DSpace at VNU: Magnetic Properties of FePd Nanoparticles Prepared by Sonoelectrodeposition

Journal of ELECTRONIC MATERIALS DOI: 10.1007/s11664-016-4565-7 Ó 2016 The Minerals, Metals & Materials Society Magnetic Properties of FePd Nanoparticles Prepared by Sonoelectrodeposition NGUYEN HOANG LUONG,1,3 TRUONG THANH TRUNG,1 TRAN PHUONG LOAN,1 LUU MANH KIEN,2 TRAN THI HONG,1 and NGUYEN HOANG NAM1 1.—Hanoi University of Science, Vietnam National University, Hanoi, 334 Nguyen Trai Road, Hanoi, Vietnam 2.—Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan 3.—e-mail: luongnh@hus.edu.vn Fe60Pd40 nanoparticles were prepared by sonoelectrodeposition After annealing at various temperatures from 450°C to 700°C, the nanoparticles were found to have an ordered L10 structure and to show hard magnetic properties Among the samples investigated, the nanoparticles annealed at 600°C exhibited the highest coercivity which amounts to 2.31 kOe at K and 1.83 kOe at 300 K Key words: FePd, L10 structure, sonoelectrodeposition, magnetic nanoparticles, hard magnetic materials INTRODUCTION FePd nanoparticles have attracted interest for their potential applications in ultrahigh-density magnetic recording media due to the large uniaxial magnetocrystalline anisotropy of Ku $ 1.8 107 erg cmÀ3 of the L10 ordered structure.1–11 Ordered face-centered tetragonal (fct) L10 FePd materials are normally obtained from disordered face-centered cubic (fcc) materials via the order–disorder transition Several approaches to the preparation of FePd nanoparticles have been reported including epitaxial growth by electron beam deposition,4–6 chemical synthesis7,8,11 (which is modified from the FePt nanoparticles synthesis method by Sun et al.12), modified polyol process,9 and microwave irradiation2 As pointed out by Watanabe et al.,9 FePd nanoparticles synthesized by the modified polyol process including thermal decomposition not exclusively show the ordered L10 phase transition similar to L10-type materials such as FePt and CoPt Especially, the FePd nanoparticles prepared by Chen and Nikles11 did not transform to the L10 phase after annealing at a sufficiently high temperature of 700°C (Received October 12, 2015; accepted April 21, 2016) We have previously reported the hard magnetic properties of FePd nanoparticles synthesized by sonochemistry.13 In this paper, we report the use of the sonoelectrodeposition method for the preparation of FePd nanoparticles To our knowledge, FePd nanoparticles have never been fabricated by sonoelectrodeposition, which is a technique combining the advantages of electrodeposition and the mechanical waves of ultrasound to produce metallic nanoparticles.14 Recently, Co–Pt nanoparticles encapsulated in carbon cages prepared by sonoelectrodeposition have been reported by Luong et al.15 Magnetic properties of FePt nanoparticles also prepared by sonoelectrodeposition have been reported by Nam et al.16 EXPERIMENTAL The experimental setup employed by us is similar to that described in Ref 17 A titanium horn of diameter of 1.3 cm acted as both the cathode and ultrasound emitter (Sonics VCX 750) The electroactive part of the sonoelectrode was the planar circular surface at the bottom of the Ti horn, while an isolating plastic jacket covered the immersed cylindrical part This sonoelectrode produced a sonic pulse that immediately followed a current pulse A home-made galvanostat was used to control the constant current regime (without using a reference Luong, Trung, Loan, Kien, Hong, and Nam Fig TEM image and size distribution of the as-prepared Fe60Pd40 nanoparticles Fig TEM image and size distribution of the annealed Fe60Pd40 nanoparticles (600°C/1 h) electrode) A platinum plate of cm2 was used as a counter electrode The density of the current pulse was 15 mA/cm2 The duration, ton, of the current pulse was 0.5 s, then the current was turned off for a duration, toff, of 0.8 s During ton, FePd nanoparticles were deposited on the surface of the electrode When the current was