Estudo estrutural e magnético do nanocompósito CoFe2/CoFe2O4

Abstract

The main objectives of this work is to obtain and study the Cofe2/CoFe2O4 nanocomposite, observe the occurrence of Exchange Spring effect in the samples and the enhancement of the coercivity and (BH)máx by mechanical milling. Cobalt ferrite samples were prepared from stoichiometric combustion method, and later reducted in H2 atmosphere during 5 hours at 350ºC to obtain the iron-cobalt powder. After, the samples were submited to oxidation in O2 atmosphere for different times at 380ºC to obtain another cobalt ferrite layer. The precursor materials samples and the nanocomposite samples were characterized by XRD, VSM, Mossbauer Spectroscopy and TEM. The results showed the obtention of Cofe2/CoFe2O4 nanocomposite in different quantities of CoFe2 and CoFe2O4 and the occurrence of Exchange Spring effect by the visualization of the histeresis curves. The Mossbauer Spectroscopy were presented as a rebliable technique to quantify the precursor material in the nanocomposite. The samples of CoFe2/CoFe2O4, as well the cobalt ferrite sample, were milled in a Spex-8000 ball mill during 1,5 hours. The magnetic results showed the enhancement of coercivity and (BH)máx values in the cobalt ferrite sample, but not in the nanocomposite samples, including a verification of lower (BH)máx values to the last ones. However, the TEM analysis showed structural strain formation by the visualization of regular and irregular shear bands and the fracture of some grains, confirming the milling treatment action in the studied samples.