The synthesis of rhodium substituted ε-iron oxide exhibiting super high frequency natural resonance

Abstract

In this study, we demonstrate a synthesis of rhodium substituted 3-iron oxide, 3-Rh x Fe 2Àx O 3 (0 # x # 0.19), nanoparticles in silica. The synthesis features a sol-gel method to coat the metal hydroxide sol containing Fe 3+ and Rh 3+ ions with a silica sol via hydrolysis of alkoxysilane to form a composite gel. The obtained samples are barrel-shaped nanoparticles with average long-and short-axial lengths of approximately 30 nm and 20 nm, respectively. The crystallographic structure study using X-ray diffraction shows that 3-Rh x Fe 2Àx O 3 has an orthorhombic crystal structure in the Pna2 1 space group. Among the four nonequivalent substitution sites (A-D sites), Rh 3+ ions mainly substitute into the C sites. The formation mechanism of 3-Rh x Fe 2Àx O 3 nanoparticles is considered to be that the large surface area of the nanoparticles increases the contribution from the surface energy to Gibbs free energy, resulting in a different phase, 3-phase, becoming the most stable phase compared to that of bulk or single crystal. The measured electromagnetic wave absorption characteristics due to natural resonance (zero-field ferromagnetic resonance) using terahertz time domain spectroscopy reveal that the natural resonance frequency shifts from 182 GHz (3-Fe 2 O 3) to 222 GHz (3-Rh 0.19 Fe 1.81 O 3) upon rhodium substitution. This is the highest natural resonance frequency of a magnetic material, and is attributed to the large magnetic anisotropy due to rhodium substitution. The estimated coercive field for 3-Rh 0.19 Fe 1.81 O 3 is as large as 28 kOe.

Self-assembly of iron oxide precursor micelles driven by magnetic stirring time in sol–gel coatings

“…Several studies have demonstrated the modulation of the resonance frequency depending on different elements substituted in the crystalline structure of the 3-Fe 2 O 3 phase. [5][6][7][8] Specially in thin lm form, this polymorph shows a ferromagnetic and ferroelectric response. Thus it opens the possibility of using it as a room temperature multiferroic in a real device.…”

Resonance Frequency Tuning of a 200 GHz Band Absorber by an External Magnetic Field

“…This synthetic route differs from our previously reported methods. [27,28] Rhodium nitrate (0.9 mmol (1), 1.2 mmol (2)) and iron oxide hydroxide (28.9 mmol (1), 25.6 mmol (2)) were DOI: 10.1002/adpr.202100319…”

“…These particle sizes are smaller than those previously synthesized by the sol-gel method, d ¼ 19-32 nm. [28] Powder X-ray diffraction (XRD) patterns were measured using a Rigaku Ultima IV (Cu Kα source, λ ¼ 1.5418 Å) (Figure 1c and S1, Table S1, Supporting Information). 1 consisted of 93 wt% of ε-iron oxide (orthorhombic, Pna2 1 ) and 7 wt% of α-iron oxide (rhombohedral, R3c).…”

“…Rhodium-substituted epsilon iron oxide, ε-Rh x Fe 2Àx O 3 , shows even higher resonance frequencies above 182 GHz by increasing the Rh/Fe ratio. [27,28] Consequently, ε-Rh x Fe 2Àx O 3 holds promise as a millimeter-wave absorber because electromagnetic waves of 6 G or 7 G should use highfrequency millimeter-wave bands, especially around 220 GHz. From the viewpoint of industrial applications, tuning the resonance frequency by the magnetic field effect is important.…”

Electromagnetic wave absorption properties of mesoporous Fe3O4/C nanocomposites

“…Considerable attention has been given to the absorbing materials in the filed of anti-EM interference coatings and self-concealing technology [4,5]. The microwave absorber is considered as a specially designed material in order to suppress the reflected electromagnetic energy incident on the surface of the absorber by dissipating the magnetic and/or electrical fields of the wave into heat [6].…”