K.L. Yadav

Study of room temperature magnetoelectric coupling in Ti substituted bismuth ferrite system

Dielectric, magnetic, and magnetoelectric properties of Ti substituted bismuth ferrite (BiFeO3) ceramic synthesized by solid state reaction are reported. Ti substitution for Fe in BiFeO3 increased the room temperature electrical resistivity by approximately six orders of magnitude and also increased the dielectric constant and reduced the loss tangent. The remanent polarization, coercive field, and maximum polarization were 0.081μC∕cm2, 2.571kV∕cm, and 0.658μC∕cm2, respectively at 20kV∕cm. An anomaly in the dielectric constant and loss tangent around Neel temperature was observed. The ferroelectric and magnetic hysteresis loops were measured which are not really saturated in BiFe0.75Ti0.25O3 compound and represented a partial reversal. The magnetoelectric coupling between electric dipoles and magnetic dipoles at room temperature was demonstrated by measuring the effect of magnetic poling on ferroelectric hysteresis loop and the change in the dielectric constant with the external magnetic field.

Rapid liquid phase sintered Mn doped BiFeO3 ceramics with enhanced polarization and weak magnetization

Single-phase BiFe1−xMnxO3 multiferroic ceramics have been synthesized by rapid liquid phase sintering method to study the influence of Mn substitution on their crystal structure, dielectric, magnetic, and ferroelectric behaviors. From XRD analysis it is seen that Mn substitution does not affect the crystal structure of the BiFe1−xMnxO3 system. An enhancement in magnetization was observed for BiFe1−xMnxO3 ceramics. However, the ferooelectric hysteresis loops were not really saturated, we observed a spontaneous polarization of 10.23μC∕cm2 under the applied field of 42kV∕cm and remanent polarization of 3.99μC∕cm2 for x=0.3 ceramic.

Pr doped bismuth ferrite ceramics with enhanced multiferroic properties

Pr modified Bi(0.9-x)La(0.1)Pr(x)FeO(3) (BLPFO-x, x = 0, 0.1 and 0.2) ceramics were prepared by the conventional method based on the solid state reaction of mixed oxides and a detailed study of electrical and magnetic properties of Pr modified bismuth ferrite (BLPFO) is reported. X-ray analysis shows the formation of a bismuth ferrite rhombohedral phase. Pr doping significantly increases the resistivity and leads to a successful observation of electrical polarization hysteresis loops. All the samples have been found to possess a spontaneous magnetic moment at room temperature which increases further at low temperatures. The strong dependence of remnant polarization and dielectric constant on the strength of magnetic field is a direct evidence of magnetoelectric coupling in BLPFO-2 ceramics.

Room temperature multiferroic properties of Eu doped BiFeO3

We have studied the multiferroic properties of Bi1−xEuxFeO3, x=0.03, 0.05, 0.07, and 0.1 ceramics prepared by conventional solid state reaction method. The substitution of Eu in place of Bi increases the magnetization at room temperature. An anomaly in the dielectric constant is observed at ∼400 °C which corresponds to TN. Room-temperature dielectric polarization–electric field (P-E) curves indicate that higher doped compositions exhibit saturated P-E loops with Pr (remnant polarization) of these BFO-based samples increasing with the degree of Eu modification. As a result, improved multiferroic properties of the Bi0.9Eu0.1FeO3 ceramics with remnant polarization and magnetization (Pr and Mr) of 11 μC/cm2 and 0.0347 emu/g, respectively, were obtained. The evidence of weak ferromagnetism and saturated ferroelectric hysteresis loops in Bi1−xEuxFeO3 system at room temperature makes it a good candidate for potential applications.We have studied the multiferroic properties of Bi1−xEuxFeO3, x=0.03, 0.05, 0.07, and 0.1 ceramics prepared by conventional solid state reaction method. The substitution of Eu in place of Bi increases the magnetization at room temperature. An anomaly in the dielectric constant is observed at ∼400 °C which corresponds to TN. Room-temperature dielectric polarization–electric field (P-E) curves indicate that higher doped compositions exhibit saturated P-E loops with Pr (remnant polarization) of these BFO-based samples increasing with the degree of Eu modification. As a result, improved multiferroic properties of the Bi0.9Eu0.1FeO3 ceramics with remnant polarization and magnetization (Pr and Mr) of 11 μC/cm2 and 0.0347 emu/g, respectively, were obtained. The evidence of weak ferromagnetism and saturated ferroelectric hysteresis loops in Bi1−xEuxFeO3 system at room temperature makes it a good candidate for potential applications.

The effect of Ti substitution on magnetoelectric coupling at room temperature in the BiFe1-xTixO3 system

Magnetoelectric compounds BiFe1−xTixO3 (x = 0.1, 0.2 and 0.3) have been synthesized by the conventional solid state reaction method and the effect of Ti substitution on the ferroelectric and magnetic properties studied. It is seen that Ti substitution does not affect the ferroelectric transition temperature (Tc) of the BiFe1−xTixO3 system. An anomaly in the dielectric constant and dielectric loss in the vicinity of the antiferromagnetic Neel temperature (TN) and a small enhancement in magnetization have been observed. No systematic variation in the antiferromagnetic Neel temperatures has been observed on Ti substitution. Furthermore, it is seen that this system shows coupling between electric and magnetic dipoles exhibiting a magnetoelectric effect at room temperature and possesses a high dielectric constant.

