Chemical synthesis, structure and magnetic properties of Co nanorods decorated with Fe_3O_4 nanoparticles

Magnetic anisotropic nanocomposites have attracted tremendous interests, due to their unexpected properties originating from the interactions of the interfaces except for the intrinsic features. In this work, we develop a facile solution chemistry synthesis method to prepare the one-dimensional(1 D) Co-Fe3O4 heterostructures with hard magnetic property. Interestingly, the Fe precursor firstly decompose and nucleate individually, and then grow on the surface of the hexagonal closed-packed(hcp) Co nanorods(NRs) upon prolonging heating time at higher temperature, which is different from the general seed-mediated growth model. The distribution density of Fe3O4 nanoparticles(NPs) on the surface of the Co NRs can be varied with the addition of Fe source,modulating the values of coercivity and saturation magnetization for the Co-Fe3O4 heterostructures. The as-synthesized Co-Fe3O4 heterostructures maintain the hard magnetic properties with a coercivity value more than 2.5 kOe as well as a saturation magnetization value up to 128.3 emu g-1, indicating the preservation of the anisotropy of the hcp Co NRs.

Monodisperse Fe3O4 spheres: Large-scale controlled synthesis in the absence of surfactants and chemical kinetic process

Fe3 O4 has attracted tremendous interest in vast areas of biomedicine and catalysis as well as environment engineering.However,it is highly desired to fully understand the chemical kinetic process and propose a general,surfactantfree,large-scale synthesis approach for Fe3 O4 spheres.Herein,we developed a facile scalable solvothermal method in the absence of surfactants to produce Fe3 O4 spheres with the yield of 5.1 g,which present tunable sizes from 107 to 450 nm by modulated molar ratio of Fe3+/COO-in the solution.Particularly,it is observed that the reactants undergo a redox process,composed of a precipitation-dissolution equilibrium combined with a coordination reaction(termed as RPC),to the final product based on the LaMer model.It is worth noting that the generation of di-carboxyl group and its coordination with iron cations determine the formation of Fe3 O4 spheres.This work not only offers a strategy to precisely tailor the particle size in scalable synthesis process,but also gives the insight on the role of dihydric alcohol in the formation mechanism of Fe3 O4 spheres in the absence of surfactants.