The electrical and magnetic properties of barium manganite solid solutions Ba<sub>4-x</sub>A<sub>x</sub>Mn<sub>3</sub>O<sub>10</sub>, Ba<sub>6-x</sub>A<sub>x</sub>Mn<sub>5</sub>O<sub>16</sub>, (A = La, Sr and Nd), Ba<sub>4-x</sub>Sr<sub>x</sub>Mn<sub>3-y</sub>Fe<sub>y</sub>O<sub>10</sub> and Ba<sub>6</sub>Mn<sub>5-y</sub>Fe<sub>y</sub>O<sub>16</sub> have been investigated. Initially, Ba<sub>4</sub>Mn<sub>3</sub>O<sub>10</sub> and Ba<sub>3.9</sub>La<sub>0.1</sub>Mn<sub>3</sub>O<sub>10</sub> were synthesised. XPS<sup>1</sup> measurements suggested that the latter phase was substoichiometric in oxygen. A.C. impedance showed that the La-doped sample displayed insulator-like behaviour, whereas the pure one exhibited a metallic to insulator transition. ND<sup>2</sup> results showed both samples are antiferromagnetic (with T<sub>N</sub> = 170 K for Ba<sub>4</sub>Mn<sub>3</sub>O<sub>10</sub>). In addition, a decrease of the ordered Mn magnetic moment was observed in the La-doped sample. SEM<sup>3</sup> and a.c. impedance data for Ba<sub>4-x</sub>Sr<sub>x</sub>Mn<sub>3</sub>O<sub>10</sub> revealed that conductivity drops as grain size decreases. It has also been shown that doping with a smaller ion causes a decrease in the Mn magnetic moment and can increase the resistivity of the sample. Doping with a higher valence ion prompts a change in the conduction mechanism leading to semiconductor behaviour above room temperature. A loss of oxygen induces a creation of Mn<sup>3+</sup> - O – Mn<sup>4+</sup> interactions which may affect the magnetic properties. Comparison between the properties of Ba<sub>3.9</sub>La<sub>0.1</sub>Mn<sub>3</sub>O<sub>10</sub> and Ba<sub>3.9</sub>Nd<sub>0.1</sub>Mn<sub>3</sub>O<sub>10 </sub> was one of the major contributions of this thesis. The former is antiferromagnetic, whilst the latter became ferromagnetic below 100 K. Both compounds exhibit semiconductor behaviour above room temperature. However, Ba<sub>3.9</sub>La<sub>0.1</sub>Mn<sub>3</sub>O<sub>10</sub> has lower resistivity than Ba<sub>3.9</sub>Nd<sub>0.1</sub>Mn<sub>3</sub>O<sub>10</sub>.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:439947 |
| Date | January 2006 |
| Creators | Mubumbila, Mpoyi |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU224732 |
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