FePt Nanoparticle Films Under in-situ Applied Magnetic Field

FePt Nano mite Films to a lower place unchanged Applied Magnetic correctionSynthesis and characteristics of FePt nanoparticle films to a lower place in-situ use charismatic scope of viewMo-Yun Gao, Xu Qian, Ai-Dong Li*, Xiao-Jie Liu, Yan-Qiang Cao, Chen Li, Di WuAbstractFePt nanoparticle with L10- cast has extremely in high spirits magnetocryst tout ensembleine anisotropy, good chemic substance stability, and bulwark to oxidation, and has been considered as the most promising supportdidate for untra-high-density magnetic arrangement media.In this work, in-situ magnetic scope was employ during the tax write-off of FePt nanoparticles via a chemical substance solution method. FePt nanoparticle films were prepared by a move method. The effect of in-situ applied magnetic scene of action on the body structure, morphology and magnetic properties of FePt nanoparticle films was characterized. Under magnetic field as-synthesized FePt nanoparticles are mono disperse and gouge be self-assembled everywhere big sphere by a dropping method. The chemic all(prenominal)y ordered L10-stage FePt can be compassed by and by normalizeing at 700 C for 60 mo in forming hitman (7% H2+93% Ar). It is revealed that applied magnetic field during the synthesis of FePt nanoparticles not only significantly improves the nanoparticles c-axis like orientation course with the larger plumb line c-axis preferred orientation degree D(001) of 3.47, but in any case benefits the phase passing of FePt nanoparticles from fcc to fct structure during the annealing execute. The FePt nanoparticle films synthesized downstairs magnetic field also verbalizes nigh magnetic anisotropy.Keywords L10-phase FePt Chemical solution synthesis Applied magnetic field C-axis oriented Magnetic anisotropy1. IntroductionWith the rapid development of magnetic record technique, the superparamagnetic effect becomes the bottlefulneck to further increase magnetic storage density. The ferromagnet ic L10 FePt assemblies with face-centered tetragonal (fct) structure has extremely high magnetocrystalline anisotropy, good chemical stability, and immunity to oxidation 1-3, considered as the most promising candidate for ultra-high-density magnetic recording media.Chemical solution method has become an attractive route to obtain FePt nanoparticles (NPs) with the controllable size, well-defined shape, and ordered monolayer assemblies since Sun et al. puzzle out great achiever in preparing monodisperse FePt NPs 4. Based on this, a lot of studies have been conducted to explore and optimize the synthesis of FePt NPs, such as modifying fabrication methods 5-13, optimizing assembly methods 7,14-21 and fabricating FePt analogue nanorods /nanowires 22-28 and so on.As-prepared fcc-FePt NPs need to be transformed to ferromagnetic fct-FePt, high temperature annealing will produce severe grain growth and particle aggregation, leading(a) to the decrease of the particle positional order 29 . Great efforts have been made to suppress the unfavorable phenomenon upon annealing and worked. For example, ingredient such as Ag 30, Au 31, and Sb 32 with low surface skill is doped into FePt NPs to forbear from the influence of annealing by decreasing the phase transition temperature of FePt. However, whizz defect is that the phase transition temperature is too high to avoid particle aggregation, some other is that the morphology of FePt nanoparticle