Monodisperse Fe_3O_4 nanocubes have been successfully synthesized by a facile solvothermal method at 260 °C in the presence of oleic acid and oleylamine. Well-defined assembly of uniform Fe_3O_4 nanocubes with an average size of 12 nm could be obtained without a size-selection process. The shape of as-prepared Fe_3O_4 nanoparticles could be reversibly interchanged between spheres and cubes by adjusting the reaction parameters. The phase structures, morphologies, and sizes of as-prepared products were investigated in detail by X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The magnetic properties of Fe_3O_4 nanocubes were measured by using a quantum design superconducting quantum interference device (SQUID). The magnetic study reveals that the as-synthesized nanocubes are ferromagnetic at 2 K while they are superparamagnetic at 300 K.
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