Evolution of structure and magnetic properties with annealing temperature in nanoscale high-energy-milled nickel ferrite
Abstract
Metastable nanocrystalline nickel ferrite (NiFe 2O 4) with crystallite size ∼9 nm produced by high-energy milling the bulk material has been annealed at elevated temperatures to investigate the changes induced in the microstructure and the magnetic properties. High-temperature X-ray diffraction, thermogravimetric measurements, Mössbauer spectroscopy, electron microscopy, and magnetisation experiments have been used for this purpose. The results show that the range of the thermal stability of the mechanically induced defects in the structure of milled NiFe 2O 4 extends up to 600 K. Owing to the thermally induced variability of the cation arrangement and the spin configuration, the milled NiFe 2O 4 annealed at temperatures above 600 K exhibits a wide range of magnetic behaviour. The observed magnetic softening and an increase of both the saturation magnetisation and the Néel temperature with increasing annealing temperature are attributed to the cation reequilibration process and to the disappearance of the canted spin arrangement.
- Publication:
-
Journal of Magnetism and Magnetic Materials
- Pub Date:
- February 2003
- DOI:
- 10.1016/S0304-8853(02)01279-9
- Bibcode:
- 2003JMMM..257..377S