Vibhav Pandey

Direct evidence for multiferroic magnetoelectric coupling in 0.9BiFeO3-0.1BaTiO3.

Magnetic, dielectric and calorimetric studies on 0.9BiFeO3-0.1BaTiO3 indicate strong magnetoelectric coupling. XRD studies reveal a very remarkable change in the rhombohedral distortion angle and a significant shift in the atomic positions at the magnetic Tc due to an isostructural phase transition. The calculated polarization using Rietveld refined atomic positions scales linearly with magnetization. Our results provide the first unambiguous, atomic level evidence for magnetoelectric coupling of intrinsic multiferroic origin in a BiFeO3-based system.

Unambiguous evidence for magnetoelectric coupling of multiferroic origin in 0.73BiFeO3–0.27PbTiO3

Magnetization, frequency dependent dielectric, and structural studies on 0.73BiFeO3–0.27PbTiO3 in the temperature range from 300 to 600 K reveal anomalies in the unit cell parameters and the intrinsic value of the dielectric constant, free from space charge contributions, at the antiferromagnetic transition temperature (TN). Our results provide unambiguous confirmation of magnetoelectric coupling of multiferroic origin at TN and evidence for monoclinic distortion of the ferroelectric phase.

Influence of Fe segregation at grain boundaries on the magnetoresistance of Sr2Fe1+δMoO6 polycrystals

In this paper, we report the influence of Fe impurities on the magnetoresistance (MR) of double perovskite Sr2Fe1+δMoO6 (0.00 ≤ δ ≤ 0.20) system. The significant Fe impurities have been created by two different approaches: one by adding the extra amount of Fe2O3 at starting of the synthesis and other by sintering the pristine Sr2FeMoO6 sample at high temperature (1300 °C) in high reducing environment (∼8% H2 + 92% Ar). A remarkable 11% magnetoresistance at room temperature under the presence of low magnetic field (0.72 T) has been observed in the pristine sample. The achieved high low field magnetoresistance value in the sample may be due to the optimized synthesis conditions to get better inter-granular tunneling through grain boundaries. However, the presence of Fe impurity results into the sharp reduction in magnetoresistance because of reduced spin polarized tunneling. The loss of insulating nature of the grain boundaries and the inelastic scattering of the charge carriers through the metallic impurit...

Increased low field magnetoresistance in electron doped system Sr0.4Ba1.6−xLaxFeMoO6

Magnetotransport properties of electron doped polycrystalline system Sr0.4Ba1.6−xLaxFeMoO6 are presented in this paper. We have observed increased low field magnetoresistance values with significant Curie temperature increase in the electron doped system Sr0.4Ba1.6−xLaxFeMoO6. The low field magnetoresistance value (at 1000 Oe) in 20% La3+ doped sample is observed to be 2.17% at 300 K. At 0.64 T and 80 K, the magnetoresistance change measured in this sample is 21.4%. This sample also showed 50 K increase in Curie temperature over the pristine sample. The increased low field magnetoresistance values are associated with modified grain boundary barriers of the system. The results confirm the fact that the modification of grain boundary barriers has enough potential to possess high low field magnetoresistance values even in the systems with lower spin polarization values. The role of grain to grain connectivity is observed to be dominantly determining the low field magnetoresistance values in grain to grain tunnel type magnetoresistance.

Magnetic and Electrical Properties of Ti Substituted Lithium Zinc Ferrites

The effect of Ti on the magnetic, power loss and structural properties of Li0.35+x/2Zn0.3Mn0.05TixFe2.30–1.5xO4 ferrites (x = 0.0 to 0.25 in step of 0.05) + 0.5 wt% Bi2O3, prepared by standard ceramic technique, has been investigated. Phase formation of all samples has been confirmed by XRD. The magnetic properties have been measured by VSM. A continuous decrease is found in saturation magnetization with Ti concentration in Li0.35+x/2Zn0.3Mn0.05TixFe2.30–1.5xO4 ferrites. Complex permeability (μ* = μ′−jμ″) have been analysed at room temperature in frequency range from 1 MHz to 103 MHz. It was found an enhancement in permeability with Ti concentration in Li0.35+x/2Zn0.3Mn0.05TixFe2.30–1.5xO4 and exhibits the maximum value of 160 for x = 0.05 sample. Power loss measurements have been carried out in induction field B = 10 mT in frequency range of 50 KHz to 3 MHz. Power loss has been found to be quite low with the substitution of Ti in lithium zinc ferrite.

Modified Composition of Cobalt Ferrite as Microwave Absorber in X-Band Frequencies

The magnetic and electromagnetic wave absorbing properties were investigated in the Ni substituted cobalt ferrites, Co1-xNixFe1.9Mn0.1O4 (0≤ x ≤ 1.0), prepared by solid state technique with the increase in concentration of Ni doping uniformly in grain size and densification have improved, while permeability increased remarkably. Saturation magnetization and coercivity both decreased with Ni concentration in cobalt ferrite. Electromagnetic parameters of ferrite samples were measured in X-band frequency range (8–12 GHz) by vector network analyzer (VNA) and their absorbing properties were calculated according to transmission-line theory. Phase formation of all samples has been confirmed by XRD. Ferromagnetic resonance frequency shift has been observed with concentration of Ni concentration which is an important phenomenon of cobalt ferrite to absorb microwave at higher frequencies in X-band. Based on magnetic and microwave measurements Co1-xNixFe1.9Mn0.1O4 (x = 0.8) may be a good potential candidate for electromagnetic compatibility and for other practical applications at high frequencies.

Establishement of the magnetic flux density standard in the range 100 µT to 1000 µT

The magnetic flux density standard in the range 100 µT to 1000 µT has been established using a standard Helmholtz coil. The ambient magnetic field including earths magnetic field components inside the room and other noises has been compensated to a level of the order of 100 nT. A circular triaxial Helmholtz coil pair of size nearly 800 mm has been used for compensating the ambient magnetic field. The standard Helmholtz coil of size 300 mm has been placed in the geometrical centre of the triaxial Helmholtz coil pair. The magnetic flux density has been measured using triaxial and single axis fluxgate magnetometers. The coil constant of the standard Helmholtz coil has been found to be 850.6808 ± 0.0036804 µT/A, which is in good agreement with the manufactures specification viz, 850 µT/A, with an uncertainty of < ± 0.5 %.

Synthesis And Characterization Of Cadmium Doped Lithium Ferrite By Sol‐gel Technique

Cadmium substituted lithium ferrite Li0.5−x/2CdxFe2.5−x/2O4 were prepared by sol‐gel method. Saturation magnetization versus composition shows a maximum Ms = 80 emu/g at for = 0.3. In all samples, dielectric constant decreases with increasing frequency while dielectric loss tangent first increases and attains a maximum value followed by a decrease. Dielectric constant is in the range of 105 for sample x = 0.1 & 0.3 with a low dielectric loss. High dielectric constant and low dielectric loss are essential requirement of ferrite for power applications.