Vasant Sathe

Effect of strain on the phase separation and devitrification of the magnetic glass state in thin films of La5/8 − yPryCa3/8MnO3 (y = 0.45)

We present our study of the effect of substrate induced strain on La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.45) thin films grown on LaAlO(3), NdGaO(3) and SrTiO(3) substrates that show large scale phase separation. It is observed that unstrained films grown on NdGaO(3) behave quite similarly to bulk material but the strained films grown on SrTiO(3) show melting of the insulating phase to the metallic phase at low temperatures. However, the large scale phase separation and metastable glass-like state is observed in all the films despite differences in substrate induced strain. The measurements of resistivity as a function of temperature under a cooling and heating in unequal field (CHUF) protocol elucidate the presence of a glass-like metastable phase generated due to kinetic arrest of the first order transformation in all the films. Like structural glasses, these magnetic glass-like phases show evidence of devitrification of the arrested charge order antiferromagnetic insulator (CO-AFI) phase to the equilibrium ferromagnetic metallic (FMM) phase with isothermal increase of magnetic field and/or iso-field warming. These measurements also clearly show the equilibrium ground state of this system to be FMM and the metastable glass-like phase to be AFI phase.

Raman spectroscopic studies on mixed alkali borotungsten glasses

Mixed alkali borate glasses of composition xLi2O-(30−x)K2O-10WO3-60B2O3 (0 ≤ x ≤ 30 mol%) were prepared by melt quench technique. The structure of present glass system was investigated by Raman spectroscopy. The characteristic bands of these glasses due to the stretching and bending vibrations were identified and analyzed by the increasing of alkali content. This fact allowed us to identify the specific structural units which appear in these glasses and thus to point out the network modifier role of alkali oxide for low concentrations and its former role at high concentrations.