5551

325 دكتري

دكتري

فيزيك ماده چگال

اصفهان: دانشگاه صنعتي اصفهان، دانشكده فيزيك

1389

دوازده،140ص.: مصور،جدول،نمودار

ص.ع.به فارسي و انگليسي

هادي سلامتي

پرويز كاملي

15/9/89

ناصر تجبر،محمدعلي شاهزمانيان،مجتبي اعلايي

فيزيك

ID325 دكتري

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

۱۳۵Preparation and study of magnetic electrical and structural properties ofPr1 xAgxMnO3 manganites and LaFeO3 Ni NiO and NiO nanoparticles Hossein Ahmadvand E mail ahmadvand@ph iut ac ir Date of Submission July 24 2010 Department of Physics Isfahan University of Technology Isfahan 84156 83111 IranSupervisor Hadi Salamati salamati@cc iut ac irAdvisor Parviz KameliDepartment Graduate Program Coordinator Farhad ShahbaziAbstractWe have studied structural magnetic and electrical properties of Pr1 xAgxMnO3 0 x 0 25 manganites and also LaFeO3 Ni NiO and NiO nanoparticles Firstly we have investigatedthe role of Ag in Pr1 xAgxMnO3 manganites and discussed that the Ag ions do not substitutefor the Pr3 site and locate at the grain boundaries in the metallic form Detailed acsusceptibility measurements on the samples show unusual and interesting features which areassociated with the domain walls and the effects of grain boundaries on their movements We haveproposed a mechanism based on the pinning of the magnetic domain walls at the grain boundaries The magnetocaloric effect heat capacity resistivity magnetoresistance FC ZFC magnetization andhysteresis loops at different temperatures have been also studied We report the first observation ofexchange bias effect in the nanoparticles of antiferromagnetic LaFeO3 After field cooling from roomtemperature the exchange bias increases while the coercivity decreases with decreasing temperature Thermally activated reversal of the antiferromagnetic spins can explain the appearance of exchangebias without the conventional field cooling the sample through the N el temperature as well as thetemperature dependence of exchange bias and coercivity Ni NiO nanoparticles have been preparedusing a relatively new method and their magnetic properties have been studied The advantage of thismethod is that the percentage of Ni can be easily controlled by the heating temperature Finally arelatively rapid and simple method has been used to prepare NiO nanoparticles which is also suitableto prepare other metal oxides Keywords Manganite Pr1 xAgxMnO3 Ag doping Domain wall dynamics ac Susceptibility Magnetocaloric effect Magnetoresistance Magnetic nanoparticles LaFeO3 exchange bias Ni NiO Spin glass NiO Superparamagnetism IntroductionSince the discovery of colossal magnetoresistive effects 1 the study of perovskitemanganites Ln1 xAxMnO3 Ln La3 Pr3 A Ca2 Sr2 Na K Ag receivedconsiderable interest due to fascinating fundamental physics as well as due to their potentialapplications Substitution of different ions at Ln A sites in the perovskite manganitesprovides a systematic way to study the physical properties and discover interesting effects Physical properties of Ag doped RMnO3 R La Nd have been studied by other researchers In this thesis we are interested in the systematic study of the Ag doping and understandingits role in the PrMnO3 manganite We present a detailed ac susceptibility study of the highdoped Pr1 xAgxMnO3 x 0 15 and 0 20 We observed significant and unconventionalmagnetic domain walls effects below the ferromagnetic transition temperature The resultsare interpreted in terms of the dynamics of the domain walls in the presence of grain boundaries as the dominant pinning centers

هادي سلامتي

پرويز كاملي

ناصر تجبر،محمدعلي شاهزمانيان،مجتبي اعلايي