Magnetic properties of cobalt ferrite octahedrons obtained from calcination of granular nanotubes growing on bacterial nanocellulose.

• The granular nanotubes calcination of cobalt ferrite produces octahedrons. • Particles grow as octahedrons due to a minimization of the surface free-energy. • The heat treatment increases the sizes of the crystallites and particles. • The curves ZFC and FC are characterized by a peak and irreversibility temperatures. • Irreversibility temperature behavior is similar to superparamagnetic systems. • The magnetic domain structure is highly dependent on the applied magnetic field. We present an in-depth magnetic study of polycrystalline, microstain-free, magnetic, and thermally stable cobalt ferrite (CoFe 2 O 4) octahedrons with an edge dimension of 214 nm. Nanoparticles were synthesized from granular CoFe 2 O 4 nanotubes growing on bacterial nanocellulose and annealed at T = 1273 K. SEM, XRD, and VSM were used to investigate the morphology, structure and magnetic properties of the octahedral particles. The results indicate that heat treatment increases the sizes of the crystallites (2 times) and of the particles (4 times), compared with the starting material. The particles show a change of the magnetization saturation and magnetic anisotropy around 150 K compared with canonical ferrimagnetic materials, associated with a First Order Magnetization Process. The magnetization process as a function of temperature, cooling without (ZFC) and with (FC) different applied magnetic fields are explained by multi-domain theory. ZFC-FC curves show an irreversible branching temperature, which is highly sensitive to the applied magnetic field. In contrast, the temperature for the maximal magnetization value in the ZFC curves, change slightly with the external applied magnetic field, H. [ABSTRACT FROM AUTHOR]