OALib Journal期刊

ISSN: 2333-9721



匹配条件: “Chandrabhas Narayana” ,找到相关结果约537条。
Raman based imaging in biological application- a perspective
Partha P. Kundu,Chandrabhas Narayana
Journal of Medical and Allied Sciences , 2012,
Abstract: Imaging by means of Raman spectroscopy has emerged as a powerful technique in the study of various chemical processes occurring in biology. This technique is non-invasive, label-free, capable of providing molecular identity and can be performed in robust conditions. However, one major drawback is its inherently weak signal. The ways to overcome this issue is to use Raman based methods e.g. Resonance Raman Spectroscopy (RRS), Surface Enhanced Raman Spectroscopy (SERS), Tip Enhanced Raman Spectroscopy (TERS). In this review, we gave a brief introduction of all these methods, with special emphasis on their recent advances and applications in various fields of life science.
Spin-phonon coupling in multiferroic RCrO$_3$ (R-Y, Lu, Gd, Eu, Sm): A Raman study
Venkata Srinu Bhadram,B. Rajeswaran,A. Sundaresan,Chandrabhas Narayana
Physics , 2012, DOI: 10.1209/0295-5075/101/17008
Abstract: Raman study on a select few orthochromites, RCrO$_3$ (R = Y, Lu, Gd, Eu and Sm) shows that the phonon behavior at TN in compounds with magnetic R-ion (Gd and Sm) is remarkably different from that of non-magnetic R-ion (Y, Lu and Eu). While anomalies in most of the observed phonon frequencies in all these compounds may result from the distortion of CrO$_6$ octahedra due to size effect and magnetostriction arising from Cr-ordering, the anomalous behavior of their linewidths observed at TN for the compounds with only magnetic R-ion suggests spin-phonon coupling. The presence of spin-phonon coupling and the anomalies in the low frequency modes related to R-ion motion in orthochromites (R = Gd and Sm) support the suggestion that the coupling between 4f-3d moments play important role in inducing switchable electric polarization.
Electronic and vibrational Raman spectroscopy of Nd$_{0.5}$Sr$_{0.5}$MnO$_3$ through the phase transitions
Md. Motin Seikh,A. K. Sood,Chandrabhas Narayana
Physics , 2005,
Abstract: Raman scattering experiments have been carried out on single crystals of Nd$_{0.5}$Sr$_{0.5}$MnO$_3$ as a function of temperature in the range of 320-50 K, covering the paramagnetic insulator-ferromagnetc metal transition at 250 K and the charge-ordering antiferromagnetic transition at 150 K. The diffusive electronic Raman scattering response is seen in the paramagnetic phase which continue to exist even in the ferromagnetic phase, eventually disappearing below 150 K. We understand the existence of diffusive response in the ferromagnetic phase to the coexistence of the different electronic phases. The frequency and linewidth of the phonons across the transitions show significant changes, which cannot be accounted for only by anharmonic interactions.
Elastic and structural instability of cubic Sn3N4 and C3N4 under pressure
Gopal K. Pradhan,Anil Kumar,Umesh V. Waghmare,Sudip K. Deb,Chandrabhas Narayana
Physics , 2010, DOI: 10.1103/PhysRevB.82.144112
Abstract: We use in-situ high pressure angle dispersive x-ray diffraction measurements to determine the equation of state of cubic tin nitride Sn3N4 under pressure up to about 26 GPa. While we find no evidence for any structural phase transition, our estimate of the bulk modulus (B) is 145 GPa, much lower than the earlier theoretical estimates and that of other group IV-nitrides. We corroborate and understand these results with complementary first-principles analysis of structural, elastic and vibrational properties of group IV-nitrides, and predict a structural transition of Sn3N4 at a higher pressure of 88 GPa compared to earlier predictions of 40 GPa. Our comparative analysis of cubic nitrides shows that bulk modulus of cubic C3N4 is the highest (379 GPa) while it is structurally unstable and should not exist at ambient conditions.
