Terahertz permeability of hard ferromagnetic L1₀-FePt alloy nanowire

It is commonly thought that ferromagnetic materials can not find applications in terahertz domain because of their very weak dynamic magnetic responses. However, our results in this paper show that the terahertz (THz) permeability of an isolated L1₀-FePt alloy nanowire with super hard ferromagnetic properties is significant at 0.348 THz, as long as it is at proper remanent states (for instance, Mr/Ms = 1.0), which are ever thought only possible in some metamaterials. Compared to the gigahertz (GHz) permeability of single Fe nanowire, the THz permeability spectra of L1₀-FePt are shown obviously different. Unusual negative imaginary parts of permeability (μ″ < 0) is found related to the equivalent negative damping constant, which is explained from the perspective of abnormal precession of natural resonance at THz for FePt nanowire.