Influence of heat treatment on magnetic, structural and elastic properties of as-prepared Mg-nanoferrites

Influence of heat treatment on magnetic, structural and elastic properties of as-prepared Mg-nanoferrites

Journal of Magnetism and Magnetic Materials 401 (2016) 150–158 Contents lists available at ScienceDirect Journal of Magnetism and Magnetic Materials...

2MB Sizes 0 Downloads 5 Views

Journal of Magnetism and Magnetic Materials 401 (2016) 150–158

Contents lists available at ScienceDirect

Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm

Influence of heat treatment on magnetic, structural and elastic properties of as-prepared Mg-nanoferrites M.A. Amer a,n, T. Meaz a, S. Attalah b, F. Fakhry a a b

Physics Department, Faculty of Science, Tanta University, 31527 Tanta, Egypt Reactor Physics Department, NRC, Atomic Energy Authority, 13759 Cairo, Egypt

art ic l e i nf o

a b s t r a c t

Article history: Received 24 July 2015 Received in revised form 1 October 2015 Accepted 9 October 2015

This investigation presents the effect of heat treatment on the magnetic, structural and elastic properties of as-prepared MgFe2O4 nanoferrites. Five amounts of MgFe2O4 nanoparticles were heating at a different temperature for each one. The techniques used for examine the samples were XRD, VSM and FT-IR and Mössbauer spectra. Heating the samples at different temperatures led to increasing the crystallite size R from 3 to 81 nm and saturation magnetization Ms from 5.4 to 17.1 emu/g. The theoretical and experimental density and strain showed increase against heating temperature T, whereas the porosity P, oxygen parameter, specific surface area, distortion parameter showed decrease and the lattice constant and parameters showed independence on T. Seven absorption bands were observed in the IR spectra where the positions of bands ν1 and ν2, force constants, Debye temperature and stiffness constant C11 were decreased with T, whereas the trend of stiffness constant C12 were increased. Mössbauer spectra proved that the hyperfine magnetic fields and line widths of the magnetic pattern at the A- and B-sites and fractional area ratio were affected by T. The cation distributions were deduced. The coercivity, squareness and crystal anisotropy constant showed independence on T whereas the remanent magnetization and magneton number showed dependence and Ms proved dependence on P and R. & 2015 Elsevier B.V. All rights reserved.

Keywords: Mg-nanoferrites Annealing process Structural parameters Magnetic properties Elastic parameters

1. Introduction Nanoferrites are very interesting materials used in many new applications of technical, agricultural, medical, environmental and scientific research fields [1,2,3]. Nanotechnology is very important field in developing innovative methods in treatment of human diseases and in enhancement of normal human physiology [4]. It has great interest for producing new nanomaterials to improve performance resulting in less consumption of energy and materials and reduced harm to the environment [5]. The nanoparticle ferrites have physical and chemical properties different from those of the bulk ferrites. Nanoferrites are one of the leading scientific fields since it combines knowledge from the fields of physics, chemistry, biology, medicine, informatics and engineering [6]. The magnesium ferrites has sensing response of gases for hydrogen sulfide, chlorine, methanol, ethanol, liquid petroleum gas, NH3, H2 and CO as reported early [7]. The physical and chemical properties of nanoferrites depend on the chemical composition, electronic structure of the magnetic n

Corresponding author. Fax: þ20 403350804. E-mail addresses: [email protected], [email protected] (M.A. Amer). http://dx.doi.org/10.1016/j.jmmm.2015.10.032 0304-8853/& 2015 Elsevier B.V. All rights reserved.

ions, preparation conditions, crystal structure of the lattice and sintering temperature and time [2,8–11]. Many researchers studied the structural properties of nanocrystalline Mg-ferrites [10– 14], which prepared by different methods, and studied the effect of thermal treatment and different annealing temperatures on the sample properties. They obtained new interesting results where the different parameters such as crystallite and grain sizes, lattice parameters, molecular resonant frequencies, strain, Debye temperature, coercivity and saturation magnetization were affected by the substitution process, preparing method and annealing temperature [8–14]. Some investigations have indicated that the substitution process and thermal treatment can control the magnetic and structural properties, resonant frequency and morphological properties of nanoparticle ferrites [1–5]. The thermal treatment causes different cation distributions where the ions can migrate towards the lowest energy state, i.e. their most stable site against their site preference [1–5,8,9]. The published researches of sintering effect on as-synthesized nanoparticle ferrites are scarce, therefore this research is concerned on preparing the MgFe2O4 nanoparticles by the coprecipitation method and heating them at different temperatures. The samples were examined using XRD, FT-IR and Mössbauer spectroscopy and vibrating sample magnetometry.