will become undisciplined and self-assembled array over large area are destroyed after Sb doping. In addition, the core-shell structure of inorganic substance such as ZnO 33,34, MnO 35, NiO 36 and SiO2 37 covering on FePt NPs solves the problem of sintering and aggregation of NPs. However, as the thickness and morphology of core-shell structure is uncontrolled and there exists strong magnetic dipole interaction between FePt magnetic NPs, making it difficult for self-assembled of NPs and orderly array over large area fail to fo rm. Recently it reported that nonmagnetic films like Al2O3 deposited by nuclear layer deposition (ALD) upon FePt NPs self-assembly array can improve the stability of FePt NPs downstairs high temperature, preventing NPs from sintering and aggregation 38. Other work like dispersing FePt NPs into the TiO2 substrate by sol-gel is a good way to protect FePt NPs during annealing 39, but element Fe of FePt will be lost in acidic TiO2 sol.In this work, we reported that in-situ magnetic field was applied during the synthesis process of FePt NPs and the dip cultivation process to form FePt NPs films. The FePt NPs were prepared via chemical decrement of Pt(acac)2 and thermal decomposition of Fe(CO)5 under different magnetic conditions in the front line of oleic acid (OA) and oleylamine (OAm) at 220. The prepared FePt NPs films were than annealed at 700 for 60 min in forming gas (7% H2 + 93% Ar) to form the L10 phase of FePt. It is revealed that applied magnetic field not only significantl y improves the c-axis preferred orientation, but also benefits the phase transition of FePt NPs from fcc to fct structure. The FePt NPs thin film synthesized under magnetic field also shows some magnetic anisotropy. Under magnetic field as-synthesized FePt NPs are monodispersed and can be self-assembled over larger area by a dropping method.2. Experimental2.1 Synthesis of FePt NPsFePt nanoparticles were synthesized through a standard polyol process with a modified synthetic condition using standard airless procedures under a gentle flow of pure normality (N2) 12,39. Typically, the FePt nanoparticles were prepared via chemical reduction of Pt(acac)2 and thermal decomposition of Fe(CO)5 under different magnetic conditions in the presence of oleic acid (OA) and oleylamine (OAm) at 220.In a typical procedure, 0.125 mmol of Pt(acac)2 was intricate with 20 mL of phenyl ether under the gentle nitrogen gas flow. The mixture was heated to 50C, and stir until the platinum source change sta te completely in the solvent. After that the mixed solution was heated to clC and 40 L of oleic acid (OA),42.5 L of oleylamine (OAm), and 80 L of Fe(CO)5 were added step by step under different magnetic conditions with unremitting stream of nitrogen. After that, the solution was heated up to 220 C at the rate of 10 C per minute., and refluxed for 30 min under the nitrogen protection. After the prepared black solution cooling down to the live temperature naturally, 50 L of oleic acid (OA), 50 L of oleylamine (OAm) and absolute fermentation alcohol were added into the mixture to a total volume of 80 mL. The black products were because decreased by centrifugation (8000 r/min for 10 min) and the solution supernatant was discarded. The precipitate was then dissolved in 10 mL of hexane and precipitated again in 40 mL of absolute ethanol by centrifugation. The black FePt NPs were synthesized by repeating the separation process for 23 times. The