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Influence of Cu dope on the structural behavior of MgFe2O4 at various temperatures
Physica B: Condensed Matter 544 (2018) 73–78
Contents lists available at ScienceDirect
Physica B: Condensed Matter journal homepage: www.elsevier.com/locate/physb
Influence of Cu dope on the structural behavior of MgFe2O4 at various temperatures
T
I. Khishigdemberela,∗, E. Uyangaa, H. Hirazawab, D. Sangaaa a b
Institute of Physics and Technology, MAS, Peace Avenue 54 B, Ulaanbaatar 13330, Mongolia National Institute of Technology, Niihama College, Ehima, 792 – 8580, Japan
A R T I C LE I N FO
A B S T R A C T
Keywords: Ferrites X-ray and neutron diffraction High temperature FT-IR Hysteresis loss
The influence of Cu doping on the MgFe2O4 crystal and magnetic structure has been studied at various temperatures. A series of Mg1-xCuxFe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) spinels have been prepared by a chemical solid-state reaction method. The diffraction patterns confirmed that the formation of the single cubic spinel phase obtained for samples with a Cu content of up to 0.6. The second phase of a small amount of tetragonal CuFe2O4 phase was observed in the sample with x = 0.8. Cu doping increased and stabilized the magnetization of MgFe2O4 at a high temperature. The crystal phase of Cu doped MgFe2O4 was not changed up to 753 K.
1. Introduction Amongst the spinel ferrite families, magnesium ferrite (MgFe2O4) is a soft magnetic n-type semiconducting material that finds applications in the fields of heterogeneous catalysis, adsorption, sensors and magnetic technologies [1,2]. Numerous studies have been carried out on the spinel ferrites which had the general formula (M1-δFeδ)[MδFe2-δ]O4 due to their chemical and structural simplicity. The divalent metal element M (Mg, Zn, Cu, Fe, Co, Ni, or the mixture of them) can occupy either tetrahedral 8a (marked A) or octahedral 16b [marked B] sites of a spinel structure as depicted by the parentheses and brackets, respectively [3–5]. The crystal structure lies between a normal and an inverse spinel type that depends on the fraction of Fe3+-ions at the tetrahedral sites [6]. MgFe2O4 has a partially inverse spinel structure with the preference of Mg2+ cations mainly on octahedral sites [7,8], while copper ferrite (CuFe2O4) has an inverse spinel structure, in which all Cu2+ cations occupy octahedral sites [9,10]. Substitution of copper for MgFe2O4 resulted in the enhancement of permeability as well as magnetization values [11]. In our previous work [12], we performed a detailed investigation of the crystal structure of Cu doped MgFe2O4 at room temperature. In the present paper, structural properties of magnesium ferrite were explored at various temperatures. In order to test the phase stability and observe the structural evolution of the magnesium ferrite, some in-situ and exsitu annealing experiments were performed under different temperatures, ranging from 298 to 753 K. Structural characteristics were studied by x-ray and neutron diffraction. Formation of ferrite was also
∗
Corresponding author. E-mail address: [email protected] (I. Khishigdemberel).
https://doi.org/10.1016/j.physb.2018.05.032 Received 16 April 2018; Received in revised form 15 May 2018; Accepted 21 May 2018 Available online 23 May 2018 0921-4526/ © 2018 Elsevier B.V. All rights reserved.
confirmed by using Fourier-transform infrared spectroscopy (FT-IR). The main attention was paid to the evolution of the Mg1-xCuxFe2O4 under various annealing conditions. 2. Experimental Mg1-xCuxFe2O4 type powder was prepared by a solid reaction method using MgO, CuO, Fe2O3 powder as a starting material [13]. Phase analysis of the samples were carried out using an x-ray powder diffractometer, Shimadzu XRD-7000 with CuKα radiation and λ = 1.5406 Å. Neutron diffraction measurements were performed on the HRFD (High Resolution Fourier Diffractometer) instrument at the IBR-2 reactor, Joint Institute for Nuclear Research, Dubna, Russia [9]. FT-IR spectra were recorded for all samples in range of 4000 cm−1 to 400 cm−1 on Shimadzu IR Prestige-21 spectrometer. The annealing temperatures ranged from 298 to 753 K and the holding time for 2 h with a heating ramp of 10 °C/min. The hysteresis loss value in the AC magnetic field was obtained using a BeH analyzer (HP5060A, HewlettPackard, Co., Ltd). 3. Result and discussion 3.1. Phase analysis Fig. 1 shows the XRD patterns of the Mg1-xCuxFe2O4 samples with x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0 which the peaks identified with Miller indices. The data showed intense sharp peaks and revealed well-crystalline single spinel structures. The result of phase analysis of patterns
Physica B: Condensed Matter 544 (2018) 73–78
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The small change in frequency of the bands v1 and v2 was observed due to the replacement of Cu2+ ion. Some ex-situ annealing experiment results of FT-IR at different temperatures were shown in Fig. 2b. It was evident that wavenumbers and intensities of absorption bands decrease by heating above room temperature. The absorption band shift to a lower wavenumber corresponded to the increase of bond lengths. The obtained position of v1 and v2 bands at various temperatures were compared in Fig. 3a and (b), respectively. The bond lengths of tetrahedral (A-O) and octahedral (BeO) sites in cubic spinel structure were estimated by using Standely's equations [15] and were given in Table 1.
