Magnetic properties of carbon-encapsulated Fe–Ni alloy nanocomposites

Magnetic properties of carbon-encapsulated Fe–Ni alloy nanocomposites

Accepted Manuscript Magnetic properties of carbon-encapsulated Fe-Ni alloy nanocomposites Aibing Wu, Jiajia Gao, Xiaodong Chen, Xuwei Yang, Hua Yang P...

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Accepted Manuscript Magnetic properties of carbon-encapsulated Fe-Ni alloy nanocomposites Aibing Wu, Jiajia Gao, Xiaodong Chen, Xuwei Yang, Hua Yang PII: DOI: Reference:

S0925-8388(13)02031-8 http://dx.doi.org/10.1016/j.jallcom.2013.08.155 JALCOM 29290

To appear in: Received Date: Revised Date: Accepted Date:

28 June 2013 10 August 2013 24 August 2013

Please cite this article as: A. Wu, J. Gao, X. Chen, X. Yang, H. Yang, Magnetic properties of carbon-encapsulated Fe-Ni alloy nanocomposites, (2013), doi: http://dx.doi.org/10.1016/j.jallcom.2013.08.155

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Magnetic properties of carbon-encapsulated Fe-Ni alloy nanocomposites Aibing Wu a, b, Jiajia Gaoa, Xiaodong Chen a, Xuwei Yang a and Hua Yang*a

Abstract Carbon-encapsulated Fe-Ni alloy nanoparticles ([email protected]) have been fabricated with different Ni/Fe ratio by an solid-state route using melamine as carbon source. The structure and morphology of [email protected] nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The XRD characterization results reveal that all products are alloys with no carbide impurity. The TEM and HRTEM observations show that the alloy nanoparticles are encapsulated in carbon shells. Additionally, the reactions involved in the syntheses are speculated. The variation of magnetic properties of [email protected] with Ni/Fe has been discussed according to the room temperature VSM measurement results. Keywords: Alloys; Coating; Nano composites; Magnetic properties; Functional composites

1. Introduction Ferromagnetic iron-based alloys have been intensively studied from the viewpoints of both fundamental research and practical applications. The iron group metals (Fe, Co, Ni) exhibit ferromagnetism at room temperature. Fe-Ni and Ni-Co alloys exhibit excellent soft magnetic properties, such as high saturation magnetization and low coercivity. Iron-based alloy nanoparticles are prone to rapid environmental degradation like elemental metal nanoparticles. Carbon is one of the best solutions for protecting alloy nanoparticles [1]. The carbon encapsulation can effectively immunize the nanoparticles against environmental degradation and therefore retain their intrinsic nanocrystalline properties. Furthermore, carbon encapsulation can improve electrical conductivity, mechanical performance and biocompatibility

a

College of Chemistry, Jilin University, Changchun, 130012, P. R. China.

b

Department of Environmental and Chemical Engineering, Tangshan College, Tangshan, 063000, P.R. China. E-mail: [email protected]; Tel: +86 431 85167712 1

