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Morphology and magnetic properties of Fe3O 4 nanodot arrays using template-assisted epitaxial growth.

Guan XF, Chen D, Quan ZY, Jiang FX, Deng CH, Gehring GA, Xu XH - Nanoscale Res Lett (2015)

Bottom Line: The calculated nanodot density was as high as 0.18 Tb in.(-2) when 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.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Magnetic Molecules and Magnetic Information Materials of Ministry of Education and School of Chemistry and Materials Science, Shanxi Normal University, Linfen, 041004, China, guanxiaofen325@163.com.

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 (D int) 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.

No MeSH data available.


XRD patterns for the film and dot arrays. The sample of D = 70 nm and film deposited at various substrate temperatures and after annealing. Except for the peaks of FeO (002) and Fe3O4 (004), the rest are peaks of the substrate.
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Fig3: XRD patterns for the film and dot arrays. The sample of D = 70 nm and film deposited at various substrate temperatures and after annealing. Except for the peaks of FeO (002) and Fe3O4 (004), the rest are peaks of the substrate.

Mentions: The θ-2θ scans of the series of film and nanodot arrays deposited at different substrate temperatures (Ts), as well as the scans after annealing, are shown in Figure 3. The XRD patterns of the nanodot arrays without in situ annealing showed peaks that correspond to FeO (002), as well as the Fe3O4 (004) reflections. The intensity of the Fe3O4 (004) peaks increased, whereas the FeO (002) peaks decreased with an increase of Ts. These trends indicate that high substrate temperature favors the formation of the Fe3O4 (004) phase. The peak of FeO (002) disappeared after 2 h of in situ annealing at 700°C. In this condition, epitaxial growth of Fe3O4 nanodots with (004) orientation was obtained. The Fe3O4 (004) film could have epitaxial growth at a Ts of 600°C. Clearly, epitaxial growth of Fe3O4 nanodots is more difficult to achieve compared with that of the corresponding film. This difficulty may be attributed to the following reasons: (1) The edge of the nanosized pore may hinder deposition resulting in some of the atoms losing part of their energy so that atom hopping time and length are reduced, which is unfavorable for epitaxial growth. (2) The atoms enter the nanosized pores rather than on the flat substrates. Part of the atoms neighboring the wall of the pore obviously cannot move to the normal direction of the wall. This limitation also influences epitaxial growth. (3) The atoms in the pores may be separated by PAA from the activated oxygen atoms. Meanwhile, the energy for FeO formation was lower than that of Fe3O4[18], so part of the Fe3O4 may have been reduced. From the above analysis, we can conclude that with the aid of high Ts and in situ annealing, the deposited atoms which gained more thermal dynamic energy finally resulted in the good quality of Fe3O4 nanodot arrays. Following the optimal parameters of a 70-nm nanodot array, with D = 40, 140-nm-sized arrays all grow at Ts = 700°C and 2 h of in situ annealing at 700°C.Figure 3


Morphology and magnetic properties of Fe3O 4 nanodot arrays using template-assisted epitaxial growth.

Guan XF, Chen D, Quan ZY, Jiang FX, Deng CH, Gehring GA, Xu XH - Nanoscale Res Lett (2015)

XRD patterns for the film and dot arrays. The sample of D = 70 nm and film deposited at various substrate temperatures and after annealing. Except for the peaks of FeO (002) and Fe3O4 (004), the rest are peaks of the substrate.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493851&req=5

Fig3: XRD patterns for the film and dot arrays. The sample of D = 70 nm and film deposited at various substrate temperatures and after annealing. Except for the peaks of FeO (002) and Fe3O4 (004), the rest are peaks of the substrate.
Mentions: The θ-2θ scans of the series of film and nanodot arrays deposited at different substrate temperatures (Ts), as well as the scans after annealing, are shown in Figure 3. The XRD patterns of the nanodot arrays without in situ annealing showed peaks that correspond to FeO (002), as well as the Fe3O4 (004) reflections. The intensity of the Fe3O4 (004) peaks increased, whereas the FeO (002) peaks decreased with an increase of Ts. These trends indicate that high substrate temperature favors the formation of the Fe3O4 (004) phase. The peak of FeO (002) disappeared after 2 h of in situ annealing at 700°C. In this condition, epitaxial growth of Fe3O4 nanodots with (004) orientation was obtained. The Fe3O4 (004) film could have epitaxial growth at a Ts of 600°C. Clearly, epitaxial growth of Fe3O4 nanodots is more difficult to achieve compared with that of the corresponding film. This difficulty may be attributed to the following reasons: (1) The edge of the nanosized pore may hinder deposition resulting in some of the atoms losing part of their energy so that atom hopping time and length are reduced, which is unfavorable for epitaxial growth. (2) The atoms enter the nanosized pores rather than on the flat substrates. Part of the atoms neighboring the wall of the pore obviously cannot move to the normal direction of the wall. This limitation also influences epitaxial growth. (3) The atoms in the pores may be separated by PAA from the activated oxygen atoms. Meanwhile, the energy for FeO formation was lower than that of Fe3O4[18], so part of the Fe3O4 may have been reduced. From the above analysis, we can conclude that with the aid of high Ts and in situ annealing, the deposited atoms which gained more thermal dynamic energy finally resulted in the good quality of Fe3O4 nanodot arrays. Following the optimal parameters of a 70-nm nanodot array, with D = 40, 140-nm-sized arrays all grow at Ts = 700°C and 2 h of in situ annealing at 700°C.Figure 3

Bottom Line: The calculated nanodot density was as high as 0.18 Tb in.(-2) when 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.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Magnetic Molecules and Magnetic Information Materials of Ministry of Education and School of Chemistry and Materials Science, Shanxi Normal University, Linfen, 041004, China, guanxiaofen325@163.com.

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 (D int) 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.

No MeSH data available.