The dynamic magnetic response of immobilized superparamagnetic nanoparticles to an ac field with arbitrary amplitude is studied using numerical simulations. The nanoparticles are considered to be distributed randomly within an implicit solid matrix, but the easy axes of the particles are aligned parallel to the ac magnetic field. Modeling of dynamic response is based on the Fokker-Planck-Brown equation in which the interparticle dipole-dipole interactions are included within the framework of the modified mean-field theory. The effects of the magnetic crystallographic anisotropy barrier, the ac field amplitude, and the interparticle interactions on the dynamic magnetization, susceptibility, and relaxation time are analyzed. It is shown that an increase in the amplitude of the ac field significantly accelerates relaxation processes in the system under consideration whereas an increase in magnetic anisotropy of a particle and interparticle dipole-dipole interactions slows them down. The numerical results for dynamic susceptibility and relaxation time are compared against theories reliable in the weak ac field, and an excellent agreement is obtained. Submitted to: Modelling Simul. Mater. Sci. Eng.

中文翻译：

---

相互作用的超顺磁性粒子对任意振幅交流场的磁响应的数值模拟

使用数值模拟研究了固定化超顺磁性纳米粒子对任意振幅交流场的动态磁响应。纳米粒子被认为是随机分布在隐含的固体基质中，但粒子的易轴平行于交流磁场排列。动态响应的建模基于 Fokker-Planck-Brown 方程，其中粒子间偶极-偶极相互作用包含在修正平均场理论的框架内。分析了磁性晶体各向异性势垒、交流场幅度和粒子间相互作用对动态磁化强度、磁化率和弛豫时间的影响。结果表明，交流场振幅的增加显着加速了系统中的弛豫过程，而粒子磁各向异性和粒子间偶极-偶极相互作用的增加会减慢它们的速度。动态磁化率和弛豫时间的数值结果与弱交流场中可靠的理论进行了比较，获得了极好的一致性。提交给：建模仿真。母校。科学。英。