Colossal Magnetoresistance of Ferromagnetic Manganites: Structural Tuning and Mechanisms

The amplitude Δρ(T,H)/ρ and temperature TM, where the colossal magnetoresistance (CMR) response of L_1-xCaₓMnO₃ manganites are maximum, are found to be controlled by the radius of the lanthanide (L³⁺) which modifies the bending of the Mn-O-Mn bond. Increasing the bond distortion lowers TM and enhances Δρ(T,H)/ρ. Enhanced CMR arises from (1) a shift to lower temperatures of TM, (2) a reduced mobility of the doping holes, and (3) an increase of the coupling between itinerant and localized electrons. The resistivity ρ(H) follows an ≈BM²(H) law and the parameter B is also tuned by the Mn-O-Mn bond angle. The narrowing of the electronic bandwidth is the fundamental parameter controlling the observed CMR.