4352

4112

كارشناسي ارشد

ماده چگال

اصفهان : دانشگاه صنعتي اصفهان

87

نه، 80، [II] ص: جدول، نمودار

ص. ع به: فارسي و انگليسي

پرويز كاملي

هادي سلامتي

20/12/87

علي اكبر بابايي، فرهاد فضيله

1398/01/22

كتابنامه

مهندسي برق و كامپيوتر

ID4112

به فارسي و انگليسي: قابل رويت در نسخه ديجيتال

abstract In this project we have investigated the effects of grain size on the electrical and magnetic properties ofLaMnO3 powder samples Then the effect of sintering temperature and LMO dopingon the structure magnetic and magnetotransport properties of La0 8Sr0 2MnO3 LSMO xLaMnO3 LMO composite have been investigated The resistivity of LMO samples increases by the decrease of grain size All samples show the paramagnetic to ferromagnetic transition The saturation magnetization decreasesby increasing milling time An increase of the width of the transition and a small reduction of thetransition temperature Tc are observed All of LSMO xLMO samples show the paramagnetic toferromagnetic transition Results show that the rate of decreasing of transition temperature is much higherfor high temperaure sintered samples The presence of LMO at the surfaces of the grains increases themagnetically disordered states in the surface suppresses the double exchange mechanism Therefore themagnetization and transition temperature decreases by the increase of LMO concentration Also the resistivity of samples increases by the increase of LMO doping level There is a small peak athigh temperature Tp1 and a second broad peak at low temperature Tp2 in high temperaure sinteredsamples Tp1 reflects the intrinsic metal insulator transition temperature But the resistivity peak attemperature well below Tc Tp2 does not mean a metal insulator like transition for the granular systemand indicates the interfacial tunneling due to the difference in magnetic order between surface and body Results also show that the LMO doping has an effect on a LFMR For low temperaure sintered samples the value of MR increases for low doping level of 0 x 15 and decreases at high doping Level of x 15 The spin dependent tunneling and scattering at the interfaces of the grain boundaries are responsible forthe increasing of LFMR in 0 x 15 while reduction of LFMR at x 15 may result from the grainboundary becoming too thick for electron tunneling In contrust for high temperaure sintered samples MR versus doping level plot has a peak in x 10 Weakening of double exchange mechanism due to thehigher degree of reaction between LMO and LSMO at high sintering temperatures is another reason fordecrease of MR

پرويز كاملي

هادي سلامتي

علي اكبر بابايي، فرهاد فضيله