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Pawan Kumar,Rakesh Kumar Dwivedi,Pawan Kumar,Ravikant Prasad,Praveen Kumar Siwach,Hari Krishna Singh 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.1
Thin films of La_(0.80)Sr_(0.20)Mn_(1−x)Cu_xO_3 with x = 0.00, 0.04, 0.08, 0.10, 0.15, and 0.20 were deposited on single-crystal LaAlO_3 (100) (LAO) substrates at 250 ± 10 ℃ by using a nebulized spray pyrolysis technique. Structural, surface, and transport characterizations were done by X-ray diffraction (XRD), atomic force microscopy (AFM) and the standard four probe technique, respectively. XRD patterns revealed the formation of single-phase polycrystalline films with a rhombohedral crystal structure. Cu substitution resulted in a uniform decrease in the metal insulator transition (T_(IM)) temperature up to x = 0.10, followed by a drastic decrease in T_(IM) for x = 0.15. Finally, the metal-insulator transition vanished for higher Cu concentrations (x = 0.20) in the observed temperature range. The variation in T_(IM) with the amount of added Cu is explained on the basis of the double exchange mechanism. Cu substitution has been found to perturb the Mn^(3+)-O-Mn^(4+) network and has a strong influence on T_(IM). The variation in resistivity maxima with temperature for different Cu concentrations showed a systematic trend up to x ∼ 0.10. We also explored the electrical conduction at T > T_(IM) in the framework of small polaron hopping in the adiabatic limit. The activation energy showed a strong dependence on the Cu concentration. The maximum magneto-resistance (MR) up to 10%, was observed for x = 0.15 at low temperatures.