Correlation between structural and magnetic properties of substituted (Cd, Zr) cobalt ferrite nanoparticles

Correlation between structural and magnetic properties of substituted (Cd, Zr) cobalt ferrite nanoparticles

Chinese Journal of Physics 57 (2019) 6–13 Contents lists available at ScienceDirect Chinese Journal of Physics journal homepage: www.elsevier.com/lo...

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Chinese Journal of Physics 57 (2019) 6–13

Contents lists available at ScienceDirect

Chinese Journal of Physics journal homepage: www.elsevier.com/locate/cjph

Correlation between structural and magnetic properties of substituted (Cd, Zr) cobalt ferrite nanoparticles

T



Pourya Motavalliana, Behzad Abashtb, , Omid Mirzaeea, Hassan Abdollah-Poura a b

Faculty of Materials Science and Engineering, Semnan University, Semnan, Iran Space Thrusters Research Institute, Iranian Space Research Center, Tabriz, Iran

A R T IC LE I N F O

ABS TRA CT

Keywords: Sol–gel processes Ferrites Nano-particle Magnetic properties

This work correlates the magnetic properties to the microstructure of the calcined nanocrystalline CdxCo1-xZr0.05Fe1.95O4 (0.0 ≤ x ≤ 0.3 in a step of 0.05) powders produced by Pechini sol–gel method. The dry gel was grinded and calcined at 700 °C in a static air atmosphere for 1 h. The thermal decomposition process of dried gel was studied by thermo gravimetric analysis (TGA) combined with differential analysis (DTA). Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and vibrating sample magnetometer (VSM) were carried out to investigate the structural bonds identification, crystallographic properties, morphology and magnetic properties of the obtained powders. The XRD pattern of the samples showed that the synthesized materials were of a single cubic phase with the nanocrystalline Co–Zr–Cd ferrite which had an average crystallite size of 32–40 nm and particle size of 55 nm resulted from FE-SEM. The magnetic properties were measured from the hysteresis loops. The magnetic measurements had indicated that the coercivity and the magnetization decreased by increasing the Cd content.

1. Introduction Magnetic spinel nanostructured ferrites have attracted considerable interest due to their remarkable electrical, dielectric, optical, mechanical, thermal and magnetic [1]. One of the most important magnetic ceramics is spinel [2–4]. Among spinel ferrites, cobalt ferrite is a hard magnetic material with an inverse spinel structure [5], which has extensively been engaging a result of its huge magnetic multi-axial anisotropy, moderate saturation magnetization, high Curie temperature and astounding chemical stability [6–9]. This feature of CoFe2O4 has been extensively used in modern electronic technologies, especially on magnetic and magnetooptical recording [1]. The magnetic properties of the substituted cobalt ferrites have been widely examined by numerous exploration gatherings [10–15]. The properties of the ferrites are found to be strongly dependent on the method of preparation, reaction conditions, composition of ferrites and the cation distribution [10]. Scientists are endeavoring to streamline these components by choosing the synthesis route and changing exploratory conditions [16]. With a specific end goal to accomplish exceptionally homogeneous ultra-fine particles and dodge the processing procedure, distinctive blend strategies have been utilized to prepare cobalt ferrite, for example, solvothermal [17], chemical coprecipitation [5,18], hydrothermal [19,20], combustion route [21,22] and sol–gel techniques [23–25]. Among the specified procedures, the cobalt ferrite powders have been synthesized utilizing sol–gel based Pechini technique.



Corresponding author. E-mail address: [email protected] (B. Abasht).

https://doi.org/10.1016/j.cjph.2018.12.018 Received 12 July 2018; Received in revised form 23 November 2018; Accepted 17 December 2018 Available online 04 January 2019 0577-9073/ © 2019 The Physical Society of the Republic of China (Taiwan). Published by Elsevier B.V. All rights reserved.

