Abstract:
The Lil{I,~.,Y,CaG,oSro2GMI\OJpowders with various X values were
synlhesized using a slandard ceramic lechnique. Powders of LaJO) (Aldrich 99,99%),
CaCO) (BDH 99.9%), SrCOJ (I3DlI 99.9%), Y10) (n-kem, 99.99%) and Mn20)
Aldrieh 99.99%) were used to make the samples, The ingredienls wer~ weighed with
app"'priate proporlions arrd then mixed lhoroughl} in dry and acetone media. The
mixed powders were calcined at I] oooe for 60 hours, After calcinations powders
were pressed in the form of pellets. The pellets of five different samples were sintered
al IJOO"Cfor 5h, X-ray diiTraction WtiSearried out in the powder sample for structural
characterization, Eleclrical resistances were mea,ured in each sample in the absence
of applied field and in presence of applied magnetic field (0.7 T) in the temperature
range 295-17K. It was observed that all samples ,how metal-insulator transition til
certain temperature (Tp). Meml-in"Llator transition temperature ,arie; for different
compositions. It ,~os observed that as Yttrium eoncentralion increases in the
polycry'lalline Lac'o.,Y,CaOlOSr010MnO) sample, the metal-insLLlator transition
lemperalulC Tp dcclCti,"s. Magneloresi,tance (MR) as a function ficid, MR(H), at
constant temperatures (17K and room tempcralure) were measured. Ali s~mples show
significant AiR at RT and at 17K, ~or all somples MR at 17K ,howed two slopes, A
sharp decrease of resiSlance is obscrved up lOtipplied field it beyond which the MR
is a ,ery weak function of H was obscrved. The sharp decrease of resiSlance is due to
lhe domain wall movement and (he weak dependence is ,elated to (h~ grain
boundaries of the rQ1ycryslailine sampics. Th~ LaO)o.,Y,C"-:JIOS'<lojMnO, sample
sintercd at ]300"C for 5h shows 3% AiR ~( RT and 14% MR at Ll\T in presc~~e of
O.7T applied fieid, Thc pol}cT)'staliine sample of nominal chcmictil compQsition
Lao'0.,Y,Cao toSrO,oMnO) alsQ has highest T,. (286K) without Yttri\lm dQping.