of the materials. It is enormously significant for practical and prospective applications such as magnetic data storage [2-4], fuel cells [5,6] , magnetic sensors [7-9] and human tumour treatment [10,11]. Carbon-encapsulated iron-based alloy nanoparticles have drawn extensive attention on account of their important applications. Among them, carbon-encapsulated Fe-Ni and Fe-Co alloy nanoparticles are in the center of interest owing to their superior magnetic properties. The synthesis routes of carbon-encapsulated alloy nanoparticles involve various methods, such as arc discharge, chemical vapor condensation and thermal decomposition. Dong et al. prepared carbon coated Fe-Ni (C) and Fe-Co (C) nanocapsules by arc discharge in methane [12-14]. Dai and co-workers synthesized FeCo/single-graphitic-shell nanocrystals using chemical vapour deposition from methane [15]. Gedanken et al. fabricated air stable FeCo/C alloy nanoparticles via a one-stage thermal decomposition process [16]. In this work, we report a simple and economic method of synthesizing carbon-encapsulated Fe-Ni alloy nanoparticles. It has been reported that melamine can be used as carbon source for synthesizing carbon-encapsulated Fe-Co alloy nanoparticles respectively [17]. The hydrothermally prepared iron-nickel alloy/nickel ferrite nanocomposites are used as alloy precursors. Melamine is as carbon source for synthesizing carbon-encapsulated Fe-Ni alloy nanoparticles. The structure, morphology of the nanocapsules are investigated. The effects of the Ni/Fe ratio (0 < Ni/Fe ≤ 1) on the magnetic properties of nanocapsules are discussed. 2. Experimental 2.1 Preparation of iron-nickel alloy/nickel ferrite nanocomposites All reagents were of pure analytical grade materials purchased from commercial sources and were used without further purification. The preparation of iron-nickel alloy/nickel ferrite nanocomposites was accomplished by hydrothermal method. Typically, a stoichiometric mixture of ferrous chloride (FeCl2·4H2O) and nickelous chloride (NiCl2·6H2O) was dissolved in 20 mL distilled water under flowing nitrogen with vigorous stirring for 10 min. After the mixture was dissolved completely, 20 mL KOH aqueous solution (1 mol/L) was added slowly drop by drop into the above solution while the nitrogen gas was kept flowing. The reaction mixture was further stirred for 10 min under flowing nitrogen and then charged in a 50 mL Teflon-lined stainless steel autoclave followed by uniform heating at 180 ℃ for 6 h. After the reaction the autoclave was allowed to cool to room temperature naturally, the resulting powder was collected by centrifugation, washed with deionized water and ethanol several times. The precipitate was dried under vacuum at 60 ℃ for 6 h. 2.2 Synthesis of carbon-encapsulated Fe-Ni alloy nanoparticles

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The synthesis of carbon-encapsulated Fe-Ni alloy nanoparticles ([email protected]) was carried out by solid-state reaction at atmospheric pressure. The above prepared alloy precursor (AP) of iron-nickel alloy/nickel ferrite nanocomposites and melamine were mixed together at various molar ratios. The mixed powders were ground by hand using an agate mortar and pestle for 20 min to reduce agglomerations, crush large particles and increase contact area between the carbon source and nanocomposite powder. In a typical process, the ground powder with a predetermined molar ratio of melamine to nanocomposite was put in an alumina boat and then the boat was loaded into the center of a quartz glass tube. The tube was placed into a horizontal electric tube furnace. A thermocouple was inserted into the center of the tube and kept very near to the boat to measure its exact temperature. Ultra pure nitrogen (purity; >99.999%) was introduced into the tube and after purging air for 10 min, the furnace was heated at a rate of 15 ℃/min to required temperature and kept for a certain period of time. Finally the furnace power switch was turned off and the product was allowed to cool to room temperature while maintaining the flow of nitrogen. The product powders were collected from the furnace and once again ground up into a fine powder. 2.3 Sample characterization The X-ray powder diffraction (XRD) patterns were collected on a Shimadzu diffractometer with Cu Kα radiation (λ = 0.15405 nm). The transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images were obtained on a field-emission transmission electron microscope (TECNAI G2, 200 kV). The room temperature magnetic hysteresis (M-H) loops were measured using a vibrating sample magnetometry (VSM) system (JDAM-2000D) with a maximum magnetic field of 10000 Oe. 3. Results and discussion 3.1 Structure

Fig. 1 XRD patterns of the as-prepared iron-nickel alloy/nickel ferrite (FexNi1-x/FeyNi1-yFe2O4) nanocomposites.

Fig. 1 displays the XRD patterns of the as-prepared iron-nickel alloy/nickel ferrite nanocomposites. All five XRD patterns show seven clear peaks characteristic of inverse cubic spinel structure nickel ferrite (FeyNi1-yFe2O4) (JCPDS card no. 85-1436). The small peaks at around 2θ = 44° are corresponding to body centered cubic (bcc) Fe-Ni alloy. It can be found that bcc Fe-Ni alloy exsits in all five samples as a minor phase. Except the peaks of nickel ferrite and Fe-Ni alloy, the rest small and wide peaks can be attributed to trace amount of nickel hydroxide (Ni(OH)2) whose strongest peak is located at around 2θ = 39°.

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Fig. 2 XRD patterns of [email protected] nanoparticles synthesized with different Ni/Fe ratios at constant molar ratio melamine : AP = 4:1 at 650 ℃ for 3 h.

