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|Title: ||Size correlated long and short range order of ternary Co2FeGa Heusler nanoparticles|
|Authors: ||Yeu-Kuang Hwu|
Gerhard H. Fecher
|Issue Date: ||2018-07-10T02:40:08Z
|Publisher: ||APPLIED PHYSICS LETTERS|
|Abstract: ||Abstract: The long and short range order of chemically prepared Co2FeGa Heusler nanoparticles with various sizes are determined by x-ray diffraction (XRD) and extended x-ray absorption fine structure (EXAFS) spectroscopy. Specifically, EXAFS fittings reveal the size dependent crystal structure and short range order of the Heusler type Co2FeGa nanoparticles. With decreasing particle size, the degree of L21 order in the nanoparticles decreases and the probability of B2 disorder increases simultaneously. The consequences of antisite disorder on the size correlated structure of Co2FeGa nanoparticles are also discussed.
Heusler alloys are intermetallic compounds with the formula X2YZ and have the L21 structure. Normally X and Y are transition metals and Z is a main group element. Heusler nanoparticles have emerged as a platform to study the effects of size and surface on the structural, electrical, and magnetic properties of devices in emerging nanospintronics.1,2 Generally, a well-ordered crystalline structure (L21 or B2) is required to achieve a high degree of spin polarization.3–5 To unambiguously determine the crystal structure of Heusler nanoparticles by x-ray diffraction (XRD) is not a trivial task. For example, the particle size-induced broadening or even disappearance of characteristic (111) and (200) reflections renders difficulty in identifying the structure of Heusler nanoparticles.
Extended x-ray absorption fine structure (EXAFS) spectroscopy has been utilized to provide complementary long range order of bulk Heusler compounds.6 Recently Heusler nanoparticles have been prepared by a variety of approaches.7–10 However, less information on the short range order of Heusler nanoparticles is available in the literature. Furthermore, the dependence the long and short range structure of Heusler nanoparticles on particle size is to be explored. In this contribution, the long and short range orders of ternary Co2FeGa Heusler nanoparticles of various particle sizes are investigated.
Co2FeGa nanoparticles of various sizes have been prepared by a wet impregnation method as previously reported8 and the surfaces of the nanoparticles were covered by carbon to protect from oxidation. The particle size of Co2FeGa nanoparticles are controlled by varying the amount of silica supports. The compositions of Co2FeGa nanoparticles were determined by comparing the edge jumps in the x-ray absorption spectra.11 Particle size analysis was carried out by a transmission electron microscope. The saturation magnetizations of Co2FeGa nanoparticles were measured by a superconducting quantum interference device. The composition, size, derived crystal structure by EXAFS fitting and saturation magnetization of the Co2FeGa nanoparticles are listed in Table I.
|Appears in Collections:||[光電科學研究所] 期刊論文|
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