Hard Magnetic Ferrite: ε-Fe2O3

Abstract

Iron oxide Fe 2 O 3 has four polymorphs: ¡-, ¢-, £-, and ¾-phases. ¡-Fe 2 O 3 (hematite) and £-Fe 2 O 3 (maghemite) are abundant in nature, whereas ¢-and ¾-Fe 2 O 3 phases are very rare and must be artificially synthesized in the laboratory. Pure ¾-Fe 2 O 3 phase was first synthesized in 2004 using a combination of reverse-micelle and solgel techniques, and it shows the largest coercive field value (H c ) among metal oxide-based magnets of 20 kOe at room temperature. Successively, several kinds of metal-substituted ¾-iron oxides, ¾-M x Fe 2¹x O 3 (M = In, Ga, and Al), have been synthesized, and their magnetic properties are controlled by the degree of the metal substitution. Such iron oxides with a high H c are attractive from industrial application viewpoints, e.g., magnetic recordings and electromagnetic wave absorbers. A series of ¾-M x Fe 2¹x O 3 shows high-frequency electromagnetic wave absorption due to zero-field ferromagnetic resonance at 35 182 GHz in the millimeter range, which is useful for next-generation high-speed wireless communications. In this article, we describe (i) the synthesis, crystal structure, and magnetic properties of ¾-Fe 2 O 3 , (ii) generation mechanism of ¾-Fe 2 O 3 , the origin of the gigantic coercive field, and theoretical analysis of magnetic ordering, (iii) metal-substituted ¾-iron oxides, ¾-M x Fe 2¹x O 3 , and (iv) electromagnetic wave absorption in the millimeter wave range.

Epitaxially stabilized thin films of ε-Fe2O3 (001) grown on YSZ (100)

“…Such two epitaxial matches between ε-Fe 2 O 3 and YSZ (100) are shown below in a graphical representation drawn with the software VESTA 40 , where we paid a special attention ensuring the best possible continuity between the oxygen octahedra and tetrahedra framework of the ε-Fe 2 O 3 crystal structure and the oxygen octahedra framework of the substrate crystal structure: the first epitaxial match is given by the parallel alignment of the b ε lattice parameters of epsilon ferrite with the [100] and [010] directions of YSZ. While there is a good match between a ε and a YSZ , resulting in a tensile strain of −0.58% (using strain  =  a film  −  a sub /a sub , and the lattice parameters of ε-Fe 2 O 3 reported for nanoparticles, a  = 5.08 Å, b  = 8.78 Å, and c  = 9.47 Å as the relaxed state 41 , and a sub  =  a YSZ  = 5.12 Å, as listed by the manufacturer CrysTec GmbH), the match for b is given by the so-called “3 for 5 tiling”, having 3 b ε  ≈ 5 b YSZ (Fig. 1c).…”

Nanometer-size hard magnetic ferrite exhibiting high optical-transparency and nonlinear optical-magnetoelectric effect

“…The magnetism of ε-Fe 2 O 3 is considered to be collinear ferrimagnetism1819, in which the sublattice magnetizations of Fe B and Fe C are antiparallel to those of Fe A and Fe D . Based on the molecular-field (MF) theory29, the magnetic structure of ε-Fe 2 O 3 can be understood from the product value between the superexchange interaction ( J ) and the number of exchange pathways ( z ).…”

“…In addition, development of an optically transparent magnet is highly desirable for new applications, such as transparent electromagnetic wave-absorbing windows or magnetic color pigments for printers. In light of the above requirements, epsilon iron oxide ε-Fe 2 O 3 is an attractive material because it exhibits a large H c value at room temperature71819202122232425. In the present work, we develop a synthetic method for the preparation of single-nanosize ε-Fe 2 O 3 spherical particles.…”

Magnetic properties of Hagi ware

“…4)8) The ¡-phase and the £-phase are abundant in the natural world, but the ¢-and ¾-phases are rare and are therefore artificially synthesized. 8) The ¡-phase (termed hematite) has a rhombohedral crystal structure, and it exhibits weak ferromagnetism at temperatures between ¹13 and 672°C 9) as a result of the DzyaloshinskiiMoriya interaction. 10),11) The coercive field (H c ) can have a value as great as 1 kOe, and the color of the hematite powder is red.…”

“…Finally, the ¾phase does not naturally exist; however, its chemical synthesis, detailed structure and magnetic properties have been investigated recently. 8) Thus, Fe 2 O 3 is not only the subject of fundamental research but also has many possibilities for industrial applications. One of the applications of native Fe 2 O 3 includes its use in the production of reddish-brown earthen-ware termed "Hagi ware".…”