Dependence of the physical properties of Nd0.5Ca0.5MnO3+δ on the oxidation state of Mn

We present a comparative study of the magnetic, transport, and structural properties of Nd0.5Ca0.5MnO3+delta [delta=0.02(1) and 0.04(1)]. We have found significant differences between the low-temperature magnetic order and magnetization below T(CO)approximate to 250 K of the two samples. In particular, one component of the magnetic moment presents a ferromagnetic coupling between the (001) planes (Pbnm setting) changing the angle between neighboring Mn ions from 180 degrees (perfect charge-exchange-type order) to 150 degrees[delta=0.02(1)1 and 130 degrees[delta=0.04(1)]. These results imply a remarkable delta dependence that is discussed in the light of a nonrandom spatial distribution of defects in the perfect charge order scheme.