Please use this identifier to cite or link to this item: https://scholarbank.nus.edu.sg/handle/10635/119532
DC FieldValue
dc.titleMAGNETISM, ELECTRICAL AND THERMAL TRANSPORT IN SELECTED PERVOSKITE COBALTITES
dc.contributor.authorPAWAN KUMAR
dc.date.accessioned2015-05-04T18:00:12Z
dc.date.available2015-05-04T18:00:12Z
dc.date.issued2014-08-21
dc.identifier.citationPAWAN KUMAR (2014-08-21). MAGNETISM, ELECTRICAL AND THERMAL TRANSPORT IN SELECTED PERVOSKITE COBALTITES. ScholarBank@NUS Repository.
dc.identifier.urihttp://scholarbank.nus.edu.sg/handle/10635/119532
dc.description.abstractTransition metal oxides with perovskite structures are known to exhibit a wide ranging of physical phenomena ranging from superconductivity to ferroelectricity to ferromagnetism. Among them, cobaltites of the general formula R1-xAxCoO3 where R is a trivalent rare earth ion and A is divalent cation, show notorious spin-state transition of Co3+ ions, carrier density and temperature driven paramagnetic semiconductor/metal to ferromagnetic metal transition, giant Hall effect and giant magnetostriction. La1-xSrxCoO3 is the most widely studied system among cobaltites by different experimental techniques. Investigation of thermopower and resistance under an external magnetic field is not reported so far. In this work, I have investigated dc magnetotransport, magnetocaloric effect and thermoelectric properties of selected cobaltites and established a correlation between electrical and thermal properties. The investigated systems are: Nd1-xSrxCoO3 (x= 0- 0.5), Nd1-y-xLaxSryCoO3 (x = 0- 0.8 for y = 0.2 and x = 0-0.7 for y = 0.3) and R0.5Sr0.5CoO3 (R = La, Pr, Nd, Sm, Eu, Gd). It is found that Nd1-xSrxCoO3 (x = 0- 0.5) show unusually a strong ferrimagnetic coupling between Nd-4f and Co-3d sublattices. We studied the impact of varying magnetic field on the ferrimagnetic interaction. Magnetothermopower is found to be much larger than magnetoresistance in metallic compositions. R site doping with a non-magnetic ion (La3+) enhances the ferrimagnetic interaction up to certain doping. MR and MTEP are also enhanced with La3+ doping. The impact of rare earth magnetism is studied in R0.5Sr0.5CoO3 series. It is found that decreasing the size of the R-site cation increases the resistivity and changes the sign of thermopower. Rare earth dependence of magnetothermopower and magnetoresistance is reported. I show existence of a linear relation between magnetoresistance and magnetothermopower in these oxides near the Curie temperature.
dc.language.isoen
dc.subjectPerovskite Oxide, Resistivity, Thermopower
dc.typeThesis
dc.contributor.departmentPHYSICS
dc.contributor.supervisorRAMANATHAN MAHENDIRAN
dc.description.degreePh.D
dc.description.degreeconferredDOCTOR OF PHILOSOPHY
dc.identifier.isiutNOT_IN_WOS
Appears in Collections:Ph.D Theses (Open)

Show simple item record
Files in This Item:
File Description SizeFormatAccess SettingsVersion 
PAWAN KUMAR.pdf8.91 MBAdobe PDF

OPEN

NoneView/Download

Page view(s)

146
checked on Nov 18, 2021

Download(s)

155
checked on Nov 18, 2021

Google ScholarTM

Check


Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.