Griffiths phase-like behaviour and spin-phonon coupling in double perovskite Tb$_{2}$NiMnO$_{6}$
Harikrishnan S. Nair,Diptikanta Swain,Hariharan N.,Shilpa Adiga,Chandrabhas Narayana,Suja Elizabeth
Physics , 2011, DOI: 10.1063/1.3671674
Abstract: The Griffiths phase-like features and the spin-phonon coupling effects observed in Tb$_2$NiMnO$_6$ are reported. The double perovskite compound crystallizes in monoclinic $P2_1/n$ space group and exhibits a magnetic phase transition at $T_c \sim$ 111 K as an abrupt change in magnetization. A negative deviation from ideal Curie-Weiss law exhibited by 1/$\chi(T)$ curves and less-than-unity susceptibility exponents from the power-law analysis of inverse susceptibility are reminiscent of Griffiths phase-like features. Arrott plots derived from magnetization isotherms support the inhomogeneous nature of magnetism in this material. The observed effects originate from antiferromagnetic interactions which arise from inherent disorder in the system. Raman scattering experiments display no magnetic-order-induced phonon renormalization below $T_c$ in Tb$_2$NiMnO$_6$ which is different from the results observed in other double perovskites and is correlated to the smaller size of the rare earth. The temperature evolution of full-width-at-half-maximum for the {\it stretching} mode at 645 cm$^{-1}$ presents an anomaly which coincides with the magnetic transition temperature and signals a close connection between magnetism and lattice in this material.
Brillouin scattering studies in Fe$_3$O$_4$ across the Verwey transition
Md. Motin Seikh,Chandrabhas Narayana,P. A. Metcalf,J. M. Honig,A. K. Sood
Physics , 2003, DOI: 10.1103/PhysRevB.71.174106
Abstract: Brillouin scattering studies have been carried out on high quality single crystals of Fe$_3$O$_4$ with [100] and [110] faces in the temperature range of 300 to 30 K. The room temperature spectrum shows a surface Rayleigh wave (SRW) mode at 8 GHz and a longitudinal acoustic (LA) mode at 60 GHz. The SRW mode frequency shows a minimum at the Verwey transition temperature $T_V$ of 123 K. The softening of the SRW mode frequency from about 250 K to $T_V$ can be quantitatively understood as a result of a decrease in the shear elastic constant C$_{44}$, arising from the coupling of shear strain to charge fluctuations. On the other hand, the LA mode frequency does not show any significant change around $T_V$, but shows a large change in its intensity. The latter shows a maximum at around 120 K in the cooling run and at 165 K in the heating run, exhibiting a large hysteresis of 45 K. This significant change in intensity may be related to the presence of stress-induced ordering of Fe$^{3+}$ and Fe$^{2+}$ at the octahedral sites, as well as to stress-induced domain wall motion.
Brillouin Scattering Studies of La_{0.77}Ca_{0.23}MnO_3 Across Metal-Insulator Transition
Md. Motin Seikh,Chandrabhas Narayana,L. Sudheendra,A. K. Sood,C. N. R. Rao
Physics , 2003, DOI: 10.1088/0953-8984/16/24/019
Abstract: Temperature-dependent Brillouin scattering studies have been carried out on La_{0.77}Ca_{0.23}MnO_3 across the paramagnetic insulator - ferromagnetic metal (I-M) transition. The spectra show a surface Rayleigh wave (SRW) and a high velocity pseudo surface acoustic wave (HVPSAW) besides bulk acoustic waves (BAW). The Brillouin shifts associated with SRW and HVPSAW show blue-shifts, where as the frequencies of the BAW decrease below the I-M transition temperature (T_C) of 230 K. These results can be understood based on the temperature dependence of the elastic constants. We also observe a central peak whose width is maximum at T_C.
