The magnetization curves of $\mathrm{Ca}\mathrm{Mn}{\mathrm{O}}_{3-\delta }$ ($\delta =0.20$ and 0.25) single crystals in pulsed magnetic fields up to $350\mathrm{kOe}$ were studied, and the threshold increase of magnetization at $H_{\mathrm{cr}}\sim 50\mathrm{kOe}$ and $T=4.2\mathrm{K}$ was discovered. This anomaly is explained by melting of the charge ordering, which is associated with oxygen vacancy ordering. The jump at the metamagneticlike transition is equal to 0.02 ${\mu }_B∕\mathrm{Mn}$; no hysteresis is evidenced in the field-up and field-down processes. The magnetization dependence versus magnetic field is almost linear at $T=77\mathrm{K}$. The results obtained are explained assuming high stability of the antiferromagnetic G-type charge ordering phase at $T=4.2\mathrm{K}$ and its destabilization under magnetic field or temperature increase because of the double-exchange reinforcement between ${\mathrm{Mn}}^{3+}$ and ${\mathrm{Mn}}^{4+}$ ions. The oxygen vacancy ordering can be considered as an additional degree of freedom in manganites.

• Received 19 July 2007

DOI:https://doi.org/10.1103/PhysRevB.77.052406