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While no investigation has been done on the structural and magnetic properties of (Cd, Zr) co-doped cobalt ferrite, the present work deals with synthesis of cadmium substituted cobalt ferrites with the chemical formula CdxCo1-xZr0.05Fe1.95O4 (0.0 ≤ x ≤ 0.3) via sol–gel based Pechini method. Structural properties have been studied by fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD) studies and field emission scanning electron microscopy (FE-SEM). Vibrating sample magnetometry (VSM) has been used to investigate their magnetic properties. 2. Experimental 2.1. Materials synthesis Nanocrystalline Co ferrite spinels, with chemical formula CdxCo1-xZr0.05Fe1.95O4 (0.0 ≤ x ≤ 0.3), were synthesized by sol–gel based Pechini process. All chemicals utilized as a part of this examination were of analytical grade and utilized with no further purification. The chemical reagents for this experiment are Stoichiometric amounts of Cobalt (II) nitrate hexahydrate (Co (NO3)2•6H2O), Cadmium (II) nitrate tetra-hydrate (Cd(NO3)2•4H2O), Zirconium (II) nitrate xhydrat (ZrO(NO3)2.xH2O), Iron (III) nitrate nonahydrate (Fe(NO3) 3•9H2O), Citric acid (C6H8O7.H2O) and Ethylene glycol (C2H6O2). For all the samples, the metal nitrates were dissolved together in distilled water utilizing a magnetic stirrer, which is a hydrolysis response. At 60 °C, Citric acid was added to solution. Then Ethylene glycol was added to arrangement at 80 °C. After that the solution was then warmed at 80–90 °C until the point that a wet gel of the metal nitrates was acquired. The wet gel was dried at 185 °C for 24 h in oven and then the dry gel was grinded and calcined at 700 °C in a static air atmosphere for 1 h. 2.2. Instrumental details The samples were characterized by the X-ray diffraction using Burker/D8 diffractometer (CuKα radiation λ = 1.5418 Å) and differential thermal analysis and thermo gravimetric analysis (DTA/TGA) using a 409 PCeNetzsch instrument with a heating rate of 5 °C min−1 in the air atmosphere. The ferrites particles morphologies were observed by Field emission scanning electron microscope (FE-SEM; Model Mira3-XMU, TESCAN) equipped with energy dispersive X-ray spectroscopy. The magnetic properties were measured by vibrating sample magnet meter (VSM; Model Kavir magnet) with a maximum applied field of 10 kOe at room temperature. 3. Results and discussions 3.1. Phase identification and crystallite size Fig. 1 demonstrates the X-ray diffraction pattern of the calcined CoFe2O4 and CdxCo1-xZr0.05Fe1.95O4 (0.0 ≤ x ≤ 0.3) samples. Following peaks had been found in all the samples and correctly indexed as (111), (220), (311), (222), (400), (422), (511) and (440) planes of cubic spinel phase of CoFe2O4 [26]. Sharp peaks indicate good crystallization of nanoparticles as well as maximum formation of spinel structure [27]. The crystallite sizes of the synthesized samples calculated by the Scherrer formula [28]:

D=

kλ βCosθ

(1)

Fig. 1. X-ray diffraction pattern of calcined CoFe2O4 and CdxCo1-xZr0.05Fe1.95O4 (0.0 ≤ x ≤ 0.3) samples. 7

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Table 1 Unit cell volume and crystallite size for all CdxCo1-xZr0.05Fe1.95O4 (0.0 ≤ x ≤ 0.3). Sample

Lattice constant a = b = c (Å) ± 0.0001

Unit cell volume (Å3) ± 0.0001

Average crystallite size (nm) ± 0.0001

CoFe2O4 CoZr0.05Fe1.95O4 Cd0.1Co0.9Zr0.05Fe1.95O4 Cd0.15Co0.85Zr0.05Fe1.95O4 Cd0.2Co0.8Zr0.05Fe1.95O4 Cd0.25Co0.75Zr0.05Fe1.95O4 Cd0.3Co0.7Zr0.05Fe1.95O4

