Papers by Keyword: M-Type Hexaferrite

Abstract: In this article we report on the structural and magnetic properties of BaFe_12-4xMo_xZn_3xO₁₉ hexaferrites with Mo-Zn substitution for Fe ions. The starting materials were commensurate with the BaM stoichiometry, and the Mo:Zn ratio was 1:3. The powder precursors were prepared by high energy ball milling, and subsequently sintered at temperatures from 1100 to 1300° C. The structural analyses indicated that all samples sintered at 1100° C were dominated by a major M-type hexaferrite phase. The relative abundance of the BaMoO₄ and Zn-spinel secondary phases increased with increasing the concentration of the substituents, resulting in a decrease of the saturation magnetization from about 67 emu/g (for x = 0.0) to 55 emu/g (for x = 0.3). The coercivity also decreased from 3275 Oe (for x = 0.0) to 900 Oe (for x = 0.3), demonstrating the ability to tune the coercivity to the range useful for magnetic recording by the substitution process. The saturation magnetization improved significantly with sintering at T > 1100° C, and the coercivity decreased significantly, signaling the transformation of the samples to soft magnetic materials. These magnetic changes were due to the high-temperature reaction of the spinel phase with the BaM phase to produce the W-type hexaferrite phase on the one hand, and to the growth of the particles on the other hand. The magnetic phases were further investigated using Mössbauer spectroscopy and thermomagnetic measurements. Our study indicated that the sample with x = 0.2 has the highest saturation magnetization (74 emu/g at sintering temperature of 1300° C) and a tunable coercivity between 2100 Oe and 450 Oe.

Abstract: Owing to the technological importance of M-type hexaferrites of general formula MFe12O19 (M = Ba, Sr and Pb) and their substituted analogues, a staggering number of research activities on their synthesis, magnetic properties and thermal properties are being pursued in recent years. However, many critical issues on the effect of aliovalent ion substitution either on the M-site or Fe-sites are still unexplored. This paper deals with a survey of crystallochemical and thermodynamic properties of this important class of ferrimagnetic oxides.