EPJ Appl. Metamat. 13, 10 (2026)
https://doi.org/10.1051/epjam/2026002

Original Article

HoFeO₃ with Thermo-Softened phonons for 3D-printed terahertz metamaterials

¹ School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, PR China
² State Key Laboratory of New Ceramic Materials, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, PR China
³ Institute of Materials Research, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, PR China
⁴ State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, PR China
⁵ The Ninth Research Institute of China Electronics Technology Group Corporation, Mianyang 621000, PR China
⁶ Foshan (Southern China) Institute for New Materials, Foshan 528247, PR China
⁷ School of Electronic Information Engineering, Inner Mongolia University, Hohhot 010021, PR China

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Received: 29 November 2025
Accepted: 21 January 2026
Published online: 4 March 2026

Abstract

HoFeO₃ rare earth ferrite exhibits distinctive crystallographic properties; however, its regulatory mechanisms and methods within the terahertz band remain complex. This study employed variable-temperature Raman spectroscopy to explore atomic interactions within the crystal structures of HoFeO₃ across various modes, spanning temperatures from 20 to 300 K. The fabrication of HoFeO₃ metamaterials was achieved using 3D direct ink writing additive manufacturing technology, accompanied by the design of a three-coordinate spatial intelligent control structure to manipulate terahertz electromagnetic waves. Variable-temperature Raman spectroscopy revealed twelve active peaks, which included the stretching vibrations of Ho and O, the torsion of FeO₆, and the stretching vibrations of Fe-O. Notably, these phonons exhibited softening phenomena with increasing temperature. A low transmittance (transmittance <0.1) of terahertz waves at 0.82 THz was attained through the use of 3D-printed double-layer 90° metamaterials. Furthermore, when the double-layer 45° metamaterials were rotated in the E-H plane around the propagation direction as the central axis, the terahertz waves demonstrated a rotational symmetry transmission law at 0.5 THz. This research offers effective materials and construction methods for metamaterials aimed at regulating terahertz electromagnetic waves.