The chromium and aluminium quantities required to synthesize nano-sized SrCrx Fe12-xO19 and SrAlxFe12-xO19 by the auto combustion route were optimized. XRD analysis showed that the optimum amounts were differed in two cases. A combination of 0.75 wt% of nano-sized SrFe12O19 and 0.75 wt% of the commercial additive, in chromium doped sample from solid state process(Cr2O3 addition), resulted in superior magnetic properties with increased intrinsic coercivity, remanence magnetization and rectangularity ratio.