Empirical expression for harmonics of AC magnetization of magnetic nanoparticles with core size distribution

It is well known that the core size of practical magnetic nanoparticle (MNP) samples is widely distributed. This study investigated an empirical expression for harmonics of AC magnetization of MNPs for magnetic nanoparticle thermometer (MNPT) and used two main core diameters to approximate the effect of the core size distribution. When the frequency of AC magnetic field was 200 Hz, the harmonics calculated from the Langevin function with two-core diameters (two-core-diameters model) agreed well with the experimental data. When the frequency was 3 kHz, where the effect of the Brownian relaxation could not be ignored, the harmonics could also be empirically expressed by the two-core-diameters model by adequately choosing the parameters of the model. The simple two-core-diameters model is useful when MNPs sample with core size distribution is used for MNPT. (C) 2019 The Japan Society of Applied Physics