ε-Fe₂O₃: An Advanced Nanomaterial Exhibiting Giant Coercive Field, Millimeter-Wave Ferromagnetic Resonance, and Magnetoelectric Coupling

Abstract

Nanosized iron oxides still attract significant attention within the scientific community, because of their application-promising properties. Among them, ε-Fe 2 O 3 constitutes a remarkable phase, taking pride in a giant coercive field at room temperature, significant ferromagnetic resonance, and coupled magnetoelectric features that are not observed in any other simple metal oxide phase. In this work, we review basic structural and magnetic characteristics of this extraordinary nanomaterial with an emphasis on questionable and unresolved issues raised during its intense research in the past years. We show how a combination of various experimental techniques brings essential and valuable information, with regard to understanding the physicochemical properties of the ε-polymorph of Fe 2 O 3 , which remained unexplored for a long period of time. In addition, we recapitulate a series of synthetic routes that lead to the formation of ε-Fe 2 O 3 , highlighting their advantages and drawbacks. We also demonstrate how magnetic properties of ε-Fe 2 O 3 can be tuned through the exploitation of various morphologies of ε-Fe 2 O 3 nanosystems, the alignment of ε-Fe 2 O 3 nanoobjects in a supporting matrix, and various degrees of cation substitution. Based on the current knowledge of the scientific community working in the field of ε-Fe 2 O 3 , we finally arrive at two main future challenges: (i) the search for optimal synthetic conditions to prepare single-phase ε-Fe 2 O 3 with a high yield, desired size, morphology, and stability; and (ii) the search for a correct description of the magnetic behavior of ε-Fe 2 O 3 at temperatures below the characteristic magnetic ordering temperature.

Mössbauer study of ε-Al x Fe2 − x O3 nanomagnets

“…show high-frequency millimeter wave absorption, while ε-In x Fe 2−x O 3 exhibits a phase transition between ferrimagnetism and antiferromagnetism [11][12][13]15]. In this paper, we report 57 Fe Mössbauer spectra of Al 3+ -substituted ε-Fe 2 O 3 .…”

Временная стабильность намагниченности наночастиц varepsilon-In-=SUB=-0.24-=/SUB=- Fe-=SUB=-1.76-=/SUB=-O-=SUB=-3-=/SUB=-

“…Установлена связь между магнитной вязкостью и магнитным шумом, вызванным случайными термически индуцированными перемагничиваниями отдельных наночастиц. [7]. Несмот-ря на интенсивные исследования этого соединения, вопросы о спект-ре магнитных флуктуаций, механизмах спонтанного размагничивания, временной стабильности и специфике термоактивационных процессов А.И.…”

Plasma dynamic synthesis of iron oxides in a discharge plasma jet with possibility to control final phase composition

“…The main problem is the difficulties with its synthesis. It is known that this phase is thermally unstable (converts to hematite at temperatures about 750 °C) and can exist only in nanodispersed state (also converts to hematite when interacts with other particles due to low surface energy) [10].…”