Electrical Resistivity and Magnetic Properties in (La, Ag)-Mn-O, (Nd, Ag)-Mn-O and (Y, Ce)-Mn-O Based Manganites

No Thumbnail Available
Journal Title
Journal ISSN
Volume Title
One group of fascinating compounds with many potential applications is the mixed valence perovskite manganites. The versatility of perovskite manganites for electronic applications is demonstrated by the fact that, these materials exhibit wide range of conductivity ranging from highly conducting metallic state to insulating state. The discovery of large negative magnetoresistivity in these materials has led to the expectation of potential applications in magnetic storage, magnetic sensor and magnetic switches. These materials have also potential applications as catalysts for automobile exhausts, oxygen sensors and magnetic refrigeration. The number of applications is so wide that Physicists, Chemists and Materials scientists have shown a keen interest in these materials. There are several reports on La based divalent alkaline earth doped manganites and investigations on doping of Mn site with other magnetic and non-magnetic materials to understand the nature of magnetic interactions. The doping at Mn site in these mixed valent manganites by other transitions elements (T = Co, Cr, Cu, Fe, Ti, Ni, Ru etc.) or nonmagnetic impurities like Al gives rise to change in Mn3+/Mn4+ ratio, and the nearest neighbor environment. The magnetic and transport properties of such materials were found to be quite interesting. But there was lack of information on doping of these transition elements at Mn site of CMR materials based on mono-valent substitution in rare earth site. The mono-valent substitution based CMR materials with optimum Mn3+/Mn4+ concentration with relatively small lattice distortion is already known viz. La1-xAgxMnO3, La1-xKxMnO3, etc. Moreover the research work on electron doped manganites, where there is a possible double exchange interaction in Mn2+-O-Mn3+ networks is limited. In my research work, I have mainly chosen monovalent doped compounds. The monovalent doping has the advantage of creation of optimum concentration of Mn3+/Mn4+effect in Nd-Mn-O series. To understand the magnetic interactions in Mn2+/Mn3+ networks, electron doped (Y, Ce)-Mn-O were prepared and studied. I have prepared the following compounds for the present thesis work, 1. La0.85Ag0.15Mn1-yCoyO3 (y=0-0.50) 2. La0.85Ag0.15Mn1-yCryO3 (y=0-0.20) 3. La0.85Ag0.15Mn1-yAlyO3 (y=0-0.20) 4. LaMn1-yCuyO3 (y=0-0.30) 5. Nd1-xAgxMnO3 (x=0-0.20) 6. Y1-xCexMnO3 (x=0-0.15) The above samples were characterized by using X-ray diffraction (XRD), Scanning electron micrographs (SEM), Energy-dispersive spectrum (EDS) and chemical titration. To understand the magnetic properties and different magnetic interactions involved, I have carried out temperature and frequency variations of ac susceptibility and, dc magnetization as a function of temperature and field. To explore the electronic transport properties, I have carried out temperature variations of electrical resistivity and magneto-resistivity. The present thesis is divided into seven chapters, namely, (1) Introduction (2) Experimental Techniques (3) Mn site doped (La, Ag)-Mn-O Series (4) Cu doped La-Mn-O Series (5) Hole doped (Nd, Ag)-Mn-O Series (6) Electron doped (Y, Ce)-Mn-O Series (7) Conclusions. In chapter 1, different types of crystal structure of manganites are discussed. Various types of magnetic ordering, magnetic interaction and magnetic frustrations due to competing interactions are presented. Differen....
Supervisor: S Ravi