S. M. Yusuf

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.

Magnetic behavior of iron-filled multiwalled carbon nanotubes

Using vibrating-sample magnetometry, magnetic properties of iron-filled multiwalled carbon nanotubes have been investigated. The field dependence of dc magnetization at high magnetic fields suggests that these tubes behave as a one-dimensional exchange-coupled ferromagnetic system. At 5K, the saturation magnetization (MS) of the nanowires is found to be 85emu∕g, which is much less than the expected bulk value ∼210emu∕g. The observed exchange bias, in spite of the small fraction of γ‐Fe in our samples, implies that γ‐Fe may not be the only antiferromagnetic component responsible for the exchange bias in these Fe-filled carbon nanotubes. Quantitative study on the temperature dependence of saturation magnetization, remanent magnetization and coercivity has been carried out.

Temperature- and magnetic-field-controlled magnetic pole reversal in a molecular magnetic compound

A highly reversible (bipolar) switching of magnetization in a Prussian blue type molecular magnet Cu0.73Mn0.77[Fe(CN)6]⋅zH2O using low magnetic fields is demonstrated. The studied molecular compound also shows both positive and negative magnetocaloric effects below its magnetic ordering temperature. A molecular field theory calculation has also been done to explain the observed temperature dependent magnetization reversal behavior. Possible applications of the magnetic pole reversal phenomenon in magnetoelectronic and magnetocaloric devices such as magnetic memory and magnetic cooling/heating based constant temperature bath have been revealed.

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.

Formation of shape-selective magnetic cobalt oxide nanowires: environmental application in catalysis studies

A new route for the formation of shape-selective CoO nanowires has been developed using a simple microwave (MW) heating method. The reduction of Co(II) ions was done using a new reducing agent alkaline 2,7-dihydroxy naphthalene (2,7-DHN) in cetyltrimethylammonium bromide (CTAB) micellar media. The reaction mixture was irradiated using MW for a total time of 6 min. The process exclusively generates CoO nanowires of different lengths and having diameter ∼5 ± 2 nm to 15 ± 2 nm range just by tuning the metal-ion-to-surfactant molar ratios and changing the other reaction parameters. Magnetization measurements indicate that there is no observable coercivity for the short nanowires, but the coercivity increases as the length of the nanowires increases although the magnetic moment values at the maximum applied magnetic field of 2 T decreased with an increase in the length of the nanowires. The synthesized CoO nanowires are found to serve as an effective catalyst for the mineralization of several organic dye molecules in the presence of NaBH4 in a short reaction time. The process assists the room temperature mineralization of the dyes and provides a cleanup measure of dye contaminated water bodies even in the presence or in the absence of light. The yield of the CoO nanowires with uniform shapes is found to be significantly high (>95%) and the nanowires are stable for more than a month under ambient conditions. The proposed synthesis method is efficient, straightforward, reproducible, and robust. Other than in catalysis, the cobalt oxide nanomaterials can also be applied for making pigments, lithium-ion battery materials, solid state sensors, or as anisotropy source for magnetic recording.

La1-xCexCrO3 (0.0 ≤ x ≤ 1.0): A New Series of Solid Solutions with Tunable Magnetic and Optical Properties

A new series of La(1-x)Ce(x)CrO(3) (0.0 <or= x <or=1.0) compounds in nanocrystalline form were synthesized using a two-step synthesis route, involving an initial combustion reaction followed by vacuum heating in the presence of a Zr sponge, which acted as an oxygen getter. For the first time, a homogeneous solid solution formation throughout the entire range was obtained in this series. These compounds were characterized using X-ray diffraction, diffuse reflectance UV visible spectrophotometry, and superconducting quantum interference device magnetometry. The crystallite size for the phase-pure products was confirmed to be approximately 42-44 nm by high-resolution transmission electron microscopy. All compounds (nanocrystalline) in this series are found to be predominantly antiferromagnetic in nature with a remarkable linear increasing trend in Neel temperature from 257 to 281.5 K as a function of decreasing Ce(3+) content. Interestingly, the band gap also shows a linear decrease from 3.21 to 3.02 eV as a function of increasing Ce(3+) concentration in the La(1-x)Ce(x)CrO(3) series.

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.

Improved magnetic and ferroelectric properties of Sc and Ti codoped multiferroic nano BiFeO3 prepared via sonochemical synthesis

The room temperature multiferroic properties of bulk BiFeO3 are not exciting enough for its application in devices. Here, we report the sonochemical synthesis of scandium and titanium codoped BiFeO3 nanoparticles which exhibit improved magnetic and ferroelectric properties at room temperature. The nanoparticles have been checked for phase purity and composition using powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). The size and morphology of the nanoparticles have been confirmed using scanning electron microscopy (SEM), and both low and high resolution transmission electron microscopy (TEM/HRTEM). The breaking of the spin cycloid due to the smaller size and slight structural distortion caused by the doping has been found to be instrumental for the enhancement of multiferroic properties. The electrical polarization increases significantly in the case of BiFe(0.925)Sc(0.05)Ti(0.025)O3 nanoparticles. A marked reduction in the leakage current was seen compared to undoped BiFeO3. Magnetoelectric coupling was also observed in the BiFe(0.925)Sc(0.05)Ti(0.025)O3 sample. Our results demonstrate that codoping with Sc and Ti ions is an effective way to rectify and enhance the multiferroic nature of BiFeO3.

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...