Abstract
Arrays of epitaxial Fe3O4 nanodots were prepared using laser molecular beam epitaxy (LMBE), with the aid of ultrathin porous anodized aluminum templates. An Fe3O4 film was also prepared using LMBE. Atomic force microscopy and scanning electron microscopy images showed that the Fe3O4 nanodots existed over large areas of well-ordered hexagonal arrays with dot diameters (D) of 40, 70, and 140 nm; height of approximately 20 nm; and inter-dot distances (Dint) of 67, 110, and 160 nm. The calculated nanodot density was as high as 0.18 Tb in.−2 when D = 40 nm. X-ray diffraction patterns indicated that the as-grown Fe3O4 nanodots and the film had good textures of (004) orientation. Both the film and the nanodot arrays exhibited magnetic anisotropy; the anisotropy of the nanoarray weakened with decreasing dot size. The Verwey transition temperature of the film and nanodot arrays with D ≥ 70 nm was observed at around 120 K, similar to that of the Fe3O4 bulk; however, no clear transition was observed from the small nanodot array with D = 40 nm. Results showed that magnetic properties could be tailored through the morphology of nanodots. Therefore, Fe3O4 nanodot arrays may be applied in high-density magnetic storage and spintronic devices.
Highlights
Fe3O4 has been extensively studied because of its high Curie temperature, and because it has been predicted to have a half metallicity and a full spin polarization [1,2], these properties make Fe3O4 a promising material for applications in data storage and spintronic devices such as memories or magnetic sensors [3]
The high-quality ultrathin porous anodized aluminum (PAA) template is the key in preparing epitaxial Fe3O4 nanodot arrays
In summary, well-ordered large-area arrays of epitaxial Fe3O4 nanodots were obtained on the SrTiO3 (100) substrate by laser molecular beam epitaxy (LMBE) at an elevated growth temperature (700°C) using ultrathin PAA templates as shadow templates
Summary
Fe3O4 has been extensively studied because of its high Curie temperature, and because it has been predicted to have a half metallicity and a full spin polarization [1,2], these properties make Fe3O4 a promising material for applications in data storage and spintronic devices such as memories or magnetic sensors [3]. One popular top-down method, namely, the lithography technique, has been used to pattern films into nanoarrays [7,8]. Covalent oxides of Fe3O4 being fragile are damaged during etching. In another technique, Fe3O4 nanoparticles are synthesized first by chemical methods and self-assemble on a substrate to form nanodot arrays [9,10]. Fe3O4 nanoparticles are synthesized first by chemical methods and self-assemble on a substrate to form nanodot arrays [9,10] In this case, the particles have random orientations, aggregate, and have weak bonding force with the substrate, which make the properties quite different from those of epitaxial nanodot arrays
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