Discussion on the Interparticle Interactions in NiFe2O4 and ZnFe2O4 Nanosized Systems Based on the Matrix Effects in the Magnetic Behavior

ZnFe2O4 and NiFe2O4 particles ranging from 5 to 8 nm have been prepared inside the channels of SBA-15 mesoporous material and nanowires were recovered after dissolving the silica matrix. For both ferrite compositions a hardening of the magnetic behavior has been obtained when using the mesoporous matrix. Thanks to the comparison of the magnetic behavior of the nanoparticles when contained and not in the matrix, it was possible to elucidate not only the matrix effect but also the kind of interparticle interactions depending on the ferrite composition. Thus, nickel ferrite particles are characterized by intense dipolar interactions that are responsible for the so high superparamagnetic response and that can be avoided by matrix effects only at high temperatures. On the contrary, the inherent low-intense dipolar interactions of the zinc ferrite system lead it to present lower superparamagnetic moments, and in the case of encapsulated particles, the superparamagnetic behavior would correspond to almost not-interacting particles. In addition, interactions occurring between surface spins of different particles are more visible in zinc ferrite system as consequence of its so low intense dipolar interactions and are prevented thanks to the use of the matrix.