Infrared studies of phase-separated manganite thin films
D.B. Tanner, Naveen Margankunte, Tara Dhakal, and Amlan Biswas
Dept. of Physics, University of Florida
We report optical studies of phase separated manganite thin films. Infrared reflectance
measurements were performed for a range of temperatures from 10 to 300 K. Particular
attention was given to the narrow temperature range where the insulator-metal transition
occurs. Measurements were also made in magnetic fields up to 18T. The optical constants
were extracted by fitting the measured reflectance to a Drude-Lorentz dielectric function in
conjunction with thin film optics and the measured properties of the substrate. Spectral
weight analysis shows that the growth of low energy oscillator strength occurs well above the
Curie temperature, indicating phase coexistence in the hysteresis regime seen in resistivity
measurements. Application of magnetic field at low temperatures leads to melting of the
insulating phase, and converts most of the film to ferromagnetic metal. When the field is
removed much of these new metal regions remain. The strain introduced by the choice of
substrate is believed to have an important effect on this behavior.
This research was supported jointly by NSF grant DMR-0305043 and DOE contract DE-
AI02-03ER46070.
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