An exotic uniaxial hexagonal ferrite with narrow self-biased ferrimagnetic resonance linewidths: Cu 18H hexaferrite

Traditional circulators utilize ferrites with low magnetocrystalline anisotropy driven by external magnetic bias fields. Hexagonal ferrites with a strong uniaxial anisotropy enable self-biased circulators, significantly reducing their volume, weight, and cost. Here, a unique uniaxial hexaferrite, Cu 18H hexaferrite, with narrow ferrimagnetic resonance (FMR) linewidth at zero magnetic bias field is reported. The temperature-dependent magnetic hysteresis loops show a significant decrease in coercivity from cryogenic to room temperature, indicating a transition from the hard to soft magnetic state. The crystallographic texture ensures a squareness ratio greater than 0.65 and leads to a strong internal bias field induced by the aligned easy-magnetization axes. Owing to the highly dense and oriented crystallites, the zero-field FMR exhibits excellent linewidths of similar to 270-320 Oe, which are lower than those of most hexaferrites reported at the K-a-band. These results reveal the great potential of Cu 18H hexaferrite as a low-loss microwave ferrite used for self-biased circulators.