4D printing allows the creation of 3D-printed structures with a variety of new functionalities that respond to external stimuli, including electromagnetic properties, for which research is limited, such as terahertz resonances in ferrite materials; and therefore holding great promise for a wide range of applications. However, the limited physical properties of ferrite materials, including their anisotropic properties and limited material manipulation space, pose significant challenges to the development of ferrite materials designed for progressively increasing terahertz frequencies. Therefore, this paper proposes a platform for overcoming the limitations of terahertz resonance in ferrites through the 4D printing of metamaterials. Both the elastic and viscous moduli of the slurry are sensitive to the applied shear stress; as this stress increases, these moduli sharply decrease by several orders of magnitude, resulting in the transformation of the slurry into a fluid state similar to the liquefaction of ink. Electromagnetic coupling modes between electric dipoles and magnetic dipoles endow these ferrite metamaterials with induction and switching of terahertz resonances due to orientation stimulation. Our work sheds light on the creation of electromagnetic properties and their control by 4D printing.
Ferrites are widely used in the preparation of basic components that function within the microwave band. Compared with ferromagnetic ferrites, which possess a weak internal anisotropy field so that the working frequency of ferrite ceramics cannot be increased into the terahertz band, antiferromagnetic rare earth orthoferrites undergo strong interactions on the order of 100 T so that terahertz (THz) resonances can be supported. However, the zero or near-zero magnetization and internal dipolar fields complicate the manipulation of the THz responses in antiferromagnets using the traditional magnetic method. In this article, we choose PrFeO 3 as a model of rare earth orthoferrites and report a method of cooling and thickening to tune the THz resonances and absorptions. A combination of tuned time- and frequency-domain spectroscopic responses, including variations in amplitude with the time delay, changes in the transmittance, the peak height, the extinction coefficient κ , dissipation factor tan δ , and absorption coefficient α , which varied with frequency, reveal that our approach is effective. In this work, the resonant frequency of ferrites is promoted to the THz band, providing a highly effective approach for exciting and tuning their resonances and absorptions and offering support for the application of ferrite ceramics in the field of terahertz devices.
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