Magnetic Properties of Barium Ferrite Formed by Crystallization of a Glass

A glass with composition 0.265 B2O3‐0.405 BaO‐0.33 Fe2O3 (mole ratio) was prepared by a fast‐quenching technique. When it is heat‐treated, this glass exsolves up to ∼45 wt% BaFe12O19 as the only magnetic phase. Magnetic measurements of glasses heated at various temperatures show that superparamagnetic, single‐domain, or multidomain magnetic behavior is present, depending on the thermal history. The volume of a typical superparamagnetic particle (calculated from the magnetic data) is equivalent to that of a sphere 47 Å in diameter. The intrinsic coercive forces of two heat‐treated glasses were independent of temperature at high levels of Hci (2600 and 2900 Oe) from 77° to 300°K. Another heat‐treated glass has an Hci of 5350 Oe at 300°K. Apparently, the coherent rotation model of Stoner and Wohlfarth describes the magnetic behavior of BaFe12O19 very well. The single‐domain critical size for BaFe12O19 was ∼0.5 μm. An attractive feature of this system is that the BaFe12O19 powder can be recovered from the barium‐borate‐rich matrix by leaching with a weak acid.