Cr Temperature Research Articles

Ferromagnetic half-metal with high Curie temperature in Cr P nanoribbons: good material for spintronic applications.

In this work, the stability, and electronic, magnetic, and transport characteristics of chromium phosphorus nanoribbons (CrPNRs) have been investigated. The results, obtained from the non-equilibrium Green's function and density functional theory, indicate that the nanoribbon is stable in terms of binding energies as well as dynamically. The calculated electronic structure shows that this nanoribbon has an indirect band gap of about 1.67 eV for the spin-down channel and is metallic for the spin-up channel. The metallicity of the spin-up channel originates from the P-3p orbitals and the magnetic properties are due to the Cr-3d orbitals. The obtained transport properties indicate the value of the current for the spin-up state is about 50 μA. The negative differential resistance (NDR) phenomenon and also a 100% spin filtering effect are seen between voltages of 0.4 and 0.5 V. The results showed that CrPNRs have a high Curie temperature of more than 690 K, indicating that this nanoribbon is a useful ferromagnetic material for nanoelectronic devices and spintronic applications at ambient temperature.

Modes of Occurrence of Chromium and Their Thermal Stability in Low-Rank Coal Pyrolysis

Chromium (Cr) and the emission of its compounds into the environment have caused long-term environmental contamination. In this study, the modes of occurrence of Cr in low-rank coal and their thermal stability in pyrolysis were investigated by sequential chemical extraction (SCE), single-component samples (SCS) pyrolysis, and thermochemical equilibrium simulation. The results showed that organic matter, aluminosilicate, and carbonate were the dominant modes of occurrence of Cr in low-rank coal. The modes of occurrence and chlorine (Cl) content affected the volatilization of Cr in coal. The characteristic release temperature range of Cr bounded to aluminosilicate was >600 °C and 400–600 °C for Cr bounded to a disulfide. Cr bounded to organic matter almost released completely before 600 °C. Cl enhanced the volatility of Cr and reduced its release temperature in Cr bounded to aluminosilicate. The simulation showed the content of gas products was very low, mainly chlorides. While the content of solid products, sulfides, and oxides, was much higher than gas products, showing their high thermal stability. The sulfides and oxides in chars were closely related to the carbonate and aluminosilicate bound form of Cr. The results of the equilibrium simulation were consistent with the experimental results.

Energy and exergy analysis of hydrogen production from ammonia decomposition systems using non-thermal plasma

In the current study, the energy and exergy efficiencies of three hydrogen production systems from ammonia decomposition using dielectric barrier discharge plasma (DBD) were comparatively evaluated. The hydrogen gas was separated in a cylindrical plasma membrane reactor (PMR) using the Pd–Cu40% membrane with a thickness of 20 μm. The pre-catalytic reactor (CR) is added to the second system (CR-PMR), additionally, the CR is filled with the catalytic material type of 2%Ru/Al2O3 and the CR temperature is raised to 450 °C. Furthermore, the zeolite material type of SA-600 A was added to the PMR in the third H2 production system (PMR) to enhance the hydrogen permeation through the Pd–Cu membrane. The hydrogen production rate was enhanced by combining the plasma and zeolite material in the third system (CR-CPMR). Moreover, the maximum obtained hydrogen production rates were 2.66, 81.6, and 96.6% in PMR, CR-PMR, and CR-CPMR or catalytic PMR, respectively. Also, it was observed that the energy efficiency increased by adding the CR to the system, while, the exergy efficiency values of all ammonia decomposition systems were still low due to the effect of system irreversibility. Additionally, the maximum energy efficiencies values were 0.8, 16.1, 44.1%, while the maximum exergy efficiencies values were 0.156, 4.91, and 6.344% for PMR, CR-PMR, and CR-CPMR, respectively. The exergy destruction rate of all NH3 decomposition systems was still high although using the modified systems. The depletion factor is enhanced with the feeding ammonia flow rate increased while the sustainability index decreased at the same flow rates. Moreover, it was seen that the depletion factor results of PMR only were higher than other systems due to the exergy destruction rate was high.