8.3428 8.3853 8.3847 8.3879 8.3956 8.3954 8.3975

580.6781 589.5977 589.4711 590.1463 591.7730 591.7308 592.1749

35.2667 38.9060 40.2349 37.1524 39.8405 33.7995 32.5963

Where D is crystallite size, λ is wavelength of X-ray (λ = 1.5406 Å), θ is the Bragg angle, β is full width at half maximum (FWHM), k is constant (0.94). A general increment in lattice parameter (from 8.3428 Å for CoFe2O4 to 8.3975 Å for X = 0.3), has been seen from Table 1 with progressive Cd substitution in the cobalt ferrite lattice. The observed variation in lattice constant can be comprehended based all things considered ionic radii of displaced Co2+ ions [29]. This may be due to the fact that the ionic radius of Cd2+ ion (0.97 Å) is larger than that of Co2+ (0.745 Å). The value of D decreased from 40 nm to 32 nm by increasing value of X. This can be attributed to the liberation of latent heat at the surface which raised the local temperature, consequently slowed down the growth process and lowered ferrite concentration in the vicinity [30].

3.2. Microstructure and morphology Fig. 2 shows some FE-SEM micrographs of all samples with different compositions, calcinated in a static air atmosphere at 700 °C temperatures for 1 h. The samples are composed of Nanoparticles in the average size range between 20 and 80 nm. The average grain size diminishes slightly with the addition of cadmium. The reason for the agglomeration of particles might be due to the reason that particles at nanoscale have a larger surface to volume ratio, which results in the highly interfacial surface tension [31].

Fig. 2. FE-SEM micrographs of CoFe2O4 and CdxCo1-xZr0.05Fe1.95O4 (x = 0.0, 0.1, 0.2 and 0.3) cobalt ferrite samples calcinated at 700 °C temperatures for 1 h. 8

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Fig. 3. EDS spectra of CoFe2O4 and CdxCo1-xZr0.05Fe1.95O4 (x = 0.0, 0.1, 0.2 and 0.3) ferrite nanocrystals.

3.3. EDS analysis The EDS spectra of CoFe2O4 and CdxCo1-xZr0.05Fe1.95O4 (x = 0.0, 0.1, 0.2 and 0.3) ferrite nano-crystals are shown in Fig. 3. It is seen that the stoichiometry in the samples are with no trace of impurity. The outcomes demonstrated the presence of the constitutive components. In no substituted cobalt ferrite, the EDS spectra exhibited the presence of Fe, Co and O, while not the presence of any quantity of cadmium. The spectra demonstrate that Cd peaks show up as cobalt ferrite was substituted with cadmium cation and Cd peaks intensities increment with an increase in cadmium content. It must be mentioned that EDS is a semi-quantitative investigation and the exact amount of cations could not be detected, anyway it was a fairly reasonable consistence between the atomic percentage of Fe, Co and O in synthesized nanoparticles and CoFe2O4 composition [32]. It was also observed that with a gradual increase in cadmium content, Co peaks intensities decrease. Based on the limits of the accuracuy of EDS ananlysis, since no other chemical elements were detected except than Fe, Co, Zr, Cd and O, confirms that the prepared ferrite nanocrystals were free of impurities [20]. 3.4. Thermal studies Fig. 4 shows the result of a thermogravimetric investigation (TGA) combined with differential thermal analysis (DTA) conducted on the CoFe2O4 and Cd0.3Co0.7Zr0.05Fe1.95O4 dried gel powder. As expected, the decomposition reaction is strongly exothermic. There are two exothermic peaks at 290 °C and 390 °C and one endothermic peak at 680 °C in DTA information of the dried gel powder. The

Fig. 4. TGA and DTA profiles of CoFe2O4 and Cd0.3Co0.7Zr0.05Fe1.95O4. 9

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Fig. 5. FT-IR spectra of the CoFe2O4 and CdxCo1-xZr0.05Fe1.95O4 (x = 0.0, 0.1 and 0.3) system.

