8849

8210

كارشناسي ارشد

ماده چگال

اصفهان: دانشگاه صنعتي اصفهان، دانشكده فيزيك

1392

[نه]،106ص.: مصور،جدول،نمودار

ص.ع.به فارسي و انگليسي

پرويز كاملي

حسين احمدوند

20/2/93

هادي سلامتي، جواد هاشمي فر

فيزيك

ID8210

Investigation the Effect of Co Dopping on Structural Magnetic and Electrical Properties of La0 5Ca0 5Mn1 xCoxO3 Manganites Student name Nahid Modaresi Email address n modaresi@ph iut ac ir Date of submission 2014 1 22 Department of Physics Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Dr Parviz Kameli kameli@cc iut ac irAbstractIn this thesis the La0 5Ca0 5Mn1 xCoxO3 0 x 0 25 micrometer and nanometer sized samples were synthesized bya simple method which is based on the solid state ball milling and calcinations of acetate and nitrate precursors inthe presence of citric acid and their structural magnetic and electrical properties have been investigated Reitveldrefinement of X ray diffraction patterns indicates an orthorhombic structure with Pnma space group for all thesamples In all samples with 1350 oC S1350 micrometer sized samples and 800 oC S800 nanometer sizedsamples sintering temperatures the unit cell volume doesn t change regularly with Co content in 0 x 0 025samples but it extremely decreases by further increase in Co doping level up to x 0 05 Since the average ionicradius of Mnav 0 585 is between the ionic radius of Co 2 0 65 and Co3 0 55 it can be assumed thatCo ions exist in the form of Co2 and Co3 in these samples and the charge redistribution ofMn3 Co3 Mn4 Co2 occurs for 0 x 0 025 samples In contrast by further increase in Co doping level thecharge redistribution weakened so the most of Co ions appear in the form of Co 3 in samples The drasticreduction of unit cell volume in x 0 05 sample also can be explained on the basis of appearance and increase ofCo3 ions which are smaller than Mnav ones FE ESM images confirm formation of micrometer and nanometerparticles for S1350 and S800 samples respectively In S1350 samples the magnetization M and effectivemagnetic moment eff increase initially by increasing x up to x 0 025 and after that they decrease by furtherincrease in x for x 0 05 The ac magnetic susceptibility measurements show that in all S1350 samples the chargeordering state is suppressed by increasing x The low doping S1350 samples have thermal hysteresis because ofthe coexistence of FM and AFM phases and phase separation Also we report a feature of thermal hysteresisbehavior in La0 5Ca0 5Mn1 xCoxO3 series which is the inverted thermal hysteresis loop for 0 0075 x 0 05samples The notable point of this study is the ability of a small amount of Co doping 0 5 to induce insulator metal transition in the insulating undoped sample at low temperatures in S1350 compounds The ac susceptibilitymeasurements of S800 compound indicate that all these samples have PM FM transition with no charge orderingstate Also all of these samples show insulator like behavior Kay words Manganite Thermal hysteresis ac susceptibility Co doping Charge ordering PM FM

پرويز كاملي

حسين احمدوند

هادي سلامتي، جواد هاشمي فر