Fig. 2 shows XRD patterns of [email protected] nanoparticles synthesized with different Ni/Fe ratios at constant molar ratio melamine : AP = 4:1 at 650 ℃ for 3 h. All five XRD patterns show several sharp peaks due to fcc Fe-Ni and/or bcc Fe-Ni. The small peak at 2θ = 26.4° can be attributed to graphite. In the two patterns of the Ni/Fe = 0.2 and 0.4 samples, the characteristic peaks of both fcc Fe-Ni ((111), (200) and (220) reflections) and bcc Fe-Ni ((110) and (220) reflections) can be found. The difference is that the peaks of bcc Fe-Ni are dominant in the pattern of Ni/Fe = 0.2 sample, while those of fcc Fe-Ni in the pattern of Ni/Fe = 0.4 sample. The three patterns of samples with Ni/Fe = 0.6, 0.8 and 1.0 are similar and all show characteristic peaks of only fcc Fe-Ni. Comparing the three patterns shows that the intensity of three peaks of fcc Fe-Ni increases with the increase of Ni/Fe. The small peak at 2θ = 26.4° belongs to the (002) plane of graphite.

Fig. 3 XRD patterns of [email protected] nanoparticles synthesized with different Ni/Fe ratios at constant molar ratio melamine : AP = 6:1 at 650 ℃ for 2 h.

Fig. 3 shows XRD patterns of [email protected] nanoparticles synthesized with different Ni/Fe ratios at constant molar ratio melamine : AP = 6:1 at 650 ℃ for 2 h. All five XRD patterns show five peaks due to fcc Fe-Ni and bcc Fe-Co. The small peak at 2θ = 26.4° comes from graphite. The characteristic peaks of both fcc Fe-Ni and bcc Fe-Ni can be found in the two patterns of samples with Ni/Fe = 0.2 and 0.4. The peaks of bcc Fe-Ni are also dominant in the pattern of the sample with Ni/Fe = 0.2. However, the peak intensities of bcc Fe-Ni are slightly lower than those of fcc Fe-Ni in the pattern of the sample with Ni/Fe = 0.4. Different from the other three patterns in Fig. 2, Fig. 3 shows three patterns of samples with Ni/Fe = 0.6, 0.8 and 1.0 with the characteristic peaks of both fcc Fe-Ni and bcc Fe-Ni. The peaks of fcc Fe-Ni are dominant in the three patterns. 3.2 Morphologies

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Fig. 4 TEM images of [email protected] nanoparticles synthesized with Ni/Fe = 0.4 at constant molar ratio melamine : AP = 4:1 at 650 ℃ for 3 h: (a) a low-magnification TEM image; (b) a high-magnification image; (c) a HRTEM image of the square region in (b).

Fig. 4(a) shows a typical low-magnification TEM image of [email protected] nanoparticles synthesized with Ni/Fe = 0.4. It can be seen that the dark alloy nanoparticles are dispersed in the light carbon matrix. The diameter of the nanoparticles ranges from 20 to 100 nm. Fig. 4(b) shows a high-magnification image of the sample. It displays several nanoparticles encapsulated by crystalline shells. A typical HRTEM image of the nanoparticle in the square region marked in Fig. 4(b) is shown in Fig. 4(c). It clearly reveals the core-shell structure of the carbon-encapsulated nanoparticle. The core diameter and the shell thickness are about 25 and 5 nm respectively. The shell is composed of a nanolayered material with the interlayer distance of 0.34 nm [18] typical for the graphite (002) planes. The interlayer distance 0.21 nm of the core is slightly larger than the (111) interplanar distance 0.20 nm of fcc Ni. The value 0.21 nm is consistent with the (111) interplanar distance of fcc Fe-Ni [19], which confirms that the core is Fe-Ni alloy.

Fig. 5 TEM images of [email protected] nanoparticles synthesized with Ni/Fe = 1.0 at constant molar ratio melamine : AP = 4:1 at 650 ℃ for 3 h: (a) a typical low-magnification TEM image; (b) a high-magnification image; (c) a HRTEM image of the square region in (b).

Fig. 5 shows TEM images of [email protected] nanoparticles synthesized with Ni/Fe = 1.0. As can be seen in Fig. 5(a), nearly spherical nanoparticles within the 50-100 nm size range are well dispersed in carbon matrix. Fig. 5(b) clearly reveals the core-shell structure nanoparticles. The HRTEM image of the square region in Fig. 5(b) is presented in Fig. 5(c). The interlayer distance 0.34 nm of the shell (thickness ca. 5 nm) is corresponding to graphite (002) planes. The interplanar distance 0.21 nm of the core is consistent with fcc Fe-Ni (111) planes.

