Using chemical oxidation technique, we prepared a new half-metal Sr2FeCoO6. Mossbauer study has presented a simultaneous test of stability of the oxygen content in this material. Caused by the oxygen leak, the Mossbauer spectra were progressively changed in the sample kept at room temperature. The spectra were measured within 3 months alternately with and without field of 4 kOe of a permanent magnet. The strong magnetizing effect of such a moderate field is conceptually well explained by nanostructuring, assisted by the unexpected effect of the superparamagnetic fraction permanently increasing with the "leak-time". (c) 2007 Elsevier B.V. All rights reserved.