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...

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