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 Zand W-type phases, and grain size increases. Specific saturation magnetization of samples increases significantly with increasing x and reaches the maximum (sigma s = 59.20 emu/g) at x = 0.95. Furthermore, high-frequency magnetic and dielectric properties are improved, with permeability mu ' and permittivity epsilon ' becoming almost equal in 0.1-1 GHz band. In particular, the sample with x = 0.65 exhibits excellent Snoek's product, that is ( mu _ 1)fr approximate to 23.14 GHz, normalized impedance mu/epsilon approaches 1, and miniaturization factor is around 13.45 (@500 MHz). In this case, dielectric loss tangent tan delta epsilon 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.