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Ni addition induced modification of structural, magnetic properties and bandgap of Ni-Zn nano ferrites
Materials Today: Proceedings xxx (xxxx) xxx
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Ni addition induced modification of structural, magnetic properties and bandgap of Ni-Zn nano ferrites R. Verma a, F. Mazaleyrat b, U.P. Deshpande c, S.N. Kane a,⇑ a
Magnetic Materials Laboratory, School of Physics, D. A. University, Khandwa Road, Indore 452001, India SATIE, ENS Universite Paris-Saclay, 61 Av. Pdt. Wilson, 94230 Cachan, France c UGC-DAE-Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452001, India b
a r t i c l e
i n f o
Article history: Received 1 January 2020 Received in revised form 23 January 2020 Accepted 25 January 2020 Available online xxxx Keywords: Ni-Zn ferrites Sol Gel auto-combustion method XRD Cation distribution Magnetic properties
a b s t r a c t We report synthesis, characterization of Zn1-xNixFe2O4 (x = 0.0–1.0) nano ferrites, by using x-ray diffraction ’XRD’, vibration sample magnetometery, UV–Vis spectroscopy. XRD validates the formation of fcc spinel structure. Ni-addition leads to: grain diameter modification; linear decrease of lattice parameter; un-equal distribution of both Ni2+, Zn2+, Fe3+ ions on A, B sites; changes in the degree of inversion, and oxygen parameter showing changes in disorder; linear variation of bandgap; significant reduction of coercivity with simultaneous increase of saturation magnetization. Results clearly demonstrate that Ni-addition in Ni-Zn ferrite can be effectively used to tune magnetic properties, bandgap. Ó 2020 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the Innovative Advancement in Engineering & Technology.
1. Introduction Spinel nano ferrites are important ceramic materials used in various applications including those in high frequency devices, microwave devices etc. Understanding their magnetic properties is a requirement to design, develop suitable materials, needed for a range of applications, based on magnetic properties [1]. Ferrimagnetic spinel ferrites with general formula Me2+O.Fe3+ 2 O3, display face centered cubic ’fcc’ structure, Fd3m space group, have two inter-penetrating sub-lattices A (tetrahedral), B (octahedral) [2,3]. Occupation of cations on A, B site is a complex process, dominated by a specific composition, particular synthesis technique etc., and can be used to control both structural, magnetic properties. According to the distribution of cations, there are normal, inverse and mixed spinels structures, depends on the type of ions occupying A and B sites. A site entirely occupied by divalent metal ion produces normal spinel, while B site occupied with a divalent metal ion produces inverse spinel, and presence of divalent metal ions on both A, B site results in mixed ferrites. It is known that the structural, magnetic properties of spinel ferrites depend on choice of cations, synthesis technique, thermal treatment, and distributions of cations between tetrahedral (A-site) and octahedral (B-site) [4–6].
⇑ Corresponding author.
Among magnetic nanoparticles, nanocrystalline Ni–Zn ferrite has been extensively used in several applications including recording heads, antenna rods, loading coils, microwave devices, core material for power transformers in electronics and telecommunication applications due to its improved magnetic behavior and high resistivity and low eddy current losses [4,5]. Ni ferrite has inverse spinel structure, where Ni2+ ions are located on octahedral (B-site) site. Gradual replacement of Ni in NiFe2O4 with another element e. g. – Zn, is known to form normal spinel via mixed spinel [7]. Substitution induced changes in cationic distribution, would even lead to non-equilibrium site occupancy as observed in nano-structured ferrites [6,7]. ZnFe2O4 in its bulk form shows completely normal spinel structure, and in nanocrystalline stateit shows mixed spinel structure. In ZnFe2O4 Zn2+ reside on A-site, Fe3+ at B-sites are surrounded by four and six nearest oxygen anions, respectively called as normal spinel structure. Nanocrystalline Low cost ZnFe2O4 have been extensively used due to its high coercivity, moderate saturation magnetization, electrical insulation, chemical stability [8]. Addition of Zn in Ni-Ferrite (or vice versa) distribution of cation on A, B site will get modified, which will reflect in their structural, magnetic properties. Literature provides information on synthesis of Zn-Ni Ferrite prepared by various methods e. g. – coprecipitation method [9], hydrothermal method [10], sol gel method [11], microwave method [12] etc., showing changes in structural, magnetic properties Among distinct
E-mail address: [email protected] (S.N. Kane). https://doi.org/10.1016/j.matpr.2020.01.489 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the Innovative Advancement in Engineering & Technology.
