Results in Physics (2017) 354–360 Contents lists available at ScienceDirect Results in Physics journal homepage: www.journals.elsevier.com/results-in-physics Structural, morphological and magnetic properties of Al3+ substituted Ni0.25Cu0.20Zn0.55AlxFe2xO4 ferrites synthesized by solid state reaction route K.R Rahman a, F.-U.-Z Chowdhury a,⇑, M.N.I Khan b a b Department of Physics, Chittagong University of Engineering and Technology, Chittagong 4349, Bangladesh Materials Science Division, Atomic Energy Center, Dhaka 1000, Bangladesh a r t i c l e i n f o Article history: Received September 2016 Accepted 27 December 2016 Available online 29 December 2016 Keywords: X-ray diffractometry Field emission scanning electron microscopy Initial permeability Curie temperature Vibration sample magnetometer Magnetization a b s t r a c t Ni-Cu-Zn ferrite materials have been extensively used in electronic materials because of their outstanding properties at high frequencies This work investigates the impact of Al substitution on the structure, morphology and magnetic properties of Ni0.25Cu0.20Zn0.55AlxFe2xO4 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) prepared by solid state reaction method X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), impedance analyzer and Vibrating Sample Magnetometer (VSM) were used to characterize the properties of the samples The XRD study confirmed the cubic spinel structure with single phase for all the samples The lattice constant, X-ray density and bulk density decrease while the porosity and grain size increase with the increase of Al content in the samples The frequency dependence of the complex permeability sintered at 1200 °C has been measured for toroidal samples in the frequency range between kHz and 120 MHz at room temperature The decrease in initial permeability has been explained on the basis of variation in grain size The temperature dependence of the initial permeability has been measured in the temperature range between from 30 to 250 °C Curie temperature (Tc) has been estimated from the temperature dependence of the permeability spectra for all samples It is found that Curie temperatures and initial permeability ðl0i Þ decrease on Al substitution The saturation magnetization has been measured at room temperature and it was found to decrease with increasing of Al3+ ions Ó 2016 The Authors Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Introduction Ferrite materials have drawn a considerable attention to the researchers for their soft magnetic properties and high frequency application [1] The magnetic properties are highly responsive to the technological parameters of ferrites especially on the amount of metal oxides or additives in their constituent elements [2] Important and interesting electrical and magnetic properties of spinel ferrites depend on a proper selection of cations along with Fe2+, Fe3+, and their sharing in the tetrahedral (A) and octahedral (B) sites of spinel lattice [3] The magnetic properties of Znsubstituted ferrites have a considerable position because of the importance of these materials for high frequency applications Though zinc ferrites (ZnFe2O4) have normal spinel structure, i.e., 2 2+ (Zn2+)A[Fe3+ ions reside on A-sites and Fe3+ ions ]BO4 where all Zn on B-sites, the substitution of Cu by Zn in Cu1xZnxFe2O4 is predictable to change the magnetic behavior The nature of magnetiza⇑ Corresponding author E-mail address: faruque@cuet.ac.bd (F.-U.