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Effect of In substitution on structural, dielectric and magnetic properties of CuFe2O4 nanoparticles
Accepted Manuscript Effect of In substitution on structural, dielectric and magnetic properties of CuFe2O4 Nanoparticles V. Manikandan, A. Vanitha, E. Ranjith Kumar, J. Chandrasekaran PII: DOI: Reference:
S0304-8853(17)30184-1 http://dx.doi.org/10.1016/j.jmmm.2017.02.030 MAGMA 62490
To appear in:
Journal of Magnetism and Magnetic Materials
Received Date: Revised Date: Accepted Date:
20 January 2017 16 February 2017 19 February 2017
Please cite this article as: V. Manikandan, A. Vanitha, E. Ranjith Kumar, J. Chandrasekaran, Effect of In substitution on structural, dielectric and magnetic properties of CuFe2O4 Nanoparticles, Journal of Magnetism and Magnetic Materials (2017), doi: http://dx.doi.org/10.1016/j.jmmm.2017.02.030
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 proof before it is published in its final 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 In substitution on structural, dielectric and magnetic properties of CuFe2O4 Nanoparticles V. Manikandana, A.Vanithab, E. Ranjith Kumarc* , J. Chandrasekarand a,b,
Department of Physics, Government College of Technology, Coimbatore, Tamilnadu-13, India c
Department of Physics, Dr. NGP Institute of Technology, Coimbatore, Tamil Nadu-48, India
d
Department of Physics, Sri Ramakrishna Mission Vidyalaya College of Arts & Science, Coimbatore, Tamilnadu-20, India
Abstract Cu ferrite and In substituted Cu ferrite has been successfully synthesized (InxCu1xFe2O4;
x=0.0, 0.2) at pH 11 and sintered at 300°C, 600°C, 900 °C. From the XRD analysis ,
the ferrite phase is confirmed and particle size varied from 28 to 37 nm owing to sintering temperature. TEM microstructure confirms that samples having polycrystalline nature because of superimposition of bright spots. FT-IR spectra exhibit general behaviour of ferrite. The significant change of dielectric constant has been noticed from dielectric measurement while substitution of In element. The room temperature magnetic measurements demonstrate a solid impact of sintering temperature and In substitution on saturation magnetization and coercivity.
Keywords: Ferrite nanoparticle, Dielectric properties, XRD, VSM, TEM
*Corresponding author: [email protected]
1. Introduction Nano ferrite materials because of their peculiar properties are massively used in applications such as electrical appliances, automotive, tele-communication circuit components, microwave devices, recording heads etc[1]. Among the different spinel ferrites,
1
Cu ferrite has quite interesting versatile material and highly outstanding due to its high saturation magnetization. Also, it displays phase and semiconducting properties changes that leads to electrical switching and structural variation when treated under various sintering temperature. It is extensively used for variety of applications in LPG gas sensing, photo catalytic applications, recording devices and ferrofluids[2-5]. Generally, Cu ferrite is form in cubic and tetragonal structure[6]. The tetragonal structure has smaller magnetic moment than that of cubic structure, because there are more Cu ions located at tetrahedral sites in cubic structure [7-8]. Moreover, Indium (In) is utilized as low-melting fusible alloys and also used as a covering plate for bearings and metallic surfaces. It may be used to corrosion-resistant surface: when evaporated and allowed to deposit on glass, it produces a mirror. In substituted Cu ferrite properties depend on numerous factors such as method of preparation, stoichiometric ratio, sintering temperature, and milling. Conventional methods are used to synthesizing nano ferrite materials such as double sintering ceramic technique[9], citrate precursor[10], sol-gel combustion[11], thermal method[12], chemical co-precipitation method[13] etc. Among these techniques, chemical co-precipitation method is in expansive and suitable for laboratory environment. In this present work, we report and discuss the impact of sintering temperature and In substitution on structural, dielectric and magnetic properties on Cu ferrite.The deliberated properties of the samples are discussed below.
