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synthesis of L1 0 -FePt NPs has been recently reported, such as adding a third metal element (Au, Ag), which can reduce the ordering temperature to 400°C, but the fraction of the ordered phase is usually small. [9] Compared with the method of solution phase synthesis of fcc-FePt nanoparticles followed by high temperature annealing to get L1 0 -FePt nanoparticles, one step method attracts more attention. He and Zhao have developed a simple one step synthesis of L1 0 -FePt NPs by simultaneous decomposition of Fe(NO 3 ) 3 ·9H 2 O, H 2 PtCl 6 ·6H 2 O and direct catalytic graphitization of a carbon precursor (citric acid) at high temperature in solid phase, [10] but the size of the particles was ultrasmall (mostly 2~4 nm) even sintered at temperature of 850°C for 2 hours, therefore the coercivity was just 4.56kOe. More recently, Hu and co-workers reported a solvent-free chemical synthesis of L1 0 -FePt nanoparticles using the synthesized intermediate [Fe(H 2 O) 6 ]PtCl 6 as metal precursors, which was then mixed with different ratio of NaCl before sintering. [11] For the obtained FePt nanoparticles, which can obtain chemical ordered phase at annealing temperatures as low as 400 o C due to the intermediate precursor itself has a certain chemical order, the coercivity can be as large as 10.9 kOe. In a certain degree, this method has much improvement, but it still needs at least two steps.Here, we report a simple approach for large scale and direct synthesis of L1 0 -FePt NPs with tunable coercivity and controlling size. Unlike the previously reported method, no organic solvents, surfactant, chelating agent/catalyst or intermediate precursors are used, and the composition of Fe and Pt is easy to control, which is precursors (Fe(acac) 3 and Pt(acac) 2 ) in an alumina crucible with a heating rate of 5 °C/min under Ar flow. X-ray diffraction (XRD) characterization was carried out on a Bruker AXS D8-Advanced diffractometer with Cu Kα radiation (λ = 1.5418 Å).High-resolution TEM (HRTEM) and the high angle annular dark-field scanning TEM (HAADF-STEM) images were obtained on FEI Tecnai F20 200 kV TEM. The composition of the particles was semi-quantitatively determined by energy dispersive X-ray spectroscopy (EDS). Selection area electron diffraction (SAD) was used for structure characterization. Magnetic properties were measured using a Magnetic Property Measurement System (SQUID MPMS).The procedure of the synthesis L1 0 -FePt nanoparticles is shown in Figure 1. The design of our experiment is to let Fe and Pt atoms nucleate and grow into FePt nanoparticles on a substrate and then the substrate is removed and nanoparticles are colleted. Here, Fe(acac) 3 and Pt(acac) 2 (acac = acetylacetonate) were chosen as precursors of Fe and Pt. NaCl was selected as the substrate, which has a high melting point of 801 °C. NaCl is a perfect option since it is easy to be ground down to small size and also easy be removed with deionized water after synthesizing. For synthesizing L1 0 -FePt, NaCl particles can also work as insulation media pr...

In this report, we present a novel one-step solid-phase reaction method for the synthesis of L10-CoPt@C core-shell nanoparticles (NPs) using organic metal precursors without surfactants. The obtained CoPt@C NPs have a good face-centered tetragonal single crystal structure and regular shape. The mean size of CoPt is 14 nm with a uniform carbon shell. The evolution of the core-shell structure during the synthesizing process is investigated in detail. Firstly organic metal precursors are decomposed, followed by the formation of grains/clusters in a metal-carbon intermediate state. Then the metal-carbon small grains/clusters agglomerate and recrystallize into single crystal metal alloy NPs covered with a carbon layer. The carbon shell is effective in preventing the coalescence of L10-CoPt NPs during high temperature sintering. The prepared L10-FePt nanoparticles have a high coercivity of up to 12.2 kOe at room temperature. This one-step solid-state synthesizing method could also be employed for the preparation of other types of nanostructures with high crystallinity, monodispersity and chemically ordered phase.