Investigation of the Transport Mechanism in Doped La-Based Manganite Thin Films by Traveling Wave Method
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still not clear. Initially, the mechanism of CMR is ascribed as the double exchange model [6]. But now many theoretical [7,8] and experimental papers [9-13] have shown that the magnetic interactions alone are insufficient to explain CMR and a coupling between charge and lattice is significant. Under this situation, it is necessary and important to well understand the transport mechanism of the materials in ferromagnetic and paramagnetic states. Recently, Hall measurements [12,14,15] have been used to investigate the transport properties in Lanthanum-based manganites. Since the anomalous part of Hall coefficient is not well understood, it is impossible to get information on the behavior of the drift mobility or the carrier concentration in these materials using Hall measurements [14]. However, the information on the drift mobility is indispensable to clearly understand the mechanism. In order to get insight into the transport process, we adopt the traveling wave (TW) technique to investigate the transport mechanism in manganite films. Since it was introduced by Adler et al [16], TW method has been utilized to investigate the transport in amorphous semiconductor for several years [17-19]. One of the characteristics of this method is the possibility to get information on the transport mechanism in the materials that have high resistance and low mobility. In this paper, we focus on the transport properties of La0.75Sr 0.11Ca0.14MnO3 thin films in 131 Mat. Res. Soc. Symp. Proc. Vol. 602 ©2000 Materials Research Society
the paramagnetic-insulator phase. The conductivity and the drift mobility in the films at different temperatures were measured and the values at room temperature are 1.6 X 10-2 S/cm and 2.5 X 10-2 cm2/Vs, respectively. Both conductivity and drift mobility increase with increasing temperature. The Arrhenius behaviors of the conductivity and drift mobility are consistence with a small polaron model, which indicates that the transport mechanism above the Curie temperature is dominated by the hopping of small polarons. EXPERIMENT The samples were fabricated by pulsed laser deposition method using La0.7 5Sr 0.11CaO14MnO 3 ceramic target. A 248 nm KrF excimer laser source with 5Hz in repetition rate and 30ns in pulse width. The average laser energy density was 2.5 J/cm2. The target and the substrate holder were rotated during the deposition. The films were deposited on fused silica substrates, with a thickness of 500 rm, at 800 °C in 30 Pa of oxygen. Immediately after the deposition the films were in situ annealed at 850 0C in pure oxygen of 0.5 atm. for one hour. A more detailed description on sample preparation procedure has been published in our previous work [20]. The chemical composition of the films was analyzed by inductively coupled plasma quantemeter(ICP). The result of ICP measurement shows that the films are stoichiometry. The samples are single-phase, as checked by X-ray diffraction. The Curie temperature T, of the target used in this paper is 280 K. To meet the need of the TW measurements, co-pla
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