Interfacial-antiferromagnetic-coupling driven magneto-transport properties in ferromagnetic superlattices

We explore the role of interfacial antiferromagnetic interaction in coupled soft and hard ferromagnetic layers to ascribe the complex variety of magneto-transport phenomena observed in $La_{0.7}Sr_{0.3}MnO_3/SrRuO_3$ (LSMO/SRO) superlattices (SLs) within a one-band double exchange model using Monte-Carlo simulations. Our calculations incorporate the magneto-crystalline anisotropy interactions and super-exchange interactions of the constituent materials, and two types of antiferromagnetic interactions between Mn and Ru ions at the interface: (i) carrier-driven and (ii) Mn-O-Ru bond super-exchange in the model Hamiltonian to investigate the properties along the hysteresis loop. We find that the antiferromagnetic coupling at the interface induces the LSMO and SRO layers to align in anti-parallel orientation at low temperatures. Our results reproduce the positive exchange bias of the minor loop and inverted hysteresis loop of LSMO/SRO SL at low temperatures as reported in experiments. In addition, conductivity calculations show that the carrier-driven antiferromagnetic coupling between the two ferromagnetic layers steers the SL towards a metallic (insulating) state when LSMO and SRO are aligned in anti-parallel (parallel) configuration, in good agreement with the experimental data. This demonstrate the necessity of carrier-driven antiferromagnetic interactions at the interface to understand the one-to-one correlation between the magnetic and transport properties observed in experiments. For high temperature, just below the ferromagnetic $T_C$ of SRO, we unveiled the unconventional three-step flipping process along the magnetic hysteresis loop. We emphasize the key role of interfacial antiferromagnetic coupling between LSMO and SRO to understand these multiple-step flipping processes along the hysteresis loop.Comment: 13 pages and 11 figure

Synthesis and Evaluation of Cr (III), Mn (III) and Fe (III) Schiff Base of Metals Complexes

A novel synthesized Schiff base metal complexes Cr (III), Mn (III) and Fe (III) of 2-hydroxy-5-chloro acetophenone 2-imino-4-phenyl thiazole were prepared by condensed from 2-hydroxy-5-chloro acetophenone and 2-amino-4-phenyl thiazole have been synthesized and characterized on the basis of elemental analysis, Infrared, 1H NMR, molar conductance and magnetic susceptibilities analysis. The Schiff base acts as a monobasic bidentate ligand commonly coordinates through the oxygen atom of phenolic OH group and the nitrogen atom of azomethine group, which is confirmed by IR spectral data. All the metal complexes have studies thermal properties and their thermal parameter. Keyword: Schiff base, Magnetic, Thermal studies

Tailoring the interfacial magnetic interaction in epitaxial La0.7_{0.7}Sr0.3_{0.3}MnO3_3/Sm0.5_{0.5}Ca0.5_{0.5}MnO3_3 heterostructures

Interface engineering in complex oxide heterostructures has developed into a flourishing field as various intriguing physical phenomena can be demonstrated which are otherwise absent in their constituent bulk compounds. Here we present La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) / Sm$_{0.5}$Ca$_{0.5}$MnO$_3$ (SCMO) based heterostructures showcasing the dominance of antiferromagnetic interaction with increasing interfaces. In particular, we demonstrate that exchange bias can be tuned by increasing the number of interfaces; while, on the other hand, electronic phase separation can be mimicked by creating epitaxial multilayers of such robust charge ordered antiferromagnetic (CO-AF) and ferromagnetic (FM) manganites with increased AF nature, which otherwise would require intrinsically disordered mixed phase materials. The origin of these phenomena is discussed in terms of magnetic interactions between the interfacial layers of the LSMO/SCMO. A theoretical model has been utilized to account for the experimentally observed magnetization curves in order to draw out the complex interplay between FM and AF spins at interfaces with the onset of charge ordering.Comment: 8 figure

Phenotypic and Genetic Heterogeneity in Vibrio cholerae O139 Isolated from Cholera Cases in Delhi, India during 2001-2006

Incidence of epidemic Vibrio cholerae serogroup O139 has declined in cholera endemic countries. However, sporadic cholera caused by V. cholerae O139 with notable genetic changes is still reported from many regions. In the present study, 42 V. cholerae O139 strains isolated from 2001 to 2006 in Delhi, India, were retrospectively analyzed to understand their phenotype and molecular characteristics. The majority of isolates were resistant to ampicillin, furazolidone and nalidixic acid. Though the integrative conjugative element was detected in all the O139 isolates, the 2004–2006 isolates remained susceptible to co-trimoxazole, chloramphenicol, and streptomycin. Cholera toxin genotype 1 was present in the majority of the O139 isolates while few had type 3 or a novel type 4. In the cholera toxin encoding gene (ctx) restriction fragment length polymorphism, the majority of the isolates harbored three copies of CTX element, of which one was truncated. In this study, the ctx was detected for the first time in the small chromosome of V. cholerae O139 and one isolate harbored 5 copies of CTX element, of which 3 were truncated. The ribotype BII pattern was found in most of the O139 isolates. Three V. cholerae O139 isolated in 2001 had a new ribotype BVIII. Pulsed-field gel electrophoresis analysis revealed clonal variation in 2001 isolates compared to the 2004–2006 isolates. Molecular changes in V. cholerae O139 have to be closely monitored as this information may help in understanding the changing genetic features of this pathogen in relation to the epidemiology of cholera