2. Materials and Method The Cu ferrite and In substituted Cu ferrite InxCu (1−x)Fe2O4(x=0, 0.2) is primed by mixing of Indium chloride [InCl3·6H2O], cupric chloride [CuCl2·2H2O] and anhydrous ferric chloride [FeCl3.9H2O] dissolved in de-ionizedwater. Sodium hydroxide solution was used as pH varying agent. Throughout synthesis, pH 11was maintained. The brown precipitate is scrupulously cleaned with de-ionized water to remove chlorine and other impurities. 2
Furthermore, the samples are dried for 24 hours in a hot air oven and brown powders are obtained. The dried powders are put into a mortar and grinded manually for 20minutes to obtain powder. Then samples are sintered at 300°C, 600°C, and 900°C.
2.1. Instrument used for Characterization Nano ferrite powder was exposed to Rigaku X-ray diffraction (Model ULTIMA III) to interpret the structural. Crystalline morphology can be visualized by using Scanning electron microscope (SEM with EDX- JEOL 5600V). Functional group analysis was performed by using Fourier transform infrared spectroscopy(Model-MAGNA 550). Crystalline nature was recorded with help of transmission electron microscopy and selected area electron diffraction. The dielectric properties of sintered samples were characterized by LCR meter (HIOKI 353250 LCR). Magnetic properties was analysed by using Vibrational Sample Magnetometer (Lakshore -7410).
3. Results and Discussion 3.1. Structural analysis Fig.1.depicts the XRD patterns of Cu ferrite and In substituted Cu ferrite sintered at different temperatures. The existence peaks corresponds to the characteristic of interplanar spacing between (111), (220), (311), (440), (511), (422) and (400) planes with cubic phase. These peaks are well indexed with JCPDS card (#77-0010). After substitution of In on Cu ferrite, it is observed that peak positions are slightly shifted towards higher angle diffraction[14]. This peak shift is due to smaller ionic radius of Cu than In element. The most privileged ferrite peak of (311) confirms the growth of Cu ferrite and In substituted Cu ferrite. While increase of sintering temperature, XRD patterns of Cu ferrite and In substituted Cu ferrite phases are formed. Thus, the crystalline nature was improved with respect to the sintering temperature. From XRD results, particle size is increased with increase of sintering temperatures. Following substitution of In element, particle size is increased and also lattice constant increased and then decreased with respect to sintering temperature. It is attributed to the difference of ionic radius of Cu and In element[15-16] . The particle size and lattice constant is strongly subjective by sintering temperature and also substitution of In element. The average particle size is calculated using Debye Scherrer formula[17]. The lattice parameter can be calculated using the formula[18]. XRD parameters are listed in Table.1.
3
1/d2= h2+k2+ l2 / a2
Table.1. XRD and VSM Parameters Parameters CuFe2O4 Temperature (°C)
Particle size (nm) Lattice parameter (°A) Coercivity (G) Remnant (emu/g) Saturation (emu/g) Remnant ratio
InxCu1-xFe2O4 (x=0.2)
300 28 8.377
600 33 8.374
900 34 8.288
300 -
600 26 8.401
900 37 8.391
67.60 0.00 0.03 0.06
694.73 4.33 10.43 0.41
673.84 87.47 133.52 0.65
121.18 0.00 0.12 0.04
204.76 3.07 9.20 0.33
137.90 5.10 21.24 0.24
4
Fig.1. XRD patterns of (a) CuFe2O4, (b) In0.2Cu0.8Fe2O4
3.2. Microstructure With EDAX Analysis The microstructure of Cu ferrite and In substituted Cu ferrite (X=0.0, 0.2) sintered at 600°C and 900°C is shown in Fig.2 (a-c). The above sample has been visualized through a scanning electron microscope. It is observed that the particle size is improved with increase of sintering temperature and owing to the increased agglomeration of the particle with rise of sintering temperature, particle seemed to have a cubic and spherical structure. It is due to the effect of reaction time and sintering temperature[19-20]. The compositional analysis of Cu ferrite and In substituted Cu ferrite has been examined through Energy dispersive analysis spectrum (EDX) as depicted in fig.3(a-b). The above spectrum confirms the existence of O, Fe, In and Cu elements. The atomic percentage of element is nearly close to stiochiometry value. The experimental values of the atomic percentage have some oxygen insufficiency.
