71 research outputs found
Crystal structure and physical properties of half-doped manganite nanocrystals with size < 100nm
In this paper we report the structural and property (magnetic and electrical
transport) measurements of nanocrystals of half-doped
(LCMO) synthesized by chemical route, having
particle size down to an average diameter of 15nm. It was observed that the
size reduction leads to change in crystal structure and the room temperature
structure is arrested so that the structure does not evolve on cooling unlike
bulk samples. The structural change mainly affects the orthorhombic distortion
of the lattice. By making comparison with observed crystal structure data under
hydrostatic pressure it is suggested that the change in the crystal structure
of the nanocrystals occurs due to an effective hydrostatic pressure created by
the surface pressure on size reduction. This not only changes the structure but
also causes the room temperature structure to freeze-in. The size reduction
also does not allow the long supercell modulation needed for the Charge
Ordering, characteristic of this half-doped manganite, to set-in. The magnetic
and transport measurements also show that the Charge Ordering (CO) does not
occur when the size is reduced below a critical size. Instead, the nanocrystals
show ferromagnetic ordering down to the lowest temperatures along with metallic
type conductivity. Our investigation establishes a structural basis for the
destabilization of CO state observed in half-doped manganite nanocrystals.Comment: 11 pages, 13 Figure
Electrical transport properties of nanostructured ferromagnetic perovskite oxides La_0.67Ca_0.33MnO_3 and La_0.5Sr_0.5CoO_3 at low temperatures (5 K > T >0.3 K) and high magnetic field
We report a comprehensive study of the electrical and magneto-transport
properties of nanocrystals of La_0.67Ca_0.33MnO_3 (LCMO) (with size down to 15
nm) and La_0.5Sr_0.5CoO_3 (LSCO) (with size down to 35 nm) in the temperature
range 0.3 K to 5 K and magnetic fields upto 14 T. The transport,
magnetotransport and non-linear conduction (I-V curves) were analysed using the
concept of Spin Polarized Tunnelling in the presence of Coulomb blockade. The
activation energy of transport, \Delta, was used to estimate the tunnelling
distances and the inverse decay length of the tunnelling wave function (\chi)
and the height of the tunnelling barrier (\Phi_B). The magnetotransport data
were used to find out the magnetic field dependences of these tunnelling
parameters. The data taken over a large magnetic field range allowed us to
separate out the MR contributions at low temperatures arising from tunnelling
into two distinct contributions. In LCMO, at low magnetic field, the transport
and the MR are dominated by the spin polarization, while at higher magnetic
field the MR arises from the lowering of the tunnel barrier by the magnetic
field leading to an MR that does not saturate even at 14 T. In contrast, in
LSCO, which does not have substantial spin polarization, the first contribution
at low field is absent, while the second contribution related to the barrier
height persists. The idea of inter-grain tunnelling has been validated by
direct measurements of the non-linear I-V data in this temperature range and
the I-V data was found to be strongly dependent on magnetic field. We made the
important observation that a gap like feature (with magnitude ~ E_C, the
Coulomb charging energy) shows up in the conductance g(V) at low bias for the
systems with smallest nanocrystal size at lowest temperatures (T < 0.7 K). The
gap closes as the magnetic field and the temperature are increased.Comment: 13 figure
A Hydrofluoric Acid-Free Green Synthesis of Magnetic M.Ti2CTx Nanostructures for the Sequestration of Cesium and Strontium Radionuclide
MAX phases are the parent materials used for the formation of MXenes, and are generally obtained by etching using the highly corrosive acid HF. To develop a more environmentally friendly approach for the synthesis of MXenes, in this work, titanium aluminum carbide MAX phase (Ti2AlC) was fabricated and etched using NaOH. Further, magnetic properties were induced during the etching process in a single-step etching process that led to the formation of a magnetic composite. By carefully controlling etching conditions such as etching agent concentration and time, different structures could be produced (denoted as M.Ti2CTx). Magnetic nanostructures with unique physico-chemical characteristics, including a large number of binding sites, were utilized to adsorb radionuclide Sr2+ and Cs+ cations from different matrices, including deionized, tap, and seawater. The produced adsorbents were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The synthesized materials were found to be very stable in the aqueous phase, compared with corrosive acid-etched MXenes, acquiring a distinctive structure with oxygen-containing functional moieties. Sr2+ and Cs+ removal efficiencies of M.Ti2CTx were assessed via conventional batch adsorption experiments. M.Ti2CTx-AIII showed the highest adsorption performance among other M.Ti2CTx phases, with maximum adsorption capacities of 376.05 and 142.88 mg/g for Sr2+ and Cs+, respectively, which are among the highest adsorption capacities reported for comparable adsorbents such as graphene oxide and MXenes. Moreover, in seawater, the removal efficiencies for Sr2+ and Cs+ were greater than 93% and 31%, respectively. Analysis of the removal mechanism validates the electrostatic interactions between M.Ti2C-AIII and radionuclides
Synthesis of BaTiO3-CoFe2O4 nanocomposites using a one-pot technique
Abstract Low-cost and scalable sol–gel chemistry was employed to obtain ferroelectric-ferrimagnetic BaTiO3-CoFe2O4 nanocomposites. In a novel one-pot synthesis method, both the constituent phases of nanocomposites are formed during the same time and symbiotically participate to each other's growth. X-ray powder diffraction evidences the phase purity of the systems, with average crystallite sizes in the order of 20 nm for the BaTiO3 phase. The optimization of the synthesis conditions, precursors, and chemical agents for nanoscale BaTiO3 and BaTiO3-CoFe2O4 nanocomposites is presented, together with the magnetic and/or dielectric properties of the obtained materials. BaTiO3-CoFe2O4 nanocomposites with up to 20% CoFe2O4 volume fractions were found to display ferrimagnetic properties at room temperature akin to those of CoFe2O4, while preserving a dielectric behavior reminiscent of BaTiO3. Preliminary results describing the spin coating of BaTiO3 and BaTiO3-CoFe2O4 nanocomposites as thin films are also reported
Kinetics of Oxidation of Neutralized Glyoxylic & Pyruvic Acids by Alkaline Hexacyanoferrate(III)
583-58
Exploring the magnetic properties and magnetic coupling in SrFe12O19/Co1-xZnxFe2O4 nanocomposites
Abstract Among hard/soft nanocomposites (NCs), ferrite-based materials are potentially promising for developing exchange-coupled systems, thus leading to enhanced magnetic properties. In this regard, we investigate the role of the synthesis approach in the development of SrFe12O19/CoFe2O4 (SFO/CFO) NCs, with special focus on tuning the magnetic features of the softer phase (CFO) by introducing Zn2+ in the spinel structure. X-ray powder diffraction (XRPD), transmission electron microscopy (TEM) and squid magnetometry were employed to clarify the relationship between morphology, size, and magnetic properties of the NCs, pointing out the feasibility of this method in obtaining successfully exchange-coupled systems. This work shows how optimizing the intrinsic magnetic properties of the CFO may be used to tune the extrinsic ones of the NCs. Despite the promising results in magnetic coupling, our study clearly confirms/strengthens that an enhancement of remanent magnetization is the most important factor for improving the magnetic performance
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