M.A. Amer et al. / Journal of Magnetism and Magnetic Materials 401 (2016) 150–158

151

2. Experimental 2.1. Sample preparation The MgFe2O4 nanoferrite sample was synthesized using the wet-chemical co-precipitation method as reported elsewhere [8,9,15]. Proportion amounts of high purity FeCl3 and MgCl2–6H2O salts were dissolved in 0.1 M aqueous solutions, cold to 10 °C and mixed using magnetic stirrer. NaOH solution, put in ice bath, was added to the cold mixed salt solution drop-wise to control the pH value as E13. The solution was heated to 90 °C for 2 h until the precipitation occurs. The precipitation was washed many times in distilled water to remove the unwanted salt residuals. The sample was dried at room temperature for some days and ground in an agate mortar to fine powder. Five amounts of as-prepared sample were weight as 20 g for each one. The amount was heated for 4 h at one of the temperatures; 300, 500, 700, 900 or 1100 °C. Fig. 1. XRD patterns of as-prepared and heated MgFe2O4 samples.

2.2. Measurements The X-ray diffraction patterns for the samples were taken using an X-ray diffractometer of the type Shimadzu 7000 Maxima and CuKα1 radiation with wavelength λ ¼ 1.540568 Å. A computer program was used to determine the diffraction angle θ and full width at half maximum β1/2 of the prominent peaks (311) and (440). The interplaner distance d was obtained using Bragg’s law: nλ ¼2d sin θ, where n is the order of lattice plane. The lattice constant a for the cubic structure was calculated by; a¼ d(h2 þk2 þl2)1/2, where h, k and l are the miller indices. The experimental and theoretical (X-ray) densities, sample porosity, hopping length at the tetrahedral A-sites and octahedral B-sites, oxygen positional parameter and other lattice parameters were calculated as explained early [8,9,15]. The crystallite size (R) of the nanoparticle was determined using the prominent diffraction peaks (311) and Scherrer's equation [8,9,15]: R¼0.9 λ/β1/2cos θ. The mean ionic radius of the A-and B-sublattices (RA and RB) was calculated using the cationic distribution and equations [8,9,15]:

RA = yr Mg + (1 − y) r Fe

RB = (1 − y) r Mg + (1 + y) r Fe where r is the ionic radius and y is the number of Mg2 þ ions at the A-sites. The infrared spectra were recorded using the Bruker Tensor 27 FT-IR spectrometer in the range 200–2000 cm  1. The force constant FC was calculated using the relation [8,9,15]:

3. Results and discussion 3.1. X-ray diffraction (XRD) analysis Fig. 1 shows the XRD patterns of as-prepared and heated MgFe2O4 nanoferrite samples at T¼ 300, 500, 700, 900 or 1100 °C. It is shown that the sharpness and intensity of the diffraction peaks increase with T which points to the improvement and growth of crystallite size. The patterns of the samples annealed at 300 °C and 500 °C are similar to that of as-prepared sample which may be assigned to loss of retained water in the sample [10,11,16], and point to that these samples have fine crystalline size and tend to be amorphous. The observed diffraction peaks prove the formation of a single-phase cubic spinel structure of the samples as compared with the reported JCPDS data (cards no. 01-074-2403 and 8055). Fig. 2 displays the relation between the bulk density (D), theoretical density (Dx) and porosity (P) and annealing temperature T. It is displayed that the trend of D and Dx increases with T, whereas that of P decreases. The increase of D and Dx and decrease of P may assign to increasing the densification of the samples and packing as T increases. Dependence of the crystallite size (R) on T is shown in Fig. 3. It is shown that R values lie in the range of 3–81 nm and increase against T, which confirms the improvement and growth of crystallite size as T increases [11–13]. The sharp increase of R may be

FC = 4π 2C2ν 2μ where C is the velocity of light, ν is the sublattice frequency and m is the reduced mass of Fe and O ions, m ¼2.061  10  23 g. Mössbauer spectra were recorded at room temperature by using a constant acceleration Mössbauer spectrometer and 25 mCi 57 Fe radioactive source diffused in rhodium matrix, where metallic iron foil was used for calibration. The Mössbauer spectra were fitted using the least-square fits computer program. The bold solid lines through the data points are the results of the least-squares fit to the experimental data. The solid lines above the data points are the lines of the individual components. The magnetic hysteresis loops of the samples were taken at room temperature using vibrating sample magnetometer, LDJ Electronic Inc. Troy MI, and a maximum applied field up to 20 kG for reaching the saturation magnetization.

Fig. 2. T dependence of the bulk density (D), theoretical density (Dx) and porosity (P).

