Ga-Doped Hexaferrite Submicron Particles for High-Frequency Devices

This study reports the synthesis of submicron $\mathrm{SrFe}_{12-x}\mathrm{Ga}_x\mathrm{O}_{19}$ particles exhibiting tunable magnetic anisotropy and natural ferromagnetic resonance up to $57$ GHz, enabling their use in millimeter-wave components for 5G/6G communication systems. As the authors note, “The samples display natural ferromagnetic resonance frequency in the range of 49-57 GHz”.

The Challenge

Producing single-domain M-type hexaferrite particles with controlled cation substitution is difficult due to phase separation at lower annealing temperatures and the strong dependence of magnetic properties on the exact distribution of $\mathrm{Ga}^{3+}$ among the five crystallographic Fe sites.

Innovation: Citrate Auto‑Combustion Synthesis

The researchers employed a citrate–nitrate auto‑combustion route followed by annealing at $1200\,^{\circ}\mathrm{C}$, which enabled:

• formation of a porous precursor that self-ignites,
• crystallization of uniform plate‑like particles (360–560 nm),
• precise determination of $\mathrm{Ga}^{3+}$ occupancy in the $2a$, $4f_1$, $12k$, and $2b$ sites.

According to the article, “The annealing of the porous precursor led to the formation of single‑domain hexaferrite particles with mean sizes of 360–560 nm”.

Key Results

• NFMR frequency increases to $57$ GHz at $x = 3$.
• Coercivity rises from $5.1$ to $6.4$ kOe for $x \le 4$, then drops to $0.3$ kOe at $x = 6$.
• Particle size decreases from $1400$ nm (undoped) to $360$ nm at high Ga content.
• $\mathrm{Ga}^{3+}$ preferentially occupies $2a$, $4f_1$, $12k$, and partially $2b$, reducing $T_\mathrm{C}$ to $311$ K at $x = 6$.

Impact

These Ga‑substituted hexaferrites are promising for:

• millimeter‑wave absorbers and filters,
• compact resonators for 5G/6G systems,
• high‑frequency magnetic components,
• spintronic devices requiring stable uniaxial anisotropy.

Cite this work

@article{Gorbachev2021GaHexaferrite,
  title={Submicron particles of Ga-substituted strontium hexaferrite obtained by a citrate auto-combustion method},
  author={Gorbachev, E. A. and Trusov, L. A. and Wu, M. and Vasiliev, A. V. and Svetogorov, R. D. and Alyabyeva, L. N. and Lebedev, V. A. and Sleptsova, A. E. and Karpov, M. A. and Mozharov, Y. M. and Gorshunov, B. P. and Kazin, P. E.},
  journal={Journal of Materials Chemistry C},
  year={2021},
  volume={9},
  pages={13832-13840},
  doi={10.1039/d1tc03381f}
}