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Mg substituted X-type barium-zinc hexaferrites (Ba2Zn2-xMgxFe28O46) for use in high frequency applications
Keywords: hexaferrites, high frequency, barium-zinc
There is a growing interest in the X-type hexaferrites for use at microwave (GHz) frequencies, especially as EM shielding and radar absorbing materials (RAM). Mg substituted X–type hexagonal ferrites with the chemical composition Ba2Zn2-xMgxFe28O46 (x = 0.0, 0.4, 0.8, 1.2, 1.6 and 2.0) were successfully synthesised by a sol–gel auto–combustion technique, in order to investigate the effect of Mg substitution on structural, magnetic and dielectric properties. For the first time, the room temperature magnetisation loops of Ba2Zn2Fe28O46 (Zn2X), Ba2Mg2Fe28O46 (Mg2X) and Ba2Zn2-xMgxFe28O46 (x = 0.0, 0.4, 0.8, 1.2, 1.6 and 2.0) were measured, and the saturation magnetisation showed an initial decrease with x = 0.4 - 1.2, and then an increase with x >1.2, to the largest final values of 63.29 A m2 kg-1 for the fully Mg–substituted x = 2.0. The value of coercivity lies in the range of 89.9 - 209.3 kA m-1, and the room temperature Mӧssbauer spectra are also presented as a function of Mg substitution. Dielectric parameters were measured at low frequencies (100 Hz - 2 MHz), and it was found that relative permittivity was constant between 0.3 -1.5 above 20 kHz, and all Mg substituted samples had lower losses above 20 kHz than the pure Zn2X. In complex measurements at microwave frequencies (500 MHz - 13.5 GHz), all samples had a real permittivity of around 7.5, except for the fully Mg–substituted sample (x = 2.0), which had a lower ´ of 5.5. For two samples (x = 0.4 and 1.6) we observed dielectric resonances between 12.85 - 13.25 GHz. All showed a steady real permeability of around 1.2 1.5 over the whole 1 - 13 GHz range, and ferromagnetic resonance (FMR) between 1 - 5 GHz, and at ~12.5 GHz.
Robert C. Pullar,
CICECO,University of Aveiro
Aveiro, P

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