Paolo Podio-Guidugli, Universita degli Studi di Roma Tor Vergata.
"Strain-induced phase transitions at the nanoscale: the case of colossal-magnetoresistance manganites"
Many electronically complex materials, such as cuprates and manganites, exhibit temperature-dependent, nonuniform spatial textures arising from multiscale modulations of charge, spin, polarization, and strain variables. In particular, A-doped rare-earth perovskite manganites of the form ReAMnO, with Re a rare earth and A an alkali element, are ferromagnetic metals at low temperature and paramagnetic insulators at high temperature. The applicative interest of these materials lies in the fact that they exhibit colossal magnetoresistance in the vicinity of the critical temperature for such transition. It has been experimentally proved that their critical temperature depends strongly on strain, both when they are `chemically deformed' by substituting the rare earth with an element with different atomic radius  and when deposition on a mismatching substrate induces biaxial epitaxial strain . The effect of epitaxial strain is also known to have dramatic consequences on the critical temperature of certain perovskite cuprates, which are high-T superconductors .
In this talk, which is based on ongoing work with Paolo Cermelli (University of Torino), I shall discuss a model for the epitaxial strain dependence of the ferromagnetic critical temperature of perovskite manganites using an approach similar to the one we developed to describe the strain dependence of normal-to-super T in the strontium-doped perovskite cuprate commonly referred to by the acronym LASCO .
TUESDAY, May 24, 2005