Itinerant magnetism in metallic CuFe2Ge2

Theoretical calculations are performed to understand the electronic structure and magnetic properties of CuFe$_2$Ge$_2$. The band structure reveal large electron density $N(E_F)$ at the Fermi level suggesting strong itinerant character of magnetism. The Fermi surface is dominated by two dimensional sheet like structures, with potentially strong nesting between them. The magnetic ground state appears to be ferromagnetic along $a$ and antiferromagnetic in other directions. The results show that CuFe$_2$Ge$_2$ is an antiferromagnetic metal, with similarities to the Fe-based superconductors; such as magnetism with substantial itinerant character and coupling between magnetic order and electrons at the Fermi energy.Comment: 5 pages, 6 figure

Magnetic properties of Mn-doped Ge46 and Ba8Ge46 clathrates

We present a detailed study of the magnetic properties of unique cluster assembled solids namely Mn doped Ge46 and Ba8Ge46 clathrates using density functional theory. We find that ferromagnetic (FM) ground states may be realized in both the compounds when doped with Mn. In Mn2Ge44, ferromagnetism is driven by hybridization induced negative exchange splitting, a generic mechanism operating in many diluted magnetic semiconductors. However, for Mn-doped Ba8Ge46 clathrates incorporation of conduction electrons via Ba encapsulation results in RKKY-like magnetic interactions between the Mn ions. We show that our results are consistent with the major experimental observations for this system.Comment: 6 pages, 4 figure

Evaluvation of Anti-Oxidant and Hepatoprotective Activity of Ixorea Coccinea Leaf Extracts by Using Invitro and Invivo Models

INTRODUCTION: ANATOMY OF LIVER:The liver is one of largest gland in the body and after the dermis1. The liver weights about three and a half pounds (1.6 kg). It constitutes about 2.5% of adult’s body weight2. It is located in the upper part of the abdomen that aids in digestion and removes waste products and worn-out cells from the blood. Liver is connected to two large blood vessels which include hepatic artery and portal vein2. Thirty percentage blood was pumped by the heart for one minute for body’s chemical factorial organ called liver. Liver cleanses blood and processes nutritional molecule that are distributed to the tissues. Liver accept nutritional red blood by portal circulation from lungs which has filled with essential oxygen supplied to heart. It is situated in the upper part of the abdominal cavity, inferior to the diaphragm occupying the greater part of the right hypochondriac region, part of the epigastric region and extending into the left hypochondriac region. Its upper and anterior surfaces are smooth and curved to fit the under surface of the diaphragm and its posterior surface is irregular in outline3. The different types of cells propagate from the liver lobes are parenchymal and non-parenchymal type of cells. Majority (about 80%) of the liver mass is filled by parenchymal type of cells commonly known as hepatocytes. the other type non-parenchymal type cells having forty percentage of the total counts of the liver cells but it have 6.5% of its total volume2. It also release about two and one-half ml of the bile in its own ducts which is delivered by a gallbladder via congested tube called the cystic duct for storage of these bile. Liver is regulated for this gland that control as to whether these incoming substances was useful for body or whether they are needless. Liver is an extremely important organ and exhibits multiple functions. Liver detoxifies for blood cells by proper fixation of bile solution via chemical modification to form less toxic substances, example alteration of ammonia to urea. Many chemical substances are inactivated by liver through modification of chemical structure. Liver convert glucose to glycogen as a storage form of energy and it produces glucose from disaccharides and polysaccharides such as sugars, starches and protein molecules AIM AND OBJECTIVES: Plants that cure liver diseases so considerable interest has developed in the examination of these numerous plants remedies which are useful in liver diseases. So it is necessary to find new drugs of importance in hepato protective activity with fewer side effects. Moreover it is necessary to produce scientific validation to drugs of herbal origin in common use under Ayurvedic Siddha Unani systems of medicine. Why I have to select this particular disease is few effective drugs available for modern therapy, it produce side effect during the treatment is worse than the condition of liver damage Phytochemical investigation will be a useful tool for the identification and authentication of the plant for industrial and further research purpose. Total phenol content of a tested material is related to the antioxidant activity. Antioxidants, which can scavenge free radicals, have an important role in pharmacological systems. Antioxidants are emerging as prophylactic and therapeutic agents. Hence, antioxidant was also evaluated for the potent extract. And now I have undertaken the study of evaluation of anti-oxidant and hepatoprotective activity of ixorea coccinea leaf extracts by various hepatotoxin induced albino rat models 1. To select plant based on their ethno medical uses and preparation of their extracts. 2. To screen phytochemical profile. 3. To screen the selected extract for antioxidant using various in vitro methods 4. To screen the potent plant extract for their in vivo hepatoprotective activities CONCLUSION: Hepatoprotective study results shows that the levels of SGOT, SGPT, ALP and Total Bilirubin were significantly improvement may accounts hepatoprotective activity All these observation imply that the ICLE could be regarded as a favorable antioxidant and hepatoprotective agents. As the results indicated that the extract possess significant hepatoprotective activity, after carrying out a thorough study of clinical trials, the plant can be considered as a low cost, potent, herbal medicine for liver disorders

