Improvement of the coercivity of strontium hexaferrite induced by substitution of Al3+ ions for Fe3+ ions

Abstract

Al-doped strontium hexaferrites (SrAlxFe12−xO19) with nominal Al content of x=0–4 are prepared by glycin–nitrate method and subsequent annealing in a temperature ranging from 700 to 1250°C. The content of Al in the SrAlxFe12−xO19 increases with increasing annealing temperature and the nominal Al doping content. The Al3+ ion substitutes for Fe3+ ion with spinning upward in the SrAlxFe12−xO19. The coercivity of the SrAlxFe12−xO19 increases with increasing nominal Al doping content at a fixed annealing temperature, but increases firstly with increasing annealing temperature and then decreases at a fixed nominal Al doping content. The largest coercivity of 17570Oe is obtained in the SrAl4Fe12O19 prepared at an annealing temperature of 1000°C, which is much larger than the coercivity of the SrFe12O19 (5356Oe) and exceeds even the coercivity of the Nb2Fe17B (15072Oe). The mechanism of the improvement of the coercivity induced by Al doping is discussed in the present work.