Ferrite-Based Nanoparticles Synthesized from Natural Iron Sand as the Fe³⁺ Ion Source

Abstract

Ferrite-based nanoparticles, namely, bismuth ferrite (BiFeO 3 ) and calcium ferrite (CaFe 4 O 7 ), have been synthesized via sol-gel and chemically dissolved method, respectively, employing hematite (α-Fe 2 O 3 ) as the Fe 3+ ion source. Firstly, α-Fe 2 O 3 nanoparticles were prepared from natural iron sand containing mostly magnetite (Fe 3 O 4 ) phase through coprecipitation technique continued by sintering process at 800°C for 2 h. Higher BiFeO 3 phase content was achieved after Bi-Fe gel being annealed at 650°C for 1 h in air atmosphere. Furthermore, major phase of CaFe 4 O 7 was formed with molar ratio of Fe 3+ /Ca 2+ = 6 and sintering temperature of 800°C for 3 h. Interestingly, the powders with dominant CaFe 4 O 7 phase, known as calcium biferrite, exhibit higher ferromagnetism at room temperature. The magnetic properties of the calcium biferrite are comparable to those of barium hexaferrite which can be applied for radar-absorbing material. Meanwhile, BiFeO 3 powders also show weak room temperature ferromagnetism. It has also demonstrated that Ni doping in the bismuth ferrite (BiFe 1− xNi x O 3 with x = 0.1) nanoparticles results in enhancement of the magnetic properties. Moreover, a ferroelectric hysteresis loop and a trend of frequency dependence of the dielectric constant have been observed, which were enhanced by Pb doping (Bi 1− yPb y FeO 3 with y = 0.1). These results suggest a multiferroic behavior in the BiFeO 3 nanoparticles.