Infrared Magnetic Hyperbolic Metamaterials

Magneto-optic (MO) materials represent a fascinating realm where the manipulation of magnetic spins is intricately entwined with the control of light propagation.^1,2 Our research delves into harnessing the potential of established MO effects— Faraday, Voigt, and Kerr effects—to steer, sense, manipulate, and process infrared light through ferromagnetic hyperbolic metamaterials (HMTM). The core of our innovation lies in the integration of ferromagnetic oxides with gold nanorods, creating broadband HMTM that exhibit epsilon-near-zero (ENZ) properties. Additionally, we leverage infrared surface plasmons supported at the interface between the HMTM and air to amplify MO effects, forging a synergistic relationship between magnetics and plasmonics. This magneto-plasmonic synergy not only opens avenues for developing compact nonreciprocal devices but also facilitates the creation of magnetic field-sensitive hyperbolic composite materials, enabling the precise manipulation of electromagnetic waves at the nanoscale. Our objective is to contribute to technologies at the intersection of magneto-optics and plasmonics.<br/><br/>In our fabrication process, nanocomposite films consist of vertically aligned gold (Au) nanopillars within ferromagnetic (La,Sr)MnO₃ (LSMO) oxide matrices, achieved through pulsed laser deposition. X-ray diffraction confirms the highly epitaxial nature of the (001)-oriented ferromagnetic LSMO film along, while X-ray reflectivity attests to the uniformity of electron density and high-quality surfaces and interfaces with a film thickness of approximately 30 nm. Detailed analysis through atomic force microscopy and scanning electron microscopy reveals the formation of Au nanopillars with diameter of around 45 nm within the LSMO matrix. X-ray photoelectron spectroscopy of the Au 4f and Mn 2p core levels highlights that the electronic structure of the nanocomposite displays a correlation between Fermi energy and electrical conductivity.<br/><br/>Notably, Fourier transform infrared (FTIR) microscopy uncovers a highly reflective band observed between approximately 12.2 µm and 8 µm optical phonon wavelengths. Ellipsometry microscopy further demonstrates the presence of double negative materials in our engineered nanocomposite. Further, we employed scanning near-field optical microscopy nano-FTIR, providing high-resolution insights with 10 nm spatial resolution. This technique not only enables chemical analysis but also characterizes local electromagnetic fields, offering a comprehensive understanding of the intricacies within our magneto-plasmonic nanocomposite.<br/><br/><b>References</b><b>:</b><br/>1. Jijie Huang, Han Wang, Zhimin Qi, Ping Lu, Di Zhang, Bruce Zhang, Zihao He, and Haiyan Wang, Multifunctional Metal–Oxide Nanocomposite Thin Film with Plasmonic Au Nanopillars Embedded in Magnetic La0.67Sr0.33MnO3 Matrix, <i>Nano Letters</i> 2021 21 (2), 1032-1039.<br/>2. Leigang Li, Liuyang Sun, Juan Sebastian Gomez-Diaz, Nicki L. Hogan, Ping Lu, Fauzia Khatkhatay, Wenrui Zhang, Jie Jian, Jijie Huang, Qing Su, Meng Fan, Clement Jacob, Jin Li, Xinghang Zhang, Quanxi Jia, Matthew Sheldon, Andrea Alù, Xiaoqin Li, and Haiyan Wang, Self-Assembled Epitaxial Au–Oxide Vertically Aligned Nanocomposites for Nanoscale Metamaterials <i>Nano Letters</i> 2016 16 (6), 3936-3943.