Power dissipation in magnetic nanoparticles evaluated using the AC susceptibility of their linear and nonlinear responses

The heat dissipated by magnetic nanoparticles may be used as a heat source for hyperthermic treatment of cancer and it can be estimated based on the magnetic susceptibility when an alternating current (AC) magnetic field is applied. Here, the frequency dependence of the magnetization of magnetic nanoparticles is measured for different AC fields. This is used to examine the AC susceptibility of linear and nonlinear magnetization responses. Two methods were used to evaluate the AC susceptibility based on measured magnetization properties. The first used the static susceptibility and phase delay associated with magnetic relaxation, and the second used the area under the AC magnetization curve to derive the imaginary part of the susceptibility. When the field intensity was low, the estimated AC susceptibilities were comparable. However, when the field intensity was high, the first method predicted a lower value because it did not consider the nonlinearity of the magnetization response. To optimize the material and the applied field conditions for hyperthermia it is important to understand the difference between the two methods. The intrinsic loss power and specific loss power of the magnetic nanoparticles were also evaluated. A liquid sample and a solid sample with an oriented easy axis provided high heat dissipation.