Evidence of the Topological Hall Effect in Pt/Antiferromagnetic Insulator Bilayers.

The topological Hall effect has been a primary indicator of nontrivial spin textures in magnetic materials. We observe the evidence of the topological Hall effect in Pt/Cr_{2}O_{3} bilayers grown on Al_{2}O_{3}(0001) and Al_{2}O_{3}(112[over ¯]0), where the Cr_{2}O_{3} epitaxial film is an antiferromagnetic insulator. The Pt/Cr_{2}O_{3} bilayers exhibit topological Hall resistivity for Cr_{2}O_{3} thicknesses below 6nm near and above room temperature, which is above the Néel temperature of Cr_{2}O_{3}, revealing the key role of thermal fluctuations in the formation of spin textures. The similarity of topological Hall signals in (0001)- and (112[over ¯]0)-oriented Cr_{2}O_{3} films indicates that the emergence of spin textures is insensitive to crystalline orientation.

Calorie Restriction, Longevity and Cognitive Function

besity is one of the most serious problems of public health and the fifth leading cause of death. It is estimated that 44% of diabetic load, 23% of heart ischemic load and 7-41% of all cancers load are related to obesity. Approximately 80% of older adults (+65years) have at least one of the above mentioned chronic diseases, and 50% have at least two chronic disease (1). Along with other organs, brain is also affected with aging and high calorie intake as Fitzpatrik and colleagues suggested in a review article that obese people have problems on decision-making, planning and solving skill, with fewer difficulties on the tasks of verbal fluency, learning and memory (2). In contrast, a reduction of calorie intake without malnutrition called “calorie restriction” (CR) has a wide range of benefits. Moderate CR can prevent or reverse the damaging effects of overweight/obesity, type 2 diabetes, hypertension, chronic inflammation and other age-associated metabolic diseases (1). As the first groups who worked on CR, Osborne et al. in 1917 showed that reducing calorie intake in rats increased their length of life. Since then, large amount of time and research efforts have been and continued to be devoted to the study of anti-aging and anti-cancer mechanisms underlying CR in yeasts, worms, insects, rodents and humans (3). Significant increase in life span has been reported when the nutrient availability drops between 30% and 75% of normal calorie provision, according to the species. Not only calorie restricted rodents lived longer than the adlibitum-fed counterparts but a significant part of them (about 30%) died without any apparent pathology, raising the striking possibility that aging is not necessarily tightly linked with costly pathologies (4). Preliminary results from human studies are reproducing many of the metabolic and physiological responses sobserved in rodents and monkeys. Short term CR (6-24 months) induces reduction of body weight, subcutaneous and visceral fat, lean body mass, insulin, energy expenditure, and core body temperature (5). Core body temperature, levels of dehydro-epiandrosterone sulfate (DHEAS) and insulin are biomarkers of CR and longevity in human similar to rodents and monkeys. In a 6-month CR related study on overweight individuals, a significant reduction of fasting insulin levels and core body temperature in CR and CR with exercise group has been reported; however, DHEAS and fasting glucose remained unchanged, as DHEAS falls 2-4% per year in humans. The other hypothesis to explain the antiaging effects of CR is reduced energy expenditure with a consequent reduction in the production of reactive oxygen species (ROS). In this study, a metabolic adaptation over 24 hours following 6 months of CR has also occurred (6). CR decreases serum insulin-like growth factor1 (IGF-1) concentration by approximately 40% in rodents. This is a key role in protection against cancer and slowing age; as IGF-1 promotes tumor development and inhibits apoptosis (3). Cognitive impairment and calorie restriction Evidence from clinical and basic researches points to a deep connection between brain function decline and metabolic dysregulation during senescence. Excess nutrient availability may be detrimental to brain function. Conversely, a 30% reduction in O

