Inderscience Publishers

Magnetic properties of nano–sized Co

Nano–sized samples of Co
FeSi have been synthesised by mechanical alloying using a high energy ball mill. The average crystallite size shows a systematic decrease with milling time. M?ssbauer and DC magnetisation studies show that the Co
FeSi phase is formed at 9 h of milling and is optimised after 12 h of milling. Further milling results in the formation of a superparamagnetic phase with a corresponding deterioration in magnetic properties. A distribution in crystallite size is evident from the co–existence of superparamagnetic doublets with the magnetic hyperfine field in Mossbauer spectra. The presence of a large magnetically dead layer at the surface of the particles makes the value of saturation magnetisation less in the case of the 12 h sample as compared to the bulk. After 24 h of milling, the alloying process is complete but most of the particles of Co
FeSi are now superparamagnetic.

Keywords: Heusler alloys, nano Co2FeSi, mechanical alloying, magnetic properties, 57Fe Mossbauer, nanotechnology, milling, superparamagnetic doublets

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