Influence of Co doping on crystal and magnetic properties of Gd_{2}Cu_{2}In

Physical properties of $Gd_2Cu_{2 - x}Co_{x}In$ (x = 0.1, 0.2, 0.3) samples are investigated. The paper brings results of X-ray diffraction, magnetometric as well as specific heat studies. It was found that only sample with x = 0.1 exhibits desired crystal structure. Other compositions show existence of impurities due to lack of dissolution Co atoms. For $Gd_2Cu_{1.9}Co_{0.1}In$ sample the Curie temperature of 92.5 K was evidenced. Thus, an enhancement of ferromagnetic correlations with comparison to $Gd_2Cu_2In$ sample was evidenced. It was found that $Gd_2Cu_{1.9}Co_{0.1}In$ sample exhibits magnetocaloric effect within broad temperature range

Границы устойчивости критического состояния жесткого сверхпроводника Nb₃Al на Н–Т плоскости

Впервые изучена неустойчивость критического состояния сверхпроводника второго рода Nb₃Al при одновременном учете реальных зависимостей тепловых и проводящих свойств материала от температуры Т и магнитного поля Нe. Для этого экспериментально в сильном (до 12 Тл) магнитном поле исследованы зависимости теплоемкости С(Т,Не), намагниченности М(Т,Нe) и магнитострикции ΔL(Т,Нe) сверхпроводника. На основе экспериментальных данных по теплоемкости в широком интервале температур и магнитных полей Hc₁ ≤ He ≤ Hc₂ найдена ширина щели, коэффициент при линейном члене, определяющий электронный вклад в теплоемкость, температура Дебая и другие параметры. Из экспериментальных исследований намагниченности восстановлены зависимости критического тока сверхпроводника Jc(T,He). Используя экспериментальные данные для температурной и полевой зависимостей тепловых и проводящих свойств, рассчитаны петли гистерезиса намагниченности и магнитострикции.Вперше вивчено нестійкість критичного стану надпровідника другого роду Nb₃Al при одночасному обчисленні реальних залежностей теплових та провідних властивостей матеріалу від температури Т та магнітного поля Нe. Для цього експериментально в сильному (до 12 Тл) магнітному полі досліджено залежності теплоємності С(Т,Не), намагніченості М(Т,Нe) та магнітострикції ΔL(Т,Нe) надпровідника. На основі експериментальних даних по теплоємності в широкому інтервалі температур і магнітних полів Hc₁ ≤ He ≤ Hc₂ знайдено ширину щілини, коефіцієнт при лінійному члені, який визначaє електронний вклад в теплоємність, температуру Дебая та інші параметри. З експериментальних досліджень намагніченості побудовано залежності критичного струму надпровідника Jc(T,He). Використовуючи експериментальні дані для температурної і польової залежностей теплових та провідних властивостей, розраховано петлі гістерезису намагніченості та магнітострикції.Stability of the critical state of type-II hard superconductors with respect to small fluctuations of temperature Т or magnetic field Нe is strongly dependent on material properties. For this purpose, heat capacity С(Т,Нe), magnetization М(Т,Нe) and magnetostriction ΔL(Т,Нe) of the superconductor were measured in a strong (up to 12 Т) magnetic field. The experimental data on heat capacity in a wide temperature range and in magnetic fields Hc₁ ≤ He ≤ Hc₂, were used to determine the gap width and some other parameters such as the coefficient of the linear term defining the electron contribution to the heat capacity and the Debye temperature. The experiments on magnetization allowed the critical current dependences of the superconductor Jc(T, He) to be recovered. The experimental data on temperature and field dependences of thermal and conducting properties were used to calculate magnetization and magnetostriction hysteresis loops

Microstructural magnetic phases in superconducting FeTe0.65Se0.35

In this paper, we address a number of outstanding issues concerning the nature and the role of magnetic inhomogenities in the iron chalcogenide system FeTe1-xSex and their correlation with superconductivity in this system. We report morphology of superconducting single crystals of FeTe0.65Se0.35 studied with transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy and their magnetic and superconducting properties characterized with magnetization, specific heat and magnetic resonance spectroscopy. Our data demonstrate a presence of nanometre scale hexagonal regions coexisting with tetragonal host lattice, a chemical disorder demonstrating non homogeneous distribution of host atoms in the crystal lattice, as well as hundreds-of-nanometres-long iron-deficient bands. From magnetic data and ferromagnetic resonance temperature dependence, we attribute magnetic phases in Fe-Te-Se to Fe3O4 inclusions and to hexagonal symmetry nanometre scale regions with structure of Fe7Se8 type. Our results suggest that nonhomogeneous distribution of host atoms might be an intrinsic feature of superconducting Fe-Te-Se chalcogenides and we find a surprising correlation indicating that faster grown crystal of inferior crystallographic properties is a better superconductor.Comment: 16 pages, 8 figures, 2 table

