Single-Domain Properties in Hexagonal Ferrites

Abstract

Barium ferrite platelet-shaped particles have been prepared with a diameter of 0.1 microns, which is an order of magnitude smaller than those obtained by conventional sintering and regrinding techniques. The preparation technique used has been optimized to produce the complete ferrite with σs=68 emu/g. Due to the small particle size, extremely high intrinsic coercive forces have been obtained, (Hc=5350 Oe), in good agreement with the value calculated from the Stoner-Wohlfarth (SW) coherent rotating model for single-domain noninteracting particles when shape and crystal anisotropy are both taken into account. Furthermore, the measured hysteresis loop for an unoriented sample agrees well with the theoretical SW loop. Similar hysteretic magnetization properties have been obtained in strontium ferrite. The single-domain nature of these powders is also demonstrated by their temperature dependence of coercive force where little change is obtained over the range −200° to +150°C. An estimate of the relative interaction field magnitude for the small particles of barium ferrite has been obtained by comparing its initial anhysteretic susceptibility with that of an acicular iron oxide powder.

Ultra large coercivity in barium ferrite thin films prepared by magnetron sputtering

“…However, H c in these samples was relatively small ( 600 Oe) compared with other reports. Packing of platelet-shaped particles with diameter about 0:1 mm gave intrinsic coercivity force of 5350 Oe, and the demagnetization processes were in good agreement with the prediction from the Stoner-Wohlfarth coherent rotating model [8]. Roos et al [9] measured magnetization loops of BaM particles with a diameter about 1 mm.…”

Magnetization reversal and interactions in SrFe12O19

“…Given that the calculated critical single domain diameters for Ba‐M and Sr‐M are 0.90 and 0.94 µm, respectively and due to their large uniaxial magnetocrystalline anisotropy, the high coercive field of such sub‐micronic polycrystalline samples has been often compared to the value predicted by the Stoner–Wohlfarth (SW) model that considers an isotropic assembly of non‐interacting uniaxial single‐domain particles which reverse magnetization by coherent rotation . Although these experimental H c values are high but usually below the SW theoretical value (about 80% of SW prediction), it has been often considered that M hexaferrite with sub‐micronic particles reverses magnetization by a nearly coherent rotation mechanism . Recent reports on M‐hexaferrite samples (doped or not) consider modifications in coprecipitation methods and others routes of preparation but in general coercive field is not improved in a proper extent.…”

Temperature effect on the magnetic property and ferroelectricity in hexaferrite SrFe12O19

“…M-type ferrites are also called hexagonal ferrites with the formula MFe 12 O 19 where M usually is Ba, Sr, Ca or Pb; among them, strontium hexaferrite (SrFe12O19) has attracted extensive attention in recent years, due to its properties of appropriate Curie temperature, high coercivity, large saturation magnetization, excellent chemical stability and anticorrosion [3,4].…”