1 A − O = ⎛u − ⎞ a 3 4⎠ ⎝ 5 B − O = ⎛ − u⎞ a ⎝8 ⎠ Where: a is the lattice constant and u is oxygen ion parameter (u = 0.382 for MgFe2O4). Three criteria have recently been much employed in estimating the strength and character of chemicals, the energy bonds, namely of dissociation, the inter nuclear distance, and the so-called “force constant” of the bond, that is, the force per unit displacement which would have to be applied for infinitesimal stretching or compression of the bond [16]. Force constant (k) of the bond Fe3+ - O−2 from FT-IR spectra was computed by using the following Waldron's equation [17]. As shown in Fig. 4, the force constant at A and B sites decrease for higher doping concentration due to the lattice expansion from Cu ion (ionic radii rCu > rMg).
Fig. 1. XRD patterns of ferrite sample Mg1-xCuxFe2O4 (х = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0).
points out that the nominal composition structures with different concentrations have the cubic MgFe2O4 phase without any signature of impurity. A small amount of tetragonal CuFe2O4 phases were observed in the sample with x = 0.8. The tetragonal CuFe2O4 spinel structure obtained for x = 1.0 and some peaks of cubic structure were observed at around 2θ = 41°. The tetragonal behavior of copper ferrite has been extensively studied [10] and it has been pointed out that the tetragonality of copper ferrite is a result of sufficient concentration of copper ions at the A site [14].
k = 4π 2c 2v 2μ where: c is the light velocity (2.99 × 108 m/s), ν is the vibration frequency of the sites A and the B, μ is the reduced mass. The value of force constants of the tetrahedral site rapidly decreased and the octahedral site gradually decreased with increasing temperature in Mg0.4Cu0.6Fe2O4 (Fig. 5b) and pure copper ferrite (Fig. 5c). The same evolutions were observed in other Cu doped MgFe2O4 (not shown in paper). For undoped MgFe2O4, both force constants of A and B sites rapidly decreased with temperature (Fig. 5a). These results confirmed the previous result [12] which the Cu ion occupied at site B and inhibited cation disordering from the lattice expansion at high temperature.
3.2. FT-IR analysis The FTIR measurement of Mg1-xCuxFe2O4 (х = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) ferrites in the range of 4000–400 cm−1 was performed at the various temperatures. The most interesting part of IR spectra in the range 800-400 cm−1 was the absorption bands corresponded to the vibration of tetrahedral and octahedral sites at v1 ∼ 580-569 cm−1 and v2 ∼ 426-408 cm−1 respectively, which is indication of the formation of a spinel ferrite structure [14]. In the FT-IR spectra of Mg1-xCuxFe2O4, both v1 and v2 bands were observed (Fig. 2a). The wavenumbers at room temperatures obtained from FTIR spectra were given in Table 2.
