光电工程  2020, Vol. 47 Issue (6): 190447      DOI: 10.12086/oee.2020.190447

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
Abstract: Au film is mainly used to prepare the metal structure of the terahertz (THz) microstructure. When the metal structure is fixed, it is difficult to control the terahertz wave by using the properties of Au film. In this paper, the terahertz microstructure based on the soft magnetic FeNHf film with the high permeability is designed and fabricated on the high resistivity silicon substrate. The magnetization direction of soft magnetic film is controlled by the external magnetic field H. The THz transmission characteristics and electromagnetic resonance mode of the microstructure under the control of H in split triangular structure are systematically studied. The soft magnetic FeNHf film has the characteristic of magnetic anisotropy. Therefore, the direction of the magnetization M in FeNHf film can be controlled by the external magnetic field H to be perpendicular and parallel to the magnetic field of THz wave, respectively. The THz time domain spectroscopy system is used to test the terahertz transmission characteristic of the microstructure. The finite difference time domain method is used to analyze the THz electromagnetic field distribution and modulation mechanism based on the microstructure of the FeNHf film. 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.
Keywords: terahertz waves    soft magnetic film    magnetic permeability    magnetic anisotropy

1 引言

2 实验

 图 1 (a) 超材料结构的实验照片；(b) TDS测试和非对称三角形结构尺寸示意图 Fig. 1 (a) Experimental photographs of metamaterial structures; (b) Schematic of THz TDS measurement and geometry of the asymmetric triangular structures
3 结果与讨论

 图 2 FeNHf薄膜轮廓图和表面形貌图 Fig. 2 FeNHf film thickness and surface morphology

 图 3 FeNHf薄膜。(a)磁滞回线；(b)复数磁导率与频率曲线 Fig. 3 Characterizations of FeNHf film. (a) Hysteresis loop of FeNHf film; (b) Frequency dependence of complex permeability
 ${{f_{\rm{r}}} = 2\pi \gamma \sqrt {{H_{\rm{k}}}4\pi M} , }$ (1)

 图 4 样品的THz透射率。(a) FeNHf薄膜和Au薄膜结构的实验结果；(b) FeNHf薄膜结构的模拟结果 Fig. 4 THz transmissivity of samples based on FeNHf film and Au film. (a) Experiments; (b) Simulations
 $\begin{array}{*{20}{l}} {L = 2l\left[ {{\rm{ln}}\left( {\frac{{2l}}{w} \cdot 1 + \left( {\sqrt {1 + {{\left( {\frac{w}{{2l}}} \right)}^2}} } \right)} \right)} \right.}\\ {\left. {{\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} - \sqrt {1 + {{\left( {\frac{w}{{2l}}} \right)}^2}} + \frac{\mu }{4} + \frac{w}{{2l}}} \right]{\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} , } \end{array}$ (2)

 Resonance points FeNHf microstructures Au microstructures Experiments/THz Simulations/THz Resonance points Experiments/THz M//H M⊥H Δfr M//H M⊥H Δfr a1, 2 0.175 0.177 0.002 0.250 0.253 0.003 a3 0.218 b1, 2 0.632 0.641 0.009 0.751 0.804 0.053 b3 0.668 c1, 2 0.902 0.947 0.045 0.974 1.071 0.097 c3 0.982 d1, 2 1.103 1.166 0.063 1.259 1.325 0.066 d3 1.209

 图 5 d峰位在磁化强度M分别平行和垂直H时，磁性薄膜结构在(a) fr=1.26 THz，(b) fr=1.33 THz的电场分布；(c) fr=1.26 THz，(d) fr=1.33 THz的磁场分布 Fig. 5 (a), (b) Distributions of the electric field in the structure at (a) fr=1.26 THz, (b) fr=1.33 THz; (c), (d) Distribution of the magnetic field in the structure at (c) fr=1.26 THz, (d) fr=1.33 THz. Peak d is when magnetization M is parallel and perpendicular to terahertz magnetic field H, respectively
4 结论

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