-Z Chowdhury) tion and magnetic ordering of Zn substituted ferrites have been studied by many researchers [4–7] It has been reported that Cu is used in NiCuZn ferrite to get better densification as well as electromagnetic properties [8] It is observed that the transition temperature increased with an increasing Ni concentration [9] Some researchers worked on NiCuZn ferrites, especially to appreciate the best possible concentrations that cooperation with the electrical and magnetic properties [10–14] Al substituted Ni-Zn ferrite has been prepared by standard double sintering method and the structural, electrical, dielectric and magnetic Properties have been studied by Raut et al [15] They found that the lattice constant increases while the saturation magnetization decreases with the increase in Al concentration Hossain et.al observed that both lattice constant and average grain size have decreased due to addition of Al in Ni0.27Cu0.10Zn0.63AlxFe2xO4 [16] It has been found that both initial permeability and saturation magnetization were increased significantly at a small fraction of La (0.025) substitution [17] In this article, the reports are essentially focused on synthesis and detailed study of the structural, morphological and magnetic properties of Al-substituted Ni0.25Cu0.20Zn0.55AlxFe2xO4 ferrites http://dx.doi.org/10.1016/j.rinp.2016.12.045 2211-3797/Ó 2016 The Authors Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) 355 K.R Rahman et al / Results in Physics (2017) 354–360 Experimental (311) 2 x=0.20 Intensity (arb unit) Polycrystalline ferrites with the nominal composition of Ni0.25Cu0.20Zn0.55AlxFe2xO4 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) were prepared by conventional solid state ceramic method Analytical grade high purity nitrate salts of Sigma-Aldrich, UK, were used as raw materials Proper stoichiometric ratios of the reagent of analytical grade NiO, CuO, ZnO, Al2O3 and Fe2O3 were mixed thoroughly in an agate mortar for h to achieve homogeneity in the mixed powder The mixture was calcinated in air at 800 °C in a furnace (NABER HTCT 08/16) for h and then cooled without any external aid After calcination the sample, the chunk of the sample was ground into very fine powder using an agate mortar for h The powder was mixed up with a small quantity of polyvinyl alcohol as binder and was pressed (1 kN/m2) by a hydraulic press into compacts of disk and toroid shapes Finally, sintering was performed using a programmable furnace NABER (HTCT 08/16) at 1200 °C for h with the temperature ramp of °C/min for both heating and cooling X-ray diffraction study was done using a Philips PANalytical X’pert PRO X-ray diffractometer with CuKa radiation (k = 1.5418 Å) in order to perform the structural analysis The diffraction data were recorded between 15° and 70° in steps of 0.02° at time for each step data collection was 1.0 s at room temperature The lattice constant ‘a’ of each sample was calculated x=0.05 34.0 34.5 35.0 35.5 36.0 36.5 37.0 θ (degree) Fig 1b The magnified XRD peak corresponding to the plane (3 1) of Ni0.25Cu0.20Zn0.55AlxFe2xO4 (0.0 x 0.2) sintered at 1200 °C 1=2 18 lattice constant porosity 16 8.48 8.47 14 8.46 12 0.00 0.20 Fig The variation of lattice constant (a0) and porosity (P) with Al content (x) of Ni0.25Cu0.20Zn0.55AlxFe2xO4 (0.0 x 0.2) sintered at 1200 °C (440) (422) (511) (222) (400) (220) 0.05 0.10 0.15 Al concentration, x Porosity (%) Lattice constant, a0 (au) 8.49 (311) (111) x=0.10 x=0.0 from the relation: a ẳ dh ỵ k ỵ l ị , where d and (hkl) represent the interplanar distance and Miller indices, respectively The lattice parameter for each sample was estimated using NelsonRiley function [18] The X-ray density (qx), was calculated using the relation, qx = 8M/Na3, where M is the molecular weight of the composition and N is Avogadro’s number The bulk density, qB = m/V, was determined from the mass (m) and volume (V = a3) of the cubic unit cell The porosity (P) of any composition was calculated applying the relation: P(%) = (qx qB)/qx)100 The morphologies of the samples were examined using a field emission scanning electron microscope (FESEM) (model: JEOL JSM-7600 F) The average grain size of each component was determined from micrographs by linear intercept technique The complex initial permeability of the toroid-shaped samples was measured using an impedance analyzer of Wayne Kerr Table The variation of lattice constant (a0), X-ray density (qx), bulk density (qb), porosity (P) and average grain size (D) of Ni0.25Cu0.20Zn0.55AlxFe2xO4 with different Al content (x) sintered at 1200 °C x=0.20 Intensity (arb unit) x=0.15 x=0.15 x=0.10 x a0 (Å) qx (gm/cm3) qb (gm/cm3) P (%) D (lm) 