Dear Vidit Pandey thank you for the interesting question. Please see this interesting article entitled "Supercapacitive Performance of Mn3O4 Nanoparticles Synthesized by Hydrothermal Method". This paper is available as public full text on RG:
Article Supercapacitive Properties of Mn3O4 Nanoparticles Synthesize...
In this work the authors use MnCl2x4H2O as starting material, but I assume that it can also be substituted by manganese(II) nitrate.
Dear Vidit Pandey you're very welcome! I hope the references were helpful and I wish you good luck with your experiments. At some stage perhaps you could tell us if the synthesis of your Mn3O4 nanoparticles was successful.