RESUMEN

31P nuclear magnetic resonance (NMR) measurements have been carried out to investigate the magnetic properties and spin dynamics of Fe3+(S= 5/2) spins in the two-dimensional triangular lattice (TL) compound Na3Fe(PO4)2. The temperature (T) dependence of nuclear spin-lattice relaxation rates (1/T1) shows a clear peak around Néel temperature,TN=10.9K, corresponding to an antiferromagnetic (AFM) transition. From the temperature dependence of NMR shift (K) aboveTN, an exchange coupling between Fe3+spins was estimated to beJ/kB≃1.9K using the spin-5/2 Heisenberg isotropic-TL model. The temperature dependence of1/T1Tdivided by the magnetic susceptibility (χ),1/T1Tχ, aboveTNproves the AFM nature of spin fluctuations below∼50 Kin the paramagnetic state. In the magnetically ordered state belowTN, the characteristic rectangular shape of the NMR spectra is observed, indicative of a commensurate AFM state in its ground state. The strong temperature dependence of 1/T1in the AFM state is well explained by the two-magnon (Raman) process of the spin waves in a 3D antiferromagnet with a spin-anisotropy energy gap of 5.7 K. The temperature dependence of sublattice magnetization is also well reproduced by the spin waves. Those results indicate that the magnetically ordered state of Na3Fe(PO4)2is a conventional 3D AFM state, and no obvious spin frustration effects were detected in its ground state.

RESUMEN

A series of disordered Ca1.5La0.5FeRuO6, CaLaFeRuO6 and La2FeRuO6 double perovskites were prepared by the solid-state reaction method and investigated by neutron powder diffraction, X-ray absorption near-edge structure (XANES) analysis at the Ru-K edge, Mössbauer spectroscopy, DC magnetization and resistivity measurements. All compounds crystallize in the orthorhombic crystal structure with the space group Pbnm down to 3 K, showing a random distribution of Fe and Ru at the B site. Thermogravimetric analysis indicates oxygen deficiency in the Ca-rich and formal oxygen hyperstoichiometry in the La-rich members of the present series. While Mössbauer spectra verify the Fe3+ state for all compositions, the XANES study reveals a variable Run+ oxidation state which decreases with increasing La content. The end member actually is a Ru3+/Ru4+ compound with possibly some cation vacancies. From magnetic susceptibility and neutron diffraction measurements, the presence of a G-type antiferromagnetic ordering was observed with a drastic increase in transition temperature from 275 K (Ca1.5La0.5FeRuO6) to 570 K (La2FeRuO6). Mössbauer spectroscopy confirms the presence of long-range ordering but, due to local variations in the exchange interactions, the magnetic states are microscopically inhomogeneous. All the samples are variable range hopping semiconductors. A complex interplay between structural features, charge states, anion or cation defects, and atomic disorder determines the magnetic properties of the present disordered 3d/4d double perovskite series.

RESUMEN

2H-NbSe2 is a phonon-mediated, Fermi-surface topology-dependent multiband superconductor with an incommensurate charge-density wave (CDW) that coexists at a local level with superconductivity. Usually, the intercalation in 2H-NbSe2 enriches the CDW, enhances the c-axis lattice parameter, and distorts the Fermi surface, which result in a decrease in the superconducting transition temperature (Tc). The rate of decrease of Tc depends on the electronic structure, size, valence, magnetic nature, and electronegativity of the intercalating species. Herein, we report an unusual effect of Mg intercalation on the superconductivity of 2H-MgxNbSe2 (x = 0.0, 0.02, 0.06, 0.08, 0.10, and 0.12) synthesized by a high-temperature solid-state reaction method. Unlike other s- and p-block elements/species as intercalants (Rb, Sn, Ga, and Al) that have a sharp detrimental effect on the Tc of 2H-NbSe2 within 1-5% of intercalation, Mg is found to be an exception. Upon Mg intercalation up to x = 0.06, no remarkable changes in Tc as compared to the parent 2H-NbSe2 (Tc ∼ 6.7 K) are observed, and further intercalation results in a small decrease in Tc (for x = 0.12, Tc = 6.2 K). From heat-capacity measurements, it is inferred that superconducting Mg-intercalated 2H-NbSe2 exhibits strong electron-phonon coupling. Electronic structure calculations on two s-block element intercalated compounds of formula M0.125NbSe2 (M = Mg, Rb) show that Rb s-, p-, and d-states completely overlap with the Nb d states, while the Mg s states lie in a low-energy region as compared to Nb d states, indicating a weak interaction between the intercalant and the Nb sublattice in Mg0.125NbSe2 as compared to Rb0.125NbSe2. These results suggest that the electronic states of the Nb network in 2H-NbSe2 are least altered with Mg intercalation, which could be one of the reasons for the minimal effect on the Tc with intercalation.

