High fidelity and regularity structures of nanoscale materials has opened up new opportunities for developing miniaturized devices. A simple yet robust approach of magnetic field assisted controlled evaporative self-assembly (CESA) is developed to achieve Fe₃O₄ nanoparticle (NP) micro- and nano-patterns in a two dimensional (2D) direction. In the magnetic field assisted CESA process, the self-assembly morphology can be well controlled by varying extrinsic and intrinsic variables such as temperature, external magnetic field, and concentration of Fe₃O₄ NPs. Under the optimized magnetic field rotation frequency and temperature, 2D self-assembly of Fe₃O₄ NPs can be well realized. In addition, as photoactive sites, double bonds on the surface of Fe₃O₄ NPs allow the growth of polymer brushes by self-initiated photografting and photopolymerization (SIPGP), and the further achievement of free-standing magnetic composite films with well-defined patterns.