Electromagnetic Wave Absorption and Resonance in Infinite Cobalt Nano-Prisms

Author / Creator

MMM 2020 (2020)

Conferences

MMM 2020 L3: Magnetization Dynamics and Damping III (2020)

Available as

Online

Summary

There is increased interest in conductive ferromagnetic materials and structures due to their higher moments and compatibility with semiconductor fabrication methods and technology. They offer enha...

There is increased interest in conductive ferromagnetic materials and structures due to their higher moments and compatibility with semiconductor fabrication methods and technology. They offer enhancement in resonance frequencies and higher permeabilities in composites and nano-structures for applications in telecommunications and wave absorption [1,2]. The electromagnetic wave interaction with conductive ferromagnetic structures in these applications is complex due to coupling of both electric and magnetic fields with the magnetic material. This leads to non-uniform electromagnetic fields with different skin depths (both non-magnetic and magnetic). Early theoretical work focused on simple and saturated magnetic structures, excited in the linear region with uniform fields and involved solving the linearised system of Maxwell's equations and the Landau-Liftshitz equation for simplicity. This included planar structures [3], thin-films [4], and infinite cylinders [5]. Practical confined 2-D and 3-D magnetic structures found, for example, in composites have complex ground states and magnetic pinning, multi-layered with dielectrics, and experience non-uniform internal electromagnetic fields that yield complex precession and resonance modes that are not well understood. In this work, we solved the coupled system of Maxwell's and Landau-Lifshitz-Gilbert equations using a stable algorithm based on the finite-difference time-domain (FDTD) method to study the transient electromagnetic wave propagation and resonance in infinitely long cobalt nano-prisms with square cross-section of sides 50-1000 nm, excited by a 70 GHz plane wave [6]. The simulations revealed a curling exchange resonance mode excited by the induced axial current for prism sizes less than 100 nm. Larger prisms exhibited confined edge and corner resonance modes due to local power absorption and skin effects. The magnetic skin depth at resonance was estimated to be 50 nm from the calculated local power absorption spectra (see Fig. 1).References: [1] Y. Shirakata; N. Hidaka, M. Ishitsuka, A. Teramoto, and T. Ohmi, IEEE Trans. Magn. 44, 2100 (2008). [2] Y-B. Feng, T. Qiu, C-Y. Shen, and X-Y. Li, IEEE Trans. Magn. 42, 363 (2006). [3] W. S. Ament and G. T. Rado, Phys. Rev. 97, 1558 (1955). [4] J. W. Hartwell, Proc. IEEE 56, 23 (1968). [5] L. Kraus, Czech. J. Phys. B 32, 1264 (1982). [6] M. M. Aziz and C. McKeever, Phys. Rev. Applied 13, 034073 (2020).

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