Unusual Temperature Dependence of Zero-Field Ferromagnetic Resonance in Millimeter Wave Region on Al-Substituted ε-Fe2O3

Abstract

In this chapter, we first introduce the synthesis, crystal structure, magnetic properties, and the formation mechanism of the original ε-Fe2O3 [8-10]. Then we report the physical properties of Al-substituted ε-Fe2O3, mainly focusing on its millimeter wave absorption properties due to zero-field ferromagnetic resonance. The resonance frequency was widely controlled from 112-182 GHz by changing the aluminum substitution ratio [23]. Furthermore, from a scientific point of view, temperature dependence of zero-field ferromagnetic resonance was investigated and was found to show an anomalous behavior caused by the spin reorientation phenomenon [28]. ε-Fe2O3This section introduces the synthesis, crystal structure, magnetic properties, and the formation mechanism of ε-Fe2O3. ε-Fe2O3 had only been known as impurity in iron oxide materials, and its properties were clarified for the first time after our success in the synthesis of single-phase ε-Fe2O3 in 2004 [8].

Synthesis, structural characterization and broadband ferromagnetic resonance in Li ferrite nanoparticles

“…In order to avoid interference noise, there is strong interest in materials that absorb electromagnetic radiation energy in this band [12]. For broadband operation in L, C or S bands inexpensive, lightweight microwave absorbers are needed, so that magnetic nanoparticles can be used [13]. Regarding metals, the low conductivity of ferrites reduces the skin effect at high frequencies, so that they can attenuate EM waves efficiently in the GHz range.…”

Origin of the magnetic transition at 100 K inε-Fe2O3nanoparticles studied by x-ray absorption fine structure spectroscopy

“…In this respect, a new generation of hard magnets without rareearth compounds based on this kind of Fe oxides seems to be feasible [3]. Furthermore, this material has the potential to be employed in high speed wireless communication technologies since the ferromagnetic resonance frequency falls within the mTHz range [2,4,5]. In addition to the abovementioned features, ε-Fe 2 O 3 is a semiconductor material with a gap of 1.9 eV [6] and presents coupling between magn etic and dielectric properties [7].…”

Nanoceramics of metastable ε-Fe2O3: effect of sintering on the magnetic properties and sub-terahertz electron resonance

“…For the nanoceramic sample, these sharp effects in the magnetic susceptibilities are not observed; thus, there are no such magnetically soft particles. In addition, in some studies, 60 the appearance of these peaks on the w 0 (T) curve and the decrease of the coercivity to zero were not reported, 60 similar to the ceramic sample. The effects described above are probably related to the differences in the microstructure of the samples, e.g., the effects of the sintering, and not to the features of the crystal structure.…”

“…The magnetic transitions in ε-Fe 2 O 3 have rarely been studied using terahertz spectroscopy; 60 however, this method can give direct information on the changes in the magnetocrystalline constant K MCA . According to terahertz time-domain spectroscopy at 300 K, the initial ε-Fe 2 O 3 sample demonstrates a resonance absorption at f r = 170 GHz (Fig.…”