Correlation between spin–phonon coupling and magneto-electric effects in CoFe2O4/PMN-PT nanocomposite: Raman spectroscopy and XMCD study

We have investigated strain-induced spin lattice coupling in the CoFe₂O₄/0.65Pb (Mg_1/3Nb_2/3)O₃–0.35PbTiO₃(PMN-PT) composite system, evident by temperature-dependent Raman spectroscopy and magnetization measurements. The strain interactions lead to magneto-electric coupling, and the measured magneto-electric voltage coefficient is 40 mV/cm^?1Oe^?1 for the CoFe₂O₄/PMN-PT composite samples. X-ray magnetic circular dichroism (XMCD) analysis establishes modified spin structure in the electrically poled CoFe₂O₄/PMN-PT composite, further validating the coupling between magnetic and electric ordering in the composite. The magneto-electric coupling coefficient α vs dc magnetic field curves revealed hysteretic behavior and enhanced α values after electric poling, which originates from the strain-induced modifications in the magnetic structure of composite in the electrically poled samples. These findings suggest that the existence of spin lattice coupling may lead to the mechanism of strong magneto-electric effects via strain interactions in CoFe₂O₄/PMN-PT composite.

     

Residues of DDT and HCH in wheat samples collected from different states of India and their dietary exposure: A multicentre study

Under a multicentre study conducted by the Indian Council of Medical Research, 1712 samples of wheat grain/flour were collected from urban and rural areas in 11 states representing different geographical regions of India. These samples were analysed for residues of DDT (2,2-bis (p-chlorophenyl)-1,1,1-trichloro ethane) and different isomers of HCH (1,2,3,4,5,6-hexachloro cyclohexane, a mixture of isomers) by gas-liquid chromatography. Residues of DDT were detected in 59.4% of 1080 samples of wheat grain and in 78.2% of 632 samples of wheat flour. Different isomers of HCH were present in about 45-80% of the samples of wheat grain/flour. Medians of DDT and total HCH, respectively, for pooled samples of wheat grain were 0.013 and 0.035 mg kg^-1, while those for wheat flour were 0.01 and 0.02 mg kg^-1. Estimated daily intakes of DDT and different isomers of HCH through the consumption of wheat contaminated at their median and 90th percentiles constituted a small proportion of their acceptable daily intakes. Amongst the pesticide residues analysed, statutory maximum residue limits have been fixed only for γ-HCH in wheat in India, as 0.1 mg kg^-1 in wheat grain and zero in wheat flour. Residue levels of γ-HCH exceeded these maximum residue limits in five of 1080 samples of wheat grain and in 340 of 632 samples of wheat flour. The failure to meet the requirement of the γ-HCH maximum residue limit in large number of wheat flour samples was attributed to the fixation of practically unachievable zero limit. Comparing the previous studies and the present one, the levels of residues of DDT and HCH in wheat were significantly decreased.     

Structural,microstructural and magneto-electric properties of single-phase BiFeO3 nanoceramics prepared by auto-combustion method

Polycrystalline nano BiFeO₃ powders were synthesized by auto-combustion method using urea as fuel and metal nitrates (Fe(NO₃)₃·9H₂O, Bi(NO₃)₃·5H₂O) as oxidizers. In order to optimize the single-phase synthesis condition of BiFeO₃, different fuel to oxidizer ratios have been investigated. The preliminary structural investigation using X-ray diffraction shows the samples were of single phase and crystallize in rhombohedral structure (R3c). The ferroelectric and antiferromagnetic ordering temperatures of BiFeO₃ were found to be 832 °C and 364 °C respectively, from differential thermal analysis. The temperature dependent dielectric study shows an anomaly around 215 °C which corresponds to magneto-electric coupling in the material. Field-emission scanning electron micrographs show effect of fuel to oxidizer ratio on grain size evolution. The ferroelectric hysteresis loops for all the samples were measured at a frequency of 100 Hz confirming the ferroelectric nature. An evidence of magneto-electric coupling was also observed at room temperature from magneto-capacitance measurements.     

A magnetic nano-composite soft polymeric membrane

There is an increased need for low cost actuation technologies at the micro and nanoscale. Magnetically responsive polymer-based materials are good candidates for numerous applications in microsystems for actuation and sensing purposes. In this work, we report on nano-polymer composite magnetic silicone-based membranes, which provide the low elastic modulus needed for magnetic actuation to be effective at small scales. Passivated crystalline cobalt (~37 nm) and water based iron/cobalt (~100 nm) nanoparticles (NPs) have been synthesized using a chemical route at 50 °C and at room temperature, respectively. The NPs were characterized by Fourier Transform Infrared Spectroscopy, X-Ray Diffraction, Atomic Force Microscopy and Vibrating Sample Magnetometry (VSM). The NPs are then uniformly dispersed in a polydimethyl siloxane (PDMS) polymer matrix in order to fabricate smooth and flexible magnetic composite membranes. The magnetic properties of the membranes for different amounts of cobalt and iron NPs (16 and 25 wt%) were characterized by VSM and deflection measurements. Co/Fe PDMS composite membranes of about 50 mm diameter and ~250 μm thickness were used under the application of ~400 Oe magnetic fields. The cobalt-PDMS membrane shows the largest deflection (~900 vs. ~80 μm for an iron-PDMS membrane). The deflections observed on these membranes are found to have a linear dependence on the applied magnetic field.     

DDT and HCH residues in dairy milk samples collected from different geographical regions of India: a multicentre study.

Under a multicentre study conducted by the Indian Council of Medical Research, 2205 samples of dairy milk were collected from rural and urban areas of 12 states representing different geographical regions of India. These samples were analysed for residues of DDT and different isomers of HCH by gas-liquid chromatography. Analytical quality assurance between various participating laboratories was ensured through analysis of check samples. The residues of DDT and HCH were detected in more than 80% of samples analysed. Concentrations of DDT residues, alpha-HCH, beta-HCH, gamma-HCH and delta-HCH exceeded their maximum residue limits prescribed by the Ministry of Health and Family Welfare of the Indian Government in 37, 21, 42, 28 and 4% of the samples, respectively. Median values of DDT and HCH found in dairy milk in India were more than the corresponding values reported from most other countries. The results showed significant variations in the incidence as well as level of these contaminants in dairy milk from different regions of the country.