Food Supply and Seawater pCO2 Impact Calcification and Internal Shell Dissolution in the Blue Mussel Mytilus edulis

Progressive ocean acidification due to anthropogenic CO2 emissions will alter marine ecosytem processes. Calcifying organisms might be particularly vulnerable to these alterations in the speciation of the marine carbonate system. While previous research efforts have mainly focused on external dissolution of shells in seawater under saturated with respect to calcium carbonate, the internal shell interface might be more vulnerable to acidification. In the case of the blue mussel Mytilus edulis, high body fluid pCO2 causes low pH and low carbonate concentrations in the extrapallial fluid, which is in direct contact with the inner shell surface. In order to test whether elevated seawater pCO2 impacts calcification and inner shell surface integrity we exposed Baltic M. edulis to four different seawater pCO2 (39, 142, 240, 405 Pa) and two food algae (310–350 cells mL−1 vs. 1600–2000 cells mL−1) concentrations for a period of seven weeks during winter (5°C). We found that low food algae concentrations and high pCO2 values each significantly decreased shell length growth. Internal shell surface corrosion of nacreous ( = aragonite) layers was documented via stereomicroscopy and SEM at the two highest pCO2 treatments in the high food group, while it was found in all treatments in the low food group. Both factors, food and pCO2, significantly influenced the magnitude of inner shell surface dissolution. Our findings illustrate for the first time that integrity of inner shell surfaces is tightly coupled to the animals' energy budget under conditions of CO2 stress. It is likely that under food limited conditions, energy is allocated to more vital processes (e.g. somatic mass maintenance) instead of shell conservation. It is evident from our results that mussels exert significant biological control over the structural integrity of their inner shell surfaces

Abiotic conditions in cephalopod (Sepia officinalis) eggs: embryonic development at low pH and high pCO2

Low pO(2) values have been measured in the perivitelline fluids (PVF) of marine animal eggs on several occasions, especially towards the end of development, when embryonic oxygen consumption is at its peak and the egg case acts as a massive barrier to diffusion. Several authors have therefore suggested that oxygen availability is the key factor leading to hatching. However, there have been no measurements of PVF pCO(2) so far. This is surprising, as elevated pCO(2) could also constitute a major abiotic stressor for the developing embryo. As a first attempt to fill this gap in knowledge, we measured pO(2), pCO(2) and pH in the PVF of late cephalopod (Sepia officinalis) eggs. We found linear relationships between embryo wet mass and pO(2), pCO(2) and pH. pO(2) declined from > 12 kPa to less than 5 kPa, while pCO(2) increased from 0.13 to 0.41 kPa. In the absence of active accumulation of bicarbonate in the PVF, pH decreased from 7.7 to 7.2. Our study supports the idea that oxygen becomes limiting in cephalopod eggs towards the end of development; however, pCO(2) and pH shift to levels that have caused significant physiological disturbances in other marine ectothermic animals. Future research needs to address the physiological adaptations that enable the embryo to cope with the adverse abiotic conditions in their egg environment

Ocean acidification and temperature rise: effects on calcification during early development of the cuttlefish Sepia officinalis

This study investigated the effects of seawater pH (i.e., 8.10, 7.85 and 7.60) and temperature (16 and 19 °C) on (a) the abiotic conditions in the fluid surrounding the embryo (viz. the perivitelline fluid), (b) growth, development and (c) cuttlebone calcification of embryonic and juvenile stages of the cephalopod Sepia officinalis. Egg swelling increased in response to acidification or warming, leading to an increase in egg surface while the interactive effects suggested a limited plasticity of the swelling modulation. Embryos experienced elevated pCO2 conditions in the perivitelline fluid (>3-fold higher pCO2 than that of ambient seawater), rendering the medium under-saturated even under ambient conditions. The growth of both embryos and juveniles was unaffected by pH, whereas 45Ca incorporation in cuttlebone increased significantly with decreasing pH at both temperatures. This phenomenon of hypercalcification is limited to only a number of animals but does not guarantee functional performance and calls for better mechanistic understanding of calcification processes