Dr Dharmalingam Prabhakaran

Abstract:

Magnetoelectronic phase separation plays an integral part in many recent advances in the understanding of correlated electron systems. We have studied the magnetically phase separated material La1-x Srx Co O3 and observe unambiguous evidence of magnetic interactions between hole-rich ferromagnetic clusters and the neighboring hole poor matrix. We suggest that this mechanism detected here plays an important role in the rich electrical and magnetic properties of La1-x Srx Co O3. © 2006 The American Physical Society.

Abstract:

The structure of bilayer manganite LaSr2Mn2O7 has been investigated under high pressure using synchrotron and laboratory X-rays in the angle-dispersive X-ray diffraction geometry up to 35 GPa at ambient temperature. The Rietveld refinement results of the powder diffraction data show a crossover between the axial and equatorial Mn-O bond length values and a significant suppression of Jahn-Teller (JT) distortion around 16 GPa. Our results imply that a re-entrant behavior in LaSr2Mn2O7, which shows equality in all the three Mn-O bond length values around 16 GPa similar to ambient conditions, may dramatically alter the orbital ordering. Further, the P-V data for the bilayer compounds indicate that the additional substitution of La3+ for Sr2+ lowers the bulk modulus and enhances lattice softening. © 2006 Elsevier Ltd. All rights reserved.

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.