Browsing by Author "J. Lourembam"

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Particle size dependence on the structural, transport and optical properties of charge-ordered Pr0.6Ca0.4MnO3
(Elsevier Ltd, 2015) Satyam Kumar; G.D. Dwivedi; J. Lourembam; Shiv Kumar; U. Saxena; A.K. Ghosh; H. Chou; Sandip Chatterjee
Abstract Structural, transport and optical properties of nano-crystalline Pr0.6Ca0.4MnO3 have been investigated to emphasize on the semiconducting properties of charge-ordered manganite. Rietveld refinement of X-ray diffraction pattern of Pr0.6Ca0.4MnO3 nanoparticles show that due to increase in sintering temperature, MnO6 octahedra elongated along z-direction and compressed in x-y plane. Both Mn-O-Mn angles are found to decrease with increasing sintering temperature. Fourier transform infrared (FTIR) spectroscopy measurements reveal that the stretching and bending vibration of Mn-O-Mn is responsible for the change in Mn-O-Mn bond length and bond angle respectively. With increasing sintering temperature, these vibrations tend to increase, which resulted in the further distortion of MnO6 octahedra. Magnetic measurements suggest that charge ordering is established and system becomes antiferromagnetic with increasing particle size. Resistivity behavior of Pr0.6Ca0.4MnO3 nanoparticles clearly exhibit semiconducting nature of these systems, which is due to the formation of charge-ordered state of Mn3+ and Mn4+. Estimated optical band-gap of ∼3.7 eV for Pr0.6Ca0.4MnO3 nanocrystals, makes it a potential candidate for wide band-gap magnetic semiconductors. © 2015 Published by Elsevier B.V.
Signature of ferroelectricity in magnetically ordered Mo-doped CoFe 2O4
(2010) G.D. Dwivedi; K.F. Tseng; C.L. Chan; P. Shahi; J. Lourembam; B. Chatterjee; A.K. Ghosh; H.D. Yang; Sandip Chatterjee
Coexistence of both magnetic ordering and ferroelectricity (with giant dielectric constant) have been observed for the first time in Co(Fe 1-xMox)2O4. The magnetization of Co(Fe1-xMox)2O4 ranges from 0 to 0.1) was found to increase with doping concentration of Mo. The magnetic properties indicate that Mo goes into the tetrahedral site. The giant dielectric constant may be attributed to the Maxwell-Wagner relaxation mechanism. © 2010 The American Physical Society.