P. K. Manna

Fabrication of porous β-Co(OH)2 architecture at room temperature: a high performance supercapacitor.

A facile, cost-effective, surfactant-free chemical route has been demonstrated for the fabrication of porous β-Co(OH)2 hierarchical nanostructure in gram level simply by adopting cobalt acetate as a precursor salt and ethanolamine as a hydrolyzing agent at room temperature. A couple of different morphologies of β-Co(OH)2 have been distinctly identified by varying the mole ratio of the precursor and hydrolyzing agent. The cyclic voltammetry measurements on β-Co(OH)2 displayed significantly high capacitance. The specific capacitance obtained from charge-discharge measurements made at a discharge current of 1 A/g is 416 F/g for the Co(OH)2 sample obtained at room temperature. The charge-discharge stability measurements indicate retention of specific capacitance about 93% after 500 continuous charge-discharge cycles at a current density of 1 A g(-1). The capacitive behavior of the other synthesized morphology was also accounted. The nanoflower-shaped porous β-Co(OH)2 with a characteristic three-dimensional architecture accompanied highest pore volume which made it promising electrode material for supercapacitor application. The porous nanostructures accompanied by high surface area facilitates the contact and transport of electrolyte, providing longer electron pathways and therefore giving rise to highest capacitance in nanoflower morphology. From a broad view, this study reveals a low-temperature synthetic route of β-Co(OH)2 of various morphologies, qualifying it as supercapacitor electrode material.

Coexistence of sign reversal of both magnetization and exchange bias field in the core-shell type La0.2Ce0.8CrO3 nanoparticles

We report an extraordinary coexistence of sign reversal of both magnetization and exchange bias field in the La0.2Ce0.8CrO3 nanoparticles. From the high resolution transmission electron microscopy image, and field dependence of thermoremanent and isothermoremanent magnetization measurements, the nanoparticles are found to be of core-shell nature. The core-shell configuration with an antiferromagnetic core of the Cr3+ and Ce3+ spins and a disordered shell with the uncompensated spins, explains the sign reversal of both magnetization and exchange bias field. The present study shows an excellent way of tuning the sign of both magnetization and exchange bias field in a single magnetic system.

Enhanced grain surface effect on magnetic properties of nanometric La0.7Ca0.3MnO3 manganite: Evidence of surface spin freezing of manganite nanoparticles

We have investigated the effect of nanometric grain size on magnetic properties of La0.7Ca0.3MnO3 nanoparticles having average particle size (Φ) of ∼17 nm. Temperature dependence of field-cooled (FC) and zero-FC (ZFC) dc magnetization indicate the existence of two different types of relaxation processes: a relatively high temperature regime where there is a broad maximum of the ZFC curve at T=Tmax (>40 K) and another is a relatively low temperature regime that is characterized by a sharp maximum at T=TS (≈40 K). We believe that the broad maximum at Tmax is associated with the blocking of core particle moments, whereas the sharp maximum at TS is related to the freezing of surface spins. Waiting time (tw) dependence of ZFC relaxation measurements at T=50 K show weak dependence of relaxation rate [S(t)] on tw and dM/d ln(t) following a logarithmic variation in time. These features strongly support superparamagnetic (SPM) blocking of core particle moments at Tmax. At T=20 K, S(t) attains a maximum at tw=1000 ...

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.

Tin oxide with a p–n heterojunction ensures both UV and visible light photocatalytic activity

Tuning of the tin oxide (SnO/SnO2) heterojunction (TOHJ) has been made possible by heating the as-prepared p-type SnO semiconductor in air in a controlled fashion. Thus a better photocatalytic activity for dye degradation under UV, visible as well as solar light irradiation was achieved. Multiple reflection of light and the TOHJ of SnO plates facilitate the photocatalysis reactions.

A study of exchange bias in BiFeO3 core/NiFe2O4 shell nanoparticles

We have carried out magnetization measurements on BiFeO3 core/NiFe2O4 shell nanoparticles, and searched for the exchange bias phenomenon in this system. The core-shell nature of these nanoparticles has been established from the transmission electron microscopy images. The neutron diffraction study establishes that the core is G-type antiferromagnetic, while the shell is ferrimagnetic in nature. The search for an exchange bias phenomenon in the core-shell system shows a shift of the field-cooled (FC) hysteresis loops, at 5 K, along the magnetic field axis. The present investigation shows an unusual shift of the zero field-cooled (ZFC) hysteresis loop along the magnetic field axis as well. An enhancement of the remanent magnetization along with a decrease in the coercivity is also observed in the FC case, as compared to the corresponding values in the ZFC case, which is not found commonly in any conventional exchange-biased system. All these features indicate the presence of an interface exchange coupling b...

The magnetic proximity effect in a ferrimagnetic Fe3O4 core/ferrimagnetic γ-Mn2O3 shell nanoparticle system

We report the magnetic proximity effect in a ferrimagnetic Fe(3)O(4) core/ferrimagnetic γ-Mn(2)O(3) shell nanoparticle system, in terms of an enhancement of the Curie temperature (T(c)) of the γ-Mn(2)O(3) shell (~66 K) compared to its bulk value (~40 K), and the presence of magnetic ordering in its so-called paramagnetic region (i.e. above 66 K). The ferrimagnetic nature of both core and shell has been found from a neutron diffraction study. The origin of these two features of the magnetic proximity effect has been ascribed to the proximity of the γ-Mn(2)O(3) shell with a high-T(c) Fe(3)O(4) core (~858 K in bulk form) and an interface exchange coupling between core and shell. Interestingly, we did not observe any exchange bias effect, which has been interpreted as a signature of a weak interface exchange coupling between core and shell. The present study brings out the importance of the relative strength of the interface coupling in governing the simultaneous occurrence of the magnetic proximity effect and the exchange bias phenomenon in a single system.

Pole-reversal of magnetization in core-shell type La1?xCexCrO3(x = 0.8-1.0) nanoparticles

We report, for the first time, temperature dependent pole-reversal of magnetization for La1−xCexCrO3 (x = 0.8, 1.0) nanoparticles. The Rietveld refinement of the x-ray diffraction patterns confirmed the single phase nature of the samples (Orthorhombic: Pbnm). From the transmission electron microscopy (TEM) image, the average particle size is found to be ~ 44 nm. High resolution TEM reveals surface defects/roughness which corroborates a core-shell nature. The magnetic properties of these nanoparticles have been tuned by Ce3+ substitution. The novel pole-reversal phenomenon has been explained using the core-shell model, and can be exploited to fabricate advanced magnetic memory devices.

Magnetic Ordering in La1−xCexCrO3 (x = 0.2, 0.8, 1.0) Nanoparticles

We report the exact nature of magnetic ordering in La1−xCexCrO3 (x = 0.2, 0.8, 1.0) nanoparticles (diameter: ∼43 nm) using microscopic and macroscopic measurement techniques. The variable temperature neutron diffraction experiments revealed a G‐type antiferromagnetic ordering of Cr3+ ions in an orthorhombic perovskite structure with magnetic moment oriented along the crystallographic b‐axis. A decrease in Neel temperature has been observed with increasing x, which has been assigned to a decrease in the Cr‐O‐Cr bond angle obtained from the Rietveld refinement analysis of the neutron diffraction patterns. The observed decrease in lattice parameters with increasing x has been explained in terms lesser ionic radius of Ce3+ (1.34 A) ion compared to that of La3+ (1.36 A).