Growth and Characterization of Ce- Substituted Nd2Fe14B Single Crystals

Single crystals of (Nd1-xCex)2Fe14B are grown out of Fe-(Nd,Ce) flux. Chemical and structural analysis of the crystals indicates that (Nd1-xCex)2Fe14B forms a solid solution until at least x = 0.38 with a Vegard-like variation of the lattice constants with x. Refinements of single crystal neutron diffraction data indicate that Ce has a slight site preference (7:3) for the 4g rare earth site over the 4f site. Magnetization measurements show that for x = 0.38 the saturation magnetization at 400 K, a temperature important to applications, falls from 29.8 for the parent Nd2Fe14B to 27.6 (mu)B/f.u., the anisotropy field decreases from 5.5 T to 4.7 T, and the Curie temperature decreases from 586 to 543 K. First principles calculations carried out within density functional theory are used to explain the decrease in magnetic properties due to Ce substitution. Though the presence of the lower-cost and more abundant Ce slightly affects these important magnetic characteristics, this decrease is not large enough to affect a multitude of applications. Ce-substituted Nd2Fe14B is therefore a potential high-performance permanent magnet material with substantially reduced Nd content.Comment: 11 Pages, 8 figures, 5 table

Enhancement of Friction between Carbon Nanotubes: An Efficient Strategy to Strengthen Fibers

Interfacial friction plays a crucial role in the mechanical properties of carbon nanotube based fibers, composites, and devices. Here we use molecular dynamics simulation to investigate the pressure effect on the friction within carbon nanotube bundles. It reveals that the intertube frictional force can be increased by a factor of 1.5 ~ 4, depending on tube chirality and radius, when all tubes collapse above a critical pressure and when the bundle remains collapsed with unloading down to atmospheric pressure. Furthermore, the overall cross-sectional area also decreases significantly for the collapsed structure, making the bundle stronger. Our study suggests a new and efficient way to reinforce nanotube fibers, possibly stronger than carbon fibers, for usage at ambient conditions.Comment: revtex, 5 pages, accepted by ACS Nano 10 Dec 200

Tight binding model for magneto-crystalline anisotropy in MnBi

Abstract With the help of density functional theory based first-principles calculations and a tightbinding model Hamiltonian we studied the origin of magnetic properties in the ferromagnet MnBi. The model Hamiltonian show that direct electron hopping within the nearest and next nearest Bi-p orbitals are responsible for the large band dispersions. The Mn-d bands are fairly narrow with band widths < 2 eV. A Stoner model with spin-orbit coupling leads to the observed negative MAE with this Hamiltonian

First principles calculations on the effect of pressure on SiH₄(H₂)₂

The effect of pressure on the strength of H₂ covalent bond in the molecular solid SiH₄(H₂)₂ has been investigated using quantum molecular dynamics simulations and charge density analysis. Our calculations show, in agreement with the implications of the experimental results, that substantial elongation of H₂ bond can be achieved at low pressures, with the onset of rapid changes close to 40 GPa. Model calculations show redistribution of charge from bonding to antibonding states to be responsible for the behavior. Our computed Raman spectra confirm the dynamic exchange of hydrogen atoms speculated to be operative in SiH₄–D₂ mixture by experiments. This exchange is shown to be a three step process driven by thermal fluctuations

Theoretical model for Rashba spin-orbit interaction in d electrons

We show that the Rashba spin-orbit interaction in d electron solids, which originates from the broken inversion symmetry at surfaces or interfaces, is strongly dependent on the orbital characters of the bands involved. This is studied by developing a tight-binding model in the presence of a uniform perpendicular electric field and spin-orbit coupling. We argue that for valence electrons, the spin-orbit coupling strength scales only as the square of the atomic number. The electric field distorts the d orbitals through the admixture of p and f states and also introduces intersite overlap parameters. Expressions for Rashba coefficients for the bands are obtained in both weak and strong spin-orbit interaction limits and are shown to be orbital dependent. The results are compared with first-principles calculations for model systems, showing good agreement. Our study demonstrates the orbital-dependent gate control of the Rashba effect for the purposes of oxide electronics

Electronic structure of Ba3CuSb2O9: A candidate quantum spin liquid compound

Using density-functional methods, we study the electronic structure of Ba3CuSb2O9, a candidate material for the quantum spin liquid behavior. We study both the triangular lattice as well as the recently proposed hexagonal lattice structures with flipped Cu-Sb dumbbells. The band structure near the Fermi energy is described very well by a tight-binding Hamiltonian involving the Cu (e(g)) orbitals, confirming their central role in the physics of the problem. A minimal tight-binding Hamiltonian for the triangular structure is presented. The Cu (d(9)) ions (a single e(g) hole in the band structure) present in the compound are expected to be Jahn-Teller centers, while the nature of the Jahn-Teller distortions in this material is still under debate. Solving a simple model by exact diagonalization, we show that electronic correlation effects in general enhance the tendency towards a Jahn-Teller distortion by reducing the kinetic energy due to correlation effects. Our density-functional calculations do indeed show a significant Jahn-Teller distortion of the CuO6 octahedra when we include the correlation effects within the Coulomb-corrected GGA+U method, so that the Jahn-Teller effect is correlation driven. We argue for the presence of a random static Jahn-Teller distortion in the hexagonal structure rather than a dynamical one because of the broken octahedral symmetry around the CuO6 octahedra and the potential fluctuations inherently present in the system caused by a significant disorder, which is believed to be present, in particular, due to the flipped Cu-Sb dumbbells