5
Fig. 2.SEM microstructure of (a) CuFe2O4 sintered at 900°C, (b-c) In0.2Cu0.8Fe2O4 sintered at 900°C and 600°C
Fig. 3.EDX spectrum of (a) CuFe2O4, (b) In0.2Cu0.8Fe2O4 sintered at 900°C 6
3.3. FTIR Analysis FT-IR spectra of sintered In1-xCuxFe2O4 nanoparticles (with x=0.0, 0.2) in the range of 400 to 4000 cm-1 are shown in Fig.4 (a-b) respectively. The strongest absorption shoulders (ʋ1 and ʋ2) are observed in the range of 470-475 and 600-570 cm-1 respectively. These shoulders are ascribed to the stretching vibration owing to interaction between the cation and oxygen atom in tetrahedral and octahedral sites respectively. The variation between ʋ1 and ʋ2 is because of the adjustments in bond length (Fe-O) at the octahedral and tetrahedral sites[21]. The main absorption shoulders at 470-475 cm-1 represent the stretching vibration of tetrahedral sites, while the other shoulders at 600-570 cm-1represent the octahedral sites which is a normal behaviour of ferrite material. The ʋ1shoulder gets shifted to higher frequency with addition of In elements and sintering temperature, due to stretching of Fe-O bonds. At 300 °C, sintered samples have several absorption shoulders located at about 1630, 2360, 3430 in the region of 1500- 3500 cm-1. The absorption peak around 3430 cm-1 and 1630 cm-1corresponds to stretching mode of O-H group of absorbed water and H-O-H bending vibration of residual water[22]. In addition to these, the band at 2360 cm-1 which is attributed to atmospheric[22] CO2. At 600 °C, shoulders are reduced and only two shoulders are present. Due to the sintering temperature, shoulders are reduced and the crystalline nature starts to grow in the region. At 900 °C, only one shoulder is present. Hence, the above shoulder indicates the improved crystalline nature. From FT-IR results, the crystalline nature depends on absorption peak and sintering temperature.
Fig. 4. FT-IR Spectrum of (a) CuFe2O4, (b) In0.2Cu0.8Fe2O4
7
3.4. TEM Analysis The microstructure and SAED pattern of the Cu ferrite and In substituted Cu ferrite nanoparticles sintered at 900°C has been examined through transmission electron microscope and the results are shown in fig.5(a-d). TEM microstructure of Cu ferrite and In substituted Cu ferrite shows an irregular cubic and spherical shape. The average particle size is estimated in the range of 30 to 50 nm. This average particle size is in good agreement with that obtained from XRD results. At high sintering temperature, the particles gets agglomerated due to surface energy as some degree of agglomeration is inevitable in nanoparticles preparation. From SAED pattern of Cu ferrite and In substituted Cu ferrite nanoparticles, the superimposition bright spot indicates polycrystalline nature of nanoparticles[23].
