  The magnetization behaviour of the soft Cobalt Ferrite-hard Strontium Ferrite
nanocomposite is tuned from the non exchange spring nature to the exchange
spring nature, by controlling the particle size of the soft Cobalt Ferrite in
the Cobalt Ferrite: Strontium Ferrite (1:8) nanocomposite. The relative
strength of the interaction governing the magnetization process in the
nanocomposites is investigated using Henkel plot and First Order Reversal Curve
(FORC) method. The FORC method has been utilized to understand the
magnetization reversal behaviour as well as the extent of the irreversible
magnetization present in both the nanocomposites having smaller and larger
particle size of the Cobalt Ferrite. The magnetization process is primarily
controlled by the domain wall movement in the nanocomposites. Using the FORC
distribution in the (Ha, Hb) co-ordinate, the onset of the nucleation field,
invasion of the domain wall from the soft to the hard phase, domain wall
annihilation and the presence of the reversible magnetization with the applied
reversal field for both the nanocomposites has been investigated. It has been
found that for the composite having lower particle size of the soft phase shows
a single switching behaviour corresponding to the coherent reversal of the both
soft and hard phases. However, the composite having higher Cobalt Ferrite
particle size shows two peak behaviour in the FORC distribution resembling
individual switching of the soft and hard phases. The FORC distribution in (Hu,
Hc) co-ordinate and the Henkel measurement confirms the dominant exchange
interaction in the nanocomposites exhibiting exchange spring behaviour where as
the occurrence of both the dipolar and exchange interaction is substantiated
for the non exchange coupled nanocomposite.
