Evaluation of magnetic heating of asymmetric magnetite particles

Characterization and theoretical description of relatively large (> 100 nm), asymmetric magnetic particles remain of interest particularly for applications to the mechanical damage of cells. In this work, we have examined the properties of three types of magnetite, Fe₃O₄, particles that were prepared by hydrogen reduction of hematite, α-Fe₂O₃. Transmission electron microscopy was used to measure the size and aspect ratio (AR), which were 1.8, 3.4 and 6.6, and all displayed magnetic hysteresis with corresponding saturation magnetization values of 65, 47, and 26 emu/g, respectively. With application of an alternating magnetic field to low concentrations, the temperature increased linearly with time, and the specific loss power (SLP) increased with increasing aspect ratio with values of 11.8, 24, and 26.8 W/g. The SLP increased linearly with the square of the applied magnetic field at low concentrations, but deviations were noted for high concentrations of the 2.4 and 6.6 AR particles. SLP was also dependent on frequency, but the functional relationship was not reliably determined. In consideration of the possible heating mechanisms, none provided a satisfactorily explanation for all types of particles. While these particles are not satisfactory for magnetic hyperthermia, they may have promise for causing cell death by magnetically inducing the particles to physically rotate or vibrate.