Effect of pressure on octahedral distortions in RCrO3 (R = Lu, Tb, Gd, Eu, Sm): The role of R-ion size and its implications
Venkata Srinu Bhadram,Diptikanta Swain,R Dhanya,Maurizio Polentarutti,A Sundaresan,Chandrabhas Narayana
Physics , 2013, DOI: 10.1088/2053-1591/1/2/026111
Abstract: The effect of rare-earth ion size on the octahedral distortions in rare-earth chromites (RCrO3, R = Lu, Tb, Gd, Eu, Sm) crystallizing in the orthorhombic structure has been studied using Raman scattering and synchrotron powder x-ray diffraction up to 20 GPa. From our studies on RCrO3 we found that the octahedral tilts (distortions) increase with pressure. This is contrary to the earlier report which suggests that in LaCrO3, the distortions decrease with pressure leading to a more ordered phase at high pressure. Here we observe that the rate of increase in distortion decreases with the increase in R-ion radii. This occurs due to the reduction in the compression of RO12 polyhedra with a corresponding increase in the compression of the CrO6 octahedra with increasing R-ion radii. From the Raman studies, we predict a critical R-ion radii, above which we expect the distortions in RCrO3 to reduce with increasing pressure leading to what is observed in the case of LaCrO3. These Raman results are consistent with our pressure dependent structural studies on RCrO3 (R = Gd, Eu, Sm). Also, our results suggest that the pressure dependence of N\'eel temperature, TNCr, (where the Cr3+ spin orders) in RCrO3 is mostly affected by the compressions of Cr-O bonds rather than the alteration of octahedral tilts.
Influence of lattice distortion on the Curie temperature and spin-phonon coupling in LaMn$_{0.5}$Co$_{0.5}$O$_{3}$
M. Viswanathan,P. S. Anil Kumar,Venkata Srinu Bhadram,Chandrabhas Narayana,A. K. Bera,S. M. Yusuf
Physics , 2010, DOI: 10.1088/0953-8984/22/34/346006
Abstract: Two distinct ferromagnetic phases of LaMn$_{0.5}$Co$_{0.5}$O$_{3}$ having monoclinic structure with distinct physical properties have been studied. The ferromagnetic ordering temperature $\textit{T}_{c}$ is found to be different for both the phases. The origin of such contrasting characteristics is assigned to the changes in the distance(s) and angle(s) between Mn - O - Co resulting from distortions observed from neutron diffraction studies. Investigations on the temperature dependent Raman spectroscopy provide evidence for such structural characteristics, which affects the exchange interaction. The difference in B-site ordering which is evident from the neutron diffraction is also responsible for the difference in $\textit{T}_{c}$. Raman scattering suggests the presence of spin-phonon coupling for both the phases around the $\textit{T}_{c}$. Electrical transport properties of both the phases have been investigated based on the lattice distortion.
Pressure-induced phonon-freezing in the ZnBeSe alloy: a study via the percolation mesoscope
Gopal K. Pradhan,Chandrabhas Narayana,Olivier Pages,Abedalhasan Breidi,Jihane Souhabi,Andrei Viktor Postnikov,Fouad El Haj Hassan,Sudip K. Deb,Franciszek Firszt,Wojtek Paszkowicz,Abhay Shukla
Physics , 2009, DOI: 10.1103/PhysRevB.81.115207
Abstract: We use the 1-bond -> 2-phonon percolation doublet of zincblende alloys as a mesoscope for an unusual insight into their phonon behavior under pressure. We focus on (Zn,Be)Se and show by Raman scattering that the original Be-Se doublet at ambient pressure, of the stretching-bending type, turns into a pure-bending singlet at the approach of the high-pressure ZnSe-like rocksalt phase, an unnatural one for the Be-Se bonds. The freezing of the Be-Se stretching mode is discussed within the scope of the percolation model (mesoscopic scale), with ab initio calculations in support (microscopic scale).

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