Department of Mathematics and Physics, Lappeenranta University of Technology, PO Box 20, FIN-53851 Lappeenranta, Finland.
J Phys Condens Matter. 2011 Jan 12;23(1):015802. doi: 10.1088/0953-8984/23/1/015802. Epub 2010 Dec 6.
The temperature dependence of the resistivity, ρ, of ceramic La(1 - x)Sr(x)Mn(1 - y)Fe(y)O(3) (LSMFO) samples with x = 0.3 and y = 0.03, 0.15, 0.20 and 0.25 (or simply #03, #15, #20 and #25, respectively) is investigated between temperatures T ∼ 5 and 310 K in magnetic fields B up to 8 T. Metallic conductivity in #03 is changed eventually to activated in #25. In #15 and #20 the behavior of ρ(T) is more complicated, comprising of two extremes, divided by an interval of metallic behavior in #15, and two inflections of ρ(T) in #20 within similar intervals ΔT below approximately 100 K. Mott variable-range hopping (VRH) conductivity is observed in #15 above the ferromagnetic Curie temperature, T(C). In #20 the Mott VRH conductivity takes place in three different temperature intervals at T > T(C), T close to T(C) and T < T(C). In #25, the Mott VRH conductivity is observed in two different intervals, above and below T(C), divided by an intermediate interval of the Shklovskii-Efros VRH conduction regime. Analysis of the VRH conductivity yielded the values of the localization radius, α, and the dependence of α and of the density of the localized states, g, near the Fermi level, on B. Above T(C) the localization radius in all samples at B = 0 has similar values, α approximately 1.0-1.2 Å, which is enhanced to α approximately 3.3 Å (#20) and 2.0 Å (#25) below T(C). The sensitivity of α and g to B depend on y and T. The complicated behavior of the mechanisms of the hopping charge transfer, as well as of the microscopic parameters α and g, is attributable to different electronic and magnetic phases of LSMFO varying with temperature and Fe doping.
研究了陶瓷 La(1 - x)Sr(x)Mn(1 - y)Fe(y)O(3)（LSMFO）样品在温度 T ∼ 5 到 310 K 之间，磁场 B 高达 8 T 时的电阻率 ρ 的温度依赖性，其中 x = 0.3，y = 0.03、0.15、0.20 和 0.25（分别简称为#03、#15、#20 和#25）。#03 中的金属导电性最终变为激活态，而#25 则是相反的情况。在#15 和#20 中，ρ(T)的行为更为复杂，包括两个极端，在#15 中，金属行为之间存在一个间隔，而在#20 中，在大约 100 K 以下的相似间隔内，ρ(T)有两个拐点。在铁磁共振居里温度 T(C)以上，#15 中观察到莫特变程跳跃（VRH）电导率。在#20 中，在 T > T(C)、T 接近 T(C)和 T < T(C)的三个不同温度区间内，发生了莫特 VRH 电导率。在#25 中，在 T(C)以上和以下的两个不同区间内，观察到了莫特 VRH 电导率，这两个区间被 Shklovskii-Efros VRH 传导机制的中间区间隔开。VRH 电导率的分析得出了局域化半径α的值，以及局域化状态密度 g 随 B 的依赖关系。在 T(C)以上，所有样品在 B = 0 时的局域化半径具有相似的值，α约为 1.0-1.2 Å，在 T(C)以下，α增强到约 3.3 Å（#20）和 2.0 Å（#25）。α和 g 对 B 的敏感性取决于 y 和 T。跳跃电荷转移机制以及微观参数α和 g 的复杂行为归因于 LSMFO 的不同电子和磁相随温度和 Fe 掺杂而变化。
