Tuesday, 1 October 2013

Effect of growth temperature on the terahertz-frequency conductivity of the epitaxial transparent conducting spinel NiCo2O4 films

Punam Silwal1Chan La-o-vorakiat2Elbert E. M. Chia2Dae Ho Kim3, and Diyar Talbayev1
1Department of Physics and Engineering Physics, Tulane University, 6400 Freret Street, New Orleans, LA 70118, USA
2Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
3Corporate R&D institute, Samsung Electro-Mechanics, 150 Maeyeong-ro, Suwon, Gyunggido 443-743, Korea 

Abstract


We have measured the terahertz-frequency optical conductivity of the epitaxial inverse spinel NiCo2O4 films grown at different temperatures. The low-temperature-grown film exhibits a metallic behavior with ferrimagnetic ordering, while the high-temperature-grown film shows greatly suppressed magnetization and insulating behavior. Both films exhibit band-like coherent conduction at intermediate temperatures, albeit with very different carrier densities consistent with the proposed models of cation valencies in this mixed-valence material. Both films also display a crossover to incoherent transport at low temperatures, indicating a disorder-induced tendency toward localization.


The real (ε1) and imaginary (ε2) parts of the measured dielectric function of the NCO300 film. 

Two different spectrometers were used for this study: a home-built spectrometer THz-TDS, and a commercial spectrometer mede by Teraview. TeraView's TPS Spectra 3000 was used to perform measurements.