Fig. 2. FT-IR spectra of Mg1-xCuxFe2O4 ferrites at 298 K (a) and 753 K (b) temperatures. 74
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Fig. 3. The position shift of v1 (a) and v2 (b) bands with copper concentration at various temperatures. Table 1 Obtained results from FT-IR spectra. Tetrahedral and octahedral vibration frequencies (v1 and v2) and force constants (KT and KO) of tetrahedral and octahedral sites at room temperature. x
v1 (cm−1)
v2 (cm−1)
KT (x105 dyne cm−1)
KO (x105 dyne cm−1)
Tetrahedral bond-length (Å)
Octahedral bond-length (Å)
0 0.2 0.4 0.6 0.8 1
551.64 557.42 559.35 567.07 572.57 580.27
402 405.05 410.83 412.76 416.62 418.55
2.598 2.486 2.420 2.404 2.407 2.336
1.378 1.351 1.320 1.290 1.272 1.234
1.901 1.908 1.91 1.913 1.917 1.92
2.045 2.046 2.041 2.039 2.037 2.037
3.3. Crystal structure
Table 2 Obtained crystal structure parameters for Mg1-xCuxFe2O4. Samples
Mg0.8Cu0.2Fe2O4 Mg0.6Cu0.4Fe2O4 Mg0.4Cu0.6Fe2O4
Cell parameters acub
atet
ctet
Inversion parameters δ
8.3802 8.3816 8.3819
– – –
– – –
0.867(6) 0.857(17) 0.905(5)
Magnetic moments A-site/Bsite
Crystallite sizes (nm)
4.8/1.7 4.7/1.5 5.0/1.7
11.86 11.84 10.46
Fig. 6 (a, b, c) shows the evolution of in-situ neutron diffraction patterns for the pure MgFe2O4, CuFe2O4 and doped Mg0.4Cu0.6Fe2O4 ferrites at various temperatures ranging from 298 to 753 K. Ferrites, up to x = 0.8, were found to crystallize in the cubic structure in which peak positions shifted to a higher position with increasing temperature (not shown here), corresponding with the lattice parameter increasing. Furthermore, no phase transition was observed for Cu doped MgFe2O4 under the temperature annealing condition. In the case of x = 1.0, pure
Fig. 4. Evolution of the force constant at A-site (a) and B-site (b) vs copper concentration (x) at various temperatures. 75
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Fig. 5. The evolution of force constant for MgFe2O4 (a), Mg0.4Cu0.6Fe2O4 (b) and CuFe2O4 (c) at various temperatures.
relation with the temperature based on the known thermal expansion behavior of the cubic phase. Along the structural formula of the mixed Mg1-xCuxFe2O4 ferrite, we calculated the ionic radius for the A and the B sites by the following equations [19]:
CuFe2O4 ferrite, we observed phase transition of tetragonal to cubic at 473 K, as expected (Fig. 6b). The crystal structure of Mg1-xCuxFe2O4 with a copper content of up to x = 0.6 successfully refined in a pure cubic and ferromagnetic structure with the space group Fd3m as shown in Fig. 6 (d). The results of the structural analysis of these samples, obtained by the Rietveld processing of neutron diffraction patterns, were summarized in Table 2. From the refinement results, it was seen that in samples with a Cu excess (x = 0.8), both cubic and tetragonal phases were present [12]. Moreover, the tetragonal spinel phase was obtained for x = 1.0. This was in excellent agreement with a result of the above x-ray diffraction study. The ferromagnetic structure gives a magnetic contribution to nuclear Bragg reflections. As the temperature of annealing was increased, the magnetic moments of cubic magnesium ferrites decreased, as shown in Fig. 7a. This was clearly seen from a peak of strongest magnetic contribution (d ≈ 1.9 Å, labeled as inverse rectangle in Fig. 6) disappearing at the higher temperature. For MgFe2O4, the magnetic peak vanished at 673 K, but (311) peak of copper-doped ferrites were eliminated at 753 K. We discussed from the evolution of the magnetic peaks regarding (to) temperature, the copper doping prevent the magnetic disordering of ferrites at high temperatures and influence on cation distribution in the lattice. On the other hand, Cu doping enhanced the magnetization of magnesium ferrite [18]. The change of the lattice parameter of Mg0.4Cu0.6Fe2O4 on annealing were calculated and plotted in Fig. 7b. It was clear that the lattice parameter a follows linear
(Mg12−+δ Feδ3 +)T {Mgδ2−+x Cu x2 +Fe23−+δ }OO42 −
RT = (1 − δ ) RMg2 + + (δ ) RFe3 +
RO =
1 [xRCu2+ + (δ − x ) RMg2+ + (2 − δ ) RFe3+] 2
where: RT and RO are the mean ionic radii per molecule for the A and the B sites, respectively. R Cu2 + is the ionic radius of the Cu2+ ion, R Fe3 + is the ionic radius of the Fe3+ ion, and R Mg2 + is the ionic radius of the Mg2+ ion. Fig. 8 shows the ionic radii of A and B sites (versus the composition x) and RT decreases while RO increases with rise of the Cu2+ ion concentration. This behavior was attributed to the replacement of the Mg2+ (0.72 Å) ions by the smaller ionic radius of the Fe3+ (0.60 Å) ions (cation distribution) on the sites A and the Mg2+ ions to the higher ionic radius of the Cu2+ (0.73 Å) ions on the sites B. This change was in excellent agreement with the result of the above FT-IR and neutron diffraction study. 76
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Fig. 6. Temperature dependence in-situ measurement of HRFD for MgFe2O4 (a), CuFe2O4 (b) and Mg0.4Cu0.6Fe2O4 (c) ferrites. Δ –a peak with the strongest magnetic contribution. The Rietveld refinement to the diffraction data from Mg0.8Cu0.2Fe2O4 measured at room temperature (d) and Bragg peak positions for each phase were shown as vertical bars.
