Shahid Ameer

Influence of Reduced Graphene Oxide on Effective Absorption Bandwidth Shift of Hybrid Absorbers

The magnetic nanoparticle composite NiFe2O4 has traditionally been studied for high-frequency microwave absorption with marginal performance towards low-frequency radar bands (particularly L and S bands). Here, NiFe2O4 nanoparticles and nanohybrids using large-diameter graphene oxide (GO) sheets are prepared via solvothermal synthesis for low-frequency wide bandwidth shielding (L and S radar bands). The synthesized materials were characterized using XRD, SEM, FTIR and microwave magneto dielectric spectroscopy. The dimension of these solvothermally synthesized pristine particles and hybrids lies within 30–58 nm. Microwave magneto-dielectric spectroscopy was performed in the low-frequency region in the 1 MHz-3 GHz spectrum. The as-synthesized pristine nanoparticles and hybrids were found to be highly absorbing for microwaves throughout the L and S radar bands (< −10 dB from 1 MHz to 3 GHz). This excellent microwave absorbing property induced by graphene sheet coupling shows application of these materials with absorption bandwidth which is tailored such that these could be used for low frequency. Previously, these were used for high frequency absorptions (typically > 4 GHz) with limited selective bandwidth.

Ce-Substituted Co0.5Ni0.5Fe2O4: Structural, morphological, electrical, and dielectric properties

Functional nano ceramics, especially rare earth substituted ferrites, have numerous applications in microelectronics. They have certain novel characteristics associated with various rare earth substitutions associated with electronics. A series of cerium-substituted cobalt nickel ferrite nanoparticles with nominal composition CexCo0.5Ni0.5Fe2-xO4 (where x = 0.00, 0.05, 0.10, 0.15, and 0.20) was prepared in powder form by chemical co-precipitation and sol-gel auto combustion methods. Samples were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), dielectric properties, and DC electrical resistivity. XRD analysis of all the samples confirms the formation of the spinel structure of Fd-3m space group. Crystallite size “t” was found to decrease, whereas both x-ray density “Dx” and lattice constant “a” were found to increase by increasing Ce concentration from 8.35 Å to 8.36 Å and 8.37 Å for sol-gel and coprecipitation, respectively. SEM results show the presence of uniformly distributed and almost spherical-shaped particles for both techniques. FTIR measurements were used to further confirm the composition, i.e., cation substitution. The DC electrical resistivity of the x = 0.00 sample is higher than Ce-substituted ferrite samples and in the range of 108 O-cm at 373 K. Dielectric spectroscopy is also studied from 100 Hz to 5 MHz as a function of frequency. To our knowledge, this is the first reported research of this particular composition.

Synthesis, Characterization and Hall Effect Measurements of Nanocrystalline ZnO Thin Films

ZnO thin films were prepared by sol-gel method. Prepared thin films were then characterized by SEM, XRD, EDX and Hall effect measurements. SEM confirmed the morphological studies of ZnO thin films. Crystallite size is calculated using the Scherrer formula. Crystallite and grain sizes are obtained through XRD and SEM. EDS analysis confirms mass percentage of ZnO deposited. Decreasing trend of magneto resistance with temperature is observed. The optical transmission spectra of the solgel deposited ZnO thin films showed high transmittance (>70%) in the visible region and indicates that the transmittance of ZnO films gradually decreased as the thickness increased. Decreasing trend of resistivity and sheet resistance with thickness are also observed. The IV characterization of ZnO thin films under influence of UV and dark conditions are reported. The dc electrical resistivity data follow the hoping model.

Synthesis, Structural, Electrical, Magnetic and Dielectric Spectroscopic Characterization of C-Er2Si2O7

The Polymorphic Er2Si2O7 Is Synthesized by Solid State Double Sintering Method. Structural and Morphological Characterizations Have Been Performed Using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The Electrical Characterization Has Been Performed by Two Probe Method as a Function of Temperature. the Dielectric Spectroscopic Measurements of Polymorphic Er2Si2O7 Are Performed in the Temperature Range 300-555 K and Frequency Range 3 kHz to 1 MHz. the dc Electrical Transport Data Are Analyzed According to Mott’s Variable-Range Hopping. The ac Conductivity σac(ω) Is Obtained through the Dielectric Spectroscopic Measurements. the ac Conductivity Obeys Power Law which Can Be Expressed as σac (ω) = B ωs, where S Is Slope and it Determines the ac Electrical Transport Phenomenon. the ac Electrical Transport Data and its Variation with Temperature in this Rare Earth Formulation Are Well Discussed. the Magnetic Behavior of Synthesized Material Is Analyzed and Confirmed that Material Have Non-Magnetic Behavior with Coercivity (Hc) 842 Oe. while the Values of Magnetic Saturation (MS) and Remanace (Mr) Were Found in Range 3.90emu/g and 1.07emu/g.

Electrical and Dielectric Spectroscopic Characterization of Polycrystalline Dy2Si2O7

The compound Dy2Si2O7 exists in two polymorphs, the low temperature triclinic phase (type B) and a high temperature orthorhombic phase (type E).The dc and ac electrical conductivities of E-Dy2Si2O7 are measured in the temperature range 290-510 K and frequency range 1 kHz to 1 MHz . The dc electrical transport data are analyzed according to Motts variable-range hopping model. The disorder parameter (To) and density of states at fermi level are obtained. The ac conductivity σac (ω) is obtained through the dielectric parameters. The ac conductivity can be expressed as σac (ω) =B ω s , where s is slope and it decreases with increase in temperature. The conduction mechanism in the compound is discussed in low and high temperature regions in the light of theoretical models.

Mg0.50Cu0.5-xNixFe2O4 Spinel Nanoferrites: Structural, Electrical, Magnetic and Y-K Angle Studies

Spinel Nanoferrites of Composition Mg0.50Cu0.5-XNixFe2O4 (0.00≤x≤0.50) Were Synthesized by Chemical Co-Precipitation Method. the Structural, Morphological and Magnetically Changes due to Varying Concentrations of Metal Ions of Cu and Ni in the Prepared Nanoferrites Were Studied. XRD Confirmed the Formation of Single Phase Spinel Ferrite with Crystalline Sizes in between 16-29 Nm, and the Lattice Parameter (a) Found to Decreases with Increase of Ni Concentration. Electrical Resistivity of the Prepared Nanoferrites with Varying Nickel and Copper Concentrations X Observed to Follow Arrhenius Relation and Also Exhibited the Semiconductor Behavior. the Magnetic Hysteresis Curves Clearly Indicate the Soft Nature of the Prepared Samples. Saturation Magnetization (Ms) Increases with Ni Content. This Effect Is Related to the Magnetic Moments of Ni+2 Ions. the Y-K Angles Increase with Increasing Ni Content, and Suggest a Non Collinearity Néel Type of Ordering of the Y-K Type. the Increase in the Y-K Angles Also Suggests the Increase in Triangular Spin Arrangements on B Sites, which Subsequently Lead to Increment in A-B Interactions.