Publication Date

2008-04-20

Availability

Open access

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Physics (Arts and Sciences)

Date of Defense

2008-04-15

First Committee Member

Joshua L. Cohn - Committee Chair

Second Committee Member

Fulin Zuo - Committee Member

Third Committee Member

Josef Ashkenazi - Committee Member

Fourth Committee Member

Francisco Raymo - Outside Committee Member

Abstract

A comprehensive study of transport properties of lightly electron-doped manganese oxides with perovskite structure is presented. Two similar classes are investigated in both their both paramagnetic and antiferromagnetically ordered states: Ca1-xLaxMnO3 and Ca1-ySryMnO3. Much simpler than their widely-studied hole-doped counterparts, these compounds are model systems for investigating the issue of magnetic polaron formation in perovskite manganites. Our measurements sustain the phase segregation scenario both above and below the magnetic ordering temperature in Ca1-xLaxMnO3, but it is found that for T>Tn, the small-polaron theory (successful in describing the colossal magnetoresistance compounds) is incompatible with our results and a large polaron theory should be used instead. Particularly interesting are the nominally undoped, semiconducting Ca1-ySryMnO3 compounds with a very small electron concentration associated with native oxygen vacancies. At low temperatures, electron bound near vacancies are mobilized in weak applied electric field (F<100 V/cm). This internal current source allows for a distinction between self-trapped and bound magnetic polarons and provides a new tool for studying strongly correlated electron systems with a tunable mobile carrier density.

Keywords

Transport; Manganese Oxides; Polarons

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