8
Fig. 5. TEM microstructure and SAED patterns of (a-c) CuFe2O4, (b-d) In0.2Cu0.8Fe2O4 at 900°C
3.5. Dielectric studies The dielectric constant of Cu ferrite and In substituted Cu ferrite (x=0.0, 0.2) nanoparticles sintered at different temperatures with different log frequency are shown in Fig.6 (a-b). Fig.6 shows the difference of dielectric constant with log frequency and also the entire samples show frequency dependent feature, the frequency is inversely proportional to dielectric constant which is a typical behaviour in most of the ferrite materials. With increase of sintering temperature and particle size, the dielectric properties is reduced. This type of behaviour is observed in all samples. The lessen of dielectric constant can be explained on the 9
basis of hopping conduction between Fe3+ and Fe2+ and In3+, Cu2+ ions. According to koops theory, the lessen of dielectric constant with increase of frequency can also be expressed by due to the fact the solid as composed of good conducting grains and it's separated via poor conducting grains[24]. At low frequency, the dielectric constant is increased due to the compound dielectric structure and space charge polarization[25]. At high frequency, the dielectric constant decrease and becomes constant value due to the frequency of externally applied field increase gradually, however the quantity of Fe2+ ions is decreased on the material. The above decrease arises for the reason that beyond a certain frequency of externally applied field, the electronic interchange between ferrous and ferric ions cannot follow alternating field. From dielectric results, it is found that the dielectric constant value of Cu ferrite has higher than In substituted Cu ferrite. The reason is, reduction of ferrous ions due to the substitution element maybe at octahedral sites[26-27]. Thus, the electron transfer between ferrous and ferric ions can be trapped by substitution element. Due to this cause, space charge polarization is reduced and also dielectric constant. The dielectric constant varies inversely with sintering temperature. The dielectric constant is reduced while increasing the sintered temperature. However, quantity of Fe2+ ions is reduced at high sintering temperature which could be produced at high sintering temperature.
Fig. 6. Dielectric constant of (a) CuFe2O4, (b) In0.2Cu 0.8Fe2O4
10
3.6. VSM Analysis The hysteresis loop of Cu ferrite and In substituted Cu ferrite nanoparticles (X=0.0, 0.2) are shown in fig.7 (a-f). The magnetic properties such as saturation magnetization, remanant magnetization and coercivity are listed in Table. 1. The saturation magnetization values of In substituted Cu ferrite were found to be lower than the corresponding Cu ferrite. The above value of saturation magnetization is compared to that of Cu ferrite and it can be explained on the basis of core-shell model which explain that finite size effects of nanoparticles lead to canting, thereby reducing magnetization[28-29]. The obtained saturation value is increased with increase of sintering temperature. The changes in magnetic properties of In substituted Cu ferrite can be ascribed to the change of particle sizes, which is depends upon sintering temperature. From the results, an increase of sintering temperature, the particle size is changed from 28 to 37 nm. The saturation value of In substituted Cu ferrite is low when compared to Cu ferrite and the above decrease of saturation magnetization along with particle size can be accredited to the following: In ferrimagnetic structure, the magnetization of tetrahedral sublattice is antiparallel to that of the octahedral sublattice. However, the ferrite materials have non-collinear magnetic structure on the surface of the layer. The above growth of particle size causes an increase in the proportion of non-collinear magnetic structure in which magnetic moments are not aligned with direction of external magnetic field. The above increase of non-collinear magnetic structure decreases the saturation magnetization of In substituted Cu ferrite. From the VSM results, the coercivity value is increased as increase of sintering temperature and reaching an utmost value of 694 Oe at 600 °C and then decreased for any further increase of sintering temperature. The above fluctuation of coercivity value is affected by numerous factors such as magneto-crystallinity, microstrain, size distribution, anisotropy and magnetic domain size[30-32]. The small value of coercivity at 300 °C may be due to the presence of super paramagnetic nanoparticles[33]. In the multi domain system, the coercivity is inversely proportional to the particle size and also saturation magnetization. The remnant ratio values of sintered samples are in the range of 0.04 to 0.65 and the low value of remnant ratio indicates that material has an isotropic nature[20].
11
Fig. 7. Magnetic meaurement of (a-c) CuFe2O4, (d-f) In0.2Cu0.8Fe2O4
12
4. Conclusion Cu ferrite and In substituted Cu ferrite nanoparticles (InxCu 1-xFe2O4 ,X=0.0, 0.2) was synthesized by chemical co-precipitation method. The average particle size is in the range from 28-37nm. TEM microstructure confirms that samples have polycrystalline nature. FT-IR spectra shows normal behaviour of ferrite materials. The dielectric constant is reduced with respect to sintering temperature and substitution of In element. The VSM analysis report that the saturation magnetization increased gradually with increase of sintering temperatures, although coercivity initially increased, reaching an utmost value and then decreased.