152

M.A. Amer et al. / Journal of Magnetism and Magnetic Materials 401 (2016) 150–158

Fig. 3. Variation of R against T.

Fig. 4. Dependence of S and ε on T.

due to increasing the coalescence of small crystallites as T increases [17]. The obtained lattice parameters are presented in Table 1. It is presented that the lattice constant a values lie in the range of 8.32–8.4 Å, where its trend slowly decreases with T. The variation in a may arise from the motion of metallic ions between the A- and B-sites with increasing T [18]. Table 1 explains that the hopping lengths, LA and LB, at the tetrahedral A-sites and octahedral B-sites, respectively, have the same behavior of a. As T increases the trend of the B-site ionic radius RB, bond length dBO, edge dBE and unshared edge dBEU values slowly increases, whereas that of the A-site radius RA, bond length dAO and edge dAE values slowly decreases. This variation of lattice parameters may arise from the motion of metallic ions between the A- and B-sites with increase in T. The values of oxygen positional parameter u lie in the range of 0.393–0.399, which are higher than the standard value (0.375), and decrease with T. This decrease points to reduction of the oxygen ions in the samples, i.e. decreasing the trigonal distortion of the B-site oxygen coordination with T [19]. The specific surface area (S) of the nanoparticle can be determined by the equation [20,21]:

on both R and Dx, where S is inversely proportional to R [19]. The negative values of ε reveal compressive strain [20,21]. The increase of ε proves the growth of crystal lattice as T increases [8,9,20,21]. Variation of ε reflects the expansion effect of the samples when they were annealed which is attributed to the change of spacing within and/or between the nanoparticles. The distortion parameter g can be determined by the equation [17,22]:

S=

6000 RDx

The lattice strain (ε) can be determined by the equation [8,9,20,21]:

β1/2 cos θ =

0.94λ + 4ε sin θ R

Graphing the relation between β1/2 cos θ and 4 sin θ for each sample shows a straight line its lope gives the strain value. Fig. 4 displays the variation of S and ε with T. It is displayed that S increases slowly at 300 °C and decreases sharply thereafter, whereas ε has opposite behavior. This can be explained as dependence of S

g=

β1/2 tan θ

Fig. 5 depicts the relation between g and T. It is depicted that g increases a little at 300 °C and decreases sharply thereafter. Variation of g reflects the variation of crystal structure and is a direct consequence of improving the crystalline process. It may arise from increase in the lattice strain which results from ordering the atoms or ions [8,21,22], and from that chemical structure undergoing strain affects structure's internal energy [22]. 3.2. Infrared (IR) spectra IR absorption spectra of as-prepared and annealed MgFe2O4 samples are illustrated in Fig. 6. It is illustrated that seven absorption bands ν1, ν2, ν3, ν4, νA, νB and νT are appeared in the IR spectra. The absorption band positions are given in Table 2. The characteristic absorption bands of cubic spinel ferrites; ν1 appears in the range of 570–589 cm  1 and ν2 in the range of 435–446 cm  1. The position of band ν1 decreases against T, whereas that of ν2 increases to maximum value at 500 °C and decreases thereafter. The decrease in ν1 may be due to increase in the crystallite size and concentration of the heavier Fe3 þ atomic weight (55.8) in the A-sublattice as T increases. The variation of ν2 may be due to variation of dBO and D [13,16,23,24]. The presence of these two bands in the spectra confirms the formation of cubic spinel nanoferrites. The absorption band ν3

Table 1 The lattice parameters, LA and LB are the distance between the magnetic ions (hopping length) on the A- and B-sites, RA and RB the ionic radius of A- and B-site, u the positional oxygen parameter, dAO and dBO the tetrahedral and octahedral bond length, dAE the tetrahedral edge and dBE and dBEU the octahedral shared and unshared edges, respectively. T (°C)

a (Å)

LA (Å)

LB (Å)

RA (Å)

RB (Å)

u

dAO (Å)

dBO (Å)

dAE (Å)

dBE (Å)

dBEU (Å)

Ap 300 500 700 900 1100 Error

8.35 8.4 8.32 8.3374 8.3661 8.3691 7 0.0001

3.131 3.151 3.121 3.127 3.137 3.139 7 0.001

2.088 2.101 2.08 2.084 2.091 2.093 70.001

0.675 0.67 0.659 0.669 0.643 0.67 7 0.002

1.325 1.33 1.341 1.331 1.331 1.33 7 0.002

0.399 0.397 0.397 0.396 0.394 0.393 7 0.002

2.155 2.153 2.133 2.151 2.13 2.163 7 0.002

2.094 2.112 2.093 2.09 2.11 2.1 7 0.002

3.519 3.516 3.483 3.512 3.479 3.529 7 0.002

2.385 2.423 2.4 2.381 2.438 2.391 7 0.002

2.979 2.995 2.966 2.986 2.981 2.987 7 0.002

M.A. Amer et al. / Journal of Magnetism and Magnetic Materials 401 (2016) 150–158

153

Fig. 7. The relation between Fc at A- and B-site, FA and FB, respectively, and T. Fig. 5. T dependence of the distortion parameter g.

