Biennial Report 2005-2007 - Saha Institute of Nuclear Physics

Condensed Matter Physics 109ing the coexistence of ferromagnetic and CO states. We have prepared nanocrystalline sample ofPri 0.65 (Ca 0.7 Sr 0.3 ) 0.35 MnO 3 , Pr 0.65 (Ca 0.6 Sr 0.4 ) 0.35 MnO 3 and Pr 0.65 (Ca 0.5 Sr 0.5 ) 0.35 MnO 3 . The studieson Pr 0.65 (Ca 0.6 Sr 0.4 ) 0.35 MnO 3 have indicated that the co-existence of CO and metallic stateexists. The insulator to metal transition for the nanocrystalline sample is shifted to the lower temperaturein comparison with the bulk for the smallest particle sized nanocrystalline sample (∼40nm). A large hysteresis is achieved in the temperature dependence of resistivity and the magneticfield dependence of magnetoresistance. Small magnetic field is required to melt the COfraction present in low temperature and large (∼100 %) low field magnetorestance hasbeen achieved at liquid nitrogen temperature.Anis Biswas, Indranil DasECMP4.1.1.12 Negligible domain wall contribution in magnetocaloric effect of GdPt 2Single-phase polycrystalline sample was prepared by argon arc melting. Specific heat measurementsboth in absence and in presence of magnetic field were performed using home made set-up.Magnetocaloric parameters ∆T ad and -∆S were obtained from the specific heat data.Fig.4.1.1.12. Low field magnetoresistance at the inset indicates significant domain wallcontribution in magnetoresistance. The hump in -∆ρ data around 10 K vanishes aftersubtracting domain wall contribution and the dependence becomes similar to -∆S-domain wall contribution in magneto caloric effect is insignificantMagnetoresistance measurements as a function of magnetic field as well as a function of temperaturewere carried out. There is qualitative difference between the temperature dependence of -∆ρ(=ρ(H)-ρ(0)) and -∆S. However after removing the domain wall scattering contribution from -∆ρ,the nature of -∆ρ and -∆S as a function of temperature is similar. Our study indicates thatthe domain wall contribution in MCE is negligibly small in spite of large contribution