We report a simple yet general approach to monodisperse MPt (M = Fe, Co, Ni, Cu, Zn) nanoparticles (NPs) by coreduction of M(acac)2 and Pt(acac)2 (acac = acetylacetonate) with oleylamine at 300°C. In the current reaction condition, oleylamine serves as the reducing agent, surfactant, and solvent. As an example, we describe in details the synthesis of 9.5 nm CoPt NPs with their compositions controlled from Co37Pt63 to Co69Pt31. These NPs show composition-dependent structural and magnetic properties. The unique oleylamine reduction process makes it possible to prepare MPt NPs with their physical properties and surface chemistry better rationalized for magnetic or catalytic applications. Keywords: nanoparticles, oleylamine reduction, MPt alloy, alloy structure, nanomagnetism, catalysis Y U E T A L . , N A N O L E T T E R S 1 4 ( 2 0 1 4 )2 MPt nanoparticles (NPs) with M = Mn, Fe, Co, Ni, or Cu have attracted much attention in recent years due to their strong ferromagnetism (from FePt and CoPt) 1−6 and their much enhanced catalysis for electrochemical reactions. 6−15 These alloy NPs with controlled sizes and compositions are now routinely prepared either by decomposition/reduction of metal carbonyls and metal salts, or by coreduction of two metal salts. Despite the nearly precise control achieved on NP sizes and compositions, each of these previous syntheses is specific for one typical kind of MPt NPs. For example, thermal decomposition of Fe(CO)5 and reduction of Pt(acac)2 (acac = acetylacetonate) is commonly used to prepare monodisperse FePt NPs with Fe/Pt composition controls. 16−22 When this reaction is applied to prepare CoPt NPs via decomposition of Co2(CO)8 and reduction of Pt(acac)2, only Pt-rich CoPt NPs can be produced. 23,24 The same is true for the synthesis of MnPt via decomposition of Mn2(CO)10 and reduction of Pt(acac)2. 25,26 To prepare other types of MPt (M = Ni, Cu) NPs, metal salt coreduction has to be used because Ni and Cu carbonyls are not readily available. 27−29 In principle, metal salt reduction reaction should be a general approach to different MPt NPs, but the reduction potential differences between M-and Pt-salts and the need to control MPt nucleation and growth often require the use of a specific reducing agent for each synthesis. 30−32 Considering the sensitivity of MPt NP magnetism and catalysis over M/Pt compositions and surface chemistry, it is important to have a generalized synthetic process so that each kind of MPt NPs can be prepared in a very similar reaction condition and their magnetic and catalytic properties can be better controlled and compared.Here, we report a facile, yet general, synthesis of monodisperse MPt (M = Fe, Co, Ni, Cu, Zn) alloy NPs via oleylamine (OAm) reduction of M(acac)2 and Pt(acac)2. OAm is widely used in the solution phase synthesis of NPs. 33 It is a primary amine with the boiling point around 350°C. Its −NH2 group has a relatively weak binding power to transition metals, especially to later transition metals. This, plus its long hydrocarbon...

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We report a one-pot synthesis of urchin-like FePd-Fe3O4 nanocomposites, spherical clusters of FePd nanoparticles (NPs) with spikes of Fe3O4 nanorods (NRs), via controlled thermal decomposition of Fe(CO)5 and reduction of Pd(acac)2. The FePd NPs with sizes between 6 and 9 nm self-aggregate into 60 nm superparticles (SPs), and Fe3O4 NRs grow on the surface of these SPs. Reductive annealing at 500 °C converts the FePd-Fe3O4 into exchange-coupled nanocomposites L1(0)-FePd-Fe with their Hc tunable from 0.8 to 2.6 kOe and Ms controlled from 90 to 190 emu/g. The work provides a general approach to L1(0)-FePd-Fe nanocomposite magnets for understanding exchange coupling at the nanoscale. The concept may be extended to other magnetic nanocomposite systems and may help to build superstrong magnets for magnetic applications.

A noneptaxially grown double-layered thin-film medium of nanocompsite FePt:C with a FeCoNi soft underlayer for high-density perpendicular magnetic recording was fabricated and investigated. Square-shaped perpendicular loops with a remanance ratio nearly equal to one and a coercivity as large as 8.5 kOe were obtained for this ordered FePt:C double-layered medium. The formation of the ordered L10 phase is confirmed by electron diffraction experiments. Transmission electron microscope observations reveal that FePt grains with a uniform size less than 5 nm are embedded in the C matrix and appear to be well isolated. Our results show that nonepitaxially grown (001) textured double-layered nanocomposite L10 FePt-based films with perpendicular anisotropy are a promising candidate to realize extremely high-density perpendicular recording.

Rare-earth transition-metal (R-TM) alloys show superior permanent magnetic properties in the bulk, but the synthesis and application of R-TM nanoparticles remains a challenge due to the requirement of high-temperature annealing above about 800 °C for alloy formation and subsequent crystalline ordering. Here we report a single-step method to produce highly ordered R-TM nanoparticles such as YCo(5) and Y(2)Co(17), without high-temperature thermal annealing by employing a cluster-deposition system and investigate their structural and magnetic properties. The direct ordering is highly desirable to create and assemble R-TM nanoparticle building blocks for future permanent-magnet and other significant applications.