Effect of La and Cu co-doping on structural evolution and high-frequency magnetic and dielectric properties of Z-type hexaferrites.

A series of La and Cu co-doped high-density Z-type hexaferrites, namely Ba 3− x La x Co 2 Fe 24− x Cu x O 41 (x = 0.20–0.95 in steps of 0.15), were synthesized via solid-state reaction method. Phase composition, microstructure, static magnetic properties, and high-frequency magneto–dielectric properties were studied systematically. Results show that with the addition of La and Cu, initial Z-type phase gradually transforms into a combination of Z- and W-type phases, and grain size increases. Specific saturation magnetization of samples increases significantly with increasing x and reaches the maximum (σ s = 59.20 emu/g) at x = 0.95. Furthermore, high-frequency magnetic and dielectric properties are improved, with permeability μ ′ and permittivity ε′ becoming almost equal in 0.1–1 GHz band. In particular, the sample with x = 0.65 exhibits excellent Snoek's product, that is (μ ′ − 1) f r ≈ 23.14 GHz , normalized impedance μ ′ / ε ′ approaches 1, and miniaturization factor is around 13.45 (@500 MHz). In this case, dielectric loss tangent tan δ ε is less than 0.003 below 500 MHz, and frequency range in which magnetic quality factor Q is greater than 10 is significantly broadened, covering wide bandwidth from 10 to 580 MHz. Thus, these hexaferrite ceramics are significantly promising for application to microwave communications. [ABSTRACT FROM AUTHOR]