Accordingly, extremely large magnetic anisotropies have been found. Most notably, the magnetic anisotropy alternates as easy-plane $\rightarrow$ easy-axis $\rightarrow$ easy-plane $\rightarrow$ easy-axis when progressing from $T$ = Mn $\rightarrow$ Fe $\rightarrow$ Co $\rightarrow$ Ni. This behavior can be understood based on a perturbation approach in an analytical, single-ion model. The calculated magnetic anisotropies show a surprisingly good agreement with the experiment and capture the basic features observed for the different transition metals.Comment: 5 pages, 3 figures, published as PRB Rapid Communication, Fig. 3 update

Physical Properties of Metallic Antiferromagnetic CaCo{1.86}As2 Single Crystals

We report studies of CaCo{1.86}As2 single crystals. The electronic structure is probed by angle-resolved photoemission spectroscopy (ARPES) measurements of CaCo{1.86}As2 and by full-potential linearized augmented-plane-wave calculations for the supercell Ca8Co15As16 (CaCo{1.88}As2). Our XRD crystal structure refinement is consistent with the previous combined refinement of x-ray and neutron powder diffraction data showing a collapsed-tetragonal ThCr2Si2-type structure with 7(1)% vacancies on the Co sites corresponding to the composition CaCo{1.86}As2 [D. G. Quirinale et al., Phys. Rev. B 88, 174420 (2013)]. The anisotropic magnetic susceptibility chi(T) data are consistent with the magnetic neutron diffraction data of Quirianale et al. that demonstrate the presence of A-type collinear antiferromagnetic order below the Neel temperature TN = 52(1) K with the easy axis being the tetragonal c axis. However, no clear evidence from the resistivity rho(T) and heat capacity Cp(T) data for a magnetic transition at TN is observed. A metallic ground state is demonstrated from band calculations and the rho(T), Cp(T) and ARPES data, and spin-polarized calculations indicate a competition between the A-type AFM and FM ground states. The Cp(T) data exhibit a large Sommerfield electronic coefficient reflecting a large density of states at the Fermi energy D(EF), consistent with the band structure calculations which also indicate a large D(EF) arising from Co 3d bands. At 1.8 K the M(H) data for H|| c exhibit a well-defined first-order spin-flop transition at an applied field of 3.5 T. The small ordered moment of 0.3 muB/Co obtained from the M(H) data at low T, the large exchange enhancement of chi and the lack of a self-consistent interpretation of the chi(T) and M(H,T) data in terms of a local moment Heisenberg model together indicate that the magnetism of CaCo{1.86}As2 is itinerant.Comment: 18 pages, 15 figures, 4 tables, 61 references; v2: extended the fits of experimental data by additional electronic structure calculations; published versio

Effective Bandgap Shrinkage in GaAs

Electrical measurements of the equilibrium np product (n2ie) in heavily doped n‐ and p‐GaAs were performed. The n2ieDproduct (where D is the diffusivity) was measured by fitting the collector current‐voltage characteristic of a homojunction bipolar transistor to an ideal diode equation modified to account for transport in thin base transistors.The n2ie product was then extracted from n2ieD by utilizing diffusivity results obtained with the zero‐field time‐of‐flight technique. Our results show significant effective band‐gap shrinkage in heavily doped p‐GaAs, and very little effective band‐gap shrinkage in heavily doped n‐GaAs. At extremely heavy dopings, an effective band‐gap widening is observed for both n‐ and p‐GaAs and is attributed to the effects of degeneracy

Struggling to be Fit: Identity, Integrity, and the Law

This interdisciplinary co-authored Analysis piece introduces identity and integrity, which are argued to sit at the core of the person. It analyses approaches taken to these concepts by legal regimes, particularly in the context of individuals using artificial limbs or digital avatars. The piece concludes that law engages with identity and integrity to a limited and incomplete extent; and that law is thus inadequate in its engagement with the person, and its meaning making in this respect. This piece draws on two interdisciplinary funded projects, funded by the Wellcome Trust and the Arts and Humanities Research Council

The Burst and Transient Source Experiment Earth Occultation Technique

An Earth orbiting detector sensitive to gamma ray photons will see step-like occultation features in its counting rate when a gamma ray point source crosses the Earth's limb. This is due to the change in atmospheric attenuation of the gamma rays along the line of sight. In an uncollimated detector, these occultation features can be used to locate and monitor astrophysical sources provided their signals can be individually separated from the detector background. We show that the Earth occultation technique applied to the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO) is a viable and flexible all-sky monitor in the low energy gamma ray and hard X-ray energy range (20 keV - 1 MeV). The method is an alternative to more sophisticated photon imaging devices for astronomy, and can serve well as a cost-effective science capability for monitoring the high energy sky. Here we describe the Earth occultation technique for locating new sources and for measuring source intensity and spectra without the use of complex background models. Examples of transform imaging, step searches, spectra, and light curves are presented. Systematic uncertainties due to source confusion, detector response, and contamination from rapid background fluctuations are discussed and analyzed for their effect on intensity measurements. A sky location-dependent average systematic error is derived as a function of galactic coordinates. The sensitivity of the technique is derived as a function of incident photon energy and also as a function of angle between the source and the normal to the detector entrance window. Occultations of the Crab Nebula by the Moon are used to calibrate Earth occultation flux measurements independent of possible atmospheric scattering effects.Comment: 39 pages, 24 figures. Accepted for publication in the Astrophysical Journal Supplement

Thermal velocity limits to diffusive electron transport in thin‐base np+n GaAs bipolar transistors

We present experimental evidence that minority electron transport across a thin, quasineutral p+ GaAs region is limited by the thermal velocity of the electrons rather than by conventional diffusive transport. A set of GaAs homojunction np+n transistors with base widths of 4000, 2000, 1000, and 500 Å was fabricated and characterized. The diffusive modelpredicts that the dc collector current of the 500‐Å base width transistors should be eight times larger than the collector current of transistors with a 4000‐Å‐wide base. The experimental results, however, show only a factor of ~3.5 increase in collector current. The measured collector current versus base width characteristic agrees well with theoretical treatments of thin‐base transport. These new results present evidence of quasiballistic electron transport in p+ GaAs and have important implications for GaAs transistor design

Identifying Fecal Pollution Sources through Antibiotic Resistance Analysis (ARA): Sand River, Aiken County, SC

2012 S.C. Water Resources Conference - Exploring Opportunities for Collaborative Water Research, Policy and Managemen