Fig. 7. The evolution of magnetic peak (a) and lattice parameter (b) for Mg0.4Cu0.6Fe2O4 ferrites at various temperatures.
77
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material properties and dimension, f is the frequency (Hz), B is the flux density (T), n is a material dependent exponent between 1.5 and 2.5. The highest hysteresis loss value and the magnetizing force (Hc) were calculated in the x = 0.6 sample 1169 W/kg and 3.24 Oe, respectively. 4. Conclusions The temperature dependence of doping influence, crystal and magnetic structures above room temperature of Mg1-xCuxFe2O4, (х = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) ferrites were studied in detail. No phase transition of doped and undoped MgFe2O4 was observed up to 753 K, beside cubic to the tetragonal structural transition of CuFe2O4 appeared at 473 K. The magnetization decreased with increasing temperature approaching zero at ∼753 K for Cu doped MgFe2O4, which had higher magnetic moments than undoped ferrite samples. The lattice expansion and magnetization loss processes at high temperatures had been hindered due to the presence of copper ions inside the spinel structure. The obtained experimental results would contribute to a better understanding of the high heat generation ability of Cu doped magnesium ferrites.
Fig. 8. Evolution of ionic radii RT and RO.
Acknowledgements The authors are grateful to Prof. A.M.Balagurov and Dr. I.A.Bobrikov for their help in neutron diffraction experiments on the IBR-2 (JINR, Russia) neutron source. This work was partially supported by the Mongolian Foundation of Science and Technology (Grant No: 2017/24). References [1] N. Sivakumar, A. Narayanasamy, J.M. Greneche, R. Murugaraj, Y.S. Lee, Jour. All. Comps 504 (2) (2010) 395–402. [2] S.V. Bangale, D.R. Patil, S.R. Bamane, Arch. Appl. Sci. Res. 3 (5) (2011) 506–513. [3] S.M. Antoa, I. Hassan, J.B. Parise, Am. Mineral. 90 (2005) 219–228. [4] S.B. Singh, Ch Srinivas, Indian J. Sci. Res. 5 (2016) 1524–1528. [5] S.M. Hoque, M.A. Hakim, A. Mamun, S. Akhter, K. Chattopadhayay, Mater. Sci. Appl. 2 (2011) 1564–1571. [6] M. Gateshki, V. Petkov, S.K. Pradhan, T. Vogt, J. Appl. Crystallogr. 38 (2005) 772. [7] A. Pradeep, P. Priyadharsini, G. Chandrasekaran, J. Magn. Magn Mater. 320 (2008) 2774–2779. [8] Y. Ichiyanagi, M. Kubota, S. Moritake, Y. Kanazawa, T. Yamada, T. Uehashi, J. Magn. Magn Mater. 310 (2007) 2378–2380. [9] S. Singhala, T. Namgyala, N. Laxhmi, S. Bansal, Scientia Iranica, Trans. F: Nanotechnol. 20 (2013) 2323–2331. [10] J. Smit, H. P. J. Wijn, ―Ferrites,‖ John Wiley & Sons Inc. New York, (1959) 369. [11] A. Ghasemi, A. Ashrazadeh, X. Liu, Morisako, J. Magn. Magn Mater. 322 (2010) 3064–3071. [12] E. Uyanga, et al., Jour. Mol. Str. 1160 (2018) 447–454. [13] H. Hirazawa, Y. Ito, D. Sangaa, N. Tsogbadrakh, H. Aono, T. Naohara, AIP Conf. Pros. 1763 (2016) 020009. [14] J. Smit and H. P. J. Wijn, SCI, 20(6) 2323. [15] Ch Sirinavas, B.V. Tirupanyam, S.S. Meena, J. Magn. Magn. Matter. 407 (2016) 135–141. [16] Richard M. Badger, J. Chem. Phys. 2 (1934) 128. [17] R.D. Waldron, Phys. Rev. 99 (1955) 1727–1735. [18] R.P. Patil, S.D. Delekar, D.R. Mane, P.P. Hankare, Results in Physics 3 (2013) 129–133. [19] S. Singhala, T. Namgyala, N. Laxhmib, S. Bansalc, Sci. Iran. F 20 (6) (2013) 2323–2331.
Fig. 9. The hysteresis loops for Mg1-xCuxFe2O4 (x = 0, 0.6, 1.0) in AC magnetic field (1.50 kA/m).
