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Dependence of the physical properties of $Nd_{0.5}Ca_{0.5}MnO_{3+δ}$ on the oxydation state of $Mn$

We present a comparative study of the magnetic, transport and structural properties of $Nd_{0.5}Ca_{0.5}MnO_{3+δ}$ [$δ=$ 0.02(1) and 0.04(1)]. We have found significant differences between the low temperature magnetic orders and the magnetization curves below $T_{CO}\approx 250 K$ of the two samples. In particular one component of the magnetic moment presents a ferromagnetic coupling between the $(0 0 1)$ planes ($P bnm$ setting) deviating the angle between neighboring $Mn$ ions from $180^o$ (perfect CE order) to $150^o$ [$δ=0.02(1)$] and $130^o$ [$δ= 0.04(1)$]. These results imply a remarkable $δ$ dependence which is discussed in the light of a non-random spatial distribution of defects in the perfect charge order scheme.