second exothermic peak is relatively sharp and intense. Also, there are weight loss forms happening between temperatures at 220–360 °C, 360–680 °C and 680–700 °C. In dried gel hydroxyl group, carboxyl group and nitrate (NO−3 ) ions exist [33]. The primary weight loss and the primary peak represent to the water vaporization of OeH groups (hydroxyl groups). In second step an expansive weight loss happens, which represents the decomposition of carboxyl, NO−3 ions present in the sample [34]. The ferritization temperature occured at 680 °C and formation of small crystallite occurred [33]. DTA/TGA curves of sample Cd0.3Co0.7Zr0.05Fe1.95O4 is almost the same curve of CoFe2O4, except that the curves are shifted slightly to the right. 3.5. FT-IR analysis The room temperature infrared spectra of CoFe2O4 and CdxCo1-xZr0.05Fe1.95O4 (x = 0.0, 0.1 and 0.3) are shown in Fig. 5. Spectra of the investigated samples measured in the frequency range of 400–4000 cm−1 could be used to observe chemical and structural changes and presence of different crystal phases in the materials during calcination process. The outcomes indicated great concurrence with the information detailed in the literature [35,36]. In ferrites, the band showing up at the higher wave number (500–550 cm−1) is relegated to the tetrahedral complexes, while the band showing up at the lower wave number (400–450 cm−1) is doled out to the octahedral complexes [35]. Two relegated absorption bands showed up around 600 cm−1 (υ1) which is credited to the stretching vibration of the tetrahedral metal-oxygen bond, and the absorption band around 400 cm−1 (υ2) is ascribed to the octahedral metal-oxygen bond. The watched absorption pattern uncovers the arrangement of the spinel lattice [37,38]. The broad absorption band in 3400 cm−1 and 1633 cm−1 was as the aftereffect of stretching and bending bands of the surface hydroxyl bunch (-OH) of magnetic particles obtained from wet climate during calcinations [39,24]. 3.6. Magnetic properties The magnetic properties of as-prepared CoFe2O4 and CdxCo1-xZr0.05Fe1.95O4 with 0.0 ≤ x ≤ 0.3 particles were characterized by using a vibrating sample magnetometer at room temperature and with maximum applied field of 10 kOe. The corresponding hysteresis loops are shown in Fig 6. The magnetic parameters such as saturation magnetization (Ms), coercivity (Hc) and remanent magnetization (Mr) have all been acquired from the loops and are recorded in Table 2. The deliberate estimations of the saturation magnetization (Ms) and coercivity (Hc) of the samples, at a magnetic field of 10 kOe, were in the range 57.33–67.89 emu g−1 and 1120–1500 Oe, respectively for different compositions. The overall properties of materials are governed by a complex combination of intrinsic and extrinsic properties. An intrinsic property such as saturation magnetization is controlled by the composition, whereas an extrinsic property is determined by the microstructure that is strongly influenced by the processing procedures [40,41]. Cation distribution in cobalt ferrite, that is understood to depend on the processing conditions, might also considerably affects magnetic properties which include the saturation magnetization, magnetic anisotropy, coercive field, remanent magnetization in addition to the Curie temperature. Fig. 7 shows the coercivity and magnetization values as a function of composition. As a well-established fact, larger grains tend to consist of more magnetic domains. The magnetization caused by domain wall movement requires less energy than by domain rotation. It is simple for the domain wall movement to magnetize or demagnetize samples with larger grain size. In this way, samples 10

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Fig. 6. Magnetic hysteresis loops of CoFe2O4 and CdxCo1-xZr0.05Fe1.95O4 (0.0 ≤ x ≤ 0.3) cobalt ferrite samples at room temperature. Table 2 The magnetic parameters at room temperature of the studied CoFe2O4 and CdxCo1-xZr0.05Fe1.95O4 powders (0.0 ≤ x ≤ 0.3). Sample

CoFe2O4 CoZr0.05Fe1.95O4 Cd0.1Co0.9Zr0.05Fe1.95O4 Cd0.15Co0.85Zr0.05Fe1.95O4 Cd0.2Co0.8Zr0.05Fe1.95O4 Cd0.25Co0.75Zr0.05Fe1.95O4 Cd0.3Co0.7Zr0.05Fe1.95O4

– (x = 0.0) (x = 0.10) (x = 0.15) (x = 0.20) (x = 0.25) (x = 0.30)

Ms (emu/g) ± 0.01

Hc (Oe) ± 0.01

Mr (emu/g) ± 0.01

64.92 67.89 67.71 66.55 62.72 59.02 57.33

1355 1352 1440 1500 1350 1200 1120

31.95 39.80 35.51 34.32 34.04 29.84 28.74

Fig. 7. Variation of saturation magnetization (Ms), remanent magnetization (Mr) and coercivity (Hc) with increasing doping of Cd in CoFe2O4 and CdxCo1-xZr0.05Fe1.95O4 (0.0 ≤ x ≤ 0.3).