IN-VITRO BIOREDUCTION OF HEXAVALENT CHROMIUM BY VIABLE WHOLE CELLS OF Arthrobacter sp. SUK 1201

A chromium resistant and reducing bacterium Arthrobacter sp. SUK 1201 was isolated from chromite mine overburden dumps of Orissa, India. Viable whole cells of this isolate was capable of completely reducing 100 µM Cr(VI) in chemically defined MS medium within 28 h of incubation under batch cultivation. Reduction of chromate increased with increased cell density and was maximum at a density of 1010 cells/ml, but the reduction potential of the suspended cells decreased with increase in Cr(VI) concentration in the medium. Chromate reducing efficiency was promoted when glycerol and glucose was used as electron donors, while the optimum pH and temperature of Cr(VI) reduction was found to be 7.0 and 35°C respectively. The reduction process was inhibited by divalent cations Ni, Co and Cd, but not by Cu and Fe. Similarly, carbonyl cyanide m-chlorophenylhydrazone (CCCP), N,N,-Di cyclohexyl carboiimide (DCC), sodium azide and sodium fluoride were inhibitory to chromate reduction, while in presence of 2,4 dinitrophenol (2,4 DNP) chromate reduction by SUK 1201 cells remained unaffected.

Optimization of cultural conditions for growth associated chromate reduction by Arthrobacter sp. SUK 1201 isolated from chromite mine overburden

Arthrobacter sp. SUK 1201, a chromium resistant and reducing bacterium having 99% sequence homology of 16S rDNA with Arthrobacter sp. GZK-1 was isolated from chromite mine overburden dumps of Orissa, India. The objective of the present study was to optimize the cultural conditions for chromate reduction by Arthrobacter sp. SUK 1201. The strain showed 67% reduction of 2mM chromate in 7 days and was associated with the formation of green insoluble precipitate, which showed characteristic peak of chromium in to energy dispersive X-ray analysis. However, Fourier transform infrared spectra have failed to detect any complexation of end products of Cr(VI) reduction with the cell mass. Reduction of chromate increased with increased cell density and was maximum at 1010cells/ml, but the reduction potential decreased with increase in Cr(VI) concentration. Chromate reducing efficiency was promoted when glycerol and glucose was used as electron donors. Optimum pH and temperature of Cr(VI) reduction was 7.0 and 35°C respectively. The reduction process was inhibited by several metal ions and metabolic inhibitors but not by Cu(II) and DNP. These findings suggest that Arthrobacter sp. SUK 1201 has great promise for use in Cr(VI) detoxification under a wide range of environmental conditions.

Application of magnetic extractant for the removal of hexavalent chromium from aqueous solution in high gradient magnetic separator

In this paper, we proposed a simple, rapid and continuous method of solvent extraction for hexavalent chromium from aqueous solution in high gradient magnetic separator. We constructed the theoretical modeling of the extraction and introduced the original so-called “magnetic extractant”. The feasibility of extraction using this method was verified by the experiments. The static force analysis and force balance of the magnetic extractant in separator were studied. The extraction efficiency of magnetic extractant and the porosity in separator were related to the accumulation radius. By the mathematical derivation, the accumulation radius was determined by magnetic susceptibilities of the magnetic extractant, intensity of the background magnetic field and wire radius. The influences of the designs of ferromagnetic filler in separator, types of diluent, pH values of Cr (VI) feed solution, the extractant concentration, flow rate, and temperature of Cr (VI) solution in separator were investigated. The results showed that extraction efficiency increased with the decrease of pH value and flow rate of Cr (VI) aqueous solution, and increased with the increase of TBP concentration and temperature. Under the optimum conditions, the proposed method obtained a high extraction capacity with continuous extraction process of 6h and 1800ml Cr (VI) aqueous solution.

