I dont thing calculating moment for compound is easy! in fact it is very difficult. First refer the earlier discussion on Ag nanoparticle. I will come back later to discuss this.
You can use the Langeving function. If you have a sizes distribution, you can use the integral form with moment distribution on the argument. If you have interaction between nano particles you can use the Allia model.
Some references
Allia P, et al Phys. Rev. B 64, 144420 2001
PM Zelis et al J Nanopart Res (2013) 15:1613
O Moscoso Londoño J. Phys. Chem. C, 2014, 118 (24), pp 13168–13176