The effect of Zn and Ni substitution on magnetic and microwave absorbing properties of Co2 W hexagonal ferrites

The magnetic (static, high-frequency) and microwave absorbing properties of Zn- or Ni-substituted Co-2 W hexaferrites have been investigated for application in commercial drones and wireless LANs operated at the frequency of 5.8 GHz. Powders with a composition of (BaCo2,MexFe16O27 (Me= Zn, Ni)) were prepared by calcination at 1250 degrees C, where the substitution ratio x was varied from 0.0 to 1.5. With the calcined powders, composite specimens were prepared using silicone rubber as a matrix material. Vibrating sample magnetometry measurements indicate that the composite specimens of Zn-substituted Co-2 W hexaferrite powders exhibited increased saturation magnetization and decreased coercive force. As a result, ferromagnetic resonance occurred in the frequency range below 6 GHz, which is attributed to the decreased crystal anisotropy field on the basal plane. However, with Ni substitution, the complex permeability spectrum showed an increased resonance frequency (12.9 GHz), which is attributed to the increased crystal anisotropy field by changing the easy-axis of magnetization from the basal plane to the c-axis. The specimens with Zn substitution showed superior microwave absorbing properties at C-band frequencies. For the specimen with Zn substitution with x = 1.0, a reflection loss of -35 dB was obtained at 5.8 GHz with a matching thickness of 4 mm.