Mapping of local electronic properties in nanostructured CMR thin films by Scanning Tunneling Microscopy (STM) and Local
- PDF / 197,087 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 31 Downloads / 200 Views
O10.13.1
Mapping of local electronic properties in nanostructured CMR thin films by Scanning Tunneling Microscopy (STM) and Local Conductance Map (LCMAP) Sohini Kar, Barnali Ghosh, L. K. Brar, M A. Paranjape* and A. K. Raychaudhuri# Department of Physics Indian Institute of Science, Bangalore 560 012, India Abstract We have investigated the local electronic properties and the spatially resolved magnetoresistance of a nanostructured film of a colossal magnetoresistive (CMR) material by local conductance mapping (LCMAP) using a variable temperature Scanning Tunneling Microscope (STM) operating in a magnetic field. The nanostructured thin films (thickness ≈500nm) of the CMR material La0.67Sr0.33MnO3 (LSMO) on quartz substrates were prepared using chemical solution deposition (CSD) process. The CSD grown films were imaged by both STM and atomic force microscopy (AFM). Due to the presence of a large number of grain boundaries (GB’s), these films show low field magnetoresistance (LFMR) which increases at lower temperatures. The measurement of spatially resolved electronic properties reveal the extent of variation of the density of states (DOS) at and close to the Fermi level (EF) across the grain boundaries and its role in the electrical resistance of the GB. Measurement of the local conductance maps (LCMAP) as a function of magnetic field as well as temperature reveals that the LFMR occurs at the GB. While it was known that LFMR in CMR films originates from the GB, this is the first investigation that maps the local electronic properties at a GB in a magnetic field and traces the origin of LFMR at the GB. Introduction There has been considerable interest in the physics of hole-doped manganites ever since the discovery of colossal magnetoresistance (CMR) in these materials1-4. This family of perovskite oxides having the general chemical formula Re1-xAxMnO3 (where Re is a rare earth element, A=Sr, Ca, Ba, Pb etc.) shows a transition from a paramagnetic insulating state (PMI) to a ferromagnetic metallic state (FMM) at a characteristic transition temperature (Tc). CMR in these materials refers to the suppression of the resistivity near Tc upon application of a magnetic field which makes them attractive candidates for application in magnetic field sensing and magnetic recording devices. One of the most widely researched areas in this field is the growth of high quality manganites thin films having appreciable magnetoresistance and Tc higher than room temperature (300K). It has been established that the electrical and magnetic properties of these CMR oxide films and the value of their MR depend substantially on the material processing parameters which include type of substrate, processing temperature and post-deposition conditions among others. It has also been established through studies on artificial grain boundary devices and polycrystalline materials of different grain sizes that in manganites grain boundaries play an important role. In particular, they show substantial low field magnetoresistance (LFMR) 5,6. Though there
Data Loading...
