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+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 degrees 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 Sm2Co17, and, for the first time, of Sm2Fe17N3 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.