Effects of dopant ion and Mn valence state in the La(1-x)A(x)MnO(3) (A=Sr, Ba) colossal magnetoresistance films

Abstract

The structural and electrical properties of Mn-based colossal magnetoresistance (CMR) thin films with controlled tolerance factor and Mn ion valance ratio were studied using crystal structure and chemical bonding character analyses. La0.7Sr0.3MnO3, La0.7Ba0.3MnO3, and La0.82Ba0.18MnO3 thin films with different contents of divalent cations and Mn3+/Mn4+ ratios were deposited on amorphous SiO2/Si substrate by rf magnetron sputtering at a substrate temperature of 350 degrees C. The films showed the same crystalline structure as the pseudocubic structure. The change in the sheet resistance of films was analyzed according to strain state of the unit cell, chemical bonding character of Mn-O, and Mn3+/Mn4+ ratio controlling the Mn3+-O2--Mn4+ conducting path. Mn L-edge x-ray absorption spectra revealed that the Mn3+/Mn4+ ratio changed according to different compositions of Sr or Ba and the Mn 2p core level x-ray photoelectron spectra showed that the Mn 2p binding energy was affected by the covalence of the Mn-O bond and Mn3+/Mn4+ ratio. In addition, O K-edge x-ray absorption spectra showed covalently mixed Mn 3d and O 2p states and matched well with the resistivity changes of CMR films. Temperature coefficient of resistance values were obtained at approximately -2.16%/K to -2.46%/K of the CMR films and were correct for infrared sensor applications. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3256197]