3.4. Hysteresis loops analysis For the details of the hysteresis loops in an AC magnetic field (370 kHz, 1.50 kA/m) for x = 0, 0.6, 1.0 samples were shown in Fig. 9. The area of hysteresis loops was greater with increase of the Cu substitution below x = 0.6 compared with the x = 0 sample. The hysteresis loss Ph were estimated by using Steinmetz's equations [13],
Ph = kh fBn where kh is hysteresis coefficient which is a constant dependent on the
78
Contents lists available at ScienceDirect
Physica B: Condensed Matter journal homepage: www.elsevier.com/locate/physb
Influence of Cu dope on the structural behavior of MgFe2O4 at various temperatures
T
I. Khishigdemberela,∗, E. Uyangaa, H. Hirazawab, D. Sangaaa a b
Institute of Physics and Technology, MAS, Peace Avenue 54 B, Ulaanbaatar 13330, Mongolia National Institute of Technology, Niihama College, Ehima, 792 – 8580, Japan
A R T I C LE I N FO
A B S T R A C T
Keywords: Ferrites X-ray and neutron diffraction High temperature FT-IR Hysteresis loss
The influence of Cu doping on the MgFe2O4 crystal and magnetic structure has been studied at various temperatures. A series of Mg1-xCuxFe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) spinels have been prepared by a chemical solid-state reaction method. The diffraction patterns confirmed that the formation of the single cubic spinel phase obtained for samples with a Cu content of up to 0.6. The second phase of a small amount of tetragonal CuFe2O4 phase was observed in the sample with x = 0.8. Cu doping increased and stabilized the magnetization of MgFe2O4 at a high temperature. The crystal phase of Cu doped MgFe2O4 was not changed up to 753 K.
1. Introduction Amongst the spinel ferrite families, magnesium ferrite (MgFe2O4) is a soft magnetic n-type semiconducting material that finds applications in the fields of heterogeneous catalysis, adsorption, sensors and magnetic technologies [1,2]. Numerous studies have been carried out on the spinel ferrites which had the general formula (M1-δFeδ)[MδFe2-δ]O4 due to their chemical and structural simplicity. The divalent metal element M (Mg, Zn, Cu, Fe, Co, Ni, or the mixture of them) can occupy either tetrahedral 8a (marked A) or octahedral 16b [marked B] sites of a spinel structure as depicted by the parentheses and brackets, respectively [3–5]. The crystal structure lies between a normal and an inverse spinel type that depends on the fraction of Fe3+-ions at the tetrahedral sites [6]. MgFe2O4 has a partially inverse spinel structure with the preference of Mg2+ cations mainly on octahedral sites [7,8], while copper ferrite (CuFe2O4) has an inverse spinel structure, in which all Cu2+ cations occupy octahedral sites [9,10]. Substitution of copper for MgFe2O4 resulted in the enhancement of permeability as well as magnetization values [11]. In our previous work [12], we performed a detailed investigation of the crystal structure of Cu doped MgFe2O4 at room temperature. In the present paper, structural properties of magnesium ferrite were explored at various temperatures. In order to test the phase stability and observe the structural evolution of the magnesium ferrite, some in-situ and exsitu annealing experiments were performed under different temperatures, ranging from 298 to 753 K. Structural characteristics were studied by x-ray and neutron diffraction. Formation of ferrite was also
∗
Corresponding author. E-mail address: [email protected] (I. Khishigdemberel).
https://doi.org/10.1016/j.physb.2018.05.032 Received 16 April 2018; Received in revised form 15 May 2018; Accepted 21 May 2018 Available online 23 May 2018 0921-4526/ © 2018 Elsevier B.V. All rights reserved.
confirmed by using Fourier-transform infrared spectroscopy (FT-IR). The main attention was paid to the evolution of the Mg1-xCuxFe2O4 under various annealing conditions. 2. Experimental Mg1-xCuxFe2O4 type powder was prepared by a solid reaction method using MgO, CuO, Fe2O3 powder as a starting material [13]. Phase analysis of the samples were carried out using an x-ray powder diffractometer, Shimadzu XRD-7000 with CuKα radiation and λ = 1.5406 Å. Neutron diffraction measurements were performed on the HRFD (High Resolution Fourier Diffractometer) instrument at the IBR-2 reactor, Joint Institute for Nuclear Research, Dubna, Russia [9]. FT-IR spectra were recorded for all samples in range of 4000 cm−1 to 400 cm−1 on Shimadzu IR Prestige-21 spectrometer. The annealing temperatures ranged from 298 to 753 K and the holding time for 2 h with a heating ramp of 10 °C/min. The hysteresis loss value in the AC magnetic field was obtained using a BeH analyzer (HP5060A, HewlettPackard, Co., Ltd). 3. Result and discussion 3.1. Phase analysis Fig. 1 shows the XRD patterns of the Mg1-xCuxFe2O4 samples with x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0 which the peaks identified with Miller indices. The data showed intense sharp peaks and revealed well-crystalline single spinel structures. The result of phase analysis of patterns
Physica B: Condensed Matter 544 (2018) 73–78
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The small change in frequency of the bands v1 and v2 was observed due to the replacement of Cu2+ ion. Some ex-situ annealing experiment results of FT-IR at different temperatures were shown in Fig. 2b. It was evident that wavenumbers and intensities of absorption bands decrease by heating above room temperature. The absorption band shift to a lower wavenumber corresponded to the increase of bond lengths. The obtained position of v1 and v2 bands at various temperatures were compared in Fig. 3a and (b), respectively. The bond lengths of tetrahedral (A-O) and octahedral (BeO) sites in cubic spinel structure were estimated by using Standely's equations [15] and were given in Table 1.
