Preparation of submicron-sized Sm2Fe17N3 fine powder with high coercivity by reduction-diffusion process

Multi-scale electron microscopy of overnitrided Sm-Fe-Mn-N powder

“…[4][5][6][7] On the other hand, many researchers have been striving to improve the coercivity of the ingredient powder for producing bulk magnets by refining particle size. 3,[8][9][10][11][12] Several researchers however demonstrated that overnitridation of relatively coarse powder (∼ 60 µm) of Sm 2 (FeMn) 17 N x magnets (x > 3) introduces a unique microstructure that is composed of nanocrystalline cells (= below 100 nm) surrounded by amorphous cell walls into formerly monocrystalline powder, making it possible to achieve quite high coercivity (∼12 kOe) without reducing the particle size. 3,11,13 It is also known that similar coercivity enhancement phenomena can be observed when Cr, Ti, V are added to Sm-Fe-N powder.…”

“…3,[8][9][10][11][12] Several researchers however demonstrated that overnitridation of relatively coarse powder (∼ 60 µm) of Sm 2 (FeMn) 17 N x magnets (x > 3) introduces a unique microstructure that is composed of nanocrystalline cells (= below 100 nm) surrounded by amorphous cell walls into formerly monocrystalline powder, making it possible to achieve quite high coercivity (∼12 kOe) without reducing the particle size. 3,11,13 It is also known that similar coercivity enhancement phenomena can be observed when Cr, Ti, V are added to Sm-Fe-N powder. [14][15][16] However, there was a drawback that remanence and squareness are significantly degraded when coercivity is reasonably enhanced by increasing x.…”

Improvement of magnetization of submicron-sized high coercivity Sm2Fe17N3 powder by using hydrothermally synthesized sintering-tolerant cubic hematite

“…6,9 Cubic hematite powder of 150 nm average diameter was newly developed by a hydrothermal reaction using Ca(NO 3 ) 2 as a structure directing agent. KOH aqueous solution (2 mol/L) was added dropwise to a mixture of Fe(NO 3 ) 3 · 9H 2 O and Ca(NO 3 ) 2 aqueous solution in which the Fe/Ca and OH -/NO 3 -molar ratio was adjusted to 3.0 and 1.0, respectively.…”

“…5,6 While both the powders with submicron-sized particles (denoted hereafter as "submicron-sized powder") exhibited high coercivity, considerable aggregation of particles was observed, which made the remanent magnetization low. Although pulverization treatment of a milling with media increased remanence magnetization, the coercivity was decreased as shown in Fig.…”

“…Also in previous studies, the powders prepared by a pulverization process exhibited lower coercivity than the powders prepared by a non-pulverization process because of defects, such as edges, strains, oxide and etc., which formed by the pulverization treatment and decreased local anisotropy field of particle. [5][6][7][8] Thus, a method for preparing a well-dispersed submicron-sized Sm 2 Fe 17 N 3 powder without pulverization is needed to produce an anisotropic powder having both high remanent magnetization and high coercivity.…”