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

Abstract

We investigated the cause of forming of aggregates which decreases magnetization of a submicron-sized Sm2Fe17N3 powder. The aggregation was considered to be caused through sintering and growth of α-Fe particles in a hydrogen reduction treatment. We newly synthesized cubic hematite powder which has tolerance for the sintering of particles in a hydrogen reduction treatment. The aggregation of submicron-sized Sm2Fe17N3 particles was significantly reduced by using the cubic hematite as a precursor, and the magnetization was improved without decreasing the high coercivity.

TbCu7-type Sm-Fe(-N) powder synthesized by low-temperature reduction-diffusion process using the Li–Ca reductant

“…The molar ratios of the Li–Ca reductant/precursors examined in this study were 7.8, 9.8, and 11.7. The ɑ-Fe powder was prepared by hydrogen reduction of hematite, as explained in detail in our previous research [ 19 , 28 ]. Next, the prepared iron crucibles were covered with iron lids and heat-treated at various temperatures for 10 h under Ar.…”

“…Among various synthesis methods for TbCu 7 -type Sm-Fe based magnets, such as melt spinning [ 2 , [5] , [6] , [7] , [8] , [9] , [10] , [11] ], the hydrogenation-disproportionation-desorption-recombination process [ [12] , [13] , [14] ], mechanical alloying [ [15] , [16] , [17] ], and the low-temperature reduction-diffusion (LTRD) process [ [18] , [19] , [20] , [21] , [22] ], only the LTRD process is capable of producing a raw single-crystalline powder for an anisotropic magnet. It is well known that the reduction-diffusion (RD) process can synthesize single-crystalline Sm 2 Fe 17 N z magnetic powder by reduction of samarium oxide using Ca as a reductant (Sm 2 O 3 (s) + 3Ca (l) → 2Sm + 3CaO) and diffusion of Sm atoms to Fe particles through liquid Ca at a temperature over 850 °C, which is the melting point of Ca [ [23] , [24] , [25] , [26] , [27] , [28] , [29] , [30] ]. Our group successfully synthesized single-crystalline TbCu 7 -type Sm-Fe by the LTRD process using LiCl molten salt as a solvent for Ca to decrease the reaction temperature, which is limited to the melting point of Ca [ 18 ].…”

One-Pot Synthesis and Large-Scale Production Strategies for Preparing Ultrafine Hard Magnetic Sm2Fe17N3 Nanoparticles

“…Sm–Fe intermediates obtained from each oxide phase (e.g., SmFeO 3 , Sm 2 O 3 , and Fe 2 O 3 ) or soluble nitrate complex can be thermally decomposed and reduced to Sm 2 Fe 17 through calciothermic reduction at 900 °C, and thereafter, nitridation at a temperature >420 °C using N 2 or NH 3 , resulting in Sm 2 Fe 17 N 3 submicron particles. ,− However, the high annealing temperature is detrimental to size-dependent coercivity because it causes overgrowth of intermediates (e.g., α-Fe), leading to an inhomogeneous Sm–Fe particle size distribution and a coarse morphology. In addition, due to their nonuniform microstructures, the particles obtained after this overgrowth of intermediates have a low maximum energy product ((BH) max ) and low applicability for sintered magnets.…”