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16
Peak shift is due to smaller ionic radius of Cu than In element. Particle size is increased and also lattice constant increased and then decreased with respect to sintering temperature. The average particle size is estimated in the range of 30 to 50 nm.
17
S0304-8853(17)30184-1 http://dx.doi.org/10.1016/j.jmmm.2017.02.030 MAGMA 62490
To appear in:
Journal of Magnetism and Magnetic Materials
Received Date: Revised Date: Accepted Date:
20 January 2017 16 February 2017 19 February 2017
Please cite this article as: V. Manikandan, A. Vanitha, E. Ranjith Kumar, J. Chandrasekaran, Effect of In substitution on structural, dielectric and magnetic properties of CuFe2O4 Nanoparticles, Journal of Magnetism and Magnetic Materials (2017), doi: http://dx.doi.org/10.1016/j.jmmm.2017.02.030
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 proof before it is published in its final 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 In substitution on structural, dielectric and magnetic properties of CuFe2O4 Nanoparticles V. Manikandana, A.Vanithab, E. Ranjith Kumarc* , J. Chandrasekarand a,b,
Department of Physics, Government College of Technology, Coimbatore, Tamilnadu-13, India c
Department of Physics, Dr. NGP Institute of Technology, Coimbatore, Tamil Nadu-48, India
d
Department of Physics, Sri Ramakrishna Mission Vidyalaya College of Arts & Science, Coimbatore, Tamilnadu-20, India
Abstract Cu ferrite and In substituted Cu ferrite has been successfully synthesized (InxCu1xFe2O4;
x=0.0, 0.2) at pH 11 and sintered at 300°C, 600°C, 900 °C. From the XRD analysis ,
the ferrite phase is confirmed and particle size varied from 28 to 37 nm owing to sintering temperature. TEM microstructure confirms that samples having polycrystalline nature because of superimposition of bright spots. FT-IR spectra exhibit general behaviour of ferrite. The significant change of dielectric constant has been noticed from dielectric measurement while substitution of In element. The room temperature magnetic measurements demonstrate a solid impact of sintering temperature and In substitution on saturation magnetization and coercivity.
Keywords: Ferrite nanoparticle, Dielectric properties, XRD, VSM, TEM
*Corresponding author: [email protected]
1. Introduction Nano ferrite materials because of their peculiar properties are massively used in applications such as electrical appliances, automotive, tele-communication circuit components, microwave devices, recording heads etc[1]. Among the different spinel ferrites,
1
Cu ferrite has quite interesting versatile material and highly outstanding due to its high saturation magnetization. Also, it displays phase and semiconducting properties changes that leads to electrical switching and structural variation when treated under various sintering temperature. It is extensively used for variety of applications in LPG gas sensing, photo catalytic applications, recording devices and ferrofluids[2-5]. Generally, Cu ferrite is form in cubic and tetragonal structure[6]. The tetragonal structure has smaller magnetic moment than that of cubic structure, because there are more Cu ions located at tetrahedral sites in cubic structure [7-8]. Moreover, Indium (In) is utilized as low-melting fusible alloys and also used as a covering plate for bearings and metallic surfaces. It may be used to corrosion-resistant surface: when evaporated and allowed to deposit on glass, it produces a mirror. In substituted Cu ferrite properties depend on numerous factors such as method of preparation, stoichiometric ratio, sintering temperature, and milling. Conventional methods are used to synthesizing nano ferrite materials such as double sintering ceramic technique[9], citrate precursor[10], sol-gel combustion[11], thermal method[12], chemical co-precipitation method[13] etc. Among these techniques, chemical co-precipitation method is in expansive and suitable for laboratory environment. In this present work, we report and discuss the impact of sintering temperature and In substitution on structural, dielectric and magnetic properties on Cu ferrite.The deliberated properties of the samples are discussed below.