0.00 0.05 0.10 0.15 0.20 8.488 8.478 8.468 8.461 8.459 5.19 5.18 5.17 5.15 5.12 4.59 4.53 4.41 4.34 4.24 11.56 12.55 14.70 15.73 17.19 7.39 8.87 13.04 18.54 23.03 x=0.05 x=0.0 20 30 40 50 60 70 θ (degree) Fig 1a X-ray diffraction patterns of Ni0.25Cu0.20Zn0.55AlxFe2xO4 (0.0 x 0.2) sintered at 1200 °C (6500B) at room temperature over a frequency range kHz– 120 MHz The Curie temperature measurements have been done by an inductance analyzer from Wayne Kerr (3255B) at 100 kHz in the temperature range from 30 to 250 °C The real ðl0i Þ and imaginary part ðl00i Þ of the complex initial permeability were computed using the relations l0i ¼ Ls =L0 where, Ls is the self-inductance of the sample core, Lo represents the inductance of the winding coil with where N is the out the sample core, l00 ¼ l0 tan d L0 ¼ l N S=pd, i i 356 K.R Rahman et al / Results in Physics (2017) 354–360 number of turns of the coil (N = 5), S equal to d1 d h where, d1, d2 and h represent outer (1.14 cm) and inner (0.66 cm) diameters and height (0.31 cm) of the toroid shaped sample, respectively S and ẳ d1 ỵd2 represent the cross-sectional area and mean diameter d of the toroid-shaped sample, respectively The relation, Q ¼ l0i = tan d, where tand is the loss factor, was used to calculate the relative quality factor, Q To measure the magnetization behavior of the prepared samples, the field dependence magnetization has been measured at room temperature by using Vibrating Sample Magnetometer (VSM) (Model EV7) Fig (a–e) FESEM micrographs of Ni0.25Cu0.20Zn0.55AlxFe2xO4 system sintered at 1200 °C (2000) 357 K.R Rahman et al / Results in Physics (2017) 354–360 Results and discussion Curie temperature Structural analysis The temperature stability of initial permeability ðl0i Þ is very important for designing a magnetic material The Curie temperature (Tc) is an important magnetic property and is a compositional dependent parameter The temperature at which l0i abruptly drops is considered as the Curie temperature The initial permeability as a function of temperature of the toroid-shaped samples are shown in Fig The l0i initially remains steady with the rise of temperature and then falls sharply near the Curie temperature, Tc [23] The curves are typical of multi-domain grains showing a sudden drop in the values of l0i at the Curie temperature which is determined at the rapid decrease of l0i It is evident that the decrease can be attributed to the decrease in saturation magnetization At Tc, Ms drops sharply with temperature leading to the rapid decrease in l0i A similar trend of Tc value is reported for Al substitution in MgCuZn ferrite [24,25] The variation of Curie temperature on the Al concentration of the samples is shown in Fig It is seen that the Curie temperature decreases with increasing Al concentration The decrease in Curie temperature is due to decrease of A-B interactions resulting from Fe replacement by Al on tetrahedral sites [26] The increasing or decreasing trend of Tc depends on the distance between the moments of A- and B-sites, i.e the number of magnetic ions presents in the two sublattices where, h is the Bragg’s angle The values of lattice parameter (a) of all the peaks for each sample were plotted against F(h) The exact value of lattice constant, a0 for each sample was estimated from the extrapolation of the straight line obtained from the least square fit method at F(h) = The variation of lattice constant (a0) and porosity with Al content is shown in Fig Decrease in lattice constant is observed with increasing Al concentration and it could be explained on the basis of ionic radius where the substitution of smaller Al3+ ion (0.535 Å) for large Fe3+ ion (0.645 Å) in the NiCuZnAl system [20] The increase in porosity with Al addition might be due to the replacement of Fe3+ by Al3+, which leaves relatively more empty spaces in the samples The values of lattice constant (a0), X-ray density (qx), bulk density (qB), porosity (P) and average grain size (D) of the samples sintered at 1200 °C for h are summarized in Table From the Table 1, it is seen that