The magnetization curves of CaMnO3−δ (δ = 0.20 and 0.25) single crystals in pulsed magnetic fields up to 350kOe were studied, and the threshold increase of magnetization at Hcr~50kOe and 4.2K was discovered. This anomaly was explained by melting of the charge ordering, which was associated with O vacancy ordering. The jump at the metamagnetic-like transition was equal to 0.02µB/Mn; no hysteresis was evidenced in the field-up and field-down processes. The magnetization dependence versus magnetic field was almost linear at 77K. The results obtained were explained assuming high stability of the antiferromagnetic G-type charge ordering phase at 4.2K and its destabilization under magnetic field or temperature increase because of the double-exchange reinforcement between Mn3+ and Mn4+ ions. The O vacancy ordering could be considered as an additional degree of freedom in manganites.

Charge Ordering Melting in CaMnO3−δ Single Crystals with Ordered Oxygen Vacancies. N.N.Loshkareva, N.V.Mushnikov, A.V.Korolyov, E.A.Neifeld, A.M.Balbashov: Physical Review B, 2008, 77[5], 052406 (4pp)