Dr Dharmalingam Prabhakaran

Abstract:

We report the growth of single crystals of La1−xSrxCoO3+δ (x=0.0 and 0.33) by the floating-zone technique in an image furnace under high pressure (7–9 atm). Single crystals of diameter 10 mm and length 100 mm have been obtained. The phase purity, composition, oxygen stochiometry and quality of the crystals were analysed. We discuss the effect on the crystal growth of the growth atmosphere. We also present some of the magnetization data for the grown crystals.

Abstract:

An ac photopyroelectric calorimeter has been used to measure the thermal diffusivity of the perovskite manganite family La1-xSr xMnO3 on a set of single crystals with doping range 0≤x≤0.35. Taking into account that the inverse of the thermal diffusivity has the same critical behavior as the specific heat, the critical exponent a of the magnetic transitions has been obtained. The results point to short-range interaction models for pure magnetic transitions. In the pure and lightly doped samples (x<0.10), where the transition is antiferromagnetic-paramagnetic, the critical exponent is consistent with the Heisenberg model (α=-0.11). For the highly doped samples (x>0.28), where there is a pure ferromagnetic- paramagnetic transition, the critical exponent is exactly that of an Ising behavior (α=+0.11). For 0.10≤x<0.28 no universality class was found and this behavior has been discussed taking into account the complexity of the phase diagram in this concentration range.

Abstract:

Muonium centres in Cu2O, Ag2O and CdO show hyperfine parameters spanning four orders of magnitude. They exemplify the three different categories of hydrogen defect centre in semiconducting and dielectric solids, with very different electronic structure and electrical activity, namely quasi-atomic (possibly deep acceptor), deep donor and shallow donor. © Springer 2005.