switched off, a 0.2-s ultrasound pulse of power density 100 W/cm2 was activated to remove the nanoparticles from the electrode The volume of the electrolysis cell was 100 ml containing 0.15 M iron(II) acetate [Fe(C2H3O2)2], 0.1 M palladium(II) acetate [Pd(C2H3O2)2], and 0.5 M Na2SO4, which were mixed under (Ar + 5%H2) atmosphere After deposition, the FePd nanoparticles were washed and separated from the solution by using a centrifuge (Hettich Universal 320) at 5000 rpm for 30 Nanoparticles were dried in air at 70°C for 30 The as-prepared samples were then annealed at various temperatures from 450°C to 700°C for h under (Ar + 5%H2) atmosphere The structure of the nanoparticles was characterized by an x-ray diffractometer (XRD; D5005, Bruker) The average crystallite size, d, was calculated from the line broadening using Scherrer’s formula, d = 0.9k/ (Bcosh), where k is the wavelength of x-rays and B is the half-maximum line width The particle morphology was examined by a transmission electron microscope (TEM; JEM1010, JEOL) The chemical composition of our sample was Fe60Pd40 as revealed from energy dispersion spectroscopy (EDS; OXFORD-ISIS 300) measurements Magnetic properties of samples were studied by using Quantum Design’s superconducting quantum interference device (SQUID) with a magnetic field up to 50 kOe in the temperature range from K to 300 K RESULTS AND DISCUSSION Figures and show the TEM images and size distributions of the as-prepared and Fe60Pd40 nanoparticles annealed at 600°C, respectively Particle size of the as-prepared Fe60Pd40 sample was Magnetic Properties of FePd Nanoparticles Prepared by Sonoelectrodeposition Fig XRD patterns of the as-prepared and annealed Fe60Pd40 nanoparticles (600°C/1 h) about 7–10 nm After annealing, the particle size increased to about 15–20 nm, showing that the particles were agglomerated The XRD patterns of the as-prepared and Fe60Pd40 nanoparticles annealed at 600°C are shown in Fig Before annealing, the XRD results showed the reflections of a pure Pd structure, as observed in Ref 13 in FePd nanoparticles prepared by sonochemistry The reflections from Fe are very weak due to the fact that their atomic weight is much less than that of Pd, which is similar to the XRD result of FePt foils prepared by cold deformation18 and of FePt nanoparticles prepared by sonoelectrodeposition.16 The average crystallite size calculated by using Scherrer’s formula was found to be 10 nm, in agreement with the particle size obtained from the TEM image Upon annealing, the formation of the ordered L10 fct phase occurred Samples showed the tetragonal order phase of FePd alloy with diffraction peaks at 24°, 33°, 41°, 47°, 49°, 53.5°, 60.5°, 69° which can be assigned to (001), (110), (111), (200), (002), (201), (112), (220) reflections, respectively The diffraction peak at 44.5° can be due to the formation of the a-Fe phase in the sample By using Scherrer’s formula, the average crystallite size was estimated to be 20.1 nm for the sample annealed at 600°C, in agreement with that obtained from the TEM image Magnetic measurements of the as-prepared sample (data not shown) exhibited low saturation magnetization, MS, and coercivity, HC After annealing, the hard magnetic FePd phase was formed Figure presents the magnetic curves of the Fe60Pd40 nanoparticles annealed at 600°C for h at different temperatures The curves show typical hard magnetic hysteresis loops, indicating the effect of annealing The temperature dependence of the coercivity of Fe60Pd40 nanoparticles annealed at various temperatures from 450°C to 700°C is shown in Fig 5, from which it can be Fig Magnetic curves of Fe60Pd40 nanoparticles annealed at 600°C for h at different temperatures clearly seen that the Fe60Pd40 nanoparticles annealed at 600°C exhibit the highest coercivity For this sample, the coercivity was 2.31 kOe at K and slightly decreases with increasing temperature to the value of 1.83 kOe at 300 K Watanabe et al.9 prepared Fe49.2Pd50.8 nanoparticles by the