Please cite this article as: R. Verma, F. Mazaleyrat, U. P. Deshpande et al., Ni addition induced modification of structural, magnetic properties and bandgap of Ni-Zn nano ferrites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.489
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R. Verma et al. / Materials Today: Proceedings xxx (xxxx) xxx
advantages of sol gel auto-combustion method are – synthesis is done at relatively lower temperature 115 °C (helps in controlling grain diameter which has major effect on structural, magnetic properties), formation of spinel phase can be achieved without any postpreparation sintering, which is an energy efficient process with diminishing thermal costs while keeping the quality of materials. Therefore, in the present work we report Ni addition induced variation of structural, magnetic properties and bandgap of Zn1xNixFe2O4 (x = 0.0, 0.25, 0.45, 0.65, 0.85, 1.0) nano ferrites, studied by XRD, magnetic properties, and UV–Vis spectroscopy. 2. Experimental details A series of Zn1-xNixFe2O4 (x = 0.0, 0.25, 0.45, 0.65, 0.85, 1.0) ferrites are synthesized by sol–gel auto-combustion method. For the synthesis of Zn–Ni spinel ferrite, stoichiometric amounts of citrate–nitrate/acetate precursors [Zinc nitrate—Zn(NO3)2 6H2O, Nickel acetate—Ni(CH3COO)2 4H2O, and Ferric nitrate Fe(NO3)3 9H2O] were mixed with citric acid. The ratio of metal salt-fuel (citric acid) was taken as 1:1. In the synthesis process, citric acid has a dual function: i) firstly it acts as a chelator, and ii) as a fuel [13]. The synthesis was carried out by dissolving all the precursors in 10 ml deionized water, and then ammonia solution (NH4OH) was added to maintain the pH at 7. Now the solution was heated at 115 °C in air till the loose powder (fluffy) was formed, called as ‘dry gel or as-burnt powder,’ was used to study their structural, magnetic properties, and for bandgap calculation by means of UV– Vis spectroscopy. Obtained results show strong compositional dependence [14]. 3. Data analysis Room temperature x-ray diffraction (XRD) measurements (h – 2h configuration) were done by Bruker D8 diffractometer utilizing CuKa radiation (wavelength ’k’ = 0.1540562 nm) equipped with fast counting detector (Bruker Lynx Eye detector) based on Silicon strip technology. Cation distribution of all the studied samples was estimated using x-ray diffraction intensities, which directly depend on the position of atoms in the spinel unit cell while the position of the x-ray diffraction peaks depend on the shape and size of the unit cell. In this work, Bertaut method [15] is used to determine the cation distribution. The reflections (2 2 0), (4 0 0), (4 4 0) and (4 2 2) were used to calculate x-ray intensity as these reflections are sensitive to cation distribution among tetrahedral, octahedral sites of the spinel lattice, used to calculate theoretical lattice parameter (ath), oxygen parameter (u), bond angles (h1, h2, h3, h4, h5). Best cationic distribution for which experimental, theoretical ratios evidently agree, is taken to be the accurate one to compute the following cationic distribution parameters: theoretical lattice constant (ath), oxygen parameter (u). Diffuse reflectance spectra were converted into absorption readings according to the Kubelka–Munk (K–M) method [16]. The absorption spectrum of the samples transformed from the diffuse reflection spectra using Kubelka–Munk function: F(R) = [1 R2]/2R, where R is diffuse reflectance. Bandgap is obtained by TAUC plot [17], by straight line fitting of the diffuse reflectance data, extrapolating it to zero on energy axis (x-axis). Room temperature hysteresis loops were measured by vibrating sample magnetometer ’VSM’ (Lakeshore Model 7410) by applying maximum field – Hmax ± 1.9 T, were used to get coercivity (Hc), saturation magnetization (Ms), calculated as described in [18]. Lattice parameter (aexp) corresponding to plane [3 1 1] was obtained by using formula [19],
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 2 2 aexp ¼ d h þ k þ l
ð1Þ
where d – Inter planner spacing, (h, k, l) – Miller indices. X-ray density (qxrd) of the studied samples was calculated by using formula,
qXRD ¼
8M NA a3exp
ð2Þ
where M – Molecular weight, NA – Avagrado’s Number, aexp – Lattice parameter. Specific surface area S is obtained by:
S ¼ ½6=ðDs qXRD Þ
ð3Þ
where DW-H – particle size, qXRD – x-ray density, where k – Wavelength of x-ray used, b – Line width, h – Peak position (in 2h scale). Theoretical lattice parameter (ath.) was estimated by using following expression,
i pffiffiffi 8 h ath ¼ pffiffiffi ðrA þ Ro Þ þ 3ðr B þ R0 Þ 3 3
ð4Þ
where, rA – ionic radius of A-site, rB – ionic radius of B-site, Ro = 0.138 nm (ionic radius of oxygen ion) Oxygen positional parameter (u) was obtained by using following equation, ð r A þ Ro Þ 1 þ u4 3m ¼ pffiffiffi 4 3 aexp
ð5Þ
4. Results and discussion The XRD patterns (shown in Fig. 1) of the studied samples, confirm the formation of nanocrystalline cubic spinel structure. Rietveld refinement of XRD patterns was done by using software MAUD (Material Analysis Using Diffraction) [20] for samples with x = 0.0, 0.25, 0.45, 0.65, 0.85, 1.0 are shown in Fig. 2(a, b, c, d, e, f). XRD pattern reveal the single phase nature corresponding to cubic spinel ferrite with minor presence of Fe2O3 in x = 1.0, ascribable to synthesis of samples at relatively lower temperature (115 °C), whose presence was also detected in earlier studies [21], when low sintering temperature is used, and it disappears at higher sintering temperature. Experimental, theoretical lattice parameter (aexp, ath.), crystallite size (D), x-ray density (qXRD) specific surface area (S) obtained by analyzing XRD data, and bandgap (obtained by UV–Vis data), are depicted in Table 1. Both aexp, ath, decrease with increasing Ni content is ascribed to the substitution of an ion with higher ionic radius (Zn2+ =
Fig. 1. XRD patterns of the studied Zn1-xNixFe2O4 ferrites.
Please cite this article as: R. Verma, F. Mazaleyrat, U. P. Deshpande et al., Ni addition induced modification of structural, magnetic properties and bandgap of Ni-Zn nano ferrites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.489
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Fig. 2. (a–f): Rietveld refined XRD patterns respectively for samples with x = 0.0, 0.25, 0.45, 0.65, 0.85, 1.0. Fig. 4. Ni-content dependence of bandgap.
