Effect of Multilayered Structure on the Static and Dynamic Properties of Magnetic Nanospheres

The development of flexible and lightweight electromagnetic interference (EMI)-shielding materials and microwave absorbers requires precise control and optimization of core-shell constituents within composite materials. Here, a theoretical model is proposed to predict the static and dynamic properties of multilayered core-shell particles comprised of exchange-coupled layers, as in the case of a spherical iron core coupled to an oxide shell across a spacer layer. The theory of exchange resonance in homogeneous spheres is shown to be a limiting special case of this more general theory. Nucleation of magnetization reversal occurs through either quasi-uniform or curling magnetization processes in core-shell particles, where a purely homogeneous magnetization configuration is forbidden by the multilayered morphology. The energy is minimized through mixing of modes for specific interface conditions, leading to many inhomogeneous solutions, which grow as 2(n) with increasing layers, where n represents the number of magnetic layers. The analytical predictions are confirmed using numerical simulations.