Soumen Basu

Effect of Y-doping on optical properties of multiferroics BiFeO3 nanoparticles

We have synthesized yttrium-doped bismuth ferrite nanoparticles through a modified Pechini technique. X-ray diffractometer, transmission electron microscope (TEM) and ultraviolet–visible spectrophotometer (UV–Vis) probes have been utilized to characterize the nanoparticles. Average particle size estimated from TEM found to be 29xa0nm for Bi0.99Y0.01FeO3 samples. The band gap of the prepared BFO and BYFO nanoparticles varies from 1.97 to 2.29xa0eV, that is, within the visible range of the sunlight. This property of these nanoparticles can be utilized in photo catalytic decomposition of organic contaminants, such as Rhodamine-B (RhB) under visible light irradiation. We have explored and observed that RhB degrade up to 8xa0% while mixed with Bi0.90Y0.1FeO3 for 1xa0h under 40xa0W lamp due to photo catalysis together with sensitization.

Giant magnetodielectric and enhanced multiferroic properties of Sm doped bismuth ferrite nanoparticles

Improvements in magnetodielectric and multiferroic properties are essential for visualizing the real application of multiferroics, precisely, BiFeO3 (BFO). An enhancement of multiferroic and magnetodielectric properties has been achieved for chemically prepared nanocrystalline BFO by virtue of Sm doping. The X-ray diffraction study confirms the growth of single phase nanocrystalline BFO which corroborates TEM observation. The magnetic study delineates the ferromagnetic behavior of nanocrystalline Sm-doped BFO samples even at room temperature, which is absent in pristine samples. Surprisingly, a few orders of magnitude increase in resistivity is observed in Sm doped samples. Room temperature ferroelectric measurement showed that Sm doping improves the polarization significantly. In addition, we have achieved a giant change in the magnetodielectric properties of Sm doped samples which has not been reported so far. Large lattice strain arising due to the mismatch of ionic radii and the decrease of oxygen vacancies combined could play an important role in the enhancement of multiferroic properties of nanocrystalline Sm-doped BFO which is a promising multiferroic material.

Enhanced multiferroic properties of Y and Mn codoped multiferroic BiFeO3 nanoparticles

Enhancement of multiferroic properties of bismuth ferrite (BFO) is a real challenge to the scientific community. We are able to achieve improved magnetic and electric properties in chemically prepared nanocrystalline BFO by virtue of the beneficial effect of Y and Mn codoping. Phase purity and nanocrystalline nature of the samples have been confirmed using X-ray diffractometer and transmission electron microscope. The decrease in oxygen vacancies, local ferromagnetic spin configuration, and breaking of spin cycloid due to smaller size of crystallites are instrumental behind the enhancement of multiferroic properties. Large magnetodielectric coefficient (5.8xa0% at 1.5xa0T) for 1Y1Mn combination is observed at room temperature due to enhance coupling between ferromagnetic and ferroelectric ordering achieved by Y and Mn co-doping. We are able to achieve highest saturation magnetization, resistivity, dielectric constant, and lowest dielectric loss in 1Y1Mn co-doped samples compared with both pure BFO and with the other single or co-doped BFO. Our results demonstrate that the co-doping is an effective way to rectify various issues relevant for device applications.

Room temperature multiferroicity in orthorhombic LuFeO3

From the measurement of dielectric, ferroelectric, and magnetic properties, we observe simultaneous ferroelectric and magnetic transitions around ∼600u2009K in orthorhombic LuFeO3. We also observe suppression of the remanent polarization by ∼95% under a magnetic field of ∼15 kOe at room temperature. The extent of suppression of the polarization under magnetic field increases monotonically with the field. These results show that even the orthorhombic LuFeO3 is a room temperature multiferroic of type-II variety exhibiting quite a strong coupling between magnetization and polarization.

Gadolinium substitution induced defect restructuring in multiferroic BiFeO3: case study by positron annihilation spectroscopy

Positron annihilation spectroscopy (PAS) comprising of the measurements of positron lifetime and coincidence Doppler broadening spectra has been carried out to understand and monitor the evolution of the vacancy-type defects arising from the ionic deficiencies at lattice points of the multiferroic perovskite bismuth ferrite (BiFeO3) doped with 1, 5 and 10at% gadolinium (Gd 3+ ) ions. Negatively charged defects in the form of Bi 3+ monovacancies (V 3− Bi ) were present in the undoped nanocrystallites, which strongly trapped positrons. During the successive doping by Gd 3+ ions, the positron trapping efficiency decreased while the doped ions combined with the vacancies to form complexes, which became neutral. A fraction of the positrons got annihilated at the crystallite surfaces too, being evident from the very large positron lifetimes obtained and confirming the nano-size-specific characteristics of the samples. Further, the intercrystallite regions provided favourable sites for orthopositronium formation, although in minute concentrations. The dopant ion-complex formation was also depicted clearly by the defect characteristic S‐W plot. Also, the large change of electrical resistivity with Gd concentration has been explained nicely by invoking the defect information from the PAS study. The study has demonstrated the usefulness of an excellent method of defect identification in such a novel material system, which is vital information for exploiting them for further technological applications. (Some figures may appear in colour only in the online journal)