0.060 nm) by an ion with lower ionic radius (Ni2+ = 0.055 nm) [22]. Fig. 3(a) depicts the linear decrease of aexp. with inversion parameter, whereas linear variation of aexp. With Ni-content, shown as inset of Fig. 3(a). Crystallite size (D) is obtained from Scherrer’s equation clearly shows the formation of nano crystalline ferrite, values of D varies between 18.86 and 30.69 nm. Increase of D is attributed to grain growth. Increase of x-ray density with increase of Ni content is ascribable to the density difference between Ni and Zn. In general, high surface area implies small particle size. Smaller the particle size, larger is the surface area. Specific surface area of the studied nano-particles range between 36.37–59.29 m2/g, which initially increases for x = 0.45, with further increase in Ni content S decreases. Such non-monotonic variation of S is ascribable to the variation of particle size of Zn-Ni ferrite.
UV–Visible studies depict the change in band gap (obtained TAUC plot) due to inclusion of Ni ions, as was also observed e. g. – in [17,23]. Representative TAUC plot for sample with x = 0.25 is depicted in Fig. 3b. With increase of Ni content in the sample, there is linear variation of band gap, ascribed to changes in structure, are consistent with observed aexp. values (shown in Table 1 and Fig. 4). Results clearly indicate that Ni-addition can be utilized for tuning band gap (range between 1.85 eV and 1.95 eV) in the studied samples. Cation distribution of the studied Ni-Zn ferrites, inversion parameter (d), oxygen positional parameter (u) are depicted in Table 2. Closest agreement between observed, calculated aexp.,
Table 1 Variation of experimental and theoretical lattice parameter (aexp, aTh), grain diameter (Ds), x-ray density (qxrd), specific surface area (S) and band gap as a function of Ni content. x
aexp (nm)
aTh (nm)
D (nm)
qxrd (kg/m3)
S (m2/gm)
Bandgap (eV)
0.0 0.25 0.45 0.65 0.85 1.0
0.8437 0.8401 0.8384 0.8387 0.8379 0.8337
0.8437 0.8354 0.8398 0.8399 0.8355 0.8356
27.57 22.68 18.86 22.54 21.26 30.69
5331.13 5362.26 5364.58 5325.35 5313.96 5373.05
40.80 49.32 59.29 49.96 53.08 36.37
1.84 1.87 1.85 1.85 1.95 1.91
Fig. 3. (a) Variation of aexp with d, inset: variation of aexp with Ni content, (b) TAUC plot for sample with x = 0.25.
Please cite this article as: R. Verma, F. Mazaleyrat, U. P. Deshpande et al., Ni addition induced modification of structural, magnetic properties and bandgap of Ni-Zn nano ferrites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.489
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Table 2 Cation distribution (for A, B site), inversion parameter (d), oxygen parameter (u) of Zn1-xNixFe2O4 as a function of Ni content (x). x
Cation distributions
d
u
0.0 0.25 0.45 0.65 0.85 1.0
3+ A B (Zn2+ 0.74Fe0.26) [Zn0.26Fe1.74] (Zn0.25Ni0.25Fe0.50)A[Zn0.50Ni0.0Fe1.50]B (Zn0.55Ni0.0Fe0.45)A[Zn0.0Ni0.45Fe1.55]B (Zn0.15Ni0.20Fe0.65)A[Zn0.20Ni0.45Fe1.35]B (Zn0.15Ni0.0Fe0.85)A[Zn0.0Ni0.85Fe1.15]B (Ni0.05Fe0.95)A[Ni0.95Fe1.05]B
0.26 0.50 0.45 0.65 0.85 0.95
0.3835 0.3847 0.3824 0.3829 0.3806 0.3803
ath. (Shown in Table 1) suggest that the estimated cation distribution is in good agreement with the real distribution [24]. Cation distribution shows that, increase of Ni content in the samples, Fe-concentration on B site is modified, whereas Zn ions preferentially remain more populated on A site than on B site (as can be seen in Table 2). This result is consistent with the known tendency of Zn preferentially occupying the A-site, thus disturbing the population of Fe3+ ions on B site. In accordance with ideal spinel structure, Ni2+ preferentially occupies B site, but in the studied samples it occupies both A and B site, and with increasing Ni2+ content, its concentration on A and B sites also gets affected considerably, and presence of Ni2+ on A-site clearly demonstrates the presence of non-equilibrium cation distribution in the studied samples, as was also reported earlier [11,25]. Observed changes in d with Niaddition (shows linear decrease of aexp., as shown in Fig. 3a), are attributable to changes in population of Fe3+ ions on A, B site shrinking the unit cell. Observed changes on Oxygen position parameter (u) with increasing Ni content (shown in Table 2), are attributed to changes in the population of Ni2+, Zn2+ and Fe3+ ions on A, B site. Observed value of oxygen parameter (u) range between 0.3803 and 0.3847, are greater than its ideal value (uideal 0.375), can be used as quantitative measurement of oxygen displacement (caused by Ni-addition) as discussed earlier e. g. – in [20] shows changes of disorder in the studied samples. With increasing Ni2+content, inversion parameter (d) values (depicted in Table 2) range between 0. 26– 0.95 shows mixed-ferrite nature of the studied samples.
Fig. 6. MH loop of Zn1-xNixZnFe2O4 ferrite. Inset: Variation of Hc with Ni content.
