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Uniform-sized, monodisperse, and single-crystal magnetite hollow spheres with a diameter of 200−300 nm and a shell thickness of ∼50 nm have been successfully synthesized in high yield using a template-free solvothermal route. The reaction duration and the ethylenediamine amount are shown to play important roles in the formation of the magnetite hollow spheres. X-ray diffraction, X-ray photoelectron spectroscopy, Fourier tranform IR, scanning electron microscopy, transmission electron microscopy (TEM), and high-resolution TEM were used to characterize the products. The results show that the prepared single-crystalline hollow spheres are composed of well-aligned magnetite and have a cubic structure. The magnetite hollow spheres show a high saturation magnetization of ca. 68 emu/g, a remnant magnetization of ca. 13 emu/g, and a coercivity of ca. 94 Oe at room temperature. A possible mechanism for …