Abstract
Nanocrystalline particles of the Fe2−xAlxCoO4 (0 ≤ x ≤ 1) ferrites with cubic spinel structure have been synthesized by the sol-gel method. Size of the particles decreases from 39 nm to 6 nm as the Al content x increases. In the present work magnetic hysteresis curves and ZFC-FC curves have been studied. The magnetization of the Fe2CoO4 nanoparticles is lower than the magnetization of the bulk sample due to the surface and finite size effects. Saturation magnetization and remanent magnetization decrease as the x increases because of substitution of magnetic Fe ions with non-magnetic Al ions and possibly due to the spin canting and changes in ferrimagnetic structure. Coercive field changes with x in a complex way. Anisotropy barrier is lowered by reducing the size of the particle, but it can be increased by changing the distribution of Fe and Al ions in the spinel structure. The observed splitting between ZFC-FC curves in a rather high field indicates the presence of particles with the large anisotropy barrier for all samples.
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