Chemical Synthesis of Magnetically Hard and Strong Rare Earth Metal Based Nanomagnets

Abstract

We report a general chemical approach to synthesize strongly ferromagnetic rare‐earth metal (REM) based SmCo and SmFeN nanoparticles (NPs) with ultra‐large coercivity. The synthesis started with the preparation of hexagonal CoO+Sm2O3 (denoted as SmCo‐O) multipods via decomposition of Sm(acac)3 and Co(acac)3 in oleylamine. These multipods were further reduced with Ca at 850 °C to form SmCo5 NPs with sizes tunable from 50 to 200 nm. The 200 nm SmCo5 NPs were dispersed in ethanol, and magnetically aligned in polyethylene glycol (PEG) matrix, yielding a PEG‐SmCo5 NP composite with the room temperature coercivity (Hc) of 49.2 kOe, the largest Hc among all ferromagnetic NPs ever reported, and saturated magnetic moment (Ms) of 88.7 emu g−1, the highest value reported for SmCo5 NPs. The method was extended to synthesize other ferromagnetic NPs of Sm2Co17, and, for the first time, of Sm2Fe17N3 NPs with Hc over 15 kOe and Ms reaching 127.9 emu g−1. These REM based NPs are important magnetic building blocks for fabrication of high‐performance permanent magnets, flexible magnets, and printable magnetic inks for energy and sensing applications.

Chemical Synthesis of Magnetic Nanoparticles for Permanent Magnet Applications

“…A better synthetic approach to achieve the SmCo‐O NP size and composition controls was by decomposition of Sm(acac) 3 and Co(acac) 3 in oleylamine (OAm) at 230 °C to form hexagonal CoO and amorphous Sm 2 O 3 with Sm 2 O 3 and CoO co‐precipitated within one multipod nanostructure . The size of the SmCo‐O NPs was controlled from 60 nm to 220 nm by adjusting the precursor concentration (Figure a–c).…”

“…i) Hysteresis loops of aligned 50 nm, 100 nm, and 200 nm SmCo 5 NPs at 300 K. Reprinted with permission from ref. . Copyright 2019 Wiley‐VCH, scale bar: 200 nm.…”

“…The conventional method used to fabricate Sm 2 Fe 17 N 3 is nitrogenization of Sm 2 Fe 17 with N 2 or NH 3 under high‐temperature/pressure conditions, which has less control of phase purity and sizes . Recently, the recipe for the synthesis of SmCo 5 NPs was extended successfully to the preparation of Sm 2 Fe 17 NPs, which were further reacted with melamine to form Sm 2 Fe 17 N 3 NPs . The synthesis started with the decomposition of Sm(acac) 3 and Fe(acac) 3 in oleic acid (OAc) and OAm at 300 °C to form cubic SmFeO NPs (Figure a).…”

A Flame‐Reaction Method for the Large‐Scale Synthesis of High‐Performance SmxCoy Nanomagnets

“…This is the highest value ever reported for SmCo 5 materials made by chemical methods. [4][5][6]8] When the initial ratio of Sm(NO 3 ) 3 /Co(NO 3 ) 2 was adjusted to 1:7.2 in the flame-synthesis process,S mCo 7.2 -O particles formed were 240 AE 8nmindiameter (Figures S8 and S9). Theratio of SmCoO 3 and Co 3 O 4 is 1:2.02 for SmCo 7.2 -O according to the XRD refinement data (Table S2), which is close to the ratio of Sm/Co (1:7.2).…”

“…Thec ore/shell (SmCoO 3 ) 1 (Co 3 O 4 ) 0.93 /CaO was then reduced by Ca at 900 8 8Cf or 1.5 h, then cooled to room temperature and washed with am ethanol solution of NH 4 Cl under Ar protection to remove Ca and CaO and prevent oxidation of the SmCo 5 particle surface. [8] Starting from 5.8 g of (SmCoO 3 ) 1 (Co 3 O 4 ) 0.93 particles,4 .2 go fm agnetic SmCo 5 particle powder was obtained (Figure 2a). TheXRD pattern of the as-prepared SmCo 5 ( Figure S4) shows the typical SmCo 5 phase (JCPDS No.…”