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with larger grains are relied upon to have a low coercivity (Hc) and high saturation magnetization [42–45]. Magnetic properties of these ferrite nanoparticles are of tremendous enthusiasm for the fundamental comprehension of magnetic connections and have great significance attributable to their technological applications [30]. It is observed from Fig. 7 that the saturation magnetization first increments up by Zr substitution and after that it diminishes by Cd substitution. This might be credited to the way that the substitution of non- magnetic divalent Cd2+ ions on the A-sites, exchanges the trivalent Fe3+ particles to B-sites and the magnetization of A-sub-lattice is so much diluted that the A–B lattice interaction turns out to be excessively weak and consequently B–B sub-lattice interaction becomes strong [46–48]. This disturbs the parallel arrangements of spins on the B-site and thus canting of spin occurs. This gives rise to Yafet–Kittel (Y–K) angle, due to which the saturation magnetization decreases [49,50]. In other words, one of the most remarkable feature of spinel ferrites is the strong dependence of properties on the state of chemical order, i.e., on the cation distribution [51]. As discussed earlier CoFe2O4 forms inverse spinel ferrite with Co2+ ions occupying the octahedral (B) site and Fe3+ are equally distributed among tetrahedral (A) and octahedral (B) site. On the other hand Zr2+ and Cd2+ have a site preference for A-site.The replacement of Co2+ with non-magnetic Zr2+ and Cd2+ ions causes a reduction in A–O–B super exchange interaction. This would further disturb some magnetic coupling and lead to an overall reduction in magnetism as to the large magnetic moment of Fe3+ ions [14]. The coercivity is seen to increments at first and then diminishes with increment in Cd2+ concentration because of lessening in magneto-crystalline anisotropy, which thus diminishes the domain wall energy [52–55]. The diminishing in magnetization with Cd2+ substitution in cobalt ferrite could connect with the non-collinear course of action of the magnetic moment of Fe3+ [56]. For additionally study, Mossbauer spectroscopy would be a suitable technique to infer data of the site occupancy of the magnetic ions in the lattice and additionally the system for the magneto crystalline anisotropy. 4. Conclusion Nano-crystalline and single phase CoFe2O4 and CdxCo1-xZr0.05Fe1.95O4 (0 ≤ x ≤ 0.3) cobalt ferrite with the average crystallite size in the range of 32–40 nm were successfully synthesized via the Pechini sol–gel technique followed by calcinations at the temperature of 700 °C. X-ray spectral analysis indicated only the presence of cubic-spinel phase and the lattice parameter (a) has been found to increase with increasing Cd2+ substitution in the cobalt ferrite lattice. Moreover, the crystallite size of the spinel structure was decreased. FE-SEM images show that the products consist of agglomerated nanoparticles with particle size ranging from 20 to 80 nm. The atomic ratio had been obtained through EDS matches by the stoichiometric ratio of cobalt ferrite. DTA/TG thermal analysis proved the ferrite crystallites formation in the final composition. The nanocrystalline Cd-Zr-Co ferrite shows the absorption bands near 400 and 600 cm−1. The high frequency band, around 600 cm−1, is attributed to the tetrahedral complexes and the band near 400 cm−1 corresponds to the octahedral complexes. Saturation magnetization (Ms) had been increased by Cd content up to x = 0.1 due to the migration of increased Fe3+ ion on the B-sites resulted in reduction of Fe3+ ions on the A-sites. Progressive decrease of magnetization with increasing Cd content above x > 0.1 is observed and is attributed to the non-collinear spin canting effect in the B-site. As the Cd content had increased, the magnetic coercivity decreased. The decrease of the saturation magnetization from 67.89 emu g−1 (x = 0) to 57.33 emu g−1 (x = 0.3) and the coercivity (Hc) from 1352 Oe (x = 0) to 1120 Oe (x = 0.3) with the Cd ion concentration was observed. Acknowledgment This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Also, the authors would like to thank dear Dr Simin Mohammadi for a very helpful presubmission review. 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