Design of modern magnetic materials with giant coercivity

Abstract

The review is devoted to compounds and materials demonstrating extremely high magnetic hardness. The recent advances in the synthesis of modern materials for permanent magnets are considered, and a range of exotic compounds interesting for fundamental research is described. The key details of chemical composition, crystal structure and magnetic microstructure responsible for the appearance of high magnetic anisotropy and giant coercivity are analyzed. The challenges of developing the title materials are noted and strategies for their solution are discussed. The bibliography includes 389 references.

Giant coercivity and spin clusters in high pressure polymorphs of Mn2LiReO6.

“…Magnetic materials with large coercivity are desirable as permanent magnets. 1 However, there is a need to move away from rare-earth-based hard-magnets. In oxides, besides the hexaferrites just a handful of materials show giant or even large magnetic coercivities and it is thus important to understand the mechanisms to obtain those values.…”

High-coercivity hexaferrite ceramics featuring sub-terahertz ferromagnetic resonance

“…1,2 The rare-earth magnets are dominating today in the market since they can produce strong magnetic fields, possess high coercivity and, consequently, demonstrate record maximum energy product values. 3,4 However, due to the low availability of rare-earth metals, their high processing cost and their poor chemical stability, the usage of rare-earth magnets is limited. Magnetically hard ferrites are an alternative in the fields of application where the reduction of the production costs matters, and high magnetization is not an essential requirement.…”

Glass-Ceramic Synthesis of Cr-Substituted Strontium Hexaferrite Nanoparticles with Enhanced Coercivity

“…Hard magnetic hexaferrites MFe 12 O 19 (M = Ba, Sr) are well known and widely used materials in the production of ceramic permanent magnets [1][2][3]. However, they are also very promising for various applications in nanotechnology.…”

“…Typical reported colloidal hexaferrite nanoparticles with diameters of 10-100 nm display coercivity values between zero and 360 kA m −1 (4500 Oe) for the largest particles [7,15,[22][23][24]. A common way to increase the coercivity of the hexaferrites is the partial substitution of iron ions with aluminum [1,3,21,[25][26][27], e.g., this can result in a coercivity of submicron single-domain particles of up to 3180 kA m −1 (40 kOe) [25]. However, the aluminum substitution requires high annealing temperatures above 1000 • C, which makes the preparation of nanoparticles quite challenging.…”

“…Nevertheless, this approach allowed one to produce nonsintered submicron hexaferrite particles with coercivities over 800 kA m −1 (10 kOe) [29] and colloidal nanoparticles with a coercivity of up to 445 kA m −1 (5600 Oe) [7]. Chromium substitution should have a similar coercivity increase effect [1,3,21,31]; however, the preparation of nonsintered submicron or nanosized particles of Cr-substituted hexaferrite has not been described so far.…”