the bulk density decreased from 4.59 to 4.24 gm/cm3 as Al3+ concentration (x) is increased from 0.0 to 0.20 in the series This can be explained in terms of the difference between the atomic weight of Fe3+ and Al3+ Al has smaller atomic weight (26.98 amu) as compared to Fe (55.85 amu) The decrease in X-ray density from 5.19 gm/cm3 to 5.12 gm/cm3 with increasing Al contents in the samples is observed and it might be due to the decrease in volume of the unit cell [21] The difference between two types of density ensures the presence of pores in the samples Surface morphology Typical micrographs (2000) obtained by field emission scanning electron microscopy (FESEM) of NiCuZnAl ferrite system sintered at 1200 °C for h are shown in Fig 3(a–e) The FESEM characterization is used to see the microstructure character of the prepared ferrites The FESEM micrographs show non-uniform grains with an average grain size in the range from 7.39 to 23.03 lm as estimated using the linear intercept method which depends on the Al content [22] The increase in grain size is an indication that more pores exist when Al3+ concentrations is increased in the composite [16] The addition of Al improves the increase of the average grain size at the same time with porosity increase 700 0.0 0.05 0.10 0.15 0.20 600 500 400 / cos2 h cos2 h ỵ sin h h i Fhị ¼ 300 200 100 50 100 150 200 250 Temperature ( C) Fig Variation of initial permeability with temperature for the spinel system Ni0.25Cu0.20Zn0.55AlxFe2xO4 (0.0 x 0.2) sintered at 1200 °C Curie temperature, Tc (oC) Al-substituted composites with chemical formula Ni0.25Cu0.20Zn0.55AlxFe2xO4 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) sintered at 1200 °C in air for h, have been prepared by the solid state reaction technique The Fig 1a shows the indexed peaks of all samples as revealed from the XRD patterns The well-defined sharp peaks in the spectra are the indication of polycrystalline behavior with good crystallinity The peaks have been indexed as (1 1), (2 0), (3 1), (2 2), (4 0), (4 2), (5 1) and (4 0), which are the characteristics of cubic single phase spinel structure of the samples belonging to the space group Fd3m From the XRD patterns it is observed that the peak positions match with the earlier report and no traces of impurities were found [19] The magnified XRD peak located at around 2h–35°Corresponding to plane (311) of the samples are presented in (Fig 1b) The shifting of this peak towards low angle region of Al-substituted NiCuZnAl ferrites indicates the replacement of Fe ions by Al ions Nelson-Riley extrapolation method was used to find out the exact lattice constant (a0) and the Nelson-Riley function F(h) is given as [18]: 160 140 120 100 0.00 0.05 0.10 0.15 0.20 Al concentration, x Fig The variation of Curie temperature (Tc) with the Al concentration (x) of the samples Ni0.25Cu0.20Zn0.55AlxFe2xO4 sintered at 1200 °C 358 K.R Rahman et al / Results in Physics (2017) 354–360 The saturation magnetization, remanent magnetization, coercivity and Curie temperature are tabulated in Table Hysteresis loop study It is a common practice to analyze dynamic magnetic hysteresis loop for describing the magnetic behavior of soft ferrites The variation of magnetization (M) as a function of applied field (H) at room temperature for all samples at kHz is depicted in Fig (a–e) It is clear that the magnetization increases with increasing applied field and attains its saturation which is similar to any soft magnetic materials It has been found that the increase of Al3+ concentration contributes to the decrease of saturation magnetization (Ms) and coercive magnetic field strength The saturation magnetization has a maximum value for the sample x = 0, whereas it decreases with Al addition The increase in Al content in the samples might be described as the improvement in collinearity between A-B interaction, further replacement of Fe3+ by nonmagnetic Al3+ leads to decrease B-site magnetic moment as well as increase in porosity and therefore decreasing net magnetic moment The composition dependence of