Magnetic anisotropy and (BH)max studies in microwave sintered Al-substituted strontium hexaferrite

Al-substituted strontium hexaferrite (SrFe12-xAlxO19) has been synthesized by the sol-gel auto-combustion method, followed by microwave sintering at 1100 degrees C. The Rietveld refinement of XRD patterns reveals the hexagonal crystal symmetry with P6(3)/mmc space group. Lattice contraction has been observed with the increasing Al3+ concentration in SrFe12-xAlxO19. The anisotropy field is found to be similar to 25 kOe for SrFe11.5Al0.5O19. The (BH)(max) (maximum energy product) of 1.20 MGOe is obtained for x = 0.0 whereas there is a 63.66% enhancement of coercivity for SrFe11.5Al0.5O19 at 300 K. However, the highest (BH)(max) of 1.84 MGOe has been achieved at 60 K for SrFe11.5Al0.5O19. The criterion for a permanent magnet is satisfied by analyzing the hardness parameter. All the samples are found to be magnetically hard with (BH) max in the range (1.00-1.20) MGOe at 300 K.