Genetic variants of renin on the prevalence of diabetic nephropathy

Aim: Renin, a component of the Renin-Angiotensin-Aldosterone System (RAAS), is produced in the juxtaglomerular cells of the kidney. It is an important factor for the regulation of blood pressure and electrolyte balance and encoded by the REN gene. Recent studies suggest that the RAAS is a regulator of kidney functions. Individuals with REN variants have been associated with high blood pressure. We substantiated the hypothesis that genetic variants of REN gene have significant association with prevalence of nephropathy and in the development of nephropathy in type 2 diabetes mellitus (T2DM).Methods: We enrolled to the study 718 consecutive subjects who were registered patients in two individual hospitals in Kolkata city, India. They consisted of 246 (34.26%) T2DM patients without nephropathy cases, 168 (23.40%) type 2 diabetes with nephropathy cases (T2DNH) and 304 (42.34%) healthy controls. Genotypes were assayed with genomic DNA for two known variants of the REN gene, i.e., rs16853055 and rs41317140 using sequencing methods.Results: Association between the REN gene variants and prevalence of T2DM and T2DNH was tested. A significant association of T2DNH and variant rs41317140 was obtained and it was evident that the rs41317140 (C>T) shows a significant difference between T2DM and T2DNH (X2 = 4.92; P = 0.03; OR = 0.6162; 95% CI: 0.4006-0.948). The results from the multiple model test that additive model predicted the association at genotype level and shows a significant difference between T2DM and T2DNH (OR = 0.6067; P = 0.03). There was no significant association between T2DNH or T2DM and variant rs16853055.Conclusion: Thus, it is concluded that a genetic variant of the REN gene should have a significant impact on the onset of type 2 diabetic nephropathy

Molecular evidence favouring step-wise evolution of Mozambique Vibrio cholerae O1 El Tor hybrid strain

The ctxAB operon, encoding cholera toxin (CT) in Vibrio cholerae, is carried by the genome of a filamentous phage, CTXΦ. Usually, specific CTXΦ infect each of the two important biotypes, classical and El Tor, of epidemic V. cholerae strains belonging to serogroup O1, and are called CTXclassF and CTXETΦ, respectively. However, an unusual hybrid El Tor strain carrying CTXclassΦ caused the cholera epidemic in Mozambique in 2004. To understand the evolution of that strain, we have further analysed some representative hybrid El Tor strains isolated in Kolkata, India, in 1992, and the results indicate that both the Mozambique and the Indian strains are infected with a unique CTXclassΦ having only four copies of the tandem heptamer repeat sequence 5'-TTTTGAT-3' present in the ctxAB promoter (PctxAB) region, like in CTXETΦ. Usually, the PctxAB of the classical biotype contains seven to eight copies of such sequences. However, sequence analyses of the PctxAB regions of several classical strains indicated that the copy number of heptamer repeat sequences might vary from four to eight copies, which was previously unknown. Since the hybrid strains analysed in this study carry four copies of the heptamer sequences, it may thus serve as a marker to trace the strain in future. Interestingly, while the Mozambique strain is devoid of an El Tor-specific free RS1 element or pre-CTX prophage, the Indian hybrid strains carry such elements. The free RS1 has been mapped, cloned and sequenced. As in pre-CTX and CTX prophages, multiple copies of free RS1 elements were found to be integrated in tandem in the large chromosomal dif site. Since Indian hybrid El Tor strains carry either free RS1 or pre-CTX prophage in their large chromosomes, it is possible that the Mozambique hybrid El Tor strain has evolved from these progenitor strains by step-wise deletion of CTX genetic elements from their large chromosomes

Small Chromosomal Integration Site of Classical CTX Prophage in Mozambique Vibrio Cholerae O1 Biotype El Tor Strain

An unusual strain of Vibrio cholerae O1 biotype El Tor harbouring multiple tandem copies of classical CTX prophage caused a cholera epidemic in Mozambique in 2004. However, the location of the classical CTX prophage in the genome of the Mozambique strain was unknown. In this study, pulsed Weld gel electrophoresis (PFGE) of the whole genome along with Southern hybridization experiments indicated that the classical CTX prophage present in the Mozambique strain is located in the small chromosome. To determine the CTX prophage integration site in the small chromosome of Mozambique strain, the 5_and 3_ junctions of the prophage and small chromosome were PCR ampliWed, cloned and sequenced. Sequence analysis indicated that the prophage was integrated in the conserved dif site of the replication terminus region of the Mozambique strain. While using an O1 El Tor isolate VC44 as a control strain, which carries tandem copies of CTX prophage in its small chromosome like the Mozambique strain, it was unexpectedly detected that the strain VC44 also possesses classical cholera toxin B gene allele. Since the strain VC44 was isolated in India in the year 1992, it appears that the Mozambique strain has probably originated from a VC44-like strain