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

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+Sm₂ O₃ (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 (H_c ) of 49.2 kOe, the largest H_c among all ferromagnetic NPs ever reported, and saturated magnetic moment (M_s ) of 88.7 emu g^-1 , the highest value reported for SmCo₅ NPs. The method was extended to synthesize other ferromagnetic NPs of Sm₂ Co₁₇ , and, for the first time, of Sm₂ Fe₁₇ N₃ NPs with H_c over 15 kOe and M_s 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.