1 A − O = ⎛u − ⎞ a 3 4⎠ ⎝ 5 B − O = ⎛ − u⎞ a ⎝8 ⎠ Where: a is the lattice constant and u is oxygen ion parameter (u = 0.382 for MgFe2O4). Three criteria have recently been much employed in estimating the strength and character of chemicals, the energy bonds, namely of dissociation, the inter nuclear distance, and the so-called “force constant” of the bond, that is, the force per unit displacement which would have to be applied for infinitesimal stretching or compression of the bond [16]. Force constant (k) of the bond Fe3+ - O−2 from FT-IR spectra was computed by using the following Waldron's equation [17]. As shown in Fig. 4, the force constant at A and B sites decrease for higher doping concentration due to the lattice expansion from Cu ion (ionic radii rCu > rMg).
Fig. 1. XRD patterns of ferrite sample Mg1-xCuxFe2O4 (х = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0).
points out that the nominal composition structures with different concentrations have the cubic MgFe2O4 phase without any signature of impurity. A small amount of tetragonal CuFe2O4 phases were observed in the sample with x = 0.8. The tetragonal CuFe2O4 spinel structure obtained for x = 1.0 and some peaks of cubic structure were observed at around 2θ = 41°. The tetragonal behavior of copper ferrite has been extensively studied [10] and it has been pointed out that the tetragonality of copper ferrite is a result of sufficient concentration of copper ions at the A site [14].
k = 4π 2c 2v 2μ where: c is the light velocity (2.99 × 108 m/s), ν is the vibration frequency of the sites A and the B, μ is the reduced mass. The value of force constants of the tetrahedral site rapidly decreased and the octahedral site gradually decreased with increasing temperature in Mg0.4Cu0.6Fe2O4 (Fig. 5b) and pure copper ferrite (Fig. 5c). The same evolutions were observed in other Cu doped MgFe2O4 (not shown in paper). For undoped MgFe2O4, both force constants of A and B sites rapidly decreased with temperature (Fig. 5a). These results confirmed the previous result [12] which the Cu ion occupied at site B and inhibited cation disordering from the lattice expansion at high temperature.
3.2. FT-IR analysis The FTIR measurement of Mg1-xCuxFe2O4 (х = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) ferrites in the range of 4000–400 cm−1 was performed at the various temperatures. The most interesting part of IR spectra in the range 800-400 cm−1 was the absorption bands corresponded to the vibration of tetrahedral and octahedral sites at v1 ∼ 580-569 cm−1 and v2 ∼ 426-408 cm−1 respectively, which is indication of the formation of a spinel ferrite structure [14]. In the FT-IR spectra of Mg1-xCuxFe2O4, both v1 and v2 bands were observed (Fig. 2a). The wavenumbers at room temperatures obtained from FTIR spectra were given in Table 2.
Fig. 2. FT-IR spectra of Mg1-xCuxFe2O4 ferrites at 298 K (a) and 753 K (b) temperatures. 74
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Fig. 3. The position shift of v1 (a) and v2 (b) bands with copper concentration at various temperatures. Table 1 Obtained results from FT-IR spectra. Tetrahedral and octahedral vibration frequencies (v1 and v2) and force constants (KT and KO) of tetrahedral and octahedral sites at room temperature. x
v1 (cm−1)
v2 (cm−1)
KT (x105 dyne cm−1)
KO (x105 dyne cm−1)
Tetrahedral bond-length (Å)
Octahedral bond-length (Å)
0 0.2 0.4 0.6 0.8 1
551.64 557.42 559.35 567.07 572.57 580.27
402 405.05 410.83 412.76 416.62 418.55
2.598 2.486 2.420 2.404 2.407 2.336
1.378 1.351 1.320 1.290 1.272 1.234
1.901 1.908 1.91 1.913 1.917 1.92
2.045 2.046 2.041 2.039 2.037 2.037
3.3. Crystal structure
Table 2 Obtained crystal structure parameters for Mg1-xCuxFe2O4. Samples
Mg0.8Cu0.2Fe2O4 Mg0.6Cu0.4Fe2O4 Mg0.4Cu0.6Fe2O4
Cell parameters acub
atet
ctet
Inversion parameters δ
8.3802 8.3816 8.3819
– – –
– – –
0.867(6) 0.857(17) 0.905(5)
Magnetic moments A-site/Bsite
Crystallite sizes (nm)
4.8/1.7 4.7/1.5 5.0/1.7
11.86 11.84 10.46
Fig. 6 (a, b, c) shows the evolution of in-situ neutron diffraction patterns for the pure MgFe2O4, CuFe2O4 and doped Mg0.4Cu0.6Fe2O4 ferrites at various temperatures ranging from 298 to 753 K. Ferrites, up to x = 0.8, were found to crystallize in the cubic structure in which peak positions shifted to a higher position with increasing temperature (not shown here), corresponding with the lattice parameter increasing. Furthermore, no phase transition was observed for Cu doped MgFe2O4 under the temperature annealing condition. In the case of x = 1.0, pure
Fig. 4. Evolution of the force constant at A-site (a) and B-site (b) vs copper concentration (x) at various temperatures. 75
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Fig. 5. The evolution of force constant for MgFe2O4 (a), Mg0.4Cu0.6Fe2O4 (b) and CuFe2O4 (c) at various temperatures.
