Dr Dharmalingam Prabhakaran

Abstract:

The effect of uniaxial pressure on resistivity along the ab plane (ρab) and c axis (ρc) in single crystals of bilayer manganite La1.25 Sr1.75 Mn2 O7 has been investigated. A prominent finding is the asymmetric role of pressure on charge transport phenomenon. With increasing pressure along the c axis, ρab decreases and the metal-insulator (MI) transition temperature shifts towards higher temperature at the rate of 46 K GPa. In contrary to this, ρc increases and the MI transition temperature decreases with increasing pressure along the ab plane. The resistivity ratio ρc ρab is quite large, increases with pressure, and shows a peak at around the MI transition. We believe that the unusual behavior of transport properties is related to the Mn-O-Mn linkage between MnO2 layers and the spin reorientation from the c axis to the basal plane and vice versa with pressure. © 2006 The American Physical Society.

Abstract:

We present the results of a muon-spin relaxation study of Ge Ni2 O4. We provide further clarification of the two transitions to the antiferromagnetic state and measure the magnetic field dependence of the heat capacity up to 14 T. Both oscillatory and relaxing signals are observed below the lower transition (at temperature TN2) in the muon-decay positron asymmetry spectra, arising from two distinct types of magnetic environment. A possible explanation is suggested in terms of the separate ordering of two magnetic subsystems, one of which does not order fully down to the lowest measured temperature (1.8 K). © 2006 The American Physical Society.

Abstract:

We report muon-spin rotation, heat capacity, magnetization, and AC magnetic susceptibility measurements of the magnetic properties of the layered spin-1/2 antiferromagnet NaNiO2. These show the onset of long-range magnetic order below T-N = 19.5K. The temperature dependence of the muon precession frequency suggests 2D XY magnetic ordering. Rapid muon depolarization persisting to about 5 K above TN is consistent with the presence of short-range magnetic order. Our AC susceptibility measurements suggest that magnetic clusters persist above 25 K, with their volume fraction decreasing with increasing temperature, and that there is a slowing of spin fluctuations at T-sf = 3 K. A partial magnetic phase diagram has been deduced. (c) 2006 Elsevier B.V. All rights reserved.

Abstract:

We report muon-spin rotation, heat capacity, magnetization, and AC magnetic susceptibility measurements of the magnetic properties of the layered spin-1/2 antiferromagnet NaNiO2. These show the onset of long-range magnetic order below TN=19.5K. The temperature dependence of the muon precession frequency suggests 2D XY magnetic ordering. Rapid muon depolarization persisting to about 5K above TN is consistent with the presence of short-range magnetic order. Our AC susceptibility measurements suggest that magnetic clusters persist above 25K, with their volume fraction decreasing with increasing temperature, and that there is a slowing of spin fluctuations at Tsf=3K. A partial magnetic phase diagram has been deduced. © 2006 Elsevier B.V. All rights reserved.

Abstract:

Nanocrystalline CuFe2O4 and CuFe2O 4/xSnO2 nanocomposites (x=0, 1, 5 wt%) have been successfully synthesized by one-pot reaction of urea-nitrate combustion method. The transmission electron microscope study reveals that the particle size of the as synthesized CuFe2O4 and CuFe2O 4/5 wt%SnO2 are 10 and 20 nm, respectively. The SnO 2 coating on the nanocrystalline CuFe2O4 was confirmed from HRTEM studies. The resultant products were sintered at 1100 °C and characterized by XRD and SQUID for compound formation and magnetic studies, respectively. The X-ray diffraction pattern shows the well-defined sharp peak that confirms the phase pure compound formation of tetragonal CuFe2O4. The zero field cooled (ZFC) and field cooled (FC) magnetization was performed using SQUID magnetometer from 2 to 350 K and the magnetic hysteresis measurement was carried out to study the magnetic properties of nanocomposites.