Magnetic nanoparticles exhibit unique physical, dynamic and static properties. These properties have made them attractive for offering different application solutions in various fields such as medical, spintronic devices, and high-density data storage devices. Vortex spin spiral structure of nanoparticles exhibits unique magnetization dynamics including resonant precession motion of a vortex core. On the other hand, smaller-size soft magnetic nanoparticles in single-domain state exhibit collective Larmor precession hence resulting in high-value specific loss power (SLP). For example, in order to excite magnetization dynamics of single-domain nanoparticles, one can use low-power consumption when the frequency of the time-varying magnetic field is the same as that of the Larmor precession. Once individual spins experience Larmor precession motion, they also face energy dissipation during their dynamic motions. Therefore, researchers have identified that such resonant dynamic motions can provide a better mechanism related to high-value SLP as compared to the previously used non-resonant mechanisms.
Seoul National University researchers led by Professor Sang-Koog Kim investigated the magnetization dynamics of soft magnetic nanoparticles in the single domain states. They managed to accurately control high-value SLP related to high-efficiency energy-dissipation for hyperthermia applications. The work is published in the research journal, Physical Review Applied.
The research team utilized a novel approach of finite-element micromagnetic simulations to investigate the magnetization behavior of soft magnetic nanoparticles. Also, the energy dissipation rate was derived analytically in terms of the strength and frequency of the magnetic field. Eventually, the analytically calculated results are in good agreement with the simulation results, indicating the analytic equations can be used to find optimal SLP values according to externally controllable field parameters.
The authors observed that the mass-specific energy-dissipation rate for a given damping constant at steady state regime depends on the strength of the static and rotating magnetic fields. For instance, a high energy-dissipation was maximum at resonance especially for uniform magnetization where the frequencies of the Larmor precession and the rotating magnetic fields are the same for a given damping constant value. Furthermore, the similarities in the simulation and analytical calculation results showed that the developed mechanism is completely different from the previous ones and thus can be used in achieving high-value SLP in various applications.
The Seoul National University scientists successfully provided an in-depth understanding of the magnetization dynamic behaviors in soft magnetic nanoparticles and the possible effects of the energy-dissipation. Therefore, it has proposed a better and highly efficient method for obtaining high-value SLP by varying the frequency of the rotating field and strengths of the rotating and static magnetic fields. The highest SLP obtained allowed control of the mechanism through externally applied magnetic fields using magnetic particles in the single domain state. Therefore, the authors are optimistic that the findings in the study will help advance various applications of magnetic nanoparticles and particularly magnetic hyperthermia applications.
Kim, M., Sim, J., Lee, J., Kim, M., & Kim, S. (2018). Dynamical Origin of Highly Efficient Energy Dissipation in Soft Magnetic Nanoparticles for Magnetic Hyperthermia Applications. Physical Review Applied, 9(5).Go To Physical Review