Development of Z-type hexaferrites for high frequency EMI shielding applications

Barium Z-type hexaferrites (Ba3Co2Cr2xFe24−2xO41 with x = 0, 0.3, 0.6 and 0.9) were synthesised using solid state reaction technique. X-ray diffraction (XRD) analysis confirmed the formation of single phase Z-type hexaferrite structure. From transmission electron microscopy (TEM) analysis platelet morphologies were observed in all the studied samples and the average grain size were calculated, which were around 100 nm. Magnetisation measurements (M-H) and (M-T) were carried out using vibrating sample magnetometer (VSM). Saturation magnetisation (Ms) was found to decrease with increasing Cr content in the samples whereas, magnetic coercive field (Hc) and remanent magnetisation (Mr) were increased. Electromagnetic absorption properties of all the ferrite samples were tested in 2-18 GHz frequency range using Agilent Vector Network Analyser. The sample Ba3Co2Cr1.2Fe22.8O41 (x = 0.6) had exhibited maximum microwave absorption of 99.8% at 5.34 GHz. All the samples showed broad absorption bandwidth of 3-3.2 GHz as well significantly high enough reflection loss of −10 dB. Therefore, the developed Z-type hexaferrites can be used for good electromagnetic shielding/absorber applications.