Table 3 Coercivity (Hc), experimental saturation magnetization (Ms) as a function of Ni content. X
Hc (Oe)
Ms (emu/g)
0.0 0.25 0.45 0.65 0.85 1.0
570.87 723.84 805.51 974.15 104.19 172.06
8.21 23.00 18.24 11.10 29.46 30.48
It is worth noting that bond bond angles between cation and cation–anion decides the overall strength of magnetic superexchange interaction (A-B, A-A, B-B). Variation of bond angles as a function of Ni-content is shown in Fig. 5. Perusal of Fig. 5 shows that with increasing Ni content, there is an increase of h1, h2 and h5, while h3 and h4 decreases. The increase of bond angles suggest strengthening of super-exchange A–B, A–A interactions while decrease of bond angles indicate weakening of super-exchange B–B interaction [23,25], is expected to affect magnetic properties. Fig. 6 depicts the hysteresis loops of the studied samples, while inset displays coercivity variation with Ni content. Table 3 depicts the Ni content dependence of saturation magnetization Ms and coercivity Hc. With increasing Ni-content, Hc increases up to x = 0.65 and rapidly decreases for the samples with higher Ni content. Observed sharp reduction of Hc (from 974.15 Oe to 104.19 Oe) is attributed to the corresponding reduction of oxygen position parameter u (from 0.3839 to 0.3806), which is a measure of disorder in the system. Thus reduction of disorder in the studied samples, would result in easier domain wall movement, resulting in the sharp reduction of Hc. Magnetic data very clearly demonstrates that addition of Ni-content in Ni-Zn ferrite can be effectively used to tune magnetic properties. 5. Summary
Fig. 5. Ni-content dependence of bond angles (hA-O-B , hA-O-B , hB-O-B , hB-O-B , hA-O-A. ). 1 2 3 4 5
Sol gel auto-combustion method was successfully utilized to synthesize nanocrystalline spinel Zn1-xNixFe2O4 (x = 0.0–1.0) nano ferrite (validated by XRD), without any post-preparation thermal treatment. Observed changes in lattice parameter clearly shows that Ni goes into the spinel lattice, showing changes in disorder, modification of cationic distribution; changes in bond angles so modifying A–B, A–A, B–B super-exchange interactions, alteration
Please cite this article as: R. Verma, F. Mazaleyrat, U. P. Deshpande et al., Ni addition induced modification of structural, magnetic properties and bandgap of Ni-Zn nano ferrites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.489
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of band-gap. Variation in structural properties displays significant effect on magnetic properties via changes in coercivity and saturation magnetization. It is demonstrated that, successive Ni addition can be effectively used for structural modification, which in-turn can be use to tune band-gap and magnetic properties. CRediT authorship contribution statement R. Verma: Data Curation, Final Analysis. F. Mazaleyrat: Methodology, vizualization. U. P. Deshpande: Methodology. S. N. Kane: Funding Acquization, Investigation, Project Administration, Supervision, Resources, Draft writing and reviewing. All authors approve draft and participate in reviewing. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements Authors thank Dr. M Gupta, UGC-DAE CSR, Indore for XRD measurements. S. N. Kane acknowledges gratefully one month hospitality as invited professor at Ecole Normale Superieure de Cachan, University Paris-Saclay, Cachan (France), during June 2018. S. N. Kane acknowledges gratefully, partial support to this work in the form of CRS project of UGC-DAE CSR, Indore.
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[2] M. Sertkol, Y. Köseog˘lu, A. Baykal, H. Kavas, M.S. Toprak, J. Magn. Magn. Mater. 322 (2010) 866–871. [3] A.C.F.M. Costa, V.J. Silva, D.R. Cornejo, M.R. Morelli, R.H.G.A. Kiminami, L. Gama, J. Magn. Magn. Mater. 320 (2008) 370. [4] S.N. Kane, S. Raguwanshi, M. Satalkar, V.R. Reddy, U.P. Deshpande, T.R. Tatarchuk, F. Mazaleyrat, AIP Conf. Proc. 1953 (2018) 030089-1–030089-4. [5] S. Raghuvanshi, F. Mazaleyrat, S.N. Kane, AIP Adv. 8 (2018) 047804-1–04780411. [6] C. Caizer, M. Stefanescu, J. Phys. D: Appl. Phys. 35 (2002) 3035. [7] Z. Yue, Zhou Ji, Longtu Li, H. Zhang, Z. Gui, J. Magn. Magn. Mater. 208 (2000) 55. [8] R. Verma, S.N. Kane, P. Tiwari, F. Mazaleyrat, AIP Conf. Proc. 2142 (2019) 160001-1–160001-5. [9] T. Jahanbin, M. Hashim, K. Amin Mantori, J. Magn. Magn. Mater. 322 (2010) 2684–2689. [10] Yiwei Zhang, Ailin Xi, Weihua Chen, Renjun Ma, Mater. Res. [11] R. Verma, S.N. Kane, P. Tiwari, S.S. Modak, T. Tatarchuk, F. Mazaleyrat, Mol. Cryst. Liquid Cryst. (2018) 674 (1) (2019) 130–141. [12] L. Monica Sorescu, R. Diamandescu, R. Peelamedu, P. Yadoji Roy, J. Magn. Magn. Mater. 