2. Materials and Method The Cu ferrite and In substituted Cu ferrite InxCu (1−x)Fe2O4(x=0, 0.2) is primed by mixing of Indium chloride [InCl3·6H2O], cupric chloride [CuCl2·2H2O] and anhydrous ferric chloride [FeCl3.9H2O] dissolved in de-ionizedwater. Sodium hydroxide solution was used as pH varying agent. Throughout synthesis, pH 11was maintained. The brown precipitate is scrupulously cleaned with de-ionized water to remove chlorine and other impurities. 2
Furthermore, the samples are dried for 24 hours in a hot air oven and brown powders are obtained. The dried powders are put into a mortar and grinded manually for 20minutes to obtain powder. Then samples are sintered at 300°C, 600°C, and 900°C.
2.1. Instrument used for Characterization Nano ferrite powder was exposed to Rigaku X-ray diffraction (Model ULTIMA III) to interpret the structural. Crystalline morphology can be visualized by using Scanning electron microscope (SEM with EDX- JEOL 5600V). Functional group analysis was performed by using Fourier transform infrared spectroscopy(Model-MAGNA 550). Crystalline nature was recorded with help of transmission electron microscopy and selected area electron diffraction. The dielectric properties of sintered samples were characterized by LCR meter (HIOKI 353250 LCR). Magnetic properties was analysed by using Vibrational Sample Magnetometer (Lakshore -7410).
3. Results and Discussion 3.1. Structural analysis Fig.1.depicts the XRD patterns of Cu ferrite and In substituted Cu ferrite sintered at different temperatures. The existence peaks corresponds to the characteristic of interplanar spacing between (111), (220), (311), (440), (511), (422) and (400) planes with cubic phase. These peaks are well indexed with JCPDS card (#77-0010). After substitution of In on Cu ferrite, it is observed that peak positions are slightly shifted towards higher angle diffraction[14]. This peak shift is due to smaller ionic radius of Cu than In element. The most privileged ferrite peak of (311) confirms the growth of Cu ferrite and In substituted Cu ferrite. While increase of sintering temperature, XRD patterns of Cu ferrite and In substituted Cu ferrite phases are formed. Thus, the crystalline nature was improved with respect to the sintering temperature. From XRD results, particle size is increased with increase of sintering temperatures. Following substitution of In element, particle size is increased and also lattice constant increased and then decreased with respect to sintering temperature. It is attributed to the difference of ionic radius of Cu and In element[15-16] . The particle size and lattice constant is strongly subjective by sintering temperature and also substitution of In element. The average particle size is calculated using Debye Scherrer formula[17]. The lattice parameter can be calculated using the formula[18]. XRD parameters are listed in Table.1.
3
1/d2= h2+k2+ l2 / a2
Table.1. XRD and VSM Parameters Parameters CuFe2O4 Temperature (°C)
Particle size (nm) Lattice parameter (°A) Coercivity (G) Remnant (emu/g) Saturation (emu/g) Remnant ratio
InxCu1-xFe2O4 (x=0.2)
300 28 8.377
600 33 8.374
900 34 8.288
300 -
600 26 8.401
900 37 8.391
67.60 0.00 0.03 0.06
694.73 4.33 10.43 0.41
673.84 87.47 133.52 0.65
121.18 0.00 0.12 0.04
204.76 3.07 9.20 0.33
137.90 5.10 21.24 0.24
4
Fig.1. XRD patterns of (a) CuFe2O4, (b) In0.2Cu0.8Fe2O4
3.2. Microstructure With EDAX Analysis The microstructure of Cu ferrite and In substituted Cu ferrite (X=0.0, 0.2) sintered at 600°C and 900°C is shown in Fig.2 (a-c). The above sample has been visualized through a scanning electron microscope. It is observed that the particle size is improved with increase of sintering temperature and owing to the increased agglomeration of the particle with rise of sintering temperature, particle seemed to have a cubic and spherical structure. It is due to the effect of reaction time and sintering temperature[19-20]. The compositional analysis of Cu ferrite and In substituted Cu ferrite has been examined through Energy dispersive analysis spectrum (EDX) as depicted in fig.3(a-b). The above spectrum confirms the existence of O, Fe, In and Cu elements. The atomic percentage of element is nearly close to stiochiometry value. The experimental values of the atomic percentage have some oxygen insufficiency.