relation with the temperature based on the known thermal expansion behavior of the cubic phase. Along the structural formula of the mixed Mg1-xCuxFe2O4 ferrite, we calculated the ionic radius for the A and the B sites by the following equations [19]:
CuFe2O4 ferrite, we observed phase transition of tetragonal to cubic at 473 K, as expected (Fig. 6b). The crystal structure of Mg1-xCuxFe2O4 with a copper content of up to x = 0.6 successfully refined in a pure cubic and ferromagnetic structure with the space group Fd3m as shown in Fig. 6 (d). The results of the structural analysis of these samples, obtained by the Rietveld processing of neutron diffraction patterns, were summarized in Table 2. From the refinement results, it was seen that in samples with a Cu excess (x = 0.8), both cubic and tetragonal phases were present [12]. Moreover, the tetragonal spinel phase was obtained for x = 1.0. This was in excellent agreement with a result of the above x-ray diffraction study. The ferromagnetic structure gives a magnetic contribution to nuclear Bragg reflections. As the temperature of annealing was increased, the magnetic moments of cubic magnesium ferrites decreased, as shown in Fig. 7a. This was clearly seen from a peak of strongest magnetic contribution (d ≈ 1.9 Å, labeled as inverse rectangle in Fig. 6) disappearing at the higher temperature. For MgFe2O4, the magnetic peak vanished at 673 K, but (311) peak of copper-doped ferrites were eliminated at 753 K. We discussed from the evolution of the magnetic peaks regarding (to) temperature, the copper doping prevent the magnetic disordering of ferrites at high temperatures and influence on cation distribution in the lattice. On the other hand, Cu doping enhanced the magnetization of magnesium ferrite [18]. The change of the lattice parameter of Mg0.4Cu0.6Fe2O4 on annealing were calculated and plotted in Fig. 7b. It was clear that the lattice parameter a follows linear
(Mg12−+δ Feδ3 +)T {Mgδ2−+x Cu x2 +Fe23−+δ }OO42 −
RT = (1 − δ ) RMg2 + + (δ ) RFe3 +
RO =
1 [xRCu2+ + (δ − x ) RMg2+ + (2 − δ ) RFe3+] 2
where: RT and RO are the mean ionic radii per molecule for the A and the B sites, respectively. R Cu2 + is the ionic radius of the Cu2+ ion, R Fe3 + is the ionic radius of the Fe3+ ion, and R Mg2 + is the ionic radius of the Mg2+ ion. Fig. 8 shows the ionic radii of A and B sites (versus the composition x) and RT decreases while RO increases with rise of the Cu2+ ion concentration. This behavior was attributed to the replacement of the Mg2+ (0.72 Å) ions by the smaller ionic radius of the Fe3+ (0.60 Å) ions (cation distribution) on the sites A and the Mg2+ ions to the higher ionic radius of the Cu2+ (0.73 Å) ions on the sites B. This change was in excellent agreement with the result of the above FT-IR and neutron diffraction study. 76
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Fig. 6. Temperature dependence in-situ measurement of HRFD for MgFe2O4 (a), CuFe2O4 (b) and Mg0.4Cu0.6Fe2O4 (c) ferrites. Δ –a peak with the strongest magnetic contribution. The Rietveld refinement to the diffraction data from Mg0.8Cu0.2Fe2O4 measured at room temperature (d) and Bragg peak positions for each phase were shown as vertical bars.
Fig. 7. The evolution of magnetic peak (a) and lattice parameter (b) for Mg0.4Cu0.6Fe2O4 ferrites at various temperatures.
