Effect of bismuth doping on the structural and magnetic properties of zinc-ferrite nanoparticles prepared by a microwave combustion method

Effect of bismuth doping on the structural and magnetic properties of zinc-ferrite nanoparticles prepared by a microwave combustion method

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Author’s Accepted Manuscript Effect of bismuth doping on the structural and magnetic properties of zinc-ferrite nanoparticles prepared by a microwave combustion method Morteza Zargar Shoushtari, Akram Emami, Seyed Ebrahim Mosavi Ghahfarokhi www.elsevier.com/locate/jmmm

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S0304-8853(16)31045-9 http://dx.doi.org/10.1016/j.jmmm.2016.06.080 MAGMA61601

To appear in: Journal of Magnetism and Magnetic Materials Received date: 9 June 2016 Revised date: 27 June 2016 Accepted date: 27 June 2016 Cite this article as: Morteza Zargar Shoushtari, Akram Emami and Seyed Ebrahim Mosavi Ghahfarokhi, Effect of bismuth doping on the structural and magnetic properties of zinc-ferrite nanoparticles prepared by a microwave combustion method, Journal of Magnetism and Magnetic Materials, http://dx.doi.org/10.1016/j.jmmm.2016.06.080 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Effect of bismuth doping on the structural and magnetic properties of zinc-ferrite nanoparticles prepared by a microwave combustion method Morteza Zargar Shoushtari1*, Akram Emami1, Seyed Ebrahim Mosavi Ghahfarokhi1

1

Department of Physics, Shahid Chamran University of Ahvaz, I R Iran

*

Corresponding author: Tell :+98 9163108770, Fax:+98 6133738310 , E-mail address: zargar @ scu.ac.ir

Abstract In this study, we examine the bismuth doping effect on the structural, magnetic and microstructural properties of zinc-ferrite nanoparticles (ZnFe2-xBixO4 x= 0.0, 0.02, 0.04, 0.06, 0.1, 0.15) which have been prepared by a microwave combustion method. The structural, morphological and electromagnetic properties and also Curie temperature of the samples were examined by x-ray powder diffraction (XRD), field emission scanning electron microscope (FESEM), vibrating sample magnetometer (VSM), and LCR meter, respectively. In order to measure the energy band gap, the FTIR spectra of the samples were also considered. The XRD patterns of the samples revealed that all of them are ZnFe2O4 structure and no additional peak was observed in their patterns. This implied that the samples were single-phase up to bismuth solubility of 0.15 in Zinc-Ferrite. The results of XRD patterns also showed that the value lattice parameter increases with increasing the bismuth doping. The FESEM results revealed an ascending trend in the size of the nanoparticles. Also considering the VSM results characterized that an increasing the bismuth doping leads to lower the saturation magnetization. The Curie temperatures of the samples were reduced as a result of increasing the amount of bismuth.

Keywords: zinc-ferrite nanoparticles; bismuth; magnetic properties; microwave combustion method

1. Introduction Scientific researches related to ferrites began at the 19th century. Thereafter, serious research considering the industrial applications of these materials were followed by two Japanese scientists named T. Takeshi and K. Yogoro and the results of their researches on copper and cobalt ferrites were published in 1932. Scientific research has been spread out after that, and other scientists did some experiments on various compounds of iron, nickel, manganese and zinc oxides and achieved good results

[1]. Zinc-ferrite nanoparticles are soft magnetic materials and widely used in microwave absorbers and gas sensors. Zinc-ferrite is a semiconductor material that is thermally and chemically stable, and could be an appropriate choice for applications such as photocatalysts [2], catalysts, magnetic resonance imaging [3], and pigments [4]. Since one of the methods for improving the properties of a ferrite is substitution of its elements placed in tetrahedral and octahedral sites with other elements such as Bi 0.2 Zn1.5 Fe1.4O 4 , Zn Mg Fe O , ZnY Fe O [2, 5, 6]. Ferrite properties vary according to magnetic or non-magnetic materials that are substituted. In this study, we investigated the bismuth doping effect on the structural, magnetic and microstructural properties of the zinc-ferrite nanoparticles (ZnFe2-xBixO4 with x= 0.0, 0.02, 0.04, 0.06, 0.1, 0.15) which have been prepared by a microwave combustion method. 1 x

x

2

4

x

2 x

4

2. Experimental detail To fabricate ZnBi x Fe 2 x O4 with x=0, 0.02, 0.04, 0.06, 0.1, 0.15, 0.2 samples via a microwave combustion method, raw materials of iron nitrate, zinc nitrate, bismuth nitrate and glycine with proper stoichiometry were chosen according to the following reaction: [Zn( Zn

) .6

]+( +…

)

(

)

+

(

)

+ [NH2CH2COOH] =

The amount of fuel was achieved as shown in Table .1. The proper stoichiometry of the reactant materials with the optimum amount of fuel (oxidation and reduction numbers must be equal) has been mixed. Materials were mixed together for an hour until a uniform blend was obtained. Then this mixture was put inside a microwave device with power 3100 W. After combustion and completing the reaction, a spongy foam sample was obtained. By using a mortar, the foam was slowly grinded until a soft powder was obtained. This job was carried out for an hour. This powder was washed three times with deionized water and then three times with ethanol and finally it exposed to 70 in oven for an hour to dry.

