Detection of Single-Domain Co 2 FeAl Nanoparticles Using First-Order Reversal Curve Method
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TRODUCTION
FULL-HEUSLER alloy Co2FeAl presents one of the highest Curie temperatures among the reported half-metallic ferromagnets.[1] A large tunnel magnetoresistance of 47 pct at room temperature was obtained in magnetic tunnel junctions using Co2FeAl Heusler alloy electrode by Okamura et al.[2] Co2FeAl alloys also possess a lower saturation magnetization and damping constant compared with those of the other ferromagnetic materials.[3] It is clear that there is a growing interest in making high-quality structures of the magnetic nanostructures. Heusler alloy nanostructures have been produced in different geometries such as thin films,[4,5] nanocomposites,[6] and nanoparticles.[7] Commonly, magnetic nanoparticles tend to aggregate extremely owing to the large surface energy and magnetic interactions between single atoms. The increased steric hindrance produced with large molecules of a polymer as the capping agent will enhance the stability of these particles.[8] Polyvinylpyrrolidone (PVP) polymer was used here as a template to mediate the assembly of Co2FeAl (CFA) nanoparticles. Although the use of PVP has been utilized to control shape and particle size of various SIMA ALIKHANZADEH-ARANI, Assistant Professor, ZAHRA PEZESHKI-NEJAD, Ph.D. Student, and MASOUD SALAVATINIASARI, Professor, are with the Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P. O. Box 87317-51167, Iran. Contact e-mail: [email protected] MOHAMMAD ALMASI-KASHI, Professor, and ABDOLALI RAMAZANI, Associate Professor, are with the Institute of Nano Science and Nano Technology, University of Kashan, and also with the Department of Physics, University of Kashan. Manuscript submitted October 15, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
nanostructures, this work is the first successful attempt for the synthesis of Heusler alloy nanoparticles using this polymer in the coprecipitation method. It has been reported that the concentration of the utilized polymer and heating rate are two important factors for controlling the shape and particle size.[9] Samples were annealed at 873.15 K and 973.15 K (600 C and 700 C) with different heating rates. Interestingly, different heating rates led to the different nucleation rates as well as different morphologies and particle sizes. More recently, attention has shifted to the understanding of the magnetic behavior of materials using the first-order reversal curves (FORCs) analysis, concerning the interacting hysterons. In this work, we used FORCs analysis to provide additional information about the magnetic characteristics of the prepared nanostructured alloys.
II.
EXPERIMENTAL DETAILS
A. Materials and Characterization All chemicals used were of analytical grade and used as received without further purification. Aluminum(III) nitrate, iron(III) nitrate, cobalt(II) acetate, and polyvinylpyrrolidone (PVP) polymer were purchased from Merck Chemical Company. Phase identification was carried out for the as-precipitated and heat-treated samples by an X-ray diffraction (XRD) method with
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