modified polyol process, i.e simultaneous reduction of palladium acetylacetonate (Pd(acac)2) and thermal decomposition of iron pentacarbonyl (Fe(CO5)) in a solvent These authors reported the value of 2.04 kOe at K for the coercivity of Fe49.2Pd50.8 samples annealed at 600°C for h We note that the Fe49.2Pd50.8 nanoparticles in Ref have been annealed at only one temperature (600°C) Gajbhiye et al.19 also prepared Fe43Pd57 nanoparticles by the Luong, Trung, Loan, Kien, Hong, and Nam Figure shows the annealing-temperature dependence of the coercivity of Fe60Pd40 nanoparticles measured at different temperatures As can be seen from this figure, the coercivity of the Fe60Pd40 nanoparticles increases with the annealing temperature up to 600°C due to a better atomic ordering of the fct phase Further increase of the annealing temperature decreases the coercivity, suggesting that a soft phase Fe3Pd exists in the sample, as supported by our XRD results for the samples annealed at 650°C and 700°C (data not shown) CONCLUSIONS Fig The temperature dependence of the coercivity of Fe60Pd40 nanoparticles annealed at different temperatures Fe60Pd40 nanoparticles have been prepared by sonoelectrodeposition After annealing at various temperatures from 450°C to 700°C, the nanoparticles were found to have an ordered L10 phase, with good coercivity up to 2.31 kOe at K and 1.83 kOe at room temperature Sonoelectrodeposition is a promising method to make FePd magnetic nanoparticles ACKNOWLEDGEMENTS This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under Grant Number ‘‘103.022013.61’’ The authors would like to thank Prof Y Nozue of Osaka University, Japan, for providing SQUID REFERENCES Fig The annealing-temperature dependence of coercivity of Fe60Pd40 nanoparticles measured at different temperatures modified polyol process and annealed the samples at 450°C, 550°C and 600°C for h They obtained HC = 1.18 kOe at 300 K for the Fe43Pd57 sample annealed at 550°C For the sample annealed at 600°C, HC = 1.3 kOe, larger than that for the sample annealed at 550°C These authors noted, however, that the annealing at 600°C will lead to severe agglomeration, which is detrimental for technical applications Hou et al.8 synthesized Fe48Pd52 nanoparticles by a chemical method and annealed the samples at 550°C, 600°C and 700°C for 30 They reported that the coercivity of the samples increases with the annealing temperature up to 600°C, reaching a value of HC $ kOe at room temperature These authors alsso noted that further increase of the annealing temperature decreases the coercivity, suggesting the formation of a new soft phase Fe3Pd at higher temperature D Weller, A Moser, L Folks, M.E Best, W Lee, M.F Toney, M Schwikert, J.U Thiele, and M.F Doerner, IEEE Trans Magn 36, 10 (2000) H Loc Nguyen, L.E.M Howard, S.R Giblin, B.K Tanner, I Terry, A.K Hughes, I.M Ross, A Serres, H Burckstummer, and J.S.O Evans, J Mater Chem 15, 5136 (2005) A Cebollada, R.F.C 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Nanoparticles Prepared by Sonoelectrodeposition 16 N.H Nam, N.T Thanh Van, N.D Phu, T.T Hong, N.H Hai, and N.H Luong, J Nanomater 2012, 801240 (2012) 17 J.J Zhu, S.T Aruna, Yu Koltypin, and A Gedanken, Chem Mater 12, 143 (2000) 18 N.H Hai, N.M Dempsey, and D Givord, J Magn Magn Mater 262, 353 (2003) 19 N.S Gajbhiye, S Shrma, and R.S Ningthoujam, J Appl Phys 104, 123906 (2008)  ... distributions of the as -prepared and Fe60Pd40 nanoparticles annealed at 600°C, respectively Particle size of the as -prepared Fe60Pd40 sample was Magnetic Properties of FePd Nanoparticles Prepared by Sonoelectrodeposition. .. the XRD result of FePt foils prepared by cold deformation18 and of FePt nanoparticles prepared by sonoelectrodeposition. 16 The average crystallite size calculated by using Scherrer’s formula was... kOe at K and 1.83 kOe at room temperature Sonoelectrodeposition is a promising method to make FePd magnetic nanoparticles ACKNOWLEDGEMENTS This research is funded by Vietnam National Foundation