This research is made to show the impact of external magnetic source on Fe3O4 - water nanofluid treatment in a permeable cavity. Shape factor effect on nanofluid properties are taken into account. Final equations are derived by means of vorticity stream function formulation. Control volume based finite element method is employed for solving final formulae. Figures are depicted for various values of radiation parameter, Darcy number, Fe3O4 - water volume fraction, Rayleigh number and Hartmann number. Results reveal that selecting Platelet shaped nanoparticles results the highest heat transfer rate. Nanofluid velocity and heat transfer rate decrease with augment of Hartmann number. (C) 2017 Elsevier Ltd. All rights reserved.