Tunable terahertz structure based on the ferromagnetic film
Zhang Qiang, Zhang Xiaoyu, Xing Yuanyuan, Zhao Lei     
Jiangsu Key Laboratory of Micro and Nano Heat Fluid Flow Technology and Energy Application, School of Mathematics and Physics, Suzhou University of Science and Technology, Suzhou, Jiangsu 215009, China

Overview: The terahertz (THz) microstructure is generally fabricated by Au film. It is difficult to control the THz wave by using the physical properties of Au film when the dimension of Au structures are fixed. It is suggested that combination of the tunable materials with the microstructure can improve the performance of terahertz microstructure and simplify the fabrication process. In this paper, the THz microstructure based on the magnetic FeNHf film is fabricated by using the high vacuum RF magnetron sputtering on the high resistivity silicon substrate. A complete terahertz microstructure of FeNHf magnetic thin film was prepared by the semiconductor micro-nano processing technology. The transmission characteristics of magnetic microstructure were characterized by the terahertz time-domain spectroscopy (THz-TDS). The THz transmission of magnetic microstructures were measured under the different external magnetic field. The soft magnetic FeNHf film has the high magnetization of ~16000 kG and the low coercivity of 3 Oe. The magnetic field H~ 50 Oe can change the direction of the magnetization M in FeNHf film perpendicular and parallel to the terahertz magnetic field, respectively. The THz transmission and electromagnetic resonance of the magnetic THz microstructure are systematically studied with the change of the external field H. The distribution of terahertz electromagnetic field and the surface current distribution based on the FeNHf film microstructure are discussed by the finite difference time domain method. The mechanism of the modulation of THz transmittance and resonance frequency of the magnetic microstructures is clarified with the change of the magnetic field. At the same time, for the comparison, the THz transmission characteristics of the microstructures with the same dimensional Au film are also discussed. The experimental results show that the resonance frequency of the split triangular THz microstructure can be modulated under magnetic field. At the frequency of 1.3 THz, the tunability and modulation depth are about 5.7% and 15%, respectively. The change of magnetization of FeNHf film which results in the perturbation of the magnetic field of terahertz wave. Furthermore, the distribution of electrons in FeNHf film will be changed under the external field, and the effective inductor is varied in the terahertz region. Therefore, it is found that the resonance frequency of FeNHf microstructure shifts to the lower frequency when the magnetization is perpendicular to the magnetic field of terahertz. Experimental and theoretical research on the THz transmission of the magnetic microstructure can further improve the understanding of the THz modulation mechanism for the active devices. At the same time, our efforts provide more experimental data for the development of passive THz devices.

Supported by National Natural Science Foundation of China (61107093), Suzhou Key Laboratory for Low Dimensional Optoelectronic Materials and Devices (SZS201611), Jiangsu Key Disciplines of Thirteen Five-Year Plan (20168765), Natural Science Foundation of the Jiangsu Higher Education Institutions of China (19KJA140001), and the Graduate Research and Practice Innovation Project of USTS (SKCX18_Y13)