saturation magnetization is shown in Fig The decrease in saturation magnetization is more when nonmagnetic Al present in the samples is higher Complex permeability and relative quality factor The real component of permeability ðl0i Þ as a function of frequency (up to 120 MHz), at room temperature for Ni0.25Cu0.20Zn0.55AlxFe2xO4 ferrites, is presented in Fig It is found that l0i is reasonably constant at low frequencies with a maximum of 535 and 165 at kHz for x = 0.0 and 0.20, respectively, and then decreases very fast at high frequency (120 MHz) It is observed that except x = 0.0, initial permeability of all the samples shows an almost flat profile from kHz to 10 MHz This constant l0i value over a wide frequency range indicates the compositional stability and quality of ferrites prepared using solid state reaction technique The flat region up to the frequency from where it begins to fall quickly is recognized as the area of utility of the ferrites The frequency at which l0i attains the highest value and thereafter decreases, is recognized as the resonance frequency, fr [27] The resonance frequency is shifted towards higher frequency with 30 40 x= 0.0 x=0.05 20 M (emu/gm) M (emu/gm) 20 -20 20 -500 H (Oe) 500 20 M (emu/gm) M (emu/gm) 10 -10 (c) -20 -500 -10 H (Oe) 500 20 (b) -30 -1000 1000 x=0.10 -1000 -20 (a) -40 -1000 10 -500 H (Oe) 500 x=0.15 10 -10 (d) -20 1000 1000 -1000 -500 H (Oe) 500 1000 x=0.20 M (emu/gm) 10 -10 (e) -20 -1000 -500 H (Oe) 500 1000 Fig (a–e) Magnetic hysteresis loops (measured at room temperature) for the spinel system Ni0.25Cu0.20Zn0.55AlxFe2xO4 (0.0 x 0.2) sintered at 1200 °C 359 K.R Rahman et al / Results in Physics (2017) 354–360 Table Variation of saturation magnetization (Ms), remanent magnetization (Mr), Mr/Ms, coercivity (Cr), Curie temperature (Tc) and initial permeability ðl0i Þ with different Al content (x) of Ni0.25Cu0.20Zn0.55AlxFe2xO4 sintered at 1200 °C x Ms (emu/gm) Mr (emu/gm) Mr/Ms Cr (emu/gm) Tc (°C) l0i 0.0 0.05 0.10 0.15 0.20 40.9 23.9 19.4 19.3 17.8 0.93 2.33 3.03 1.35 2.25 0.02 0.09 0.16 0.07 0.13 30 76 91 60 77 163 150 123 108 93 535 325 250 220 165 400 45 35 0.0 0.05 0.10 0.15 0.20 120 100 80 ι μ// 300 μ// ι Ms (emu/gm) 40 140 0.0 0.05 0.10 0.15 0.20 60 40 20 1M 200 10M Frequency Hz 100M 30 25 100 20 15 0.00 0.05 0.10 0.15 Al concentration, x 10 0.20 Fig The dependence of saturation magnetization (Ms) on Al content (x) of Ni0.25Cu0.20Zn0.55AlxFe2xO4 sintered at 1200 °C addition Al content Two kinds of mechanisms of magnetization namely, spin rotation and domain wall motion, contribute in the complex permeability of these types of ferrites In the low frequency region, the contribution of spin rotation is not noteworthy than domain wall motion The spin rotation is essentially due to reversible motion of domain walls in the presence of a weak magnetic field The effect of domain wall motion on permeability can pffiffiffiffiffiffi be explained by the Globus relation [28]: l0i ¼ M2s D= K , where D is the average grain size, and K1 is the magneto-crystalline anisotropy constant As domain wall motion is significantly influenced by grain size, its role to the permeability is enhanced with the increase in grain size Dispersion occurs because the domain wall motion plays a relatively important role when the spin rotation reduces [29] Permeability decreased due to weak A-B interaction The dependence of permeability is proportional to the force on a 10 10 10 10 10 Frequency (Hz) Fig Variation of the imaginary part of permeability ðl00i Þ with frequency of Ni0.25Cu0.20Zn0.55AlxFe2xO4 (0.0 x 0.2) sintered at 1200 °C domain wall caused by a magnetic field and the resultant change of magnetization The frequency dependence imaginary permeabilityl00i , for the samples is shown in Fig The imaginary component rises and making a peak at a certain frequency where l0i falls rapidly [30] It is evident from the figure that the l00i falls rapidly up to 105 Hz and then remained almost constant up to 1.20 MHz After this frequency, l00i gradually increased with increasing frequency with a broad maximum