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+Sm O (denoted as SmCo-O) multipods via decomposition of Sm(acac) and Co(acac) in oleylamine. These multipods were further reduced with Ca at 850 °C to form SmCo NPs with sizes tunable from 50 to 200 nm. The 200 nm SmCo NPs were dispersed in ethanol, and magnetically aligned in polyethylene glycol (PEG) matrix, yielding a PEG-SmCo NP composite with the room temperature coercivity (H ) of 49.2 kOe, the largest H among all ferromagnetic NPs ever reported, and saturated magnetic moment (M ) of 88.7 emu g , the highest value reported for SmCo NPs. The method was extended to synthesize other ferromagnetic NPs of Sm Co , and, for the first time, of Sm Fe N NPs with H over 15 kOe and M reaching 127.9 emu g . 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.