Determination of activation volumes in BaFe and metal particle coatings

Conversion of Worm-Shaped Antiferromagnetic Hematite to Ferrimagnetic Spherical Barium-Ferrite Nanoparticles for Particulate Recording Media

“…First, our preliminary results show that the S-BaFe particle may actually be an H-BaFe particle surrounded by a nonmagnetic Fe x O y shell [Abo 2010], which causes the magnetic volume much smaller than the geometric volume. Second, it has been previously reported that an increase in activation volume is expected if the mutual particle-to-particle interaction is greater in the medium [Song 1993]. In our case, due to the spherical nature of the particles, the mutual particle-to-particle interaction is much weaker; therefore, a lower V is expected.…”

“…The shapetransformation mechanism, from the worm shape of antiferromagnetic particles to spherical shape of ferrimagnetic bariumferrite nanoparticles, is not yet understood. The saturation magnetization of σ s (50.7 emu/g) is much lower than the theoretical value of 72 emu/g [Smit 1959] for bulk single-crystal barium ferrite. This is attributed to the smaller size of the particles compared to the magnetic single domain size of 0.1 μm [Goto 1980] and low degree of crystallinity due to the lower heat-treatment temperature.…”