Anisotropic magnetization, specific heat and resistivity of RFe2Ge2 single crystals

We have grown RFe2Ge2 single crystals for R = Y and ten members of the lanthanide series (Pr, Nd, Sm, Gd-Tm, Lu) using Sn flux as the solvent. The method yields clean, high quality crystal plates as evidenced by residual resistivities and RRR values in the range of 3-12 uOhm cm and 20-90 respectively. The crystals are also virtually free of magnetic impurities or secondary phases, allowing the study of the intrinsic anisotropic magnetic behavior of each compound. Characterization was made with X-Ray diffraction, and temperature and field dependent magnetization, specific heat and resistivity. Very strong anisotropies arising mostly from CEF effects were observed for all magnetic rare earths except Gd. Antiferromagnetic ordering occurred at temperatures between 16.5 K (Nd) and 1.1 K (Ho) that roughly scale with the de Gennes factor for the heavy rare earths. For some members there is also a lower temperature transition associated with changes in the magnetic structure. Tm did not order down to 0.4 K, and appears to be a van Vleck paramagnet. All members which ordered above 2 K showed a metamagnetic transition at 2 K for fields below 70 kOe. The calculated effective moments per rare earth atom are close to the expected free ion values of R^3+ except for Sm which displays anomalous behavior in the paramagnetic state. The non-magnetic members of this series (Y, Lu) are characterized by an unusually large electronic specific heat coefficient (gamma ~ 60 mJ/mol K^2) and temperature-independent susceptibility term (chi_0 ~ 0.003 emu/mol), indicative of a relatively large density of states at the Fermi surface.Comment: 34 pages, 13 figures, 1 table, submitted to J. Magn. Magn. Mate

Multiband superconductivity in NbSe_2 from heat transport

The thermal conductivity of the layered s-wave superconductor NbSe_2 was measured down to T_c/100 throughout the vortex state. With increasing field, we identify two regimes: one with localized states at fields very near H_c1 and one with highly delocalized quasiparticle excitations at higher fields. The two associated length scales are most naturally explained as multi-band superconductivity, with distinct small and large superconducting gaps on different sheets of the Fermi surface.Comment: 2 pages, 2 figures, submitted to M2S-Rio 2003 Proceeding

Field-induced quantum critical point in CeCoIn_5

The resistivity of CeCoIn_5 was measured down to 20 mK in magnetic fields of up to 16 T. With increasing field, we observe a suppression of the non-Fermi liquid behavior, rho~T, and the development of a Fermi liquid state, with its characteristic rho=rho_0+AT^2 dependence. The field dependence of the T^2 coefficient shows critical behavior with an exponent of ~4/3. This is evidence for a new field-induced quantum critical point, occuring in this case at a critical field which coincides with the superconducting upper critical field H_c2.Comment: 2 pages, 2 figures, submitted to M2S-Rio 2003 Proceeding

Doping dependent Irreversible Magnetic Properties of Ba(Fe1-xCox)2As2 Single Crystals

We discuss the irreversible magnetic properties of self-flux grown Ba(Fe1-xCox)2As2 single crystals for a wide range of concentrations covering the whole phase diagram from the underdoped to the overdoped regime, x=0.038, 0.047, 0.058, 0.071, 0.074, 0.10, 0.106 and 0.118. Samples were characterized by a magneto-optical method and show excellent spatial uniformity of the superconducting state. The overall behavior closely follows classical Bean model of the critical state. The field-dependent magnetization exhibits second peak at a temperature and doping - dependent magnetic field, Hp. The evolution of this fishtail feature with doping is discussed. Magnetic relaxation is time-logarithmic and unusually fast. Similar to cuprates, there is an apparent crossover from collective elastic to plastic flux creep above Hp. At high fields, the field dependence of the relaxation rate becomes doping independent. We discuss our results in the framework of the weak collective pinning and show that vortex physics in iron-based pnictide crystals is much closer to high-Tc cuprates than to conventional s-wave (including MgB2) superconductors.Comment: for the special issue of Physica C on iron-based pnictide superconductor

Anisotropic London Penetration Depth and Superfluid Density in Single Crystals of Iron-based Pnictide Superconductors

