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Page 8 of 15 Ding et al. Soft Sci. 2026, 6, 2

Figure 4. RL values and effective absorption bandwidths of (A, B and I) ZnCo 2 O 4 , (C, D and J) ZnCo 2-y Fe y O 4 , (E, F and K) Zn 1-x Co 2 Ni x O 4 and
(G, H and L) Zn 1-x Co 2-y Ni x Fe y O 4 . RL: Reflection loss; EAB: effective absorption bandwidth.

reaches -38.7 dB, while the bandwidth corresponding to RL < -10 dB extends to 12.18 GHz. This confirms
that Fe incorporation effectively broadens the effective absorption window. In contrast, substitution with
3+
Ni in Zn Co Ni O [Figure 4E and F] drives the RLmin to -48.8 dB and yields an EAB of 9.71 GHz,
2+
2
1-x
4
x
demonstrating that Ni doping is particularly effective in reducing the RLmin. Notably, co-doping with both
2+
metal ions in Zn Co Ni Fe O [Figure 4G and H] achieves a RLmin of -57.6 dB and an EAB of 10.27 GHz,
2-y
1-x
x
y
4
simultaneously leveraging the advantages of each individual dopant. The thickness-dependent absorption
performance of all four materials is visualized in the histograms of Figure 4I-L, facilitating an intuitive
comparison. Progressive doping increases the structural complexity of the crystal lattice, and the dual-ion-
doped composite successfully balances the ultralow RLmin characteristic of Ni incorporation with the
2+
broad EAB associated with Fe substitution . Collectively, these findings demonstrate that the strategic
[39]
3+
integration of hierarchical porosity and judicious metal-ion doping represents a powerful approach to
significantly enhancing EM wave absorption.