3.3 Reactions involved This route is considered to be modified solid-state metathesis (SSM) [20-23] pathway. The starting materials, melamine and alloy precursors (FexNi1-x/FeyNi1-yFe2O4) are in the solid state before the reactions. The melamine can be transformed into different intermediates and meanwhile release ammonia at different temperatures [24]. Several

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intermediates such as melam ((C3N3)2(NH2)4(NH)), melem (C6N7(NH2)3), melon ((C6N7)3(NH2)3(NH)3) and graphitic carbon nitride materials (g-C3N4) can be produced during a series of condensations with the increase of temperature. Then, g-C3N4 can decompose into various chemically reactive carbon nitride species such as C3N3+, C2N2+, C3N2+, and CN2+ over 600 ℃[25-28]. These highly active species can reduce FeyNi1-yFe2O4 into corresponding alloy (Fe2+yNi1-y). The overall reactive processes can be speculated as follows:

C3N3(NH2)3 C6N7(NH2)3

-NH3 -NH3

(C3N3)2(NH2)4(NH) (C6N7)3(NH2)3(NH)3

-NH3 -NH3

C6N7(NH2)3 g-C3N4

4C3N4 + 3FeyNi1-yFe2O4 → 3Fe2+yNi1-y + 8N2 + 12CO

It is worth to note that no carbide ((Fe, Ni)3C) exists in all products synthesized in this study, which is different from our previous report about Fe/Fe3C nanocomposites [29]. Especially, carbide is still not formed when the molar ratio melamine : AP is increased from 4:1 to 6:1 and the reaction time is shortened from 3 h to 2 h. The reason is that the fromation energy of Ni substituted Fe3C is larger than that of unsubstituted Fe3C and it can not stably exist [30]. 3.4 Magnetic properties The magnetic properties of the nanoparticles are investigated by VSM at room temperature. Fig. 6 presents the magnetization curves of [email protected] nanoparticles synthesized with different Ni/Fe ratios. It can be seen that all five curves show small hysteresis loops and the samples all exhibit ferromagnetic behavior at room temperature. Their special saturation magnetization MS and coercivity HC are listed in Table 1. It is found that the MS varies in the range of 78-132 emu/g and HC in the range of 148-175 Oe. Among the five samples, [email protected] synthesized with Ni/Fe = 0.2 (Fe83Ni17(C)) has the highest MS 132 emu/g. [email protected] synthesized with Ni/Fe = 0.4 (Fe71Ni29(C)) has the lowest MS 78 emu/g. The MS of [email protected] decreases obviously when the Ni/Fe ratio is slightly raised from 0.2 to 0.4, which can be ascribed to the structure and composition changes of Fe-Ni alloy. Ferromagnetic bcc Fe-Ni is dominant in Fe83Ni17(C), while paramagnetic fcc Fe-Ni in Fe71Ni29(C) (see above Fig. 2). Only fcc structure exists in the alloy with 0.6 ≤ Ni/Fe ≤ 1.0 (see above Fig. 2). With the increase of Ni/Fe ratio in the 0.6-1.0 range, the MS firstly increases and then decreases. This trend is similar to bulk fcc Fe-Ni alloy [31]. Among the three samples, [email protected] synthesized with Ni/Fe = 0.8 (Fe56Ni44(C)) has the highest MS 120 emu/g, which is smaller than the maximum value 168 emu/g of bulk Fe-Ni [32].

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Fig. 6 Magnetization curves of [email protected] nanoparticles synthesized with different Ni/Fe ratios at constant molar ratio melamine : AP = 4:1 at 650 ℃ for 3 h. Ni/Fe = 0.2 (a), 0.4 (b), 0.6 (c), 0.8 (d) and 1.0 (e).

