Biennial Report 2005-2007 - Saha Institute of Nuclear Physics

Condensed Matter Physics 113quasi-continuous transition is due to the change in the anharmonic coupling parameter with thehole doping. The resistivity of LaMnO 3 decreases with the increase of temperature and showsan abrupt drop at T JT , becoming almost temperature independent at higher temperature. Theresistivity of La 1−x Ca x MnO 3 also decreases at T JT but the abrupt drop becomes smeared out athigher doping. The similar behavior of the unit cell volume and the resistivity at the Jahn-Tellertransition suggests that the volume contraction at T JT causes delocalization of e g electrons.T Chatterji†, D Riley†, F Fauth†, Prabhat Mandal, B GhoshECMP4.1.1.21 Electronic transport in ferroelectric-ferromagnetic La 5/8 (Ba,Ca) 3/8 MnO 3 :LuMnO 3 compositesAn almost complete immiscibility between metallic ferromagnet La 5/8 Ba 3/8 MnO 3 orLa 5/8 Ca 3/8 MnO 3 and insulating ferroelectric LuMnO 3 has been established from structural,magnetic, and transport studies. Both (x v )La 5/8 Ba 3/8 MnO 3 :(1 − x v )LuMnO 3 and(x v )La 5/8 Ca 3/8 MnO 3 :(1 − x v )LuMnO 3 show a metal-insulator transition below a critical volumefraction x vc of the metallic component. Over the entire range of volume fraction, x v > x vc , electronicconduction follows a classical percolation model. The conductivity (σ) scaling exponent tis the same as that of the universal value (=2) for the three-dimensional (3D) system; x vc is alsoclose to the theoretical prediction for the 3D continuum model.Fig.4.1.1.21. Square-root of conductivity (σ 1/2 ) versus metallic volume fraction x v :(a) (x v )La 5/8 Ba 3/8 MnO 3 : (1 − x v )LuMnO 3 and (b) (x v )La 5/8 Ca 3/8 MnO 3 : (1 −x v )LuMnO 3 . Solid lines represent linear behavior.For x v < x vc , the transport phenomenon is dominated by the insulating LuMnO 3 . The temperaturedependence of both resistivity and thermopower for 0 ≤x v ≤x vc shows that the conduction is due