High-entropy spinel ferrites MFe2O4 (M = Mg, Mn, Fe, Co, Ni, Cu, Zn) with tunable electromagnetic properties and strong microwave absorption

Abstract

Ferrites are the most widely used microwave absorbing materials to deal with the threat of electromagnetic (EM) pollution. However, the lack of sufficient dielectric loss capacity is the main challenge that limits their applications. To cope with this challenge, three high-entropy (HE) spinel-type ferrite ceramics including (Mg0.2Mn0.2Fe0.2Co0.2Ni0.2)Fe2O4, (Mg0.2Fe0.2Co0.2Ni0.2Cu0.2)Fe2O4, and (Mg0.2Fe0.2Co0.2Ni0.2Zn0.2)Fe2O4 were designed and successfully prepared through solid state synthesis. The results show that all three HE MFe2O4 samples exhibit synergetic dielectric loss and magnetic loss. The good magnetic loss ability is due to the presence of magnetic components; while the enhanced dielectric properties are attributed to nano-domain, hopping mechanism of resonance effect and HE effect. Among three HE spinels, (Mg0.2Mn0.2Fe0.2Co0.2Ni0.2)Fe2O4 shows the best EM wave absorption performance, e.g., its minimum reflection loss (RLmin) reaches −35.10 dB at 6.78 GHz with a thickness of 3.5 mm, and the optimized effective absorption bandwidth (EAB) is 7.48 GHz from 8.48 to 15.96 GHz at the thickness of 2.4 mm. Due to the easy preparation and strong EM dissipation ability, HE MFe2O4 are promising as a new type of EM absorption materials.

Structural Defects in Phase‐Regulated High‐Entropy Oxides toward Superior Microwave Absorption Properties

“…It should be noted that biphasic HE oxides tend to form rock salt phases with higher S config at lower sintering temperatures. The rock‐salt structure is considered as an EM wave transparent medium, [ 30 ] whereas the spinel‐structured phase is considered a promising EM wave absorbing constituent; [ 13 ] therefore, the ingenious regulation of phase composition can result in better impedance matching to favor the dissipation of EM waves.…”

“…For instance, the HE spinel (Mg 0.2 Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 )Fe 2 O 4 was prepared through solid state synthesis, and its minimum reflection loss ( RL min ) was −35.10 dB at 6.78 GHz with a thickness of 3.5 mm. [ 13 ] The RL min value of HE (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )C was −38.5 dB at 9.5 GHz and the effective absorption bandwidth ( E AB, RL below−10 dB) was 2.3 GHz (from 11.3 to 13.6 GHz). [ 14 ] The above forementioned singe‐phase ceramic presented the limited EM wave absorption properties.…”

High‐Entropy Enhanced Microwave Attenuation in Titanate Perovskites

“…[15b] Zhou et al designed high-entropy rare earth oxides on the surface of highentropy rare-earth silicide carbides, [16] whereby the oxide was considered as a heterogeneous phase to optimize EM absorption. Ma [17] However, the high-entropy effect of the two-component HEO is not obvious, and the enhanced microwave absorption properties might result from component effect rather than high-entropy effect. Furthermore, the intricate details of the local microstructure in HEO, such as their short-range elemental distribution, distorted lattice, oxygen defects, and shear strains, are yet to be elucidated.…”

Construction of plate‐like magnetic heterostructure for synergistic microwave absorption

“…In general, the magnetic loss of materials in the gigahertz range mainly comes from natural ferromagnetic resonance, exchange resonance, and eddy current effects 37 . When the value of C 0 ( $${C}_0 = \mu ^{\prime\prime}\ {( {\mu ^{\prime}} )}^{ - 2}{f}^{ - 1}$$) is a constant, it indicates that the magnetic loss of the material is dominated by eddy current loss 38–40 …”