magnetic NPs were dispersed in 6 mL of octane and stored in brown glass bottle under the nitrogen conditions.2.2 Preparation of FePt NPs filmsAssembled FePt NPs on the HF-treated n-Si (100) substrates (1.01.0 cm2) were prepared by droping a drop of 2 mg/mL FePt solution (FePt NPs dispersed in octane) including a small amount of OA and OAm. As the organic solvent on the surface of FePt NPs was dried under the protection of N2 at room temperature, the FePt NPs were then heated to 120 C and maintained for 2h in the baking oven to rent the organic solvent completely. In-situ magnetic field was applied in a patr of the samples during the dip screening process to form FePt NP films and another part were in nonmagnetic field for comparison. Three kinds of samples with different foreign magnetic field applied during the synthesis process and the dip coating process were listed in Table 1. The prepared FePt NP films were than annealed at 700 for 60 min in forming gas (7% H2 + 93% Ar) with a rising go of 5 C/min to form order ed fct-FePt before characterization.2.3 moving-picture showThe structure and crystalline phase were characterized by way of life of X-ray diffraction (XRD, D/max 2000, Rigaku) using Cu K radiation ( = 1.5406 ) operated at 40 kV and 40 mA. The morphology and microstructure of various samples were characterized using a transmitting electron microscopy (TEM, Tecnai G2 F20 S-twin, FEI) operating at 200 kV. The compositions of all samples were analysed by the energy dispersive X-ray spectroscopy (EDS) attached to a field-emission scanning electron microscopy (FESEM, Zeiss). Magnetic properties of the fct-FePt were measured by a superconducting quantum interference device (SQUID, MPMS XL-7, Qauntum Design) with a maximum field of 35 kOe.3. Results and discussionFigure 1 (a) and (b) show the XRD patterns of unannealed and annealed FePt NPs films under different magnetic conditions. In Fig. 1 (a), the ontogeny of two broad note at 40.3 o and 46.9 o of all samples which represent the Br agg peaks (111) and (200) illustrate the fcc-FePt NPs of average grain size of 4.1 nm cipher by Scherrer equation were obtained. It is obvious that in sample 2 and 3, the peak (200) are stronger and closer to the highest peak (111) where diffraction is most likely to sink compared with sample 1 without magnetic field applied, indicating that in-situ magnetic field applied during the synthesis process exhibit the trend for FePt NPs to align right to the (100) crystal plane. While magnetic field applied during dip coating process make no obvious effect before anneal via comparing sample 2 with 3. High temperature annealing make the phase transform from fcc to fct as indicated by the emergence of the Bragg peaks of (001), (110), (002) and (201) as shown in Fig. 1 (b). The Bragg peak (001) and (002) are much stronger with the magnetic field applied during the synthesis process among which the intensity of peak (001) has been ahead of main peak (111) and peak (002) split from peak (20 0) are higher than peak (200) apparently. It means that the fct-FePt NPs films with the magnetic field applied during the synthesis process after high temperature annealing exhibit c-axis preferred orientation that is fct-FePt NPs align along the c-axis plumb line to the surface of films which is the easy axis of magnetization 40. Magnetic field applied during both during the synthesis process and the dip coating process has jolly improve c-axis preferred