Magnetic properties of (Fe) 1− x–(Al 2O 3) x and (Fe 50Ni 50) 1− x–(Al 2O 3) x nanocomposite magnetic media synthesized using gel like Al 2O 3 matrix

Abstract

Composites with ferromagnetic nanoparticles, Fe and Fe 50Ni 50, dispersed in Al 2O 3 have been synthesized by a solution phase technique. The structure and magnetic properties of these composites with varying fractions of Al 2O 3 have been investigated. Both Fe and Fe 50Ni 50 nanoparticles are amorphous in the as-prepared state and become crystalline on heat treating with near equilibrium lattice parameters of 0.287 nm and 0.358 nm respectively. The interparticle distance increases with increasing Al 2O 3 from 0 wt.% to 20 wt.%. The size of Fe nanoparticles is ∼40 nm while the Fe 50Ni 50 nanoparticles are ∼20 nm in size. The Fe and Fe 50Ni 50 nanoparticles dispersed composites are found to be ferromagnetic at room temperature both in the as-prepared and heat treated conditions with clear coercive fields of 5.5–35 × 10 3 A m −1. The saturation magnetization increases by orders of magnitude on heat treatment, for e.g. from <1.0 emu g −1 to 143.4 emu g −1 for Fe–15 wt.% Al 2O 3 and 95.6 emu g −1 for Fe 50Ni 50–15 wt.% Al 2O 3. The Fe-composites exhibit a Curie transition at ∼1000 K while the Fe 50Ni 50 composites exhibit a transition at 880 K, both temperatures close to bulk values.