Abstract
Mixed-valence manganese oxides present striking properties like the colossal magnetoresistance, metal-insulator transition (MIT) that may result from coexistence of ferromagnetic, metallic and insulating phases. Percolation of such phase coexistence in the vicinity of MIT leads to first-order transition in these manganites. However the length scales over which the electronic and magnetic phases are separated across MIT which appears compelling for bulk systems has been elusive in (La1−yPry)1−xCaxMnO3 films. Here we show the in-plane length scale over which charge and magnetism are correlated in (La0.4Pr0.6)1−xCaxMnO3 films with x = 0.33 and 0.375, across the MIT temperature. We combine electrical transport (resistance) measurements, x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and specular/off-specular x-ray resonant magnetic scattering (XRMS) measurements as a function of temperature to elucidate relationships between electronic, magnetic and morphological structure of the thin films. Using off-specular XRMS we obtained the charge-charge and charge-magnetic correlation length of these LPCMO films across the MIT. We observed different charge-magnetic correlation length for two films which increases below the MIT. The different correlation length shown by two films may be responsible for different macroscopic (transport and magnetic) properties.
Highlights
Using polarized neutron reflectivity we observed that magnetic ordering in LPCMO film with x = 0.33 was not caused by the metal-insulator transition; rather magnetic ordering first occurs at higher temperatures[18]
The metal– insulator transition (MIT) for S2 occurred at higher temperatures (TIM = 105.6 K and TMI = 109.0 K) with a smaller thermal hysteresis ~4 K
We observed reduced surface magnetization for both the LPCMO films compared to the film bulk
Summary
Direct evidence for coexistence of magnetic and nonmagnetic regions and their length scales has been elusive in LPCMO films. We show that the in-plane length scales over which charge and magnetism are correlated in (La0.4Pr0.6)1−x CaxMnO3 films with x = 0.33 and 0.375 are different. We observed smaller in-plane charge correlation length for LPCMO film with x = 0.33 than that of film with x = 0.375, which is consistent with the length scale associated with conductivity map of the films. We observed different charge-magnetic correlation length for two films which increases below the MIT. Both chemical and magnetic surfaces show similar fractal dimension of ~2.7 with similar atomic scale roughness ~4 Å
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