The relation between the force constant Fc at the A- and B-sites, FA and FB, respectively, and T is shown in Fig. 7. It is shown that, except as-prepared sample, the force constant of the A- and B-sites decreases versus T. This decrease may result from the motion of metallic ions between the A- and B-site, which change the site radius, and variation in bond lengths, dAO and dBO [25]. The sharp increase in Fc at 300 °C may assign to losing the retained water. Debye temperature ?D was determined using the equation [26– 28]:

Fig. 6. IR spectra of as-prepared and annealed MgFe2O4 samples. Table 2 IR absorption band positions νn, n¼ 1,2,.. and B, error¼ 7 0.1. T(°C)

ν1(cm  1)

ν2(cm  1)

ν3(cm  1)

ν4(cm  1)

νA(cm  1)

νB(cm  1)

Ap 300 500 700 900 1100

587 589 580 573 574 570

438 446 441 440 435 435

– 330 330 330 1 330

– – – 239 239 239

873 874 874 874 874 877

1014 1017 1015 1015 1014 1012

appeared in the range of 336–390 cm  1 may result from splitting ν2. This band may assign to the divalent bonds Mg2 þ –O  2 among the B-sites [23,24]. The absorption band ν4 depends on the mass of the divalent tetrahedral cation and is assigned to some type of lattice vibrations involving a displacement of the tetrahedral cation [23,24]. The triple band νT appeared at around 1500 cm  1 may ascribe to the stretching modes and hydroxyl groups H–O–H bending vibration of the free or absorbed water. This water was retained in the samples when they were prepared [15,16,23,24]. Fig. 6 shows that the intensity of νT decreases with T but did not vanish completely at 1100 °C which proves that this compound is very sensitive to atmospheric humidity. Hence, this sample may be used as humidity sensor. The absorption bands; νA appeared in the range of 873–877 cm  1 and νB in the range of 1012–1017 cm  1, may assign to the divalent metal Mg2 þ ions at A- and B-sites.

?D =

ℏCνav = 1.438νav k

νav =

ν1 + ν2 2

where νav is the average value of wave numbers, ħ¼h/2π, h is Plank's constant, k is Boltzmann's constant, C ¼3  1010 cm/s; C is the velocity of light and the value of ℏC /k for the ferrite materials is taken as 1.438 [26–28]. Dependence of Debye temperature ?D on T is seen in Fig. 8. It is seen that ?D increases at 300 °C and decreases thereafter which can be explained on the bases of specific heat theory as follows [26–29]: the conduction electrons (n-type) can absorb part of the heat causing a decrease of ?D. The increase of ?D at 300 °C proves a decrease of the conduction electron number Ne and increase the number of conduction holes Np (ptype). The decrease of ?D for TZ 500 °C reveals an increase in Ne and decrease of Np. The increase in ?D may point to a transformation of the sample conductivity from conduction electrons (ntype) to holes (p-type) at 300 °C.

Fig. 8. Debye temperature ?D as a function of T.

154

M.A. Amer et al. / Journal of Magnetism and Magnetic Materials 401 (2016) 150–158

Fig. 9. Variation of C11 and C12 with T.

Fig. 10. Variation of Young's modulus E, bulk modulus K and modulus of rigidity G against T.

3.3. Elastic properties

3.4. Mössbauer spectra

The stiffness constants, C11 and C12, were determined using the relations [26,27]:

Young‵s modulus: E =

( C11 − C12 )( C11 + 2C12 ) ( C11 + C12 )

