Twin defects deteriorate the magnetic properties in conventionally-fabricated L10-type and RETM12-type permanent magnets. Herein, we propose a strategy to suppress twins’ formation by decreasing the grain and/or particle sizes below a critical size Dt~300 nm, based on the stress relief mechanism resulting from the balance of volume/surface energy. Twin-free monocrystalline nanoparticles smaller than Dt were synthesized using a comprehensive spectrum of methods for preparing field-aligned polymer bonded magnet with high texture. We propose here a roadmap for selecting the best route for manufacturing high-performance rare-earth free MnAl magnets, depending on their grain/particle size. The dependence of coercivity on grain/particle sizes shows that optimal coercivity can be reached within the range of 50-200 nm, meanwhile, twin-free microstructure is realized which allows ultrahigh remanence by field induced texture. The results reported here can be applied to other twin-containing permanent magnet compounds, offering opportunities to drastically increase their texture and maximal energy products.