Resistivity of Mixed-Phase Manganites

Abstract

The resistivity rho(dc) of manganites is studied using a random resistor-network, based on phase separation between metallic and insulating domains. When percolation occurs, both as chemical composition or temperature vary, results in good agreement with experiments are obtained. Similar conclusions are reached using quantum calculations and microscopic considerations. Above the Curie temperature, it is argued that ferromagnetic clusters should exist in Mn oxides. Small magnetic fields induce large rho(dc) changes and a bad-metal state with (disconnected) insulating domains.

Nanoscale phase separation in colossal magnetoresistance materials: lessons for the cuprates?

“…14 (b), reproduced from [8], and also Ref. [39]). * Although not discussed in detail in this paper, studies in Mn-oxides [10] have brought forward the ideas of Imry and Ma about phase competition using the Random Field Ising Model [40].…”

Random resistivity network calculations for cuprate superconductors with an electronic phase separation transition

“…It describes how a system evolves from small fluctuations around an average density p to a complete separation into low and high density regions. At each of these small regions we will associated a local resistivity derived from the work of Takagi et al [26], who performed systematic measurements on the LSCO series (La 2−p Sr p CuO 4 ) to a large range of values of T and p. Then we use the Random Resistor Network (RRN) method [33] to derive the system resistivity as a function of the temperature R(T ) in a similar way as was applied to the manganites [34]. The local density and resistivity is randomly picked and the final R(T ) result is an average of many different configurations.…”

Electron Transport in Nanogranular Ferromagnets

“…At the same time the model of weakly coupled nanoscale ferromagnetic grains proved to be useful for understanding the transport properties of doped manganite systems [5,6] that have intrinsic inhomogeneities. Recent studies showed that above the Curie temperature these materials possess a nanoscale ferromagnetic cluster structure which to a large extend controls transport in these systems [7,8,9,10]. This defines an urgent quest for understanding and quantitative description of electronic transport in ferromagnetic nanodomain materials based on the model of nanogranular ferromagnets.…”

“…Investigations of the electronic transport and magnetoresistance (MR) were mostly restricted to the SPM state [27,28], where variable range hopping was observed. The crossover region near T s c was only studied by numerical methods in the context of manganite systems [5,9,10]. The resistivity dependence below the Curie temperature T s c presented in Fig.…”