orientation, inferior to sample 2.We define the degree of c-axis preferred orientation D(001) of fct-FePt in direction 001 as follows 41D(001)= (I(001)/I(111))measure/(I(001)/I(111))standardwhere (I(001)/I(111))standard=0.3 is got in diffraction patterns of fct-FePt pulverisation with random orientation, while (I(001)/I(111))measure can be calculated from the XRD patterns of annealed sample 1, 2 and 3.Degree of the chemical ordering parameter S was introduced to illustrate the degree of order of FePt NPs films quantificationally. It is defined as follows42,43S2=1-(c/a)measure/1-(c/a)standardwhere c and a are the lattice constants for the fct-FePt, evaluated from the (001) and (110) Bragg peaks of the XRD patterns and the axial ratio (c/a)measure for the partially ordered phase can be calculated then. For the fully ordered-phase FePt, (c/a)complete = 0.9657.Some data of samples under different magnetic conditions are listed in Table 2, including unannealedI(200)/I(111), annealed I(001)/I(111), degree of the chemical ordering parameter S and degree of c-axis preferred orientation D(001).It is tardily seen from Table 2 that samples 2 and 3 with external magnetic field applied have a certain degree of 200 preferred orientation before anneal, making 001 preferred orientation more obvious after anneal. Comparing the degree of the chemical ordering parameter S of all samples, we can see that applied magnetic field during the synthesis of FePt nanoparticles not only significantly improves the NPs c-axis preferred orientation with the larger perpendicular c-axis preferred orientation degree D(001) of 3.47, but also benefits the phase transition of FePt NPs from fcc to fct structure during the annealing process. The reason for obvious c-axis preferred orientation may assign to the anisotropy induced by external magnetic field during the nucleation of FePt for that applied magnetic field changed the barrier of nucleation in different orientation ,making the ratio I(200)/I(111) larger in superparamagnetic particles and a-axis orientation enhanced, which is more likely to be transformed to c-axis orientation during the process of films formation and high temperature annealing.4. ConclusionAcknowledgeThis project is support by the Natural attainment Foundation of chinaware (Grant No. 51202107), a grant from the State Key Program for Basic Research of China (Grant No. 2011CB922104), and the Fundamental Research Funds for the Central Universities. Ai-Dong Li also thanks the support of Priority A cademic Program Development in the Jiangsu Province and the Doctoral Fund of Ministry of Education of China (Grant No. 20120091110049).References1 S. H. Sun, Adv. Mater. 18 (2006) 393.2 H. Zeng, J. Li, J. P. Liu, Z. L. Wang, and S. H. Sun, Nature. 420 (2002) 395.3 D. Weller, A. Moser, L. Folks, M. E. Bet, W. Lee, M. Toney, M. Schwieckert, J. U. Thieleand, and M. F. Doerner, IEEE Trans. Magn. 36 (2000) 10.4 S. H. Sun, C. B. Murray, D. Weller, L. Folks, A. Moser, Science 287 (2000) 1989.5 B. Jeyadevan, K. Urakawa, A. Hobo, N. Chinnasamy, K. Shinoda, K. Tohji, D. D. J. Djayaprawira, M. Tsunoda, M. Takahashi, Jpn. J. Appl. Phys. Part 2 42 (2003) L350.6 M. Chen, J. P. Liu, S.H. Sun, J. Am. Chem. Soc. 126 (2004) 8394.7 L. E. M. Howard, H. L. Nguyen, S. R. Giblin, B. K. Tanner, I Terry, A. K. Hughes, J. S. O Evans, J. Am. Chem. Soc. 127 (2005) 10140.8 S. H. Sun, S. Anders, T. Thomson, J. E.E. Baglin, M. F. Toney, H. F. Hamman, C. B. Murray, B. D. Terris, J. Phys. Chem. B 107 (2003) 5419.9 K. E. Elkins, T. S. Vedantam, J. P. Liu, H. Zeng, S. H. Sun, Y. Ding, Z. L. Wang, Nano Letters 3 (2003) 1647.10 B. Jeyadevan, A. Hobo, K.Urakawa, C.N. Chinnasamy, K. Shinoda, K. Tohji, J. Appl. Phys. 93 (2003) 7574.11 P. Gibot, E. Tronc, C. Chaneac, J. P. Jolivet, D. Fiorani, A. M. Testa, J. Magn. Magn. Mater. 