Enhancement of multiferroic properties and unusual magnetic phase transition in Eu doped bismuth ferrite nanoparticles

Improvement of the multiferroic properties of bismuth ferrite is essential for its practical application and commercialization in the growing field of spintronics. An unusual magnetic phase transition with the highest coercive field and excellent multiferroic behaviour has been observed in bismuth ferrite nanoparticles with an average size of 27 nm by proper substitution of bismuth (Bi3+) ions with europium (Eu3+) ions. The X-ray diffraction (XRD) result confirms that with up to 10% Eu substitution, the segregation of any phase other than BiFeO3 does not occur. A detailed structural analysis suggests that the substitution of Bi ions by Eu ions leads to lattice distortion and modification of the lattice parameters, micro-strain and crystallite size. The dc activation energy has been calculated from the Arrhenius relation and found to increase with an increase in Eu content. The dielectric permittivity of the sample increases with an increase in the concentration of Eu. Magnetic measurement depicts the exchange bias effect and surface phase transition near 100 K for the polycrystalline Eu-doped BiFeO3 (Bi1−xEuxFeO3) samples. The room temperature ferroelectric and magnetodielectric measurements indicate that the polarization and magnetodielectric constant increases significantly by virtue of Eu doping. All the observations suggested the materials to be potential candidates in the emerging field of spintronics.

Optical and electrical properties of codoped nanocrystalline multiferroic BiFeO3

Nanocrystalline multiferroic codoped bismuth ferrite (BFO) has been synthesized by using a sol-gel route. TEM analysis reveals that all the samples are pure and nanocrystalline in nature. We observed that electrical activation energy decreases for all the doped samples. Optical band gap also decreases for the doped samples which can be attributed to the creation of mid gap states.

Synthesis and characterization of TbMnO 3 nanorods

We report the synthesis and characterization of multiferroic TbMnO3 nanorods by sol-gel route. From XRD analysis it was observed that annealing at 700°C for 2h is the most favorable condition for the fabrication of TbMnO3 nano rods. The TEM study revealed that the diameter of these rods varied from 12.6 – 38.1nm and the length of these nanorods varied from 88.6 – 292 nm. SAED pattern of the nano rods revealed single crystalline structure. Presence of TbMnO3 nano particles was also observed alongwith the nanorods. UV, PL, F.T.I.R study on the samples annealed at different calcination condition is also reported.

Conductivity, Dielectric and Impedance Property Analysis of Y 1–X La x CrO 3 Nanoparticles

Perovskite-type La-doped Yttrium Chromite (Y1–XLaxCrO3) nanoparticles are prepared via sol–gel method. The formation of the compound is confirmed by X-ray diffraction (XRD) technique. Particle sizes are calculated by Transmission Electron Microscopy (TEM) measurements. Electrical DC conductivity is studied. DC conductivity analysis shows that all the samples have semiconducting behavior. Dc activation energy decreases when the lanthanum doping content is increased. The dielectric properties of all the samples are studied within the temperature range 298–523 K and in the frequency range 20–1 MHz. Impedance (AC) analysis suggests that the assistance of grain boundary governs over the grain.

Thermal and electrical transport properties of polyvinyl alcohol and bismuth ferrite nanocomposites film

The pure phase Bismuth ferrite (BFO) nanomaterial calcined at 500°C for 2hr. is synthesized by sol-gel method. From the TEM micrograph analysis the average particle size of BFO is calculated as 37nm. The polyvinyl alcohol (PVA) and PVA-BFO (2wt%) composites films are synthesized by drop casting method. The thermal stability of the composites films is increased with adding BFO 2wt% in PVA matrix and which is observed by TGA curve analysis. The variation of real part of dielectric constant and the ac electrical conductivity with frequency range 20Hz to 1MHz at different temperature range from 30°C to 130°C is measured. The electrical transport properties shows the correlated barrier hopping (CBH) model and it is well fitted with the experimental data which is measured from the ac conductivity plot.