Magnetic field dependence of the magnetic phase separation in Pr1-xCaxMnO3 manganites studied by small-angle neutron scattering

TL;DR

This study investigates how magnetic fields influence phase separation in Pr1-xCaxMnO3 manganites, revealing different scales of heterogeneity and their relation to colossal magnetoresistance.

Contribution

It provides a detailed analysis of magnetic heterogeneities at multiple scales using small-angle neutron scattering, highlighting their roles in CMR phenomena.

Findings

Mesoscopic inhomogeneities enable percolation leading to CMR.

Nanoscopic ferromagnetic clusters exist within AFI and FI phases.

No change in nanostructure observed under applied magnetic field.

Abstract

Transport properties of manganese oxides suggest that their colossal magnetoresistance (CMR) is due to percolation between ferromagnetic metallic (FM) clusters in an antiferromagnetic insulating (AFI) matrix. We have studied small-angle neutron scattering under applied magnetic field in CMR Pr1-xCaxMnO3 crystals for x around 0.33. Quantitative analysis of the small-angle magnetic neutron scattering shows that the magnetic heterogeneities take place at different scales. At the mesoscopic scale (200nm), the inhomogeneities correspond to the percolation of the conducting ferromagnetic phase into the insulating phases. It is at the origin of the colossal magnetoresistance of the compound. The other inhomogeneities are nanoscopic: inside the antiferromagnetic phase (AFI), there exist small ferromagnetic clusters. Inside the ferromagnetic phase which exists in absence of magnetic field in some compounds and is in fact insulating (FI), there also exist small non ferromagnetic objects. No evolution of this nanostructure is observed when the magnetic field is applied. The existence of such nanoscale objects is discussed in relation to the cationic disorder of these compounds.