3. Results and discussion 3.1. XRD analysis

X-ray diffraction patterns of the magnetite (Fe3O4) and ZnFe2-xBixO4(x=0.0, 0.02, 0.04, 0.06, 0.1, 0.15) nanoparticles are shown in Fig. 1. They have been fabricated

with the same method as the Bi-Zn ferrite nanoparticles in order to compare them. The second phase (α-Fe2O3) appears in the magnetite (Fe3O4) sample which has been seen in many synthesized materials such as hexagonal barium ferrite [7], however it doesn’t appear in the other samples. The increase of bismuth amount leads to a larger lattice constant of the samples (see Fig. 2) and so an increased the unit cell volume. Table.1 Different amounts of fuel used in combinations. Samples

NH2CH2COOH (g)

Fe3O4 ZnFe2O4

1.08 1.160

ZnFe1.98Bi0.02O4

1.159

ZnFe1.96Bi0.04O4

1.157

ZnFe1.94Bi0.06O4

1.157

ZnFe1.9Bi0.1O4

1.154

ZnFe1.85Bi0.15O4

1.151

The increasing of lattice constant is due to larger radius of bismuth cations (1.03 Å) than the iron cations (0.67 Å). This variation of the lattice constant means that the substitution of Bi was occurred. The similar results have been reported by other researchers [8, 9].

Fig. 1. XRD patterns of ZnBixFe2O4.

Fig. 2. The lattice parameter versus bismuth concentration.

If the bismuth concentration increases more than x 0.15 , the first impurity phase (Fe) appeared in x 0.2 , and the second impurity phase ( Bi 2O3 ) appeared in x 0.3 ; This shows that the solubility limit of the mentioned compound could be up to x 0.15 . Fig. 3 shows the appearance of the first and second impurity phases with increasing the bismuth concentration.

Fig. 3. X-ray diffraction pattern of the samples with impurity phases of Fe and Bi2O3.

Table 2 shows various parameters for samples obtained from the X-ray diffraction patterns of the zinc-bismuth ferrite the samples. The average crystallite size can be determined via Scherrer formula (1), unit cell volume of the cubic lat`tice (V a 3 ) where a is the cubic lattice constant which also can be determined by equation (2). In the relation (2-4), (hkl) are Miller indices, d is the distance between the planes.

(1) ƛ is X-ray wavelength; β is the peak width of the diffraction peak profile at half maximum height; and θ is the diffraction angle in radians. a  d l 2  h2  k 2

(2)

Table.2 Various parameters obtained from X-ray diffraction of the zinc-bismuth ferrite nanoparticles.

Samples

a (Å)

V (Å)3

L (Ȧ)

B-O(Å)

A-O (Å)

LB (Å)

LA (Å)

rB (Å)

rA (Å)

ZnFe2O4 ZnFe1.98Bi0.02O4 ZnFe1.96Bi0.04O4 ZnFe1.94Bi0.06O4 ZnFe1.9Bi0.1O4 ZnFe1.85Bi0.15O4

8.374 8.379 8.381 8.384 8.388 8.724

587.2 588.2 588.6 589.3 590.1 598.4

20 19 24 23 25 19

2.093 2.094 2.095 2.096 2.097 2.106

1.8130 1.8141 1.8145 1.8151 1.8160 1.8244

2.960 2.962 2.963 2.964 2.965 2.979

3.626 6.628 3.629 3.630 3.632 3.648

0.7435 0.7447 0.7452 0.7460 0.7470 0.7567

0.4630 0.4641 0.4645 0.4651 0.4660 0.4744

The ionic radii of the tetrahedral site (rA), the ionic radii of the octahedral site (rB), jump length in tetrahedral site (LA), jumping length of the electron in octahedral site (LB), tetrahedral bond length (A-O), octahedral bond length (B-O) which have been obtained from equations (3-8) [10]. 1 rA  (U  )a 3  r (O 2 ) 4

(3)

5 rB  (  U )a  r (O 2 ) 8

(4)

LA  a(

3 ) 4

(5)

LB  a(

2 ) 4

(6)