279 (2004) 195–201. [13] K. Rama Krishna, K. Vijaya Kumar, C. Ravindernath Gupta, Dachepalli Ravinder, Adv. Mater. Phys. Chem. 2 (2012) 149–154. [14] W. Zhang, X. Zuo, Y. Niu, C. Wu, S. Wang, S. Guan, S.R.P. Silva, Nanoscale 9 (2017) 13929–13937. [15] E.F. Bertaut, C. R. Acad. Sci. 230 (1950) 213. [16] P. Kubelka, F.Z. Munk, Tech. Phys 12 (1931) 593. [17] E.C. Devi, I. Soibam, J. Supercond. Nov. Mag. 31 (2018) 1183–1188. [18] P. Tiwari, R. Verma, S.N. Kane, T. Tatarchuk, F. Mazaleyrat, Mater. Chem. Phys. 229 (2019) 78–86. [19] B.D. Culity, Elements of X-Ray Diffraction, second ed., Addision-Wesley INC., 1978. [20] L. Lutterotti, P. Scardi, J. Appl. Cryst. 23 (246) (1990) 252. [21] E. Ranjith Kumar, R. Jayaprakash, J. Magn. Magn. Mater. 348 (2013) 93–100. [22] J. Smit, H.P.J. Wijn, Ferrites Philips, Technical Library, Eindhovan, 1959. [23] S. Chakrabarty, M. Pal, A. Dutta, Mater. Chem. Phys. 153 (2015) 221–228. [24] J. Shinde, A.B. Gadkari, P.N. Vasambekar, J. Magn. Magn. Mater. 333 (2013) 152–155. [25] R. Verma, S.N. Kane, S. Raghuvanshi, M. Satalkar, S.S. Modak, F. Mazaleyrat, AIP Conf. Proc. 2018 (1953) 030135-1–030135-4.
References [1] T. Shanmugavel, S. Gokul Raj, G. Rajarajan, G. Ramesh Kumar, Procedia Mater. Sci. 6 (2014) 1725–1730.
Please cite this article as: R. Verma, F. Mazaleyrat, U. P. Deshpande et al., Ni addition induced modification of structural, magnetic properties and bandgap of Ni-Zn nano ferrites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.489
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Ni addition induced modification of structural, magnetic properties and bandgap of Ni-Zn nano ferrites R. Verma a, F. Mazaleyrat b, U.P. Deshpande c, S.N. Kane a,⇑ a
Magnetic Materials Laboratory, School of Physics, D. A. University, Khandwa Road, Indore 452001, India SATIE, ENS Universite Paris-Saclay, 61 Av. Pdt. Wilson, 94230 Cachan, France c UGC-DAE-Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452001, India b
a r t i c l e
i n f o
Article history: Received 1 January 2020 Received in revised form 23 January 2020 Accepted 25 January 2020 Available online xxxx Keywords: Ni-Zn ferrites Sol Gel auto-combustion method XRD Cation distribution Magnetic properties
a b s t r a c t We report synthesis, characterization of Zn1-xNixFe2O4 (x = 0.0–1.0) nano ferrites, by using x-ray diffraction ’XRD’, vibration sample magnetometery, UV–Vis spectroscopy. XRD validates the formation of fcc spinel structure. Ni-addition leads to: grain diameter modification; linear decrease of lattice parameter; un-equal distribution of both Ni2+, Zn2+, Fe3+ ions on A, B sites; changes in the degree of inversion, and oxygen parameter showing changes in disorder; linear variation of bandgap; significant reduction of coercivity with simultaneous increase of saturation magnetization. Results clearly demonstrate that Ni-addition in Ni-Zn ferrite can be effectively used to tune magnetic properties, bandgap. Ó 2020 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the Innovative Advancement in Engineering & Technology.
1. Introduction Spinel nano ferrites are important ceramic materials used in various applications including those in high frequency devices, microwave devices etc. Understanding their magnetic properties is a requirement to design, develop suitable materials, needed for a range of applications, based on magnetic properties [1]. Ferrimagnetic spinel ferrites with general formula Me2+O.Fe3+ 2 O3, display face centered cubic ’fcc’ structure, Fd3m space group, have two inter-penetrating sub-lattices A (tetrahedral), B (octahedral) [2,3]. Occupation of cations on A, B site is a complex process, dominated by a specific composition, particular synthesis technique etc., and can be used to control both structural, magnetic properties. According to the distribution of cations, there are normal, inverse and mixed spinels structures, depends on the type of ions occupying A and B sites. A site entirely occupied by divalent metal ion produces normal spinel, while B site occupied with a divalent metal ion produces inverse spinel, and presence of divalent metal ions on both A, B site results in mixed ferrites. It is known that the structural, magnetic properties of spinel ferrites depend on choice of cations, synthesis technique, thermal treatment, and distributions of cations between tetrahedral (A-site) and octahedral (B-site) [4–6].
⇑ Corresponding author.