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material properties and dimension, f is the frequency (Hz), B is the flux density (T), n is a material dependent exponent between 1.5 and 2.5. The highest hysteresis loss value and the magnetizing force (Hc) were calculated in the x = 0.6 sample 1169 W/kg and 3.24 Oe, respectively. 4. Conclusions The temperature dependence of doping influence, crystal and magnetic structures above room temperature of Mg1-xCuxFe2O4, (х = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) ferrites were studied in detail. No phase transition of doped and undoped MgFe2O4 was observed up to 753 K, beside cubic to the tetragonal structural transition of CuFe2O4 appeared at 473 K. The magnetization decreased with increasing temperature approaching zero at ∼753 K for Cu doped MgFe2O4, which had higher magnetic moments than undoped ferrite samples. The lattice expansion and magnetization loss processes at high temperatures had been hindered due to the presence of copper ions inside the spinel structure. The obtained experimental results would contribute to a better understanding of the high heat generation ability of Cu doped magnesium ferrites.
Fig. 8. Evolution of ionic radii RT and RO.
Acknowledgements The authors are grateful to Prof. A.M.Balagurov and Dr. I.A.Bobrikov for their help in neutron diffraction experiments on the IBR-2 (JINR, Russia) neutron source. This work was partially supported by the Mongolian Foundation of Science and Technology (Grant No: 2017/24). References [1] N. Sivakumar, A. Narayanasamy, J.M. Greneche, R. Murugaraj, Y.S. Lee, Jour. All. Comps 504 (2) (2010) 395–402. [2] S.V. Bangale, D.R. Patil, S.R. Bamane, Arch. Appl. Sci. Res. 3 (5) (2011) 506–513. [3] S.M. Antoa, I. Hassan, J.B. Parise, Am. Mineral. 90 (2005) 219–228. [4] S.B. Singh, Ch Srinivas, Indian J. Sci. Res. 5 (2016) 1524–1528. [5] S.M. Hoque, M.A. Hakim, A. Mamun, S. Akhter, K. Chattopadhayay, Mater. Sci. Appl. 2 (2011) 1564–1571. [6] M. Gateshki, V. Petkov, S.K. Pradhan, T. Vogt, J. Appl. Crystallogr. 38 (2005) 772. [7] A. Pradeep, P. Priyadharsini, G. Chandrasekaran, J. Magn. Magn Mater. 320 (2008) 2774–2779. [8] Y. Ichiyanagi, M. Kubota, S. Moritake, Y. Kanazawa, T. Yamada, T. Uehashi, J. Magn. Magn Mater. 310 (2007) 2378–2380. [9] S. Singhala, T. Namgyala, N. Laxhmi, S. Bansal, Scientia Iranica, Trans. F: Nanotechnol. 20 (2013) 2323–2331. [10] J. Smit, H. P. J. Wijn, ―Ferrites,‖ John Wiley & Sons Inc. New York, (1959) 369. [11] A. Ghasemi, A. Ashrazadeh, X. Liu, Morisako, J. Magn. Magn Mater. 322 (2010) 3064–3071. [12] E. Uyanga, et al., Jour. Mol. Str. 1160 (2018) 447–454. [13] H. Hirazawa, Y. Ito, D. Sangaa, N. Tsogbadrakh, H. Aono, T. Naohara, AIP Conf. Pros. 1763 (2016) 020009. [14] J. Smit and H. P. J. Wijn, SCI, 20(6) 2323. [15] Ch Sirinavas, B.V. Tirupanyam, S.S. Meena, J. Magn. Magn. Matter. 407 (2016) 135–141. [16] Richard M. Badger, J. Chem. Phys. 2 (1934) 128. [17] R.D. Waldron, Phys. Rev. 99 (1955) 1727–1735. [18] R.P. Patil, S.D. Delekar, D.R. Mane, P.P. Hankare, Results in Physics 3 (2013) 129–133. [19] S. Singhala, T. Namgyala, N. Laxhmib, S. Bansalc, Sci. Iran. F 20 (6) (2013) 2323–2331.
Fig. 9. The hysteresis loops for Mg1-xCuxFe2O4 (x = 0, 0.6, 1.0) in AC magnetic field (1.50 kA/m).
3.4. Hysteresis loops analysis For the details of the hysteresis loops in an AC magnetic field (370 kHz, 1.50 kA/m) for x = 0, 0.6, 1.0 samples were shown in Fig. 9. The area of hysteresis loops was greater with increase of the Cu substitution below x = 0.6 compared with the x = 0 sample. The hysteresis loss Ph were estimated by using Steinmetz's equations [13],
Ph = kh fBn where kh is hysteresis coefficient which is a constant dependent on the
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