1 A  O  (U  )a 3 4

(7)

5 B  O  (  U )a 8

(8)

U is the oxygen ion parameter and is equal to 3 / 8 , and r (O-2) is the oxygen ion radius equaled to 1.35 Å. The results of table.1 suggest that (rA ،rB ) and (B-O, AO) increase with increasing the bismuth concentration. The jumping length in tetrahedral and octahedral sites which shows the distance between the magnetic ions increases with increasing bismuth [10]. 3.2. Energy dispersive X-ray (EDX) analysis EDX spectra of pure and bismuth doped zinc ferrite, ZnFe2-xBixO4 system (x= 0.0, 0.02, 0.04, 0.06, 0.1, 0.15) are shown in Fig. 4 (a-f). Fig. 4a, shows the peaks of Fe, Zn and O elements in the pure ZnFe2O4 and Fig. 4 (b-f), shows peaks of Fe, Zn, Bi and O elements for Bi- doped ZnFe2O4 samples. it is interesting to note that the preparation condition completely favor the formation of mixed ferrite and allow us to study effect of increasing Bi content on the properties of the zinc ferrite. The above mentioned results confirmed the formation of the pure and Bidoped ZnFe2O4 phases.

3.3. FTIR Analysis Fig. 5a shows the spectra of samples with wavelength 400-4000 cm-1. To investigate the functional groups in the compounds FTIR analysis has been used. The bond of each composition vibrates in a certain wavenumber due to the energy of radiation, and this phenomena shows itself by absorption in the spectrum. In the 1

FTIR spectrum (Fig. 5b) that are in the range 358-450 and 500-600 cm two peaks can be observed. These peaks are related to the main bands of spinel structure which the first and second peak are according to the stretching vibrations of the unit cell of spinel in tetrahedral sites, and oxygen-metal vibrations in octahedral sites, respectively. So, after adding bismuth, the peaks were the same as the ones in the ferrite spectrum, but this time they moved slightly to right. There is two bonds related to the stretching vibrations of O-H in the frequency ranges 9001

1

1000 cm and 1000-1600 cm . In the frequency of 1706, there are some stretching vibrations related to the double bond C=O. The change in the sites of the peaks depends to the construction method and preparation conditions [11, 12]. Because the peaks change towards the smaller wavenumbers (K) (see Fig. 5b), we 3

conclude that Bi cations have placed in the octahedral sites properly. Since the frequency has an inverse relationship with bond length, so this increased bond length can be due to introducing an element with a larger ionic radius .

Fig.4 EDX spectra ZnFe2-XBixO4(X= 0.0,0.02,0.04,0.06,0.1,0.15

Fig. 5. FTIR spectra of powder samples, (a) all of the samples, (b) three samples.

3.4. FESEM analysis FESEM images of the powder samples ZnFe2O4, ZnFe1.98Bi0.02O4, and ZnFe1.94Bi0.06O4 are shown in Fig.6. As one can see that the ferrite powder nanoparticles have spherical form and they are stuck together and have a massive shape. This agglomeration is due to the magnetic property of these nanoparticles and also nanoscale size of them that causes the surface energy of the particles to increase. The average size of the nanoparticles is 3247 nanometer. It has been observed that the size of the particles has increased with increasing the bismuth amount; because by increasing the bismuth value the ionic distance between the B-B cations becomes larger [13].

Fig. 6. The FESEM images of the samples.

3.5. VSM analysis Fig. 7 shows the magnetization curves of the Fe3O4 and ZnFe2O4 samples. Adding Zn to Fe3O4 causes the saturation magnetization level to decrease dramatically, which is due to the replacing of a ferromagnetic element (Fe) with a diamagnetic element (Zn).

Fig.7 Hysteresis loop of the fabricated samples of magnetite and zinc-ferrite.

Fig.8 shows the magnetization curve of the samples ZnBixFe2-xO4 which have been doped with bismuth. The very narrow hysteresis curves revealed that the samples are very soft magnetic materials. Table 3 shows the saturation magnetization magnitudes (Ms) of the samples. According to the Neil theory, the saturation magnetization of a ferrite sample is equal to the difference magnetization of the tetrahedral and octahedral sublattices (Ms=MB-MA). So, when Fe+3 ferromagnetic ions with magnetic moments of 5µB are replaced by Bi+3 diamagnetic ions with magnetic moment of 0

µB in octahedral sites, the magnitude of the saturation magnetization decreases; and the decreased magnetic moment causes the total magnetization to decrease. On the other hand, because the Fe+3 ions with radii of 0.67 Å are replaced with the Bi+3 ions which have a larger radius (1.03 Å), the distance between the ions increases and this causes the exchange interactions to weaken and therefore the magnetization decreases. Also we can say that, when a ferrite is subjected to an external field, the spins of the atoms that are placed in octahedral sites (such as Fe+3) point in the applied field direction, and the spins of the atoms that are placed in the tetrahedral sites have antiparallel directions compared to the direction of the external field. So, introducing bismuth and bringing out Fe+3 in octahedral sites causes the magnetization saturation to decrease [14]. The variation of the saturation magnetization (Ms) and the remanence magnetization (Mr) of the samples related to the bismuth concentration (x) are shown in the Fig.9a and Fig.9b, respectively. The coercivity field of the samples also is shown in the Fig.10.