5
Fig. 2.SEM microstructure of (a) CuFe2O4 sintered at 900°C, (b-c) In0.2Cu0.8Fe2O4 sintered at 900°C and 600°C
Fig. 3.EDX spectrum of (a) CuFe2O4, (b) In0.2Cu0.8Fe2O4 sintered at 900°C 6
3.3. FTIR Analysis FT-IR spectra of sintered In1-xCuxFe2O4 nanoparticles (with x=0.0, 0.2) in the range of 400 to 4000 cm-1 are shown in Fig.4 (a-b) respectively. The strongest absorption shoulders (ʋ1 and ʋ2) are observed in the range of 470-475 and 600-570 cm-1 respectively. These shoulders are ascribed to the stretching vibration owing to interaction between the cation and oxygen atom in tetrahedral and octahedral sites respectively. The variation between ʋ1 and ʋ2 is because of the adjustments in bond length (Fe-O) at the octahedral and tetrahedral sites[21]. The main absorption shoulders at 470-475 cm-1 represent the stretching vibration of tetrahedral sites, while the other shoulders at 600-570 cm-1represent the octahedral sites which is a normal behaviour of ferrite material. The ʋ1shoulder gets shifted to higher frequency with addition of In elements and sintering temperature, due to stretching of Fe-O bonds. At 300 °C, sintered samples have several absorption shoulders located at about 1630, 2360, 3430 in the region of 1500- 3500 cm-1. The absorption peak around 3430 cm-1 and 1630 cm-1corresponds to stretching mode of O-H group of absorbed water and H-O-H bending vibration of residual water[22]. In addition to these, the band at 2360 cm-1 which is attributed to atmospheric[22] CO2. At 600 °C, shoulders are reduced and only two shoulders are present. Due to the sintering temperature, shoulders are reduced and the crystalline nature starts to grow in the region. At 900 °C, only one shoulder is present. Hence, the above shoulder indicates the improved crystalline nature. From FT-IR results, the crystalline nature depends on absorption peak and sintering temperature.
Fig. 4. FT-IR Spectrum of (a) CuFe2O4, (b) In0.2Cu0.8Fe2O4
7
3.4. TEM Analysis The microstructure and SAED pattern of the Cu ferrite and In substituted Cu ferrite nanoparticles sintered at 900°C has been examined through transmission electron microscope and the results are shown in fig.5(a-d). TEM microstructure of Cu ferrite and In substituted Cu ferrite shows an irregular cubic and spherical shape. The average particle size is estimated in the range of 30 to 50 nm. This average particle size is in good agreement with that obtained from XRD results. At high sintering temperature, the particles gets agglomerated due to surface energy as some degree of agglomeration is inevitable in nanoparticles preparation. From SAED pattern of Cu ferrite and In substituted Cu ferrite nanoparticles, the superimposition bright spot indicates polycrystalline nature of nanoparticles[23].
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Fig. 5. TEM microstructure and SAED patterns of (a-c) CuFe2O4, (b-d) In0.2Cu0.8Fe2O4 at 900°C
3.5. Dielectric studies The dielectric constant of Cu ferrite and In substituted Cu ferrite (x=0.0, 0.2) nanoparticles sintered at different temperatures with different log frequency are shown in Fig.6 (a-b). Fig.6 shows the difference of dielectric constant with log frequency and also the entire samples show frequency dependent feature, the frequency is inversely proportional to dielectric constant which is a typical behaviour in most of the ferrite materials. With increase of sintering temperature and particle size, the dielectric properties is reduced. This type of behaviour is observed in all samples. The lessen of dielectric constant can be explained on the 9
basis of hopping conduction between Fe3+ and Fe2+ and In3+, Cu2+ ions. According to koops theory, the lessen of dielectric constant with increase of frequency can also be expressed by due to the fact the solid as composed of good conducting grains and it's separated via poor conducting grains[24]. At low frequency, the dielectric constant is increased due to the compound dielectric structure and space charge polarization[25]. At high frequency, the dielectric constant decrease and becomes constant value due to the frequency of externally applied field increase gradually, however the quantity of Fe2+ ions is decreased on the material. The above decrease arises for the reason that beyond a certain frequency of externally applied field, the electronic interchange between ferrous and ferric ions cannot follow alternating field. From dielectric results, it is found that the dielectric constant value of Cu ferrite has higher than In substituted Cu ferrite. The reason is, reduction of ferrous ions due to the substitution element maybe at octahedral sites[26-27]. Thus, the electron transfer between ferrous and ferric ions can be trapped by substitution element. Due to this cause, space charge polarization is reduced and also dielectric constant. The dielectric constant varies inversely with sintering temperature. The dielectric constant is reduced while increasing the sintered temperature. However, quantity of Fe2+ ions is reduced at high sintering temperature which could be produced at high sintering temperature.
