Correlation between milling-induced strain, microstructure, and magnetic properties in anisotropic SrFe12O19 powders

Strontium hexaferrite (Correlation between milling-induced strain, microstructure, and magnetic properties in anisotropic SrFe12O19 powders) powders synthesized via conventional solid-state route are mechanically milled using air jet-mill and ball-mill techniques to produce anisotropic SrFe12O19 powders. Jet-milled and dry ball-milled powders showed higher strain (0.13%) compared to wet ball-milled powders (0.05%). On annealing, jet-milled powder exhibited better recovery of strain compared to the ball-milled powders. Enhancement in coercivity after annealing is maximum in jet-milled samples (1.7 kOe to 5.2 kOe). Angle-dependent magnetic hysteresis measurements suggest a difference in the nature of strain induced in jet-mill and ball-mill methods. Maximum remanence (0.81) is observed in both jet-milled and dry ball-milled powders, however, jet-milled powders showed a better retention of remanence (0.74) after annealing than the ball-milled powders (0.64). A stark contrast in the microstructure of jet-milled and ball-milled powders is revealed from SEM images. Particle size distribution curves confirm a considerable re-agglomeration in the ball-milled samples. The role of milling-induced strain and microstructure in obtaining anisotropic SrFe12O19 powders with optimum remanence and coercivity is discussed.