Effect of Mn-substitution on coercivity of SrFe8Al4O19 nanocrystals

The effect of manganese (Mn) substitution on the magnetic properties of SrFe8−xMnxAl4O19 nanocrystals has been investigated via precise compositional modulation with x = 0, 0.25, 0.50, 0.75, and 1.0. Rod-shaped nanocrystals with hexagonal crystal structure and an average crystallite-size of 25 nm were synthesized via sol-gel method. Magnetic property measurements have been conducted including hysteresis loops and singular point detection (SPD) to investigate the impact of Mn-substitution on magnetic hardening of SrFe8Al4O19 nanocrystals. An increase in Mn-concentration from x = 0 to x = 1.0 resulted in a significant increase in magnetic coercivity from 12.5 to 17 kOe. This increasing trend in coercivity with higher Mn-content is attributed to the enhanced magnetocrystalline anisotropy (MCA). Further, Bloch’s law fittings of the temperature-dependent magnetization data revealed an increase in the value of Bloch’s constant B with an increase in Mn-content, indicating weak exchange interactions that effectively boosted the magnetic anisotropy and increased the coercivity.