Table Magnetic properties of [email protected] nanoparticles synthesized with different Ni/Fe ratios at constant molar ratio melamine : AP = 4:1 at 650 ℃ for 3 h

4. Conclusions We have demonstrated a simple approach to solid-state synthesis of carbon-encapsulated Fe-Ni alloy nanoparticles using melamine as carbon source. [email protected] nanoparticles with different Ni/Fe were synthesized throng the reactions of the melamine with hydrothermally prepared FexNi1-x/FeyNi1-yFe2O4. The Fe-Ni alloys in synthesized samples have bcc and/or fcc structures. No carbide impurity exists in all samples. The size of [email protected] nanoparticles ranges from 20 nm to 100 nm and the encapsulation graphite shows clear nanolayered structure. Magnetic measurements reveal that the synthesized samples all exhibit ferromagnetism at room temperature. The sample [email protected] with Ni/Fe = 0.2 has the highest MS 132 emu/g. Due to the simplicity of the experimental apparatus and the wide availability of melamine, the present approach can be applied to synthesize other carbon-encapsulated nanomaterials.

Acknowledgement This work is supported by the National Natural Science Foundation of China.

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near-infrared agents, Nat. Mater. 2006, 5, 971-976. [16] E. Holodelshikov, E. Perelshtein and A. Gedanken, Synthesis of Air Stable FeCo/C Alloy Nanoparticles by Decomposing a Mixture of the Corresponding Metal-Acetyl Acetonates under Their Autogenic Pressure, Inorg. Chem. 2011, 50, 1288-1294. [17] A. B. Wu, X. W. Yang and Hua Yang, [email protected] nanocomposites: preparation and magnetic properties, Dalton Trans., 2013, DOI: 10.1039/C3DT32639J. [18] H. P. Li, N. Q. Zhao, C. N. He, C. S. Shi, X. W. Du and J. J. Li, J. Alloy Compd. 458 (2008) 130-133. [19] W.Teunissen, MF de Groot, J. Geus, O. Stephan, M. Tence, C. Colliex, The Structure of Carbon Encapsulated NiFe Nanoparticles,J. Catal. 2001, 204, 169-174. [20] A. M. Nartowski, I. P. Parkin, A. J. Craven and M. MacKenzie, Adv. Mater. 10 (1998) 805-808. [21] A. M. Nartowski, I. P. Parkin, M. MacKenzie and A. J. Craven, J. Mater. Chem. 11 (2001) 3116-3119. [22] J. B. Wiley and R. B. Kaner, Science 255 (1992) 1093-1097. [23] E. G. Gillan and R. B. Kaner, Chem. Mater. 8 (1996) 333-343. [24] B. Jurgens, E. Irran, J. Senker, H. Muller, W. Schnick, J. Am. Chem. Soc. 125 (2003) 10288-10300. [25] V. N. Khabashesku, J. L. Zimmerman and J. L. Margrave, Chem. Mater. 12 (2000) 3264-3270. [26] E. G. Gillan, Chem. Mater. 12 (2000) 3906-3912. [27] B. V. Lotsch and W. Schnick, Chem. Mater. 17 (2005) 3976-3982. [28] H. Z. Zhao, M. Lei, X. A. Yang, J. K. Jian and X. L. Chen, J. Am. Chem. Soc. 127 (2005) 15722-15723. [29] A. B. Wu, D. M. Liu, L. Z. Tong, L. X. Yu and H. Yang, Magnetic properties of nanocrystalline Fe/Fe3C composites, CrystEngComm, 2011, 13, 876-882. [30] X. R. Wang and M. F. Yan, Effect of cobalt and nickel on the structure stability for Fe3C first-principles calculations, Int. J. Mod. Phs. 2009, 23, 1135-1140. [31] R. N. Panda, N. S. Gajbhiye, Magnetic Properties of nano-crystalline γ-Fe-Ni-N nitride systems, J. Appl. Phys. 1999, 6, 3295-3302. [32] X. G. Li, A. Chiba, S. Takahashi, Preparation and magnetic properties of ultrafine particles of Fe-Ni alloys, J. Magn. Magn. Mater. 1997, 170, 339-345.

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Fe-Ni(C) alloy nanoparticles were fabricated with different Ni/Fe ratio by an solid-state route using melamine as carbon source. Their structure, morphology and magnetic properties were researched by XRD, TEM, HRTEM and VSM. The highest MS of Fe-Ni(C) with Ni/Fe = 0.2 is 132 emu/g.

Figure cations Fig. 1 XRD patterns of the as-prepared iron-nickel alloy/nickel ferrite (FexNi1-x/FeyNi1-yFe2O4) nanocomposites.

