Room temperature multiferroic properties of BiFeO3–MnFe2O4 nanocomposites

The novel functionalities of multiferroic magneto-electric nanocomposites have spawned substantial scope for fast-paced memory devices and sensor applications. Following this, herein we report the development of nanocomposites with soft ferromagnetic MnFe₂O₄ and ferroelectric BiFeO₃ to fabricate a system with engineered multiferroic properties. A modified sol-gel route called Pechini method is demonstrated for the preparation of the (1-x) BiFeO₃-x MnFe₂O₄ (x = 10%, 30%, 50%, 70%) nanocomposites. The crystallographic phase, structure, and morphology are characterized by XRD, FESEM, and HRTEM. The accurate crystallite size and lattice strain are determined by Williamson-Hall plot method and a comparative study with Scherer's equation is carried out. TEM image evidences the interface between BiFeO₃ and MnFe₂O₄ nanoparticles in the composite. The room temperature magnetic response reveals the strong dependence of magnetic saturation, remanent magnetization, and coercivity of the nanocomposites on MnFe₂O₄ addition. The dielectric response and impedance analysis of the prepared nanocomposites are observed. The electrical performance of the composite is affected by grain, grain boundaries, and oxygen vacancies. The unsaturated P-E loops exhibit the leaky ferroelectric behavior for the nanocomposite. The intrinsic magnetoelectric coupling between ferroelectric BiFeO₃ and ferromagnetic MnFe₂O₄ has been determined by varying H_dc/H_ac and its maximum coupling coefficient (α) is found to be 25.39 mV/cmOe for 70% BiFeO₃ -30% MnFe₂O₄ nanocomposite. These distinctive and achievable characteristics of the nanocomposite would enable the designing of magnetic field sensors, spintronic devices, and multiferroic memory devices.     

Nonlinear optical absorption studies of sol–gel derived Yttrium Iron Garnet (Y3Fe5O12) nanoparticles by Z-scan technique

Sol–gel synthesized Yttrium Iron Garnet (Y₃Fe₅O₁₂) nanoparticles were subjected to open aperture Z-scan studies in order to investigate the nonlinear optical (NLO) properties of these materials. The investigations were carried out using a Q-switched resonant Nd:YAG laser at a wavelength of 532 nm with different laser powers. Strong reverse saturable absorption (RSA) has been found when the sample is irradiated by the laser pulse of 10 Hz. The studies show that the material is highly nonlinear, which makes it useful for optical limiting applications.     

Hydrated metal salt and Y3Fe5O12–Na0.5K0.5NbO3-incorporated P(VDF-HFP) films: a promising combination of materials with multiferroic and energy harvesting properties

Journal of Materials Science - The composite approach is very effective in developing multiferroic systems with remarkable magnetoelectric coupling coefficients. In this work, P(VDF-HFP)-based...     

A Simple Semi-distributed Hydrologic Model to Estimate Groundwater Recharge in a Humid Tropical Basin

A semi-distributed groundwater recharge model that can be used to estimate the daily water-table fluctuations on a daily basis is presented. The model is based on the water-balance concept and links atmospheric and hydrogeologic parameters to different water uses. It is calibrated and validated using 10 years of data; data for the first 6 years - from 2000 to 2005 - is used for model calibration, whereas data for the remaining 4 years - from 2006 to 2009 - is used for validation. Goodness-of-fit measures such as the Nash-Sutcliffe Efficiency (E_NS) and the coefficient of determination (R²) were evaluated to assess the performance of the model. This model can serve as a powerful tool to help engineers and decision makers in controlling excessive groundwater usage and preventing drastic depletion of groundwater resources. This is of considerable significance in basins of this type which are densely populated and the draft is reasonably high. This model demonstrated that with a reliable and detailed input database, the accuracy of predictions can be improved considerably.     

Mechanical,thermal, and viscoelastic response of novel in situ CTBN/POSS/epoxy hybrid composite system

The present study focuses on the preparation of a novel hybrid epoxy nanocomposite with glycidyl polyhedral oligomeric silsesquioxane (POSS) as nanofiller, carboxyl terminated poly(acrylonitrile‐co‐butadiene) (CTBN) as modifying agent and diglycidyl ether of bisphenol A (DGEBA) as matrix polymer. The reaction between DGEBA, CTBN, and glycidyl POSS was carefully monitored and interpreted by using Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC). An exclusive mechanism of the reaction between the modifier, nanofiller, and the matrix is proposed herein, which attempts to explains the chemistry behind the formation of an intricate network between POSS, CTBN, and DGEBA. The mechanical properties, such as tensile strength, and fracture toughness, were also carefully examined. The fracture toughness increases for epoxy/CTBN, epoxy/POSS, and epoxy/CTBN/POSS hybrid systems with respect to neat epoxy, but for hybrid composites toughening capability of soft rubber particles is lost by the presence of POSS. Field emission scanning electron micrographs (FESEM) of fractured surfaces were examined to understand the toughening mechanism. The viscoelastic properties of epoxy/CTBN, epoxy/POSS, and epoxy/CTBN/POSS hybrid systems were analyzed using dynamic mechanical thermal analysis (DMTA). The storage modulus shows a complex behavior for the epoxy/POSS composites due to the existence of lower and higher crosslink density sites. However, the storage modulus of the epoxy phase decreases with the addition of soft CTBN phase. The T_g corresponding to epoxy‐rich phase was evident from the dynamic mechanical spectrum. For hybrid systems, the T_g is intermediate between the epoxy/rubber and epoxy/POSS systems. Finally, TGA (thermo gravimetric analysis) studies were employed to evaluate the thermal stability of prepared blends and composites. POLYM. COMPOS., 37:2109–2120, 2016. © 2015 Society of Plastics Engineers     

Influence of Scale on SWAT Model Calibration for Streamflow in a River Basin in the Humid Tropics

The Soil Water Assessment Tool (SWAT) was applied to the 2,530 km² Chaliyar river basin in Kerala, India to investigate the influence of scale on the model parameters. The study was carried out in this river basin at two scales. Parameters such as land use, soil type, topography and management practices are similar at these scales. The model was initially calibrated for streamflow and then validated. Critical parameters were the curve number (CN2), soil evaporation compensation factor (ESCO), available water holding capacity (SOL_AWC), average slope length (SLSUBBSN), and base flow alpha factor (ALPHA_BF). Using the optimized value of various parameters, stream flow was estimated from parts of the basin at two different scales—an area of 2,361.58 km² and an area of 1,013.15 km². The streamflow estimates at both these scales were statistically analysed by computing the coefficient of determination (R ²) and the Nash–Sutcliffe efficiency (E_NS). Results indicate that the SWAT model could simulate streamflow at both scales reasonably well with very little difference between the observed and computed values. However, the results also indicate that there may be greater uncertainty in SWAT streamflow estimates as the size of the watershed increases.