Critical Parameters in Hydrothermal Synthesis of M-Type Barium Hexaferrite : Phase Evolution, Sintering Effect, and Comparison with Conventional Synthesis Routes
Muhammad Iqbal(1), Azwar Manaf(1*), Januar Widakdo(1**), Mas Ayu Elita Hafizah(2), Nur Ika Puji Ayu(1)

1. Department of Physics, Universitas Indonesia, Beji, Depok 16424, Indonesia
2. Universitas Pertahanan, Citeureup, Bogor 16810, Indonesia
*azwar[at]ui.ac.id
**januar.widakdo[at]ui.ac.id

Abstract

M-type barium hexaferrite (BaFe12O19) is one of the most widely studied ferrimagnetic materials due to its high magnetocrystalline anisotropy, excellent chemical stability, high curie temperature, and promising magnetic properties for permanent magnets, microwave absorbers, and electromagnetic devices. In this study, BaFe12O19 was synthesized using a modified hydrothermal method and crystallite size was systematically investigated. The synthesis was carried out using Ba(NO3)2 and Fe(NO3)3.9H2O precursors under hydrothermal conditions at 220 deg C for 24 h in a highly alkaline medium prepared using carbonate-free NaOH solution. Two synthesis routes were compared, namely hydrothermal synthesis without sintering and hydrothermal synthesis followed by sintering treatment. Phase identification was conducted using X-ray diffraction (XRD), while crystallite size was estimated using the Debye-Scherrer equation. The XRD results revealed that the sintered sample predominantly consisted of M-type BaFe12O19 with minor hematite (alpha-Fe2O3) phase, whereas the non-sintered sample was dominated by hematite with minor BaFe2O4 phase, indicating incomplete phase transformation during hydrothermal processing alone. The crystallite size of the sintered sample was found to range between 15-45 nm, while the non sintered sample exhibited larger crystallite sizes ranging from 32-78 nm. The findings confirm that post-sintering treatment plays a crucial role in promoting the complete transformation of intermediate phases into thermodynamically stable BaFe12O19. Furthermore, this study highlights several critical factors in hydrothermal synthesis, including Fe/Ba ratio, alkaline concentration, and thermal treatment, which strongly influence phase purity and crystal growth behavior of BaFe12O19.

Keywords: Barium hexaferrite, hydrothermal synthesis, sintering, phase evolution, hematite, BaFe2O4

Topic: Material Physics