Challenges toward development of rear‐earth free FeCo based permanent magnet

Abstract

Among the various permanent magnets reported to date, FeNdB exhibits the highest magnetic performance, but reducing the use of the rare‐earth elements is necessary to avoid exhaustion of rare‐earth elements. The key to improve the performance of permanent magnets is to increase magnetization and coercivity. FeCo has a very large magnetization, but has a very small coercivity caused by the extremely small magnetic anisotropy due to the cubic crystal structure, so that FeCo has long been unsuitable for permanent magnets. However, recent reports have revealed that the transformation of the crystal structure from cubic to tetragonal causes large magnetic anisotropy. In 2017, the author reported that a large coercivity can be obtained by fabricating tetragonal FeCo nanodots. This article reviews recent progress of rear‐earth free permanent magnets especially for the tetragonal FeCo based alloys.

Investigation of the body-centred tetragonal structure of Fe–Co–V–N Bulk foils using the rolling and ammonia-gas-nitriding method

“…As the nitriding temperature increases, the perpendicular magnetisation curves become more difficult to saturate. The magnetic easy axis of the bct Fe-Co-V-N phase is along the c-axis 9,12 . The XRD patterns shown in Fig.…”

“…Before bulk-forming (using method (ii)), FeCo films with added α (such as Al, Ti, and V) and β (such as C and N) elements were epitaxially grown on a Rh buffer layer. In previous studies, this resulted in the successful formation of a bct structure 7,[9][10][11][12][13] . Further, a combination of α = V and β = N proved to be the most effective in forming a bct structure with c/a ≈ 1.2 in thin (t ≤ 5 nm) and thick (t = 100 nm) films, and a large K u of 1 MJ/m 3 was obtained 9,[12][13][14] .…”

“…In previous studies, this resulted in the successful formation of a bct structure 7,[9][10][11][12][13] . Further, a combination of α = V and β = N proved to be the most effective in forming a bct structure with c/a ≈ 1.2 in thin (t ≤ 5 nm) and thick (t = 100 nm) films, and a large K u of 1 MJ/m 3 was obtained 9,[12][13][14] . Furthermore, transmission electron microscopy (TEM) imaging of non-epitaxial Fe-Co-V-N films prepared directly on an amorphous SiO 2 substrate, which does not contribute any beneficial stress to the Fe-Co-V-N layer, revealed the presence of a bct FeCo lattice with c/a ≈ 1.1 15 .…”

Novel magnetic levitation systems for the vibration control of lightweight structures and artworks

“…Neodymium magnets (also known as NdFeB, NIB, or Neo-magnets) are the most widely used type of rare-earth magnets today. 20 These PMs are made from an alloy of neodymium, iron, and boron to form the Nd 2 Fe 14 B tetragonal crystalline structure. The proposed maglev systems do not require either the use of sub-zero temperatures, like in the case of maglev systems based in superconducting materials, or electrical power, like in electromagnetic systems.…”

“…The proposed systems take advantage of the high magnetic forces delivered by neodymium magnets and the stiffening effects of 3D‐printed components to design stable levitating platforms. Neodymium magnets (also known as NdFeB, NIB, or Neo‐magnets) are the most widely used type of rare‐earth magnets today 20 . These PMs are made from an alloy of neodymium, iron, and boron to form the tetragonal crystalline structure.…”