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Phase transitions in the atomic, electronic, and magnetic subsystems of LaSrMnO films versus the synthesis temperature
Authors:Z A Samoilenko  V D Okunev  E I Pushenko  N N Pafomov  R Szymczak  M Baran  S J Lewandowski
Institution:(1) Galkin Physicotechnical Institute, National Academy of Sciences of Ukraine, ul. Rozy Lyuksemburg 72, Donetsk, 83114, Ukraine;(2) Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, Warsaw, 02-668, Poland
Abstract:The evolution of the cluster structure in amorphous LaSrMnO films as synthesis temperature T s increases from 20 to 300°C is considered. Two order-disorder phase transitions with different scale parameters are observed. One of them, the aggregation of disordered atoms into small (~20 Å) amorphous clusters at T s = 100°C, shows up as a sharp increase in the intensity of diffuse X-ray scattering (diffuse halo 1) with a simultaneous suppression of incoherent (background) scattering. At T s > 150°C, disordering dominates (I incoh = I max) until the next stage of ordering sets in at T s = 250?300°C. At this stage, the crystalline phase forms from large (>100 Å) crystalline clusters. This amorphous-crystalline phase transition is characterized by the appearance of Debye lines and a reduction of the halo intensity. The structural phase transition to long-range order is accompanied by a decrease in the LaSrMnO resistivity from 1010 to 10 Ω cm and a change from the tunneling mechanism of conductivity involving metallic clusters (which is typical of granulated systems) to the hopping mechanism with a hop variable length following the Mott law ρ ~ exp(T ?1/4). In the magnetic subsystem, the paramagnetic-ferromagnetic phase transition occurs.
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