Among magnetic nanoparticles, nanocrystalline Ni–Zn ferrite has been extensively used in several applications including recording heads, antenna rods, loading coils, microwave devices, core material for power transformers in electronics and telecommunication applications due to its improved magnetic behavior and high resistivity and low eddy current losses [4,5]. Ni ferrite has inverse spinel structure, where Ni2+ ions are located on octahedral (B-site) site. Gradual replacement of Ni in NiFe2O4 with another element e. g. – Zn, is known to form normal spinel via mixed spinel [7]. Substitution induced changes in cationic distribution, would even lead to non-equilibrium site occupancy as observed in nano-structured ferrites [6,7]. ZnFe2O4 in its bulk form shows completely normal spinel structure, and in nanocrystalline stateit shows mixed spinel structure. In ZnFe2O4 Zn2+ reside on A-site, Fe3+ at B-sites are surrounded by four and six nearest oxygen anions, respectively called as normal spinel structure. Nanocrystalline Low cost ZnFe2O4 have been extensively used due to its high coercivity, moderate saturation magnetization, electrical insulation, chemical stability [8]. Addition of Zn in Ni-Ferrite (or vice versa) distribution of cation on A, B site will get modified, which will reflect in their structural, magnetic properties. Literature provides information on synthesis of Zn-Ni Ferrite prepared by various methods e. g. – coprecipitation method [9], hydrothermal method [10], sol gel method [11], microwave method [12] etc., showing changes in structural, magnetic properties Among distinct
E-mail address: [email protected] (S.N. Kane). https://doi.org/10.1016/j.matpr.2020.01.489 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the Innovative Advancement in Engineering & Technology.
Please cite this article as: R. Verma, F. Mazaleyrat, U. P. Deshpande et al., Ni addition induced modification of structural, magnetic properties and bandgap of Ni-Zn nano ferrites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.489
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advantages of sol gel auto-combustion method are – synthesis is done at relatively lower temperature 115 °C (helps in controlling grain diameter which has major effect on structural, magnetic properties), formation of spinel phase can be achieved without any postpreparation sintering, which is an energy efficient process with diminishing thermal costs while keeping the quality of materials. Therefore, in the present work we report Ni addition induced variation of structural, magnetic properties and bandgap of Zn1xNixFe2O4 (x = 0.0, 0.25, 0.45, 0.65, 0.85, 1.0) nano ferrites, studied by XRD, magnetic properties, and UV–Vis spectroscopy. 2. Experimental details A series of Zn1-xNixFe2O4 (x = 0.0, 0.25, 0.45, 0.65, 0.85, 1.0) ferrites are synthesized by sol–gel auto-combustion method. For the synthesis of Zn–Ni spinel ferrite, stoichiometric amounts of citrate–nitrate/acetate precursors [Zinc nitrate—Zn(NO3)2 6H2O, Nickel acetate—Ni(CH3COO)2 4H2O, and Ferric nitrate Fe(NO3)3 9H2O] were mixed with citric acid. The ratio of metal salt-fuel (citric acid) was taken as 1:1. In the synthesis process, citric acid has a dual function: i) firstly it acts as a chelator, and ii) as a fuel [13]. The synthesis was carried out by dissolving all the precursors in 10 ml deionized water, and then ammonia solution (NH4OH) was added to maintain the pH at 7. Now the solution was heated at 115 °C in air till the loose powder (fluffy) was formed, called as ‘dry gel or as-burnt powder,’ was used to study their structural, magnetic properties, and for bandgap calculation by means of UV– Vis spectroscopy. Obtained results show strong compositional dependence [14]. 3. Data analysis Room temperature x-ray diffraction (XRD) measurements (h – 2h configuration) were done by Bruker D8 diffractometer utilizing CuKa radiation (wavelength ’k’ = 0.1540562 nm) equipped with fast counting detector (Bruker Lynx Eye detector) based on Silicon strip technology. Cation distribution of all the studied samples was estimated using x-ray diffraction intensities, which directly depend on the position of atoms in the spinel unit cell while the position of the x-ray diffraction peaks depend on the shape and size of the unit cell. In this work, Bertaut method [15] is used to determine the cation distribution. The reflections (2 2 0), (4 0 0), (4 4 0) and (4 2 2) were used to calculate x-ray intensity as these reflections are sensitive to cation distribution among tetrahedral, octahedral sites of the spinel lattice, used to calculate theoretical lattice parameter (ath), oxygen parameter (u), bond angles (h1, h2, h3, h4, h5). Best cationic distribution for which experimental, theoretical ratios evidently agree, is taken to be the accurate one to compute the following cationic distribution parameters: theoretical lattice constant (ath), oxygen parameter (u). Diffuse reflectance spectra were converted into absorption readings according to the Kubelka–Munk (K–M) method [16]. The absorption spectrum of the samples transformed from the diffuse reflection spectra using Kubelka–Munk function: F(R) = [1 R2]/2R, where R is diffuse reflectance. Bandgap is obtained by TAUC plot [17], by straight line fitting of the diffuse reflectance data, extrapolating it to zero on energy axis (x-axis). Room temperature hysteresis loops were measured by vibrating sample magnetometer ’VSM’ (Lakeshore Model 7410) by applying maximum field – Hmax ± 1.9 T, were used to get coercivity (Hc), saturation magnetization (Ms), calculated as described in [18]. Lattice parameter (aexp) corresponding to plane [3 1 1] was obtained by using formula [19],
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 2 2 aexp ¼ d h þ k þ l
ð1Þ
where d – Inter planner spacing, (h, k, l) – Miller indices. X-ray density (qxrd) of the studied samples was calculated by using formula,
qXRD ¼
8M NA a3exp
ð2Þ
where M – Molecular weight, NA – Avagrado’s Number, aexp – Lattice parameter. Specific surface area S is obtained by:
S ¼ ½6=ðDs qXRD Þ
ð3Þ
where DW-H – particle size, qXRD – x-ray density, where k – Wavelength of x-ray used, b – Line width, h – Peak position (in 2h scale). Theoretical lattice parameter (ath.) was estimated by using following expression,
i pffiffiffi 8 h ath ¼ pffiffiffi ðrA þ Ro Þ þ 3ðr B þ R0 Þ 3 3
ð4Þ
where, rA – ionic radius of A-site, rB – ionic radius of B-site, Ro = 0.138 nm (ionic radius of oxygen ion) Oxygen positional parameter (u) was obtained by using following equation, ð r A þ Ro Þ 1 þ u4 3m ¼ pffiffiffi 4 3 aexp
ð5Þ
4. Results and discussion The XRD patterns (shown in Fig. 1) of the studied samples, confirm the formation of nanocrystalline cubic spinel structure. Rietveld refinement of XRD patterns was done by using software MAUD (Material Analysis Using Diffraction) [20] for samples with x = 0.0, 0.25, 0.45, 0.65, 0.85, 1.0 are shown in Fig. 2(a, b, c, d, e, f). XRD pattern reveal the single phase nature corresponding to cubic spinel ferrite with minor presence of Fe2O3 in x = 1.0, ascribable to synthesis of samples at relatively lower temperature (115 °C), whose presence was also detected in earlier studies [21], when low sintering temperature is used, and it disappears at higher sintering temperature. Experimental, theoretical lattice parameter (aexp, ath.), crystallite size (D), x-ray density (qXRD) specific surface area (S) obtained by analyzing XRD data, and bandgap (obtained by UV–Vis data), are depicted in Table 1. Both aexp, ath, decrease with increasing Ni content is ascribed to the substitution of an ion with higher ionic radius (Zn2+ =
Fig. 1. XRD patterns of the studied Zn1-xNixFe2O4 ferrites.