Dielectric, magnetic and magnetoelectric properties of La and Nb codoped bismuth ferrite

Single-phase Bi(0.80)La(0.20)FeO(3) (BLFO) and Bi(0.80)La(0.20)Fe(1-x)Nb(x)O(3) (BLFNO) samples were prepared in order to study the dielectric, magnetic and magnetoelectric properties of La and Nb codoped BiFeO3. Rietveld refinement of x-ray diffraction patterns of La and Nb codoped samples has been performed using the R3c space group. Magnetic hysteresis loops revealed that codoping can effectively increase the spontaneous magnetization due to change in the bond angle of Fe-O-Fe as a result of distortion created by the Nb5+ doping. Magnetic field-induced relative change of the dielectric constant for BLFO and BLFNO samples is a signature of magnetoelectric coupling.

Magnetic field induced phase transition in multiferroic BiFe1- xTixO3 ceramics prepared by rapid liquid phase sintering

Single phase BiFe1−xTixO3 (BFTO) ceramics with varying x up to 0.35 were prepared by a rapid liquid phase sintering method to study the influence of Ti doping on their crystal structure, morphology, and magnetic behavior. Rhombohedral to orthorhombic phase was observed above x⩾0.33. The BFTO ceramics were highly resistive and with uniform morphology. Magnetic measurements revealed an increase in magnetization with the increase in Ti content and was maximum for x=0.2 ceramic. Surprisingly, a magnetic field induced phase transition from weak ferromagnetic to diamagnetic above 50kOe was observed for x=0.30 and 0.315 ceramics.

Mechanism of dc conduction in ferric chloride doped poly(3-methyl thiophene)

Abstract Poly(3-methyl thiophene) has been synthesized by chemical oxidation method in an inert atmosphere using ferric chloride as a dopant. The doping level varies from 0.1 to 2.0 M. The dc conductivity has been measured in the temperature range 20–300 K. The observed dc conductivity data has been analyzed in the light of existing theoretical models. Different Mott’s parameters such as characteristic temperature ( T 0 ), density of states at Fermi level [ N ( E F )], average hopping energy ( W ) and the average hopping distance ( R ) have been evaluated that agree well with the values reported earlier for the other conjugated polymers. A detailed analysis of the mechanism of charge transport in this system has been reported.

Double doping effect on the structural and dielectric properties of PZT ceramics

Polycrystalline samples of the modified Pb(Zr1−x Tix)O3 (PZT) composition, with representative formula Pb0.92(LazBi1−z)0.08(Zr0.65Ti0.35)0.98O3 (PLBZT), a family of relaxor ferroelectrics, were prepared via the chemical route with z = 0.3, 0.6 and 0.9. Crystalline phases of powders calcined at different temperatures and the microstructure of the sintered pellets were investigated by x-ray diffraction (XRD) analysis and scanning electron microscopy, respectively. XRD confirms the result obtained by differential scanning calorimetry. The XRD profile shows that the samples having z = 0.9 and 0.6 do not exhibit a pyrochlore phase, whereas the samples with z = 0.3, have 3% of the pyrochlore phase. Microstructural analysis suggests that the shape of grains and intergranular residual pores are modified upon La doping. The dielectric constant and dielectric losses were measured as a function of frequency at room temperature for different frequencies starting from 0.1 kHz to 1 MHz. The dielectric constant was found to be strongly influenced by frequency whereas the Curie temperature remained almost the same. Finally, we conclude that the dielectric constant, loss and activation energy of PLBZT strongly suggest that these compounds are suitable for the preparation of high value capacitors and may be good candidates for device applications.

Study of structural, dielectric and magnetic behaviour of Ni0.75Zn0.25Fe2O4–Ba(Ti0.85Zr0.15)O3 composites

A class of hybrid composites (x)Ni0.75Zn0.25Fe2O4?(1???x)Ba(Ti 0.85Zr 0.15)O 3 (for x variations 0, 0.20, 0.30 and 0.40) synthesized via a solid state reaction method is investigated. The structural analysis was carried out using an x-ray diffraction graph which reveals a mixed phase of the hybrid composites with spinel phase for ferrite component and perovskite phase for the ferroelectric component. The microstructural analysis and grain size determination is carried out using a field emission scanning electron microscope (FESEM). The relative dielectric constant with frequency variation (in the range of 100?Hz?1?MHz) and temperature at three fixed frequencies (100?Hz, 1?KHz and 10?KHz) is studied. The magnetic properties such as saturation magnetization (Ms ) and magnetic moment (?B) are calculated from the magnetic hysteresis loops obtained using a vibrating sample magnetometer (VSM). The value of remnant polarization for pure BZT is found to be 6.18??C?cm?2 and as the content of ferrite phase is increased up to 40?mol%, this value decreases. The magnetoelectric effect is studied using magnetocapacitance which takes a maximum value for 40?mol% addition of ferrite.