We present a comparative study of the magnetic, transport, and structural properties of ${\mathrm{Nd}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3+\delta }$ [δ=0.02(1) and 0.04(1)]. We have found significant differences between the low-temperature magnetic order and magnetization below $T_{\mathrm{CO}}\approx 250$ K of the two samples. In particular, one component of the magnetic moment presents a ferromagnetic coupling between the (0 0 1) planes (Pbnm setting) changing the angle between neighboring Mn ions from 180° (perfect charge-exchange-type order) to 150° [δ=0.02(1)] and 130° [δ=0.04(1)]. These results imply a remarkable δ dependence that is discussed in the light of a nonrandom spatial distribution of defects in the perfect charge order scheme.

• Received 29 February 2000

DOI:https://doi.org/10.1103/PhysRevB.62.3002