Direct Observation of Percolation in a Manganite Thin Film

Abstract

Upon cooling, the isolated ferromagnetic domains in thin films of La0.33Pr0.34Ca0.33MnO3 start to grow and merge at the metal-insulator transition temperature TP1, leading to a steep drop in resistivity, and continue to grow far below TP1. In contrast, upon warming, the ferromagnetic domain size remains unchanged until near the transition temperature. The jump in the resistivity results from the decrease in the average magnetization. The ferromagnetic domains almost disappear at a temperature TP2 higher than TP1, showing a local magnetic hysteresis in agreement with the resistivity hysteresis. Even well above TP2, some ferromagnetic domains with higher transition temperatures are observed, indicating magnetic inhomogeneity. These results may shed more light on the origin of the magnetoresistance in these materials.

Electric field driven dynamic percolation in electronically phase separated (La0.4Pr0.6)Jeen1, Biswas2 2013Phys. Rev. BSelf Cite321310View full textAdd to dashboardCite

“…Such dynamic behavior in the phase coexistence region has also been observed using magnetization, noise, and neutron diffraction measurements [25][26][27]. In the warming cycle, the phase boundaries are pinned and the FPS state is suppressed as has been directly shown using low temperature magnetic force microscopy [7]. Hence, we conclude that the fluidity of the FMM phase is necessary for the anisotropic resistance and the dynamic behavior of the FMM phase should reveal the true nature of the electric field effect.…”

“…An important feature of the resistance anisotropy is that it is observed only during the cooling cycle. It has been shown that the FPS state in which the FMM regions behave in a dynamic, fluid-like fashion, occurs only during the cooling cycle [7,12]. Such dynamic behavior in the phase coexistence region has also been observed using magnetization, noise, and neutron diffraction measurements [25][26][27].…”

“…Phase separation on a scale as large as 10 µm has been observed in LPCMO thin films [7,24]. However, for cross structures of smaller dimensions we were not able to reproducibly obtain insulator-metal transitions possibly due to presence of only the insulating phase in the small structure.…”

“…It is possible that the absence of any resistivity anisotropy in the as-grown samples is due to the large sample size (5 × 5 mm 2 ) compared to the micrometer scale phase separation in LPCMO [4,7]. Monte Carlo simulations have indeed shown that multiphase coexistence leads to non-uniform electric fields which would prevent the detection of resistivity anisotropy in samples which are large compared to the scale of phase separation [16].…”

“…An alternate route for controlling the magnetism with an electric field is offered in materials with centrosymmetric structures such as perovskite-type manganese oxides (manganites), where the ferromagnetic metallic phase is in competition with a non-ferromagnetic insulating phase close to a first order phase transition [4][5][6]. In the prototypical manganite (La 1−y Pr y ) 1−x Ca x MnO 3 , the competition among the ferromagnetic metallic (FMM), charge-ordered insulating (COI), paramagnetic insulating (PMI) phases leads to multiphase coexistence over a broad range of temperatures [4,7] and makes it possible to tune their properties using external parameters such as magnetic field, electric field, and strain [8][9][10][11].…”