Magnetic properties of cobalt oxide nanoparticles synthesised by a continuous hydrothermal method

• We apply a novel continuous method for the synthesis of magnetic nanoparticles with tailored structural and magnetic properties.
• Cubic Co3O4 nanoparticles were synthesised with an average size of 7 nm.
• Superparamagnetic behaviour was found at room temperature.
• Weak ferromagnetism appears at low temperatures.
• Observed exchange bias effect.

We use a Nozzle reactor, for the rapid and simple synthesis of antiferromagnetic Co3O4 nanoparticles with tailored structural and magnetic properties based on continuous-flow hydrothermal method. XRD and TEM studies show that the as-synthesised nanoparticles possess cubic morphology, high degree of crystallinity and an average size of 7 nm. Furthermore, SQUID and electron spin resonance (ESR) studies reveal interesting magnetic properties for practical applications such as weak ferromagnetism, spin canting, exchange bias effect at low temperatures and superparamagnetic behaviour at room temperature. The Nozzle reactor has also been successfully increased from bench-scale (grams/hour) to commercial scale (tonnes/annum) production of nanomaterials with good reproducibility, demonstrating the feasibility of developing Co3O4 nanoparticles for commercial applications.