at a frequency (shown in the inset of Fig 9), where the l0i rapidly decreased, recognized as the dispersion of l0i This could be attributed due to either domain wall displacement or domain rotation or the combined effect of these contributions [31], is known as cutoff frequency [32] The cutoff frequencies corresponding to the peaks of l00i are the results of the absorption of energy due to matching of the oscillation frequency of the magnetic dipoles and the applied frequency 600 400 / μι 300 200 100 1k 10k 100k 1M 10M 100M Frequency (Hz) Fig Variation of the real part of permeability ðl0i Þ with frequency of Ni0.25Cu0.20Zn0.55AlxFe2xO4 (0.0 x 0.2) sintered at 1200 °C 0.00 0.05 0.10 0.15 0.20 2.5k Relative quality factor (Q) 0.0 0.05 0.10 0.15 0.20 500 2.0k 1.5k 1.0k 500.0 0.0 1k 10k 100k 1M 10M 100M Frequency (Hz) Fig 10 Variation of relative quality factor (RQF) with Ni0.25Cu0.20Zn0.55AlxFe2xO4 (0.0 x 0.2) sintered at 1200 °C frequency for 360 K.R Rahman et al / Results in Physics (2017) 354–360 From the loss factor, we have calculated the relative quality factor (Q-factor), i.e Q ¼ l0i = tan d for all the compositions which is shown in Fig 10 It determines of the quality or performance of a material From the figure it is observed that Q-factor rises with the increase in frequency having a peak and then it falls with further increase in frequency It is also revealed from the figure that the values of Q-factor of Al substituted ferrites are slightly lower than that of sample with x = 0.0 This might be due to higher hysteresis loss of the sample which increases with an increase in porosity [33] Porosity works as an extra pinning center which obstructs the motion of domain wall As a consequence, higher magnetic field is necessary to switch the domain wall motion, resulting higher hysteresis losses [34] Conclusions Al substituted Ni0.25Cu0.20Zn0.55AlxFe2xO4 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) ferrites have been successfully prepared by the solid state reaction method The prepared samples, sintered at 1200 °C, were characterized for structural, morphological and magnetic properties The XRD patterns of the samples showed the existence of characteristic peaks validating the formation of single phase cubic spinel structure Lattice constant, bulk density, X-ray density decreases with increasing Al content, whereas the average grain size and porosity show the opposite trend The Curie temperature and initial permeability at room temperature also decrease with Al addition and are strongly depending on the average grain size, density and porosity Saturation magnetization decreases with the increase of Al substitution which is due to the dilution A-B interaction Magnetic measurements confirm the formation of magnetically soft materials The relative quality factors of the prepared samples decrease with Al content which is due to the decrease of saturation magnetization The hysteresis loops of the samples were measured at room temperature and the consequences of Al substitution on the saturation magnetization, coercivity and remanent magnetization were observed From the frequency characteristic of Q-factor the perfect frequency band can be identified in which these materials work well as a soft magnetic material with low losses Acknowledgements The authors express their gratitude to the authority of the Materials Science 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(arb unit) Polycrystalline ferrites with the nominal composition of Ni0. 25Cu0. 20Zn0. 55AlxFe2 xO4 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) were prepared by conventional solid state ceramic method Analytical... composites with chemical formula Ni0. 25Cu0. 20Zn0. 55AlxFe2 xO4 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) sintered at 1200 °C in air for h, have been prepared by the solid state reaction technique The Fig... dependence of saturation magnetization (Ms) on Al content (x) of Ni0. 25Cu0. 20Zn0. 55AlxFe2 xO4 sintered at 1200 °C addition Al content Two kinds of mechanisms of magnetization namely, spin rotation and