Please cite this article as: R. Verma, F. Mazaleyrat, U. P. Deshpande et al., Ni addition induced modification of structural, magnetic properties and bandgap of Ni-Zn nano ferrites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.489
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Fig. 2. (a–f): Rietveld refined XRD patterns respectively for samples with x = 0.0, 0.25, 0.45, 0.65, 0.85, 1.0. Fig. 4. Ni-content dependence of bandgap.
0.060 nm) by an ion with lower ionic radius (Ni2+ = 0.055 nm) [22]. Fig. 3(a) depicts the linear decrease of aexp. with inversion parameter, whereas linear variation of aexp. With Ni-content, shown as inset of Fig. 3(a). Crystallite size (D) is obtained from Scherrer’s equation clearly shows the formation of nano crystalline ferrite, values of D varies between 18.86 and 30.69 nm. Increase of D is attributed to grain growth. Increase of x-ray density with increase of Ni content is ascribable to the density difference between Ni and Zn. In general, high surface area implies small particle size. Smaller the particle size, larger is the surface area. Specific surface area of the studied nano-particles range between 36.37–59.29 m2/g, which initially increases for x = 0.45, with further increase in Ni content S decreases. Such non-monotonic variation of S is ascribable to the variation of particle size of Zn-Ni ferrite.
UV–Visible studies depict the change in band gap (obtained TAUC plot) due to inclusion of Ni ions, as was also observed e. g. – in [17,23]. Representative TAUC plot for sample with x = 0.25 is depicted in Fig. 3b. With increase of Ni content in the sample, there is linear variation of band gap, ascribed to changes in structure, are consistent with observed aexp. values (shown in Table 1 and Fig. 4). Results clearly indicate that Ni-addition can be utilized for tuning band gap (range between 1.85 eV and 1.95 eV) in the studied samples. Cation distribution of the studied Ni-Zn ferrites, inversion parameter (d), oxygen positional parameter (u) are depicted in Table 2. Closest agreement between observed, calculated aexp.,
Table 1 Variation of experimental and theoretical lattice parameter (aexp, aTh), grain diameter (Ds), x-ray density (qxrd), specific surface area (S) and band gap as a function of Ni content. x
aexp (nm)
aTh (nm)
D (nm)
qxrd (kg/m3)
S (m2/gm)
Bandgap (eV)
0.0 0.25 0.45 0.65 0.85 1.0
0.8437 0.8401 0.8384 0.8387 0.8379 0.8337
0.8437 0.8354 0.8398 0.8399 0.8355 0.8356
27.57 22.68 18.86 22.54 21.26 30.69
5331.13 5362.26 5364.58 5325.35 5313.96 5373.05
40.80 49.32 59.29 49.96 53.08 36.37
1.84 1.87 1.85 1.85 1.95 1.91
Fig. 3. (a) Variation of aexp with d, inset: variation of aexp with Ni content, (b) TAUC plot for sample with x = 0.25.