Fig. 8. Fabricated hysteresis loops ZnBixFe2-xO4 (x=0.0, 0.02, 0.04, 0.1 and 0.15), (a): in the range of up to 12000 Oe, (b) in the range of up to 600 Oe.

Table.3. The parameters of the saturation magnetization, the remained magnetization and the coercivity. Samples

Hc (Oe)

Mr (emu/g)

MS (emu/g)

Fe3O4 ZnFe2O4

41 40.5

12.94 7.77

64.97 33.85

ZnFe1.98Bi0.02O4 ZnFe1.96Bi0.04O4 ZnFe1.94Bi0.06O4 ZnFe1.9Bi0.1O4 ZnFe1.85Bi0.15O4

40 41 39.5 40 40

7.50 7.19 6.08 6.12 5.88

32.67 32.62 31.52 30.50 29.50

Fig.9. The variation of the saturation magnetization (Ms) and the residual magnetization (Mr) of the samples related to the bismuth concentration (x).

Fig.10. Hc of the samples vs magnetic field.

3.6. Measuring the Curie temperatures of the samples

A typical sample for measuring Curie temperature using the furnace and LCR meter equipment arrangement is shown in Fig. 11. The results of the Curie temperatures of the samples ZnBixFe2-xO4 as a function of Bi (x) are shown in Figs. 12 and 13. This results shows that the Curie temperature decreases with increasing the bismuth amount, this can be due to the increasing lattice parameter which could causes the distance between the interaction ions to decrease in tetrahedral and octahedral sites. As a result of this, the interaction strength decreases. The Curie temperature could be related to the super-transactional interactions between the Fe+3 ions -which are placed in tetrahedral and octahedral sites- and also to the crystal structure of the composition, and has a little dependency to the microstructures such as grain size and porosity. In fact, the Curie temperature is related to the exchange interaction between the ions that are placed in A, and B sublattices. According to Neil theory, interaction A-B, is the dominant interaction of the ferrites. So we can conclude that, the Curie temperature is a function of the interaction strength between A-B. Since the bismuth is a diamagnetic element, its magnetic moment is zero and when we substitute Fe (which its magnetic moment is 5µB) with it, the interaction A-B decreases in the composition, and as a result of this, the Curie temperature decreases. In a the same research, the Curie temperature has been obtained to be 520K [15- 17]. The variations have been shown.

Fig.11. A typical sample for measuring the Curie temperature, core is zinc-bismuth ferrite, with a coil around it.

Fig.12. Magnetic permeability as a function of temperature, for ZnBixFe2-xO4 samples.

Fig.13. The Curie temperature vs Bi (x).

3.6. Conclusion In this research, zinc-ferrite nanoparticles doped with bismuth (ZnBixFe2-xO4 with x=0.0, 0.02, 0.04, 0.1 and 0.15) have been synthesized using the microwave combustion method. Considering the results of X-ray diffraction showed the formation of a cubic spinel structure in the absence of impurity in the samples up to the solubility of Bi for x=0,15. FESEM images represent an increasing trend in the sizes of the particles, with increasing bismuth. From the VSM measurements one can see that with increasing the Bi amount, the saturation magnetization and the residual magnetization decrease, which is because the iron ions with larger magnetic moments are replaced by Bismuth ions with a smaller magnetic moment. The absorption bands of the FTIR patterns in the intended range for ferrites which a confirmation of the spinel structure formation can be seen. Also, variation of the absorption band related to the metal-oxygen vibrations in octahedral sites represents the substitution of Fe ions with Bi ions in the original structure of zinc ferrites. The result of Curie temperatures shows a decreasing trend in the zincbismuth ferrite with increasing the bismuth amount.

Acknowledgements The authors are thankful to Shahid Chamran University of Ahvaz that has supported this project.

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Highlights  The lattice constant of Bi-Zn ferrite samples increases linearly about 4 % with increasing Bi amount.  The solubility of Bi in ZnFe2O4 found about 0.15.  The saturation magnetization and the remanence magnetization decrease linearly.  The Curie temperatures of the samples were reduced as a result of increasing the amount of bismuth.