Abstract:
Polycrystalline samples (La, ~DYU1SrLl)Mnl_,Ni,fFe,D-r (with )\=0.0,0.1,0.2) were
prepared using the oonventional solid-state reaction technique and sintered at temperature
llOOue for 24 hours in air. Phase purity and structure were checked by powder X-ray
diffraction (XRD) using the MoKu radiation (J...= 0.710689 A).For thc structure
determination, dilfraction patterns were recorded in the 26 range from 100to 70o.The IX:
electrical resistivity for various polycrystalline samples was measured from room
temperature down to liquid nitrogen temperature both at zero field and at applied
magnetic field of 0.7T using four probe method. In the present investigation it is observed
that all the samples showed metal insulator (M-I) transition with a peck in the electrical
resistivity around M-I transition temperature Tp• With the increase ofNi or Fe doping the
resistivity increases but M-I transition temperature Tp decreases. M-I transition
temperature Tp also inl,,-nlao;edin presence of O.7T magnetic field. Magnetoresistance
(MR) measurements were carried out in a magnetic field ofO.7T in the temperature range
of77K to 300K, The MR behaviour was discussed a~ a function of magnetic field both at
room temperature and at liquid nitrogen temperature. Room temperature MR is found to
be very low, almost 0.110/••..1..69% and is almost linear with field. A large value ofMR is
observed at 78K in the presence of low applied magnetic field. The higher percentage of
Fe and Ni in these compounds enhances paramagnetic insulating phase. The plot of
In(plPol vs r' curve means that the conduction occurred tluough a thennaIly activated
pl'OCe5Sabove the transition temperature.
