Cu-doping induced ferromagnetic insulating behavior and domain wall pinning effects in LaMnO3

Abstract

A systematic study on the structural, magnetic, and electrical transport properties was performed for the LaMn(subscript 1-x)Cu(subscript x)O3 system. A single phase of orthorhombic perovskite structure was formed for x=0.05-0.40. A striking paramagnetic-ferromagnetic transition and a considerable magnetoresistance effect were observed at the ferromagnetic ordering temperature T(subscript C), but no insulator-metal transition induced by Cu-doping was observed. Below T(subscript C), a visible unexpected drop was observed in the ac susceptibility and zero-field-cooled dc magnetization for the dilute doped samples with x≤0.10, which was proven to be associated with domain wall pinning effects by milling the bulk material into single domain particles. It is validated that there is no exchange interaction between Cu and Mn, and double exchange interactions between Mn(superscript 3+) and Mn(superscript 4+) are induced by Cu-doping in the anti-ferromagnetic LaMnO3 matrix, whereas the severe distortion and disorder caused by occupied-dopant prohibits charge carriers from hopping.