RESUMEN

Antheraea assamensis Helfer, popularly known as Muga silkworm, the golden silk producer of northeast India is economically important and unique among the Saturniid silkworms. In this study, the genetic diversity and phylogeny of semidomesticated and wild morphs of Muga silkwormcollected from different geographical locations of northeast India were investigated based on the sequences of five mitochondrial loci, i.e. 12S rRNA, 16S rRNA, CoxI, Cytb and CR. All the five mitochondrial loci showed a strong bias towards higher 'A' and 'T' contents. Transitional substitutions were found to be more than the transversional substitutions. The rate of nucleotide substitution and average genetic divergence were found to be highest in CR sequences and lowest in 12S rRNA gene sequences among the morphs of Muga silkworm. The morphs collected from same geographical area had identical 12S rRNA, 16S rRNA, CoxI and Cytb gene sequences. Moreover, the 12S rRNA and 16S rRNA gene sequences of somesemi-domesticated and wild morphs collected from different geographical locations were also found to be similar. In the phylogenetic trees generated based on themitochondrial loci, mixing of semi-domesticated and wild morphs was observed as they shared the same group. The information generated in this study will help in formulating strategies to conserve the natural biodiversity present among these unique silkworms in northeast India. In addition, this will be useful in identifying diverse morphs of Muga silkworm, which will help in effective breeding programmes to improve its productivity.

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RESUMEN

Here we report a new three-dimensional nickel-based hybrid structure [Ni3(BTB)2(BPE)4(H2O)2]·2DMF·2H2O, 1 [where BTB = 1,3,5-tris(4-carboxyphenyl)benzene and BPE = 1,2-bis((4-pyridyl)ethane)], which exhibits long-range ferromagnetism and semiconductor behavior. The dipolar interaction between the magnetic spins is suggested to explain the development of long-range ferromagnetic ordering, where the superexchange interaction can be unwanted due to the large distance between the magnetic spins. Optical band gap and resistance vs. temperature measurements reveal the semiconductor nature of this compound. The density of states calculations shed light towards the origin of the low band gap value.

RESUMEN

A magnetostructural correlation has been carried out for two newly synthesized two-fold-interpenetrated three-dimensional structures. Compound 1, denoted as [Ni(L1)(L2)]·2DMF (where L1 is 1,4-benzene-dicarboxylic acid (BDC), L2 is 4,4-oxybis-(N-(pyridine-4-yl)benzamide), and DMF is N,N'-dimethylformamide), was observed to have a three-dimensional structure with two-fold interpenetration. Compound 2, denoted as [Co(L3)(L2)]·2DMF (where L3 is 2,5-thiopehene-dicarboxylic acid (TDC)), was also observed to display a three-dimensional structure with an architecture identical to that of compound 1. Both compounds were well characterised using several techniques including single-crystal X-ray diffraction, powder X-ray diffraction, TGA, and IR. Magnetism and specific heat measurements of compound 1 revealed a canted-antiferromagnetic transition at TN ≈ 4 K and a field-induced spin-flop transition at a relatively low field strength. These exotic features were attributed to the low-symmetry space group P(1[combining macron]) and single-ion anisotropy of the Ni2+ sub-lattice. In contrast, compound 2 was found to be weakly antiferromagnetic in nature with a negligible interaction between the magnetic Co2+ ions.

RESUMEN

Postsynthetic modification is a promising tool for introducing multifunctional properties in metal-organic frameworks (MOFs). The effects of postsynthetic metal addition/exchange in a barium-based MOF have been well examined toward their magnetic and electrical properties. The rattling motion of the extraframework organic cation is responsible for the ferroelectric behavior. The strong magnetic frustration in Tb@1 is found to arise from the nearly triangular arrangement of Tb3+ ions in its secondary building unit along the chain direction.

RESUMEN

Antheraea assamensis Helfer (muga silkworm) is an economically important endemic insect species of North Eastern Region of India. The silkworm is often susceptible to infection by pathogenic bacteria, leads to a disease commonly known as flacherie which causes 40% loss per annum to the silk industry. In this study, we have reported isolation, characterization and pathogenicity assessment of gut-associated bacteria of healthy and diseased muga silkworms. Thirty five bacterial isolates were screened from the gut of healthy and diseased silkworms by morphological observation and biochemical tests. 11 and 5 strains from healthy and diseased silkworm respectively were identified by 16S rRNA gene sequencing and analyzed. Pseudomonas aeruginosa (DRK1), Ornithinibacillus bavariensis (DRK2), Achromobacter xylosoxidans (KH3) and Staphylococcus aureus (FLG1) strains were commonly found in healthy as well as diseased larvae whereas, Bacillus thuringiensis (MK1) was found only in diseased larvae. Survivability analysis was performed with the identified strains by injection and oral administration (10(4)CFU/ml). The immune response of the silkworm against the pathogen was also studied by phenoloxidase and lysozyme enzyme activity assay, total and differential hemocyte count and phagocytic activity of hemocytes. It was observed that S. aureus, P. aeruginosa and B. thuringiensis significantly reduced the survivability of silkworm (p<0.001) hence found highly pathogenic. The lethal concentrations (LC50) values of the pathogenic strains were calculated at different time intervals (24, 48, 72 and 96h) within the range from 1.38×10(2) to 3.63×10(7)CFU/ml. The pathogenic groups demonstrated inhibition of phenoloxidase activity and decreased in total hemocyte count after 48h of infection. However, the lysozyme activity increased significantly in the pathogenic groups compared to the control (p<0.05). Granulocytes and plasmatocytes showed phagocytosis whereas; other types of cells did not show any phagocytic activity. Increasing granulocytes and plasmatocytes counts corroborates the results of phagocytic activity. The present study might be helpful in understanding the disease prognosis and colonization of bacteria causing the disease in muga silkworm.

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