nanoparticles*

We study the effect of distribution of coercivities with the calcination temperature, using the first order reversal curves (FORC) treatment in BiFeO₃ nanoparticles prepared by sol-gel method. We varied the calcination temperature in order to control the NP size. XRD measurements suggest that at lower temperatures (450°C and 550°C) the BFO NPs are single phase. At higher temperatures an impurity phase at higher appears with magnetic contribution. The FORC treatment was built as a linear combination for each temperature value. The coercivity distributions were obtained extracting the central ridge of the resultant FORC diagrams and contrasted with magnetization as a function of magnetic field measures. These results evidence a decreasing in the coercivity average that we associate to a decrease of magnetic domain size; then, suggesting a transition from single domain to superparamagnetic particles.