Please cite this article as: R. Verma, F. Mazaleyrat, U. P. Deshpande et al., Ni addition induced modification of structural, magnetic properties and bandgap of Ni-Zn nano ferrites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.489
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Table 2 Cation distribution (for A, B site), inversion parameter (d), oxygen parameter (u) of Zn1-xNixFe2O4 as a function of Ni content (x). x
Cation distributions
d
u
0.0 0.25 0.45 0.65 0.85 1.0
3+ A B (Zn2+ 0.74Fe0.26) [Zn0.26Fe1.74] (Zn0.25Ni0.25Fe0.50)A[Zn0.50Ni0.0Fe1.50]B (Zn0.55Ni0.0Fe0.45)A[Zn0.0Ni0.45Fe1.55]B (Zn0.15Ni0.20Fe0.65)A[Zn0.20Ni0.45Fe1.35]B (Zn0.15Ni0.0Fe0.85)A[Zn0.0Ni0.85Fe1.15]B (Ni0.05Fe0.95)A[Ni0.95Fe1.05]B
0.26 0.50 0.45 0.65 0.85 0.95
0.3835 0.3847 0.3824 0.3829 0.3806 0.3803
ath. (Shown in Table 1) suggest that the estimated cation distribution is in good agreement with the real distribution [24]. Cation distribution shows that, increase of Ni content in the samples, Fe-concentration on B site is modified, whereas Zn ions preferentially remain more populated on A site than on B site (as can be seen in Table 2). This result is consistent with the known tendency of Zn preferentially occupying the A-site, thus disturbing the population of Fe3+ ions on B site. In accordance with ideal spinel structure, Ni2+ preferentially occupies B site, but in the studied samples it occupies both A and B site, and with increasing Ni2+ content, its concentration on A and B sites also gets affected considerably, and presence of Ni2+ on A-site clearly demonstrates the presence of non-equilibrium cation distribution in the studied samples, as was also reported earlier [11,25]. Observed changes in d with Niaddition (shows linear decrease of aexp., as shown in Fig. 3a), are attributable to changes in population of Fe3+ ions on A, B site shrinking the unit cell. Observed changes on Oxygen position parameter (u) with increasing Ni content (shown in Table 2), are attributed to changes in the population of Ni2+, Zn2+ and Fe3+ ions on A, B site. Observed value of oxygen parameter (u) range between 0.3803 and 0.3847, are greater than its ideal value (uideal 0.375), can be used as quantitative measurement of oxygen displacement (caused by Ni-addition) as discussed earlier e. g. – in [20] shows changes of disorder in the studied samples. With increasing Ni2+content, inversion parameter (d) values (depicted in Table 2) range between 0. 26– 0.95 shows mixed-ferrite nature of the studied samples.
Fig. 6. MH loop of Zn1-xNixZnFe2O4 ferrite. Inset: Variation of Hc with Ni content.
Table 3 Coercivity (Hc), experimental saturation magnetization (Ms) as a function of Ni content. X
Hc (Oe)
Ms (emu/g)
0.0 0.25 0.45 0.65 0.85 1.0
570.87 723.84 805.51 974.15 104.19 172.06
8.21 23.00 18.24 11.10 29.46 30.48
It is worth noting that bond bond angles between cation and cation–anion decides the overall strength of magnetic superexchange interaction (A-B, A-A, B-B). Variation of bond angles as a function of Ni-content is shown in Fig. 5. Perusal of Fig. 5 shows that with increasing Ni content, there is an increase of h1, h2 and h5, while h3 and h4 decreases. The increase of bond angles suggest strengthening of super-exchange A–B, A–A interactions while decrease of bond angles indicate weakening of super-exchange B–B interaction [23,25], is expected to affect magnetic properties. Fig. 6 depicts the hysteresis loops of the studied samples, while inset displays coercivity variation with Ni content. Table 3 depicts the Ni content dependence of saturation magnetization Ms and coercivity Hc. With increasing Ni-content, Hc increases up to x = 0.65 and rapidly decreases for the samples with higher Ni content. Observed sharp reduction of Hc (from 974.15 Oe to 104.19 Oe) is attributed to the corresponding reduction of oxygen position parameter u (from 0.3839 to 0.3806), which is a measure of disorder in the system. Thus reduction of disorder in the studied samples, would result in easier domain wall movement, resulting in the sharp reduction of Hc. Magnetic data very clearly demonstrates that addition of Ni-content in Ni-Zn ferrite can be effectively used to tune magnetic properties. 5. Summary
Fig. 5. Ni-content dependence of bond angles (hA-O-B , hA-O-B , hB-O-B , hB-O-B , hA-O-A. ). 1 2 3 4 5
Sol gel auto-combustion method was successfully utilized to synthesize nanocrystalline spinel Zn1-xNixFe2O4 (x = 0.0–1.0) nano ferrite (validated by XRD), without any post-preparation thermal treatment. Observed changes in lattice parameter clearly shows that Ni goes into the spinel lattice, showing changes in disorder, modification of cationic distribution; changes in bond angles so modifying A–B, A–A, B–B super-exchange interactions, alteration
Please cite this article as: R. Verma, F. Mazaleyrat, U. P. Deshpande et al., Ni addition induced modification of structural, magnetic properties and bandgap of Ni-Zn nano ferrites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.489
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of band-gap. Variation in structural properties displays significant effect on magnetic properties via changes in coercivity and saturation magnetization. It is demonstrated that, successive Ni addition can be effectively used for structural modification, which in-turn can be use to tune band-gap and magnetic properties. CRediT authorship contribution statement R. Verma: Data Curation, Final Analysis. F. Mazaleyrat: Methodology, vizualization. U. P. Deshpande: Methodology. S. N. Kane: Funding Acquization, Investigation, Project Administration, Supervision, Resources, Draft writing and reviewing. All authors approve draft and participate in reviewing. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements Authors thank Dr. M Gupta, UGC-DAE CSR, Indore for XRD measurements. S. N. Kane acknowledges gratefully one month hospitality as invited professor at Ecole Normale Superieure de Cachan, University Paris-Saclay, Cachan (France), during June 2018. S. N. Kane acknowledges gratefully, partial support to this work in the form of CRS project of UGC-DAE CSR, Indore.
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Please cite this article as: R. Verma, F. Mazaleyrat, U. P. Deshpande et al., Ni addition induced modification of structural, magnetic properties and bandgap of Ni-Zn nano ferrites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.489