Magnetism of Cr in V/Crmultilayers studied by 119Sn Mössbauer spectroscopy

The magnetic properties of thin Cr layers in epitaxial V/Crmultilayered structures were investigated at room temperature and 15 K via 119Sn Mössbauer spectroscopy. The magnetic moment andthe Néel temperature of Cr, as inferred from the magnetichyperfine fields transferred to the 119Sn monatomic layersinserted in Cr layers, were found to reduce on decreasing the Crlayer thickness below 40 Å. The local magnetic structure alongthe growth direction of 80 Å thick Cr layers was investigated bychanging the Sn probe positions. The effect of the V/Cr interfaceon the Cr magnetism is discussed.

The ESR Study on Langmuir-Blodgett Films Layered with Ammontum-TCNQ Anion Radical Salts

Abstract Ammonium TCNQ anion radicals are formed with a TCNQ anion radical and an ammonium halide. Octadecylviologen-(TCNQ)2 shows a very interesting UV-visible spectrum in chloroform-acetonitrile mixture and in Langmuir-Blodgett films. The ESR characteristics of the N-docosylquinolinium-TCNQ films and octadecylviologen-(TCNQ)2 powder and films were studied to understand conducting mechanism and structure of LB films. The ESR spectra infer that the N-docosylquinolinium-TCNQ LB films exhibit anisotropic property. In other words, the LB films show angular dependence. Rotating the LB films around magnetic field results in a minimum band width at an angle close to the magic angle 54°. This results was due to the dipole-dipole interaction. The ESR spectra of octadecylviologen-(TCNQ)2 powders exhibit a narrow line at g=2 together with symmetrical structure of a triplet state arising from a dimeric species, genetic species. The LB films and powder do not show angular dependence. In the course of temperature incr...

Mössbauer spectroscopy of Cr(110)/Fe(110)/Cr(110) sandwiches

Magnetic order in ultrathin Fe(110) films in a Cr(110) matrix and its temperature dependence were analyzed using conversion electron Mössbauer spectroscopy (CEMS). The samples were characterized by flat interfaces, as tested by SPA-LEED (spot profile analysis LEED). Fe films consisting of D atomic layers with 1 ≤ D ≤ 31 were doped by 57Fe probes and analyzed using CEMS in situ in UHV, for 100 K ≤ T ≤ 450 K. All spectra could be fitted by Zeeman sextets with B hf( T) following Bloch laws. For films with 2 ≤ D ≤ 6, the first Fe layer in the CrFe interface shows a reduced ground state hyperfine field of B s(0) = 25.8 T, which differs from values determined previously for rough interfaces. It agrees roughly with the predictions from an alloy model. Spin-wave parameters are reduced in comparison with samples W(110)/Fe/Ag. For thicker films ( D > 6), two subcomponents of the interface can be distinguished, with equal abundance, but different hyperfine fields and different b parameters; apparently they belong to two magnetically inequivalent states resulting from the antiferromagnetic order in Cr. Extraordinary low values for the surface enhancement of the b parameters, α s, a = 1.5 and α s, b = 1.1, respectively, and a large value of 10 atomic distances for the interaction length are explained by the antiferromagnetic order of the matrix. The low values for the surface enhancement of the spin-wave parameters differ strongly from results reported for the case of rough interfaces. For the double layer, a break of B hf( T) was observed near the Néel temperature of Cr. Parameters of the monolayer could be roughly determined.

Magnetic properties of Mn 1− xTi xSb and Cr 1− xCo xSb (O⩽ x⩽1)

Magnetic measurements have been carried out on Mn 1− x Ti x Sb and Cr 1− x Co x Sb. The behavior near the magnetic critical concentration brings out the contrast between two systems. A spin glass phase is found in Mn 1− x Ti x Sb with 0.70≲ x≲0.90. The Néel temperature of Cr 1− x Co x Sb falls drastically with increasing x and around x=0.5 and approaches 0 K at x=0.55. The behavior of the latter system is attributed to the concentration-dependent magnetic moment of Cr atoms.

