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Scanning tunnelling microscopy of bilayer manganites

Bryant, B.E.M.; (2010) Scanning tunnelling microscopy of bilayer manganites. Doctoral thesis, UCL (University College London). Green open access

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Abstract

This thesis describes experimental work carried out on bilayer manganites with the general composition R_{2-2x}A_{1+2x}Mn_2O_7, where R is a trivalent rare earth cation and A is a divalent alkaline-earth cation. Experiments have been carried out primarily using Scanning Tunnelling Microscopy (STM) and Spectroscopy (STS); bulk electrical transport, MPMS and LEED measurements have also been made. The primary results are obtained from single crystal samples of PrSr_2Mn_2O_7. This compound provides a surface suitable for STM study when cleaved at low temperature in ultra-high vacuum: atomic resolution can be readily achieved. The expected square lattice is observed, together with a larger scale surface modulation which is not presently explained. In some areas of the PrSr_2Mn_2O_7 surface a population of adatoms and surface vacancies is observed. STS data indicate that adatoms carry a negative charge compared to the rest of the surface, and vacancies a positive charge: the adatoms and vacancies are interpreted as oxygen adatoms and oxygen vacancies. A detailed study is made of the oxygen adatoms and vacancies: this is believed to be the firrst such study made on a manganite surface. Oxygen adatoms on the PrSr_2Mn_2O_7 surface are found to be mobile: hopping and adatom-vacancy recombination are observed. Additional results are reported on the layered manganite compound La_{2-2x}Sr_{1+2x}Mn_2O_7 at a range of cation doping x. For the LaSr_2Mn_2O_7 compound (x = 0.5) spectroscopic variation has been identi_ed in a variable-temperature STS survey. This indicates the coexistence of two surface electronic phases, possibly the charge ordered and antiferromagnetic phases.

Type: Thesis (Doctoral)
Title: Scanning tunnelling microscopy of bilayer manganites
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Abstract contains LATEX text. Please see PDF for rendered formulae and equations
UCL classification: UCL > School of BEAMS > Faculty of Maths and Physical Sciences > London Centre for Nanotechnology
UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Physics and Astronomy
URI: http://discovery.ucl.ac.uk/id/eprint/19980
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