Absence of room temperature ferromagnetism in bulk Mn-doped ZnO

Structural and magnetic properties have been studied for polycrystalline Zn_1-xMn_xO (x=0.02, 0.03, 0.05). Low-temperature (~500 oC) synthesis leaves unreacted starting ZnO and manganese oxides. Contrary to a recent report, no bulk ferromagnetism was observed for single-phase materials synthesized in air at temperatures above 900 oC. Single-phase samples show paramagnetic Curie-Weiss behavior.Comment: Accepted for publication in J. Appl. Phys., RevTeX, 3 pages, 4 figure

Absence of ferromagnetism in Co and Mn substituted polycrystalline ZnO

We discuss the properties of semiconducting bulk ZnO when substituted with the magnetic transition metal ions Mn and Co, with substituent fraction ranging from $x$ = 0.02 to $x$ = 0.15. The magnetic properties were measured as a function of magnetic field and temperature and we find no evidence for magnetic ordering in these systems down to $T$ = 2 K. The magnetization can be fit by the sum of a Curie-Weiss term with a Weiss temperature of $\Theta\gg$100 K and a Curie term. We attribute this behavior to contributions from both \textit{t}M ions with \textit{t}M nearest neighbors and from isolated spins. This particular functional form for the susceptibility is used to explain why no ordering is observed in \textit{t}M substituted ZnO samples despite the large values of the Weiss temperature. We also discuss in detail the methods we used to minimize any impurity contributions to the magnetic signal.Comment: 6 pages, 4 figures (revised

The combined effects of ionizing radiation and weightlessness on calcium and phosphorus content in the mineral fraction of the calcified tissues in the rat skeleton

Phosphorus and calcium content in the ash from skeletal bones (ribs, scapula, vertebra, and crus) of 30 rats exposed to ionizing radiation (800 rads) on the flight of the Kosmos 690 biosatellite was studied. A 10 percent decrease in ash content coefficient and 29 percent decrease in phosphorus content was found immediately after the flight, and a 9 percent decrease in phosphorus content persisted after 26 days of readaptation to terrestrial conditions

Integrated assessment of the environmental hazard level of technologies of drilling and blasting operations with using emulsion explosives in quarries

Purpose. Adaptation of the “unified method of quantitative and qualitative assessment of the level of environmental hazard of the operation of industrial enterprises, facilities and introduced technologies in the field of production and ecology” to the technologies of drilling and blasting operations in quarries for extraction of ore and nonmetallic materials with the use of various types of explosives. The methods. They are based on a heuristic evaluation of the impact of priority man-made factors of the technologies used according to the 4-point scale (0, 1, 2, 3), and then – of the complex level of their environmental hazard – according to the total 15-point scale, evenly divided into three qual-itative levels. Findings. The identification of types and sources of environmental hazard for natural environments (atmosphere, hydrosphere, lithosphere, soils and biota) was performed when using emulsion and TNT-containing explosives during drilling and blasting operations in quarries. The intensity, perio-dicity and consequences of various accompanying man-made factors were taken as the criteria of influence of dangerous impact of technological processes on the condition of the above natural en-vironments. It was found that the integrated level of the environmental hazard of man-made impacts of drilling and blasting operations using emulsion explosives was 2.33, in other words, it was “low”. When using TNT-containing explosives it was 5.00, i.e. appeared on the boundary of the first and the second ranges, where the “low” hazard level changes to “moderate”. This is an evi-dence of a higher (more than 2 times) environmental efficiency of using emulsion explosives com-pared to the use of TNT-containing explosives. The originality. The system of identification and management of environmental and technology-related risks under conditions of extraction of ore and nonmetallic materials in quarries by the drill and blast method was proposed, whereupon an integrated assessment of the level of environmental hazard of mining enterprises is proposed to be defined as a sum of average grade points (for each of the man-made factors) according to quantitative-qualitative scale. Practical implications. The developed methods allow determining with a sufficient degree of reli-ability the level of environmental hazard of existing technologies of drilling and blasting operations and substantiating expediency of change-over to emulsion explosive materials

The effect of hypodynamia on mineral and protein metabolism in calcified tissues of the maxillodental system (experimental radioisotope study)

Mineral and protein metabolism was studied in experiments on 60 white rats, using P-32 and Ca-45 uptake in the mineral fractions, 2C-14-glycine in the protein fractions, and P-32 in both fractions of calcified tissues as indices over a 100 day period of experimental hypodynamia. Combined alterations in mineral and protein metabolism occurred in the calcified tissues of the experimental animals. The most pronounced changes were found in P-32 and 2C-14-glycine metabolism. In the incisors and femoral bones, these alterations occurred in two phases: P-32 and 2C-14-glycine uptake first increased, then decreased. Changes in Ca-45 metabolism were less pronounced, particularly in the initial period of the experiment. A marked reduction in P-32, Ca-45, and 2C-14-glycine uptake was found in various fractions of the calcified tissues on the 100th day of experimental hypodynamia

