Magnetic properties of lithium ferrite powders fabricated by a sol-gel method

Amorphous gel powders were prepared by heating an ethylene glycol solution containing Fe(NO3)(3). 9H(2)O and LiNO3 (Li/Fe (in molar ratio) = 0-0.31) at 353 K under a N-2 flow. The powders without lithium crystallized to gamma-Fe2O3 at 573 K and to alpha-Fe2O3 above 773 K. On annealing the powders of Li/Fe=0.18-0.31, a LiFe5O8-type phase appeared at 573 K which coexisted with alpha-Fe2O3 at above 673 K. The LiFe5O8-type phase without alpha-Fe2O3 could only be obtained on annealing the powder of Li/Fe = 0.31 at 973 K for 2 h. The saturation magnetization of the powder was 0.29 T (74% of LiFe5O8) and its coercive force was 10.5 kA . m(-1). With increasing crystallite size of the LiFe5O8-type phase, the coercive force of the powder increased until equal to 13.2 kA . m(-1) and then decreased. The estimated maximum single magnetic domain size was 40-50 nm.