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Title: Study of doped barium manganites : electrical and magnetic properties
Author: Mubumbila, Mpoyi
ISNI:       0000 0001 3428 4863
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2006
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The electrical and magnetic properties of barium manganite solid solutions Ba4-xAxMn3O10, Ba6-xAxMn5O16, (A = La, Sr and Nd), Ba4-xSrxMn3-yFeyO10 and Ba6Mn5-yFeyO16 have been investigated.  Initially, Ba4Mn3O10 and Ba3.9La0.1Mn3O10 were synthesised.  XPS1 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.  ND2 results showed both samples are antiferromagnetic (with TN = 170 K for Ba4Mn3O10).  In addition, a decrease of the ordered Mn magnetic moment was observed in the La-doped sample. SEM3 and a.c. impedance data for Ba4-xSrxMn3O10 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 Mn3+ - O – Mn4+ interactions which may affect the magnetic properties. Comparison between the properties of Ba3.9La0.1Mn3O10 and Ba3.9Nd0.1Mn3O10­  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, Ba3.9La0.1Mn3O10 has lower resistivity than Ba3.9Nd0.1Mn3O10.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available