|
Title
|
|
|
|
Transport, magnetic, and structural properties of thin films: evidence for hole-doping
| |
|
Author
|
|
|
|
| |
|
Abstract
|
|
|
|
| Cerium-doped manganite thin films were grown epitaxially by pulsed laser deposition at 720 °C and oxygen pressure pO2=125 Pa and were subjected to different annealing steps. According to x-ray diffraction (XRD) data, the formation of CeO2 as a secondary phase could be avoided for pO28 Pa. However, transmission electron microscopy shows the presence of CeO2 nanoclusters even in those films which appear to be single phase in XRD. With O2 annealing, the metal-to-insulator transition temperature increases, while the saturation magnetization decreases and stays well below the theoretical value for electron-doped La0.7Ce0.3MnO3 with mixed Mn3+/Mn2+ valences. The same trend is observed with decreasing film thickness from 100 to 20 nm, indicating a higher oxygen content for thinner films. Hall measurements on a film which shows a metal-to-insulator transition clearly reveal holes as dominating charge carriers. Combining data from x-ray photoemission spectroscopy, for determination of the oxygen content, and x-ray absorption spectroscopy (XAS), for determination of the hole concentration and cation valences, we find that with increasing oxygen content the hole concentration increases and Mn valences are shifted from 2+ to 4+. The dominating Mn valences in the films are Mn3+ and Mn4+, and only a small amount of Mn2+ ions can be observed by XAS. Mn2+ and Ce4+ XAS signals obtained in surface-sensitive total electron yield mode are strongly reduced in the bulk-sensitive fluorescence mode, which indicates hole-doping in the bulk for those films which do show a metal-to-insulator transition. |
| |
|
Language
|
|
|
|
English
| |
|
Source (journal)
|
|
|
|
Physical review : B : solid state. - Lancaster, Pa, 1970 - 1978
| |
|
Publication
|
|
|
|
Lancaster, Pa
:
2009
| |
|
ISSN
|
|
|
|
0556-2805
| |
|
DOI
|
|
|
|
10.1103/PHYSREVB.79.054416
| |
|
Volume/pages
|
|
|
|
79
:5
(2009)
, p. 054416,1-054416,8
| |
|
ISI
|
|
|
|
000263815400057
| |
|
Full text (Publisher's DOI)
|
|
|
|
| |
|
Full text (open access)
|
|
|
|
| |
|