In- and out-of-plane magnetic penetration depths were measured in three iron-based pnictide superconducting systems. All studied samples of both 122 systems show a robust power-law behavior, $\lambda (T) T^n$, with the sample-dependent exponent n=2-2.5, which is indicative of unconventional pairing. This scenario could be possible either through scattering in a $s_{\pm }$ state or due to nodes in the superconducting gap. In the Nd-1111 system, the interpretation of data may be obscured by the magnetism of rare-earth ions. The overall anisotropy of the pnictide superconductors is small. The 1111 system is about two times more anisotropic than the 122 system. Our data and analysis suggest that the iron-based pnictides are complex superconductors in which a multiband three-dimensional electronic structure and strong magnetic fluctuations play important roles.Comment: submitted to a special issue of Physica C on superconducting pnictide

Sociodemographic, health behavioral, and clinical risk factors for anotia/microtia in a population-based case-control study

Objective: Anotia and microtia are congenital malformations of the external ear with few known risk factors. We conducted a comprehensive assessment of a wide range of potential risk factors using data from the National Birth Defects Prevention Study (NBDPS), a population-based case-control study of non-chromosomal structural birth defects in the United States. Methods: Mothers of 699 infants with anotia or microtia (cases) and 11,797 non-malformed infants (controls) delivered between 1997 and 2011 were interviewed to obtain information about sociodemographic, health behavioral, and clinical characteristics. Adjusted odds ratios (aORs) and 95% confidence intervals (CIs) were estimated with logistic regression. Results: Infants with anotia/microtia were more likely to be male (aOR, 1.29; 95% CI, 1.10–1.50) and from a multifetal pregnancy (aOR, 1.68; 95% CI, 1.16–2.42). Cases were also more likely to have parents of Hispanic ethnicity (maternal aOR, 3.19; 95% CI, 2.61–3.91; paternal aOR, 2.11; 95% CI, 1.54–2.88), and parents born outside the United States (maternal aOR, 1.29; 95% CI, 1.06–1.57; paternal aOR, 1.92; 95% CI, 1.53–2.41). Maternal health conditions associated with increased odds of anotia/microtia included obesity (aOR, 1.31; 95% CI, 1.06–1.61) and pre-pregnancy diabetes (type I aOR, 9.89; 95% CI, 5.46–17.92; type II aOR, 4.70; 95% CI, 2.56–8.63). Reduced odds were observed for black mothers (aOR, 0.57; 95% CI, 0.38–0.85) and mothers reporting daily intake of folic acid-containing supplements (aOR, 0.59; 95% CI, 0.46–0.76). Conclusion: We identified several risk factors for anotia/microtia, some which have been previously reported (e.g., diabetes) and others which we investigate for perhaps the first time (e.g., binge drinking) that warrant further investigation. Our findings point to some potentially modifiable risk factors and provide further leads toward understanding the etiology of anotia/microtia

Male sex and the risk of childhood cancer: The mediating effect of birth defects

Background: There is a persistent, unexplained disparity in sex ratio among childhood cancer cases, whereby males are more likely to develop most cancers. This male predominance is also seen for most birth defects, which are strongly associated with risk of childhood cancer. We conducted mediation analysis to estimate whether the increased risk of cancer among males is partially explained by birth defect status. Methods: We used a population-based birth cohort with linked data from birth certificates, birth defects registries, and cancer registries from Arkansas, Michigan, North Carolina, and Texas. We conducted counterfactual mediation analysis to estimate the natural direct and indirect effects of sex on cancer risk, modeling birth defect status as mediator. State; birth year; plurality; and maternal race and ethnicity, age, and education were considered confounders. We conducted separate analyses limited to cancers diagnosed younger than 1 year of age. Results: Our dataset included 10 181 074 children: 15 110 diagnosed with cancer, 539 567 diagnosed with birth defects, and 2124 co-occurring cases. Birth defect status mediated 38% of the association between sex and cancer overall. The proportion mediated varied by cancer type, including acute myeloid leukemia (93%), neuroblastoma (35%), and non-Hodgkin lymphoma (6%). Among children younger than 1 year of age at cancer diagnosis, the proportion mediated was substantially higher (82%). Conclusions: Our results suggest that birth defects mediate a statistically significant proportion of the relationship between sex and childhood cancer. The proportion mediated varied by cancer type and diagnosis age. These findings improve our understanding of the causal pathway underlying male sex as a risk factor for childhood cancer

