Evolution of the conducting phase topology at the percolation threshold in colossal magnetoresistance manganites: A magnetic small-angle neutron scattering study

Abstract : We have studied by small-angle neutron scattering the magnetic field evolution of the magnetic phase separation in a colossal magnetoresistive (CMR) Pr0.7Ca0.3MnO3 crystal, in a wide range of scattering vectors Q, down to 2×10−3 Å−1 and up to 10−1 Å−1. Access to such small Q values allows measuring the Q−4 scattering from interfaces between ferromagnetic and antiferromagnetic phases appearing along the phase separation. We were able to monitor its evolution from the very beginning of the insulator-to-metal transition, characteristic of the CMR effect. Our results confirm the percolation scenario of a field-induced conducting phase of micrometric size growing within the initial antiferromagnetic insulating phase. Moreover, we show that the CMR transition occurs when the transformation mechanism starts to be driven by large-scale strain field minimization.