290 (2005) 555.12 J. L. Zhang, J. Z. Kong, A. D. Li, Y. P. Gong, H. R. Guo, Q. Y. Yan, D. Wu, J. Sol-Gel Sci. Tech. 64 (2012) 269.13 B. R. Bian, W. X. Xia, J. Du, J. Zhang, J. P. Liu, Z. H. Guo, A. Yana, Nanoscale 5 (2013) 2454.14 E. Shevchenko, D. Talapin, A. Kornowski, F. Wiekhorst, J. Kotzler, M. Haase, A.Rogach, H. Weller, Adv. Mater. 14 (2002) 287.15 M. Acet, C. Mayer, O. Muth, A. Terheiden, G. Dyker, J. Cryst. Growth 285 (2005) 365.16 S. H. Sun, Adv. Mater. 18 (2006) 393.17 A. Terheiden, B. Rellinghaus, S. Stappert, M. Acet, C. Mayer, J. Chem. Phys. 121 (2004) 510.18 A. C. C. Yu, M. Mizunno, Y. Sasaki, M. Inoue, H. Kondo, I. Ohta, D. Djayaprawira, M. Takahashi, Appl. Phy s. Lett. 82 (2003) 4352.19 H. F. Hamann, S. I. Woods, S. H, Sun, Nano Lett. 3 (2003) 1643.20 Y. Sasaki, M. Mizuno, A. C. C. Yu, T. Miyauchi, D. Hasegawa, T. Ogawa, M. Takahashi, B. Jeyadevan, K. Tohji, K. Sato, S. Hisano, IEEE Trans. Magn. 41 (2005) 660.21 S. B. Darling, N. A. Yufa, A. L. Cisse, S. D. Bader, S. J. Sibener, Adv. Mater. 17 (2005) 2446.22 C. Wang, Y. L. Hou, J. M. Kim, S. H. Sun, Angew. Chem. Int. Ed. 46 (2007) 6333.23 Y. L. Hou, H. Kondoh, R. C. Che, M. Takeguchi, T. Ohta, Small 2, No. 2 (2006) 235.24 Z. T. Zhang, D. A. Blom, Z.Gai, J. R. Thompson, J. Shen, S. Dai, J. Am. Chem. Soc. 125 (2003) 7528.25 T. L. da Silva, L. C. Varanda, Nano Res. 4, 7 (2011) 666.26 H. G. Liao, L. K. Cui, S. Whitelam, H. M. Zheng, Science 336 (2012) 1011.27 N. Poudyal, G. S. Chaubey, V. Nandwana, C. B. Rong, K. Yano, J. P. Liu, Nanotechnology 19 (2008) 355601.28 M. Chen, T. Pica, Y. B. Jiang, P. Li, K. Yano, J. P. Liu, A. K. Datye, H.Y. Fan, J. Am. Chem. Soc. 129 (2007) 6348.29 J. M. Qiu, P . Wang, Appl. Phys. Lett. 88, 19 (2006) 192505.30 S. S. Kang, J. W. Harrell, D. E. Nikles, Nano Lett. 2 (2002) 1033.31 S. S. Kang, Z. Y. Jia, D. E. Nikle, J. W. Harrell, IEEE Trans. Magn. 39 (2003) 2753.32 Q. Y. Yan, T. Kim, A. Purkayastha, Y. Xu, M. Shima, R. J. Gambino, G. Ramanath, J. Appl. Phys. 99 (2006) 08N709.33 H. Zeynali, H. Akbali, R. K. Ghasabeh, S. Arumugam, Z. Chamanzadeh, G. Kalaiselvan, Nano 7 (2012) 1250043.34 T. J. Zhou, M. H. Lu, Z. H. Zhang, H. Gong, W. S. Chin, B. Liu, Adv. Mater. 22 (2010) 403.35 S. S. Kang, G. X. Miao, S. Shi, Z.Jia, D. E. Nikles, J. W. Harrell, J. Am. Chem. Soc. 128 (2006) 1042.36 H. Zeynali, S. A. Sebt, H. Arabi, H. Akbari, S. M. Hosseinpour-Mashkani, K. V. Rao, J. Inorg. Organomet. Polym. 22 (2012) 1314.37 Q. Y. Yan, A. Purkayastha, T. Kim, A. Bose, G. Ramanath, Adv. Mater. 18 (2006) 2569.38 J. Z. Kong, Y. P. Gong, X. F. Li, A. D. Li, J. L. Zhang, Q. Y. Yan, D. Wu, J. Mater. Chem. 21 (2011) 5046.39 J. Z. Kong, M. Y. Gao, Y. D. Xia, A. D. Li, J. L. Zhang, Y. P. Gong, Q. Y. Yan, D. Wu, J. Alloys and Compounds 542 (2012) 128.40 J. M. Qiu, J. M. Bai, J. P. Wang, Appl. Phys. Lett. 89 (2006) 222506.41 M. L. Yan, H. Zeng, N. Powers, et al. J. Appl. Phys. 91 (2002) 8471.42 Q. Y. Yan, T. Kim, A. Purkayastha, P. G. Ganesan, M. Shima, G. Ramanath, Adv. Mater. 17, 18 (2005) 2233.43 B. S. Lim, A. Rahtu, P. Rouffignac, R. Gordon, Appl. Phys. Lett. 84 (2004) 3957.Figure Captions