Designing M-type hexaferrites for sub-terahertz applications

M-type hexaferrites have continued to attract attention over the years due to their potential applications in microwave devices, magneto-optical systems, magnetic recording media, and permanent magnets. Here, we present a comprehensive investigation of the physical properties of M-type hexaferrites with nominal composition Sr_0.54Ca_0.46Al_xFe_12-xO₁₉ (x = 2.0, 4.0, 5.5, and 6.5) hexaferrites, designated as SCAFO-2, SCAFO-4, SCAFO-5.5 and SCAFO-6.5, synthesized via the solid-state reaction method. The formation of high-purity M-type hexagonal ferrite phases was confirmed by X-ray diffraction (XRD), and the structural parameters were quantitatively determined using Rietveld refinement of the diffraction patterns. Magnetic measurements reveal that the highest saturation magnetization M_s = 55.01 emu/g at 5 K and 34.57 emu/g at 300 K respectively for the synthesized strontium hexaferrite material with 2% aluminum substitution. Additionally, the coercivity (H_c) exhibits a monotonic increase with increasing Al content, rising from 5.61 kOe at x = 2.0 to a peak of 14.16 Oe at x = 4.0, followed by a decline at x = 5.5. The micromagnetic simulations, revealing that the resonance frequency increases with Al content, reaching a maximum at x = 5.5 (f = 250 GHz), followed by a decline at x = 6.5. This study provides a comprehensive understanding of the structure property relationships in Sr_0.54Ca_0.46Al_xFe_12-xO₁₉, demonstrating their strong potential for magneto-optical and sub-terahertz applications and establishing M-type hexaferrites as promising materials for future advanced technologies.