Figure of Merit of W-Type BaCo1.4Zn0.6Fe16O27 Hexaferrite for Gigahertz Device Applications

Along with high resistivity, W-type hexaferrite has relatively high saturation magnetization and large magnetocrystalline anisotropy, which makes it suitable for high-frequency applications. We synthesized W-type BaCo
_1.4
Zn
_0.6
Fe
₁₆
O
₂₇
hexaferrite using a conventional solid-state reaction method. Fe precursor,
α
-FeOOH, was mixed with BaCO
₃
, Co
₃
O
₄
, and ZnO in the appropriate stoichiometric ratio, followed by firing the mixture at 950 °C for 5 h and 1300 °C for 3 h in air to obtain BaCo
_1.4
Zn
_0.6
Fe
₁₆
O
₂₇
polycrystals. We used a vibrating sample magnetometer, impedance/material analyzer, and vector network analyzer to characterize the hexaferrite for its static and dynamic magnetic properties. The ferromagnetic resonant frequency, measured from experimental permeability spectra, is in the range from 8.5 to 9.5 GHz. Its corresponding magnetocrystalline anisotropy was in the range from 10.6 to 12 kOe. This is in good agreement with the anisotropy, which was obtained from the law of approach to saturation. Spin rotation and domain wall susceptibilities were determined by fitting the experimental permeability spectrum to a permeability equation. Their corresponding resonant frequencies are 9.1 and 19.5 GHz for domain wall motion and spin rotation, respectively. Finally, the figures of merit (FOM =
$\mu ^{\prime} \,{{/ \,\tan\,}}\delta _{\mu }$
) of BaCo
_1.4
Zn
_0.6
Fe
₁₆
O
₂₇
are 84 at 1 GHz (
$\mu ^{\prime} = 2.1$
and tan
$\delta _{\mu }= 0.025$
) and 42 (
$\mu ^{\prime} = 2.1$
and tan
$\delta _{\mu }= 0.05$
) at 2.2 GHz, which are the highest ever reported FOMs in the frequency range from 1 to 2.2 GHz.