Shifting the superparamagnetic limit of nanocrystalline copper spinel ferrite phase

SILVANA JACQUELINE STEWART; R. C. MERCADER; G. PUNTE; G. CERNICCHIARO; R. B. SCORZELLI; J. DESIMONI

Hyperfine Interactions

Año: 2004 vol. 156/ p. 89 - 95

0304-3843

Using a co-precipitation method, a system formed by nanocrystalline Cu–Fe spinel, grainsize D = 6 nm, and CuO (15 wt.%) was obtained. A Mössbauer blocking temperature (TB) of thespinel particles that lies between 100 and 200 K was observed. TB progressively increases as thesample is subjected to high-energy ball milling, being higher than 298 K after milling for 10 hours.The magnetic results also showed the increment of TB. The maxima of the in-phase component ofthe AC susceptibility at Tmax shift toward higher temperatures with the milling. After 4 hours, thisshift is ≈70 K for all the AC field frequencies. Simultaneously, the increase in the mean grain sizes(up to D = 13 nm) and the decrease of the microstrain level indicate that the degree of crystallinityof the spinel phase increases with the milling. After milling for 10 h, the sample is only composedby copper iron spinel with cubic structure.