Effect of space flight on sodium, copper, manganese and magnesium content in the skeletal bones

Sodium content decreased in the human skeletal bones and rose in the rat bones following space flight. In man copper content rose in the femoral bone and decreased in the vertebral body and the sternum, but was unchanged in the rest of the bones. Magnesium content was decreased in the femoral bone and the sternum, and in the vertebrae, but remained unchanged in the rest of the bones. Possible mechanisms of the changes detected are discussed

Biophysical parameters of the oral fluid and cells of the buccal epithelium in children with diseases of the thyroid gland in the course of orthodontic treatment of maxillodental anomalies.

The thyroid status disturbance may be reflected on the biological processes which underlie orthodontic tooth movement. Aim of research – to study state of the oral fluid and buccal epithelium cells (BEC) in the course of a complex orthodontic treatment of children with thyroid gland diseases. In 79 children with a diffuse nontoxic goiter (DNG) of the I-III degrees, stability of oral fluid pH (ΔpH), rate of mobile nuclei of BEC, ratio of electrophoretic displacement range of nuclei and plasmolemms was estimated. Estimation of corresponding parameters in the initial state, in 1, 3, 6 and 8 months after fixation of the fixed orthodontic apparatus was carried out. Children of the basic group according to pathology degree in addition received a prophylactic complex including preparations: “Vitrum Perfomens", "Teraflex", "Kalcicor", «Potassium iodide», «Echinacea compositum C», "Lizodent", "Osteobios". Ap­plication of the prophylactic complex in orthodontic treatment of children with DNG prevented growth of ΔрН after fixation of brackets. Throughout all time of supervision it promoted reduction of this rate which slightly exceeded average rate for the given age of children in 8 months. Application of this prophylactic complex already in 1 month after fixation of brackets has raised quantity of mobile BEC nuclei by 44% and by 1,64 times has increased the relation of ranges of plasmolemms and nuclei displacement. In 8 months of supervision percent of mobile nuclei BEC and the relation of Apl/Aya in the basic group was by 2 times more, than in a comparison group, approaching to average rate. Сhildren with thyroid gland diseases need active treatment-and-prophylactic measures at stages of active apparatus treatment. The developed therapeutic complexes of orthodontic treatment of maxillo-dental anomalies in children with DNG allows to effectively support and improve functional reactions in the organism and in the oral cavity, compensating stressful action of fixed orthodontic apparatuses

Tuning of magnetic and electronic states by control of oxygen content in lanthanum strontium cobaltites

We report on the magnetic, resistive, and structural studies of perovskite La$_{1/3}$Sr$_{2/3}$CoO$_{3-\delta}$. By using the relation of synthesis temperature and oxygen partial pressure to oxygen stoichiometry obtained from thermogravimetric analysis, we have synthesized a series of samples with precisely controlled $\delta=0.00-0.49$. These samples show three structural phases at $\delta=0.00-0.15$, $\approx0.25$, $\approx0.5$, and two-phase behavior for other oxygen contents. The stoichiometric material with $\delta=0.00$ is a cubic ferromagnetic metal with the Curie temperature $T_{\rm C}=274$ K. The increase of $\delta$ to 0.15 is followed by a linear decrease of $T_{\rm C}$ to $\approx$ 160 K and a metal-insulator transition near the boundary of the cubic structure range. Further increase of $\delta$ results in formation of a tetragonal $2a_p\times 2a_p \times 4a_p$ phase for $\delta\approx 0.25$ and a brownmillerite phase for $\delta\approx0.5$. At low temperatures, these are weak ferromagnetic insulators (canted antiferromagnets) with magnetic transitions at $T_{\rm m}\approx230$ and 120 K, respectively. At higher temperatures, the $2a_p\times 2a_p \times 4a_p$ phase is $G$-type antiferromagnetic between 230 K and $\approx$360 K. Low temperature magnetic properties of this system for $\delta<1/3$ can be described in terms of a mixture of Co$^{3+}$ ions in the low-spin state and Co$^{4+}$ ions in the intermediate-spin state and a possible spin transition of Co$^{3+}$ to the intermediate-spin state above $T_{\rm C}$. For $\delta>1/3$, there appears to be a combination of Co$^{2+}$ and Co$^{3+}$ ions, both in the high-spin state with dominating antiferromagnetic interactions.Comment: RevTeX, 9 pages, 7 figures, to be published in Physical Review