Superparamagnetism in CoFe2O4 nanoparticles: An example of a collective magnetic behavior dependent on the medium.

Abstract Cobalt ferrite particles with homogeneous microstructure have been prepared encased in MCM-41 (Mobil Composition Matter) and SBA-15 (Santa Barbara Amorphous) silica mesoporous structures. In addition, it was possible to obtain ferrite nanowires once the silica matrix was dissolved. The variety of samples prepared has allowed to deeply analyze the matrix effect in the magnetic behavior of these particles that behave as superparamagnetic at room temperature. It was found at 5 K, a drastic magnetic hardening of the encased ferrite particles due to the employment of such matrices, while no matrix effect was observed at 250 K. Highlights • Cobalt ferrite nanoparticles encased in silica matrix. • Cobalt ferrite nanowires obtained by dissolving the silica matrix. • Magnetic behavior depending on the surrounding medium. • Superparamagnetism above room temperature. [ABSTRACT FROM AUTHOR]