Fig. 2 XRD patterns of [email protected] nanoparticles synthesized with different Ni/Fe ratios at constant molar ratio melamine : AP = 4:1 at 650 ℃ for 3 h.

Fig. 3 XRD patterns of [email protected] nanoparticles synthesized with different Ni/Fe ratios at constant molar ratio melamine : AP = 6:1 at 650 ℃ for 2 h.

Fig. 4 TEM images of [email protected] nanoparticles synthesized with Ni/Fe = 0.4 at constant molar ratio melamine : AP = 4:1 at 650 ℃ for 3 h: (a) a low-magnification TEM image; (b) a high-magnification image; (c) a HRTEM image of the square region in (b).

Fig. 5 TEM images of [email protected] nanoparticles synthesized with Ni/Fe = 1.0 at constant molar ratio melamine : AP = 4:1 at 650 ℃ for 3 h: (a) a typical low-magnification TEM image; (b) a high-magnification image; (c) a HRTEM image of the square region in (b).

Fig. 6 Magnetization curves of [email protected] nanoparticles synthesized with different Ni/Fe ratios at constant molar ratio melamine : AP = 4:1 at 650 ℃ for 3 h. Ni/Fe = 0.2 (a), 0.4 (b), 0.6 (c), 0.8 (d) and 1.0 (e).

Table Magnetic properties of [email protected] nanoparticles synthesized with different Ni/Fe ratios at constant molar ratio melamine : AP = 4:1 at 650 ℃ for 3 h

1

Fig. 1 XRD patterns of the as-prepared iron-nickel alloy/nickel ferrite (FexNi1-x/FeyNi1-yFe2O4) nanocomposites.

Fig. 2 XRD patterns of [email protected] nanoparticles synthesized with different Ni/Fe ratios at constant molar ratio melamine : AP = 4:1 at 650 ℃ for 3 h.

2

Fig. 3 XRD patterns of [email protected] nanoparticles synthesized with different Ni/Fe ratios at constant molar ratio melamine : AP = 6:1 at 650 ℃ for 2 h.

3

(b)

(a)

(c)

0. 21 nm

0.34 nm Fig. 4 TEM images of [email protected] nanoparticles synthesized with Ni/Fe = 0.4 at constant molar ratio melamine : AP = 4:1 at 650 ℃ for 3 h: (a) a low-magnification TEM image; (b) a high-magnification image; (c) a HRTEM image of the square region in (b).

4

(a)

(b)

(c ) 0.34 nm

0. 21 nm

Fig. 5 TEM images of [email protected] nanoparticles synthesized with Ni/Fe = 1.0 at constant molar ratio melamine : AP = 4:1 at 650 ℃ for 3 h: (a) a typical low-magnification TEM image; (b) a high-magnification image; (c) a HRTEM

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image of the square region in (b).

150

150

100

100

Magnetization(emu/g)

Magnetization(emu/g)

a

Ni/Fe = 0.2 50

0

-50

-100

Ni/Fe = 0.4

b

50

0

-50

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-150

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-5000

0

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-10000

-5000

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0

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10000

Magnetic Field(Oe)

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100

c

Ni/Fe = 0.6

Magnetization(emu/g)

Magnetization(emu/g)

150

50

0

-50

-100

d

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Ni/Fe = 0.8 50

0

-50

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150

e

100

Ni/Fe = 1.0 50

0

-50

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-150 -10000

-5000

0

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10000

Magnetic Field(Oe)

Fig. 6 Magnetization curves of [email protected] nanoparticles synthesized with different Ni/Fe ratios at constant molar ratio

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melamine : AP = 4:1 at 650 ℃ for 3 h. Ni/Fe = 0.2 (a), 0.4 (b), 0.6 (c), 0.8 (d) and 1.0 (e).

Table Magnetic properties of [email protected] nanoparticles synthesized with different Ni/Fe ratios at constant molar ratio melamine : AP = 4:1 at 650 ℃ for 3 h

Ni/Fe

Sample (theoretical composition)

MS (emu/g)

HC (Oe)

0.2

Fe83Ni17(C)

132

148

0.4

Fe71Ni29(C)

78

174

0.6

Fe62Ni38(C)

86

175

0.8

Fe56Ni44(C)

120

174

1.0

Fe50Ni50(C)

109

169

7