Structural and magnetic properties of RE-Al substituted nanocrystalline hexaferrites (Sr1−xRExAl2Fe10O19)

Abstract

We describe the synthesis and characterization of magnetic materials with improved magnetic properties for permanent magnet applications. Sr _1− _x RE _x Al _2 Fe _10 O _19 (RE = La, Ce, Tb, and Dy; x = 0.0 and 0.1) were prepared by ball milling and sintering at 1200 °C for 6 h. The effects of (Al ^3+ –RE ^3+ ) substitution on the structural and magnetic properties of SrM hexaferrites were investigated by x-ray diffraction, scanning electron microscopy, and magnetic measurements at low (5 K), and high temperatures (from room temperature to above Curie temperature). The sample with x = 0, and that with La substitution, consisted of a single SrM phase. The rest of the samples contained traces of secondary oxide phases, and exhibited a small reduction in lattice parameters compared with the unsubstituted SrFe _12 O _19 . The coercivity of the samples (8800 ≤ H _cM ≤ 9750 Oe) was more than double the standard value of the unsubstituted compound, and the Curie temperatures was >300 °C for all samples. Also, the saturation magnetization (32.5–46.4 emu g ^−1 ) was high enough to make the overall magnetic properties of these compounds potentially important for the permanent magnet industry.

Keywords

• hexaferrite
• rare-earth substitution
• aluminum substitution
• ball milling
• structural properties
• magnetic properties