Charge ordering and magnetoresistance in ${\mathrm{Nd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{MnO}}_3$ due to reduced double exchange

Structural, transport, and magnetic properties of ${\mathrm{Nd}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ca}}_{\mathit{x}}$ ${\mathrm{MnO}}_3$ (0≤x≤1) have been studied to probe the consequence of strong lattice distortion and reduced double exchange. Charge ordering has been observed over a large composition range of 0.30≤x≤0.80. For 0.33≤x≤0.40, at low temperatures, a magnetic field induces a first-order antiferromagnetic semiconductor to ferromagnetic metal transition and reduces the resistance by several orders of magnitude. These results illustrate the competition between double exchange and mechanisms that promote charge localization. © 1996 The American Physical Society.