Universal behaviour of thermal and electrical transport coefficients near the néel temperature of Cr 99.94Al 0.06

Measurements of electrical and thermal transport coefficients in the antiferromagnetic alloy Cr 99.94Al 0.06 reveal an anomaly near the Néel temperature T N . Temperature derivatives of the electrical resistivity and thermo-power are analysed and are shown to be proportional to each other above and below T N in the reduced temperature range 6 × 10 −2 ⩾| t|⩾ 4 × 10 −4. This is consistent with the theoretical prediction of a universal critical behaviour of all transport coefficients.

Photoemission study of the chromium(111) surface interacting with oxygen

The interaction of the Cr(111) surface with O 2 was studied by means of X-ray and UV photoemission and also work function measurements. A strong oxygen adsorption was found even at very low exposures, suggesting a high sticking coefficient. Previous treatments of the clean surface such as argon-ion bombardment or annealing result in significant changes of the surface structure reflected on work function and adsorption kinetics. No work function change was observed in the initial stage of adsorption, ruling out a model of chemisorption on top. In this range the sticking coefficient remains also constant, supporting a model of rapid regeneration of the genuine surface sites and incorporation of oxygen into the lattice. But in contrast with non transition metals like Cs or Sr, oxygen absorbed at room temperature in Cr, remains essentially in the topmost layers of the surface. At room temperature this initial stage of oxygen incorporation is followed by chemisorption on the corrosion film obtained when the uppermost layers are saturated with oxygen. The oxide layer has a stoichiometry close to Cr 2O 3 at saturation, but the detailed electronic structure depends on previous thermal treatments. Exposures at room temperature lead to a thin (about 9 Å), probably amorphous corrosion layer with a maximum work function change Δφ = +0.9 eV. Adsorption followed by heating at 500° C results in a much thicker corrosion film with a limiting work function decrease of Δφ = −1.2 eV. The XP and UP spectra differ significantly in both cases and suggest a Fermi level shift of nearly 1 eV connected with oxygen adsorption on the Cr 2O 3 surface. The thickness of the corrosion film may be further increased by heating at 500°C in oxygen. The usual XPS spectra of bulk chromium sesquioxide are then clearly observed.

Field and temperature dependence of critical magnetic relaxation in the anisotropic ferromagnet CrBr3

We present measurements of the dynamic longitudinal susceptibility near the Curie temperature of Cr${\mathrm{Br}}_{3}$ in magnetic fields up to 30 mT applied parallel to the easy magnetic axis. The frequency dependence of $\ensuremath{\chi}$ is monodispersive except very close to ${T}_{c}$, where a second unknown relaxation process comprising a small part of the total $\ensuremath{\chi}$ appears at low frequencies. Above ${T}_{c}$ the critical slowing down of the main (fast) process is explained with the help of recent mode-coupling results as arising from spin-spin relaxation in an uniaxial ferromagnet. With rising magnetic field the relaxation rate increases steeply below the dipolar crossover ($\ensuremath{\epsilon}l0.03$), while above it a gradual decrease is found. Both observations seem to be inconsistent with existing ideas about the field effect on critical relaxation. Below ${T}_{c}$ the fast (para-) process is observed to speed up again.

Antiferromagnetism in Chromium and its Alloys

Recent experimental and theoretical work on itinerant antiferromagnetism in Cr and its alloys is reviewed with particular emphasis on optical and pressure effects. At low temperatures, a peak appears in the infrared conductivity of Cr which is attributed to excitation of electrons across the antiferromagnetic energy gap. The maximum in absorption occurs at photon energy 5.1kTN, at low temperatures, which is substantially higher than the value 3.5kTN predicted by the simplest models. Both the position and shape of the absorption can be explained if the effects of electron-phonon scattering are incorporated in the model. The pressure dependence of the Néel temperature of Cr and alloys with Mo and V is described. The role of band structure is discussed, particularly its effect on the vanishing of antiferromagnetism under pressure.