Fix Weak Magnetism in MnFe₂O₄

I have been preparing MnFe₂O₄ nanoparticles through a fully green route that relies on a plant-based reducing agent, mild aqueous conditions, and a low-temperature calcination step. Unfortunately, the final powder shows almost no magnetic response—far below what the bulk ferrite should exhibit. I need a comprehensive troubleshooting and optimisation of every stage of the synthesis, from the choice or concentration of the extract, through pH control, mixing and ageing conditions, right up to the drying and heat treatment.

My goals are threefold and inseparable: (1) pinpoint why the magnetism is so weak, (2) redesign the protocol so that the saturation magnetisation reaches the typical range for well-crystallised MnFe₂O₄, and (3) keep the process strictly “green,” avoiding any organic solvents or toxic reagents.

Deliverables I expect
• A step-by-step revised synthesis protocol that stays within green-chemistry guidelines
• A brief rationale explaining how each change (e.g., temperature ramp, precursor ratio, pH, or calcination atmosphere) addresses the magnetic shortfall
• Recommended characterisation workflow (XRD, VSM, SEM/TEM, FTIR, etc.) that will let me verify crystal structure, particle size, and magnetic properties after adopting your protocol
• Troubleshooting notes so I can adapt the method if I swap to a different plant extract in future

Please draw on your experience with ferrite nanoparticles, VSM interpretation, and eco-friendly synthesis routes when proposing the solution.