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71.
Double-layered manganite La2−2xCa1+2xMn2O7 have been synthesized for compositions ‘x’=0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 by solid state reaction method. From X-ray diffraction study, their crystal structures were found to be tetragonal perovskite with lattice parameters decreasing with increasing ‘x’. The decreasing lattice parameters affect the balance between in-plane, intra-bilayer and inter-bilayer exchange interactions, which is reflected on magnetotransport properties. The metal-to-insulator transition temperature is found to vary with composition and peaked around ‘x’=0.3. From ac-susceptibility study, 2D-ferromagnetic ordering was observed at higher temperatures for all compositions whereas 3D-ferromagnetic ordering was observed at quite low temperatures. In low-temperature region, decreasing susceptibility shows antiferromagnetic state for all compositions. On the basis of electrical and magnetic properties, a magnetic phase diagram is given. 相似文献
72.
Rajesh Kumar Ajai K. Gupta Vijay Kumar Neeraj Khare 《Journal of Physics and Chemistry of Solids》2007,68(12):2394-2397
The influence of dc biasing current on temperature dependence of resistance of La0.67Ba0.33MnO3 bulk sample is reported. A decrease in the resistance (electroresistance) on the application of higher bias current is observed. The electroresistance is maximum at metal-insulator transition temperature (TMI) and decreases when the temperature is either increased or decreased from TMI. A two-phase model is proposed to explain the occurrence of electroresistance. The higher bias current leads to an increase in alignment of spins and thus, in turn, leads to an increase in spin stiffness coefficient and decrease in the resistance at TMI. 相似文献
73.
When a protein is aggregated by chemical crosslinking inside Sephadex beads of appropriate pore size, it gets trapped inside the beads. The above approach was used for immobilization of beta-galactosidase, acid phosphatase, trypsin, and concanavalin A. It was found to be a simple, convenient, and fast method for immobilization of proteins. 相似文献
74.
We describe a series of experiments in order to test a new sampling criterion for wavefront reconstruction from a carrier-frequency signal as obtained in electronic holography. Both a Fourier-transform configuration and a Fresnel-zone form of a digital holographic microscope are described. Direct coarse sampling of holograms with no phase-shifting elements can be used to obtain wavefront reconstruction, with the number of samples required reduced by the ratio f0/(2Bs), where f0 is the carrier frequency and 2Bs is the signal bandwidth. 相似文献
75.
An NMR study of the thiomalic acid complex of cobalt has been carried out at pH 2.6. The results show that the freshly prepared complex is paramagnetic and it gradually changes to the diamagnetic state, the reaction being complete in about 24 hours. It has been shown that the fresh complex has the hybridization sp3d2, whereas the stable complex has the hybridization d2sp3. The results have been confirmed by measuring the change in the magnetic susceptibility of the complex with time. 相似文献
76.
The partial wave method with a central potential has been applied to investigate the elastic scattering of electrons by the
argon atoms in the intermediate energy range (100 eV − 1 keV). The central potential includes the effects of the static field,
exchange and polarization. The results are in good accord with recent experimental data.
A brief account of this investigation was presented at the X Int. Conf. on the Physics of Electronic and Atomic Collisions
held at Paris in July 1977. 相似文献
77.
Avinash Khare 《Nuclear Physics B》1978,140(3):468-476
In view of the failure of the standard charmonium models to explain splittings, I consider various possible modifications to these models. In particular, I show that for power-law potentials the spin forces are most likely generated through the admixture of scalar-vector-Pauli moment exchanges and that this model can be tested by measuring the 1p1 mass. I also show that if instantons really generate a large spin-spin force, then the 1p1 mass must be as low as 3250–3270 MeV. 相似文献
78.
Several nonlinear systems such as the Korteweg-de Vries (KdV) and modified KdV equations and lambda phi(4) theory possess periodic traveling wave solutions involving Jacobi elliptic functions. We show that suitable linear combinations of these known periodic solutions yield many additional solutions with different periods and velocities. This linear superposition procedure works by virtue of some remarkable new identities involving elliptic functions. 相似文献
79.
Selective oxidation of ethylbenzene to acetophenone over Cr(III) Schiff base complex intercalated into layered double hydroxide
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A new heterogeneous catalyst, Cr(III) Schiff base‐containing layered double hydroxide, was synthesized using the intercalation method. The Cr(III) Schiff base complex derived from 2‐hydroxy‐1‐naphthaldehyde and 4‐aminobenzoic acid was intercalated into the layered double hydroxide. The synthesized materials were characterized using inductively coupled plasma atomic emission spectrometry, energy‐dispersive X‐ray analysis, scanning electron microscopy, X‐ray diffraction, Brunauer–Emmett–Teller surface area measurement, Fourier transform infrared spectroscopy, thermogravimetric analysis, diffuse reflectance UV–visible spectroscopy and electron paramagnetic resonance spectroscopy. The catalytic activity was investigated for the oxidation of ethylbenzene with tert‐butylhydroperoxide as an oxidant under solvent‐free conditions as well as with lower chromium concentrations. In the oxidation reaction, ethylbenzene was oxidized to acetophenone and benzaldehyde. The catalyst was recycled ten times without significant loss of catalytic activity. Leaching studies performed with hot filtration experiments showed that the chromium catalyst was heterogeneous in nature and stable under the reaction conditions. 相似文献
80.