Fig. 6. Dielectric constant of (a) CuFe2O4, (b) In0.2Cu 0.8Fe2O4
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3.6. VSM Analysis The hysteresis loop of Cu ferrite and In substituted Cu ferrite nanoparticles (X=0.0, 0.2) are shown in fig.7 (a-f). The magnetic properties such as saturation magnetization, remanant magnetization and coercivity are listed in Table. 1. The saturation magnetization values of In substituted Cu ferrite were found to be lower than the corresponding Cu ferrite. The above value of saturation magnetization is compared to that of Cu ferrite and it can be explained on the basis of core-shell model which explain that finite size effects of nanoparticles lead to canting, thereby reducing magnetization[28-29]. The obtained saturation value is increased with increase of sintering temperature. The changes in magnetic properties of In substituted Cu ferrite can be ascribed to the change of particle sizes, which is depends upon sintering temperature. From the results, an increase of sintering temperature, the particle size is changed from 28 to 37 nm. The saturation value of In substituted Cu ferrite is low when compared to Cu ferrite and the above decrease of saturation magnetization along with particle size can be accredited to the following: In ferrimagnetic structure, the magnetization of tetrahedral sublattice is antiparallel to that of the octahedral sublattice. However, the ferrite materials have non-collinear magnetic structure on the surface of the layer. The above growth of particle size causes an increase in the proportion of non-collinear magnetic structure in which magnetic moments are not aligned with direction of external magnetic field. The above increase of non-collinear magnetic structure decreases the saturation magnetization of In substituted Cu ferrite. From the VSM results, the coercivity value is increased as increase of sintering temperature and reaching an utmost value of 694 Oe at 600 °C and then decreased for any further increase of sintering temperature. The above fluctuation of coercivity value is affected by numerous factors such as magneto-crystallinity, microstrain, size distribution, anisotropy and magnetic domain size[30-32]. The small value of coercivity at 300 °C may be due to the presence of super paramagnetic nanoparticles[33]. In the multi domain system, the coercivity is inversely proportional to the particle size and also saturation magnetization. The remnant ratio values of sintered samples are in the range of 0.04 to 0.65 and the low value of remnant ratio indicates that material has an isotropic nature[20].
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Fig. 7. Magnetic meaurement of (a-c) CuFe2O4, (d-f) In0.2Cu0.8Fe2O4
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4. Conclusion Cu ferrite and In substituted Cu ferrite nanoparticles (InxCu 1-xFe2O4 ,X=0.0, 0.2) was synthesized by chemical co-precipitation method. The average particle size is in the range from 28-37nm. TEM microstructure confirms that samples have polycrystalline nature. FT-IR spectra shows normal behaviour of ferrite materials. The dielectric constant is reduced with respect to sintering temperature and substitution of In element. The VSM analysis report that the saturation magnetization increased gradually with increase of sintering temperatures, although coercivity initially increased, reaching an utmost value and then decreased.
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Peak shift is due to smaller ionic radius of Cu than In element. Particle size is increased and also lattice constant increased and then decreased with respect to sintering temperature. The average particle size is estimated in the range of 30 to 50 nm.
17