PACS. 72.20.Ht High-field and nonlinear effects – 72.60.+g Mixed conductivity and conductivity transitions
Springer Online Journal Archives 1860-2000
Abstract: The transport properties of the La1-xCaxMnO3 ( 0.5 ? x 〈 1) system in magnetic fields up to 14 T were studied. We found that the relationship between the charge ordering temperature T CO and Mn4+ content n Mn4 + obeys the formula T CO / T max = 1 - a ( n Mn4 + - n 0 ) 2 , here n0 and a are constants and T max is the maximum of T CO . For x = 0.65, T CO arrives at the maximum value of 249.5 K in zero magnetic field, while the charge ordered (CO) state is most stable around x = 0.75. For x = 0.5 when H 〈 6 T the resistivity displays Mott's variable-range hopping (VRH) behavior, when 6 〈 H 〈 12 T it is suggested that two kinds of conduction mechanism, i.e., VRH and magnetic polarons, coexist in the material, and when H 〉 12 T the resistivity shows metallic-like behavior and the transport mechanism is attributed to coexistence of magnetic polarons and free carriers. For x = 0.95, the conduction mechanism accords with the coexistence of VRH and magnetic polarons.
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