Magnetic phases and reorientation transitions in antiferromagnetically coupled multilayers

In antiferromagnetically coupled superlattices grown on (001) faces of cubic substrates, e.g. based on materials combinations as Co/Cu, Fe/Si, Co/Cr, or Fe/Cr, the magnetic states evolve under competing influence of bilinear and biquadratic exchange interactions, surface-enhanced four-fold in-plane anisotropy, and specific finite-size effects. Using phenomenological (micromagnetic) theory, a comprehensive survey of the magnetic states and reorientation transitions has been carried out for multilayer systems with even number of ferromagnetic sub-layers and magnetizations in the plane. In two-layer systems (N=2) the phase diagrams in dependence on components of the applied field in the plane include ``swallow-tail'' type regions of (metastable) multistate co-existence and a number of continuous and discontinuous reorientation transitions induced by radial and transversal components of the applied field. In multilayers (N \ge 4) noncollinear states are spatially inhomogeneous with magnetization varying across the multilayer stack. For weak four-fold anisotropy the magnetic states under influence of an applied field evolve by a complex continuous reorientation into the saturated state. At higher anisotropy they transform into various inhomogeneous and asymmetric structures. The discontinuous transitions between the magnetic states in these two-layers and multilayers are characterized by broad ranges of multi-phase coexistence of the (metastable) states and give rise to specific transitional domain structures.Comment: Manuscript 34 pages, 14 figures; submitted for publicatio

Cancer diagnostic profile in children with structural birth defects: An assessment in 15,000 childhood cancer cases

Background: Birth defects are established risk factors for childhood cancer. Nonetheless, cancer epidemiology in children with birth defects is not well characterized. Methods: Using data from population-based registries in 4 US states, this study compared children with cancer but no birth defects (n = 13,111) with children with cancer and 1 or more nonsyndromic birth defects (n = 1616). The objective was to evaluate cancer diagnostic characteristics, including tumor type, age at diagnosis, and stage at diagnosis. Results: Compared with the general population of children with cancer, children with birth defects were diagnosed with more embryonal tumors (26.6% vs 18.7%; q < 0.001), including neuroblastoma (12.5% vs 8.2%; q < 0.001) and hepatoblastoma (5.0% vs 1.3%; q < 0.001), but fewer hematologic malignancies, including acute lymphoblastic leukemia (12.4% vs 24.4%; q < 0.001). In age-stratified analyses, differences in tumor type were evident among children younger than 1 year and children 1 to 4 years old, but they were attenuated among children 5 years of age or older. The age at diagnosis was younger in children with birth defects for most cancers, including leukemia, lymphoma, astrocytoma, medulloblastoma, ependymoma, embryonal tumors, and germ cell tumors (all q < 0.05). Conclusions: The results indicate possible etiologic heterogeneity in children with birth defects, have implications for future surveillance efforts, and raise the possibility of differential cancer ascertainment in children with birth defects. Lay Summary: Scientific studies suggest that children with birth defects are at increased risk for cancer. However, these studies have not been able to determine whether important tumor characteristics, such as the type of tumor diagnosed, the age at which the tumor is diagnosed, and the degree to which the tumor has spread at the time of diagnosis, are different for children with birth defects and children without birth defects. This study attempts to answer these important questions. By doing so, it may help scientists and physicians to understand the causes of cancer in children with birth defects and diagnose cancer at earlier stages when it is more treatable

Extreme Ultra-Violet Spectroscopy of the Lower Solar Atmosphere During Solar Flares

The extreme ultraviolet portion of the solar spectrum contains a wealth of diagnostic tools for probing the lower solar atmosphere in response to an injection of energy, particularly during the impulsive phase of solar flares. These include temperature and density sensitive line ratios, Doppler shifted emission lines and nonthermal broadening, abundance measurements, differential emission measure profiles, and continuum temperatures and energetics, among others. In this paper I shall review some of the advances made in recent years using these techniques, focusing primarily on studies that have utilized data from Hinode/EIS and SDO/EVE, while also providing some historical background and a summary of future spectroscopic instrumentation.Comment: 34 pages, 8 figures. Submitted to Solar Physics as part of the Topical Issue on Solar and Stellar Flare