Fig. 11 displays RT Mössbauer spectra of as-prepared and heated MgFe2O4 samples. The spectrum for T¼ 300 °C is similar to that of as-prepared sample. They consist only of paramagnetic phase C (central doublet) and are fitted to two doublets CA and CB. The spectrum for T ¼500 °C consists of a small magnetic phase and central paramagnetic phase C and it is fitted to two central doublets CA and CB and two small magnetic subspectra A and B [29,30]. Existing the paramagnetic phase C of these samples may attribute to the fine size of the nanoparticles, i.e. volume too small (single domain) to maintain ferrimagnetic properties [30–33]. The spectrum of the sample heated at 700 °C shows a relaxed spectrum and is fitted to one central doublets CB and two magnetic subspectra A and broader B. The spectra of the sample heated at 900 and 1100 °C were fitted to the two magnetic subspectra A and broader B. The sharper subspectra A and CA were assigned to Fe3 þ ions among the A-sites and the broader subspectra B and CB were assigned to Fe3 þ ions among the B-sites. The broader magnetic subspectrum B is analyzed to four components Bn (n ¼0, 1, 2, 3 and 4) [23–25,34]. The broadening of the B-site subspectrum in the spectra for T Z700 °C may be due to the random distribution of the A-site Fe3 þ and diamagnetic Mg2 þ ions as the six nearest neighbors of the B-site Fe3 þ ion. Consequently, the distribution of the six A-site ions affect the super exchange interaction of each B-site Fe3 þ ion with its six nearest A-site neighbors. This affects the s-electron density at the B-site Fe3 þ ion nucleus, i.e. affects the hyperfine magnetic field at this nucleus [27–29]. Hence, the broader B-site magnetic subspectrum B was fitted to its multicomponents Bn (n ¼ 0, 1,…,4), where n denotes the number of A-site Mg2 þ ions as nearest neighbors of the B-site Fe3 þ ions. Using the binomial equation [30,31,35]:

Rigidity modulus: G =

E 2 (σ + 1)

⎛ 6⎞ P (n) = ⎜ ⎟ Y n (1 − Y )6 − n ⎝ n⎠

C11 =

F a

C12 =

C11σ (1 − σ )

where F is the average force constant; F =

F1 + F2 and 2

s is Poisson

ratio which is a function of pore fraction as s ¼0.324 (1–1.043p) [27]. The obtained absolute values of Poisson's ratio |s| lie between 0.1018 and 0.252, i.e. in the range of  1:0.5 which is in conformity with the theory of isotropic elasticity [26,27]. Variation of C11 and C12 with T is illustrated in Fig. 9. It illustrated that C11 increases at 300 °C and decreases thereafter, whereas the trend of C12 increases. The increase in C11 and C12 at 300 °C may be due to losing the retained water from the samples. Stiffness constants are affected by the tightness of atomic bonding and force constant, so that the decrease of C11 with T and C12 at 500 °C may be due to weakening the atomic bonding between Fe3 þ and Mg2 þ cations. The increasing trend of C12 may be due to decrease of force constant and increasing bond lengths at 900 and 1100 °C (Table 1). The elastic moduli such as; Young's modulus E, bulk modulus K and modulus of rigidity G were calculated using the relations [26,27]:

Bulk modulus: K =

1 ( C11 + 2C12 ) 3

The calculated values of E, G and K are illustrated in Fig. 10. It is illustrated that the elastic moduli: E and G decrease with T, whereas K has opposite behavior which reflects weakening of the inter-atomic bonding between various atoms in the lattice and increase of the Fe3 þ and Mg2 þ cation repulsion with increasing T [26,27]. The increase of K and decrease of E and G at 300 °C may assign to losing the retained water. Increasing K for T Z500 °C may assign to the increase of the crystallization process and crystallite size R.

where Y is the occupation percentage of Mg2 þ ions in the A-site, each component is assigned to the corresponding B-site component. The obtained Mössbauer parameters from the fits are listed in Table 3. The reduction of the hyperfine magnetic field of the Bn component depends on x (Table 3), which arises from the random distributions of Mg2 þ ions amongst the A-sites. Hence, the expected configurations for six A-nearest neighbors of the B-site Fe3 þ ions are 6Fe, 1Mg 5Fe, 2Mg 4Fe, 3Mg 3Fe and 4Mg 2Fe, respectively. Table 3 presents that the isomer shift IS values of Fe þ 3 at A-sites lie in the range of 0.1–0.35 mm/s and B-sites in the range of 0.1–0.64 mm/s. The values of IS are characteristic of the high spin Fe3 þ charge state [16,17,25,26]. The absolute quadrupole shift (or

M.A. Amer et al. / Journal of Magnetism and Magnetic Materials 401 (2016) 150–158

155

Fig. 11. RT Mössbauer spectra of as-prepared (Ap) and annealed MgFe2O4 samples. Table 3 The Mössbauer parameters; H is the hyperfine magnetic field, QS the quadrupole shift (splitting), IS the isomer shift, Γ the outermost line width, Ao the fractional area of each site and its calculated probability P, error¼ 7 0.02. T (°C)

Site

H (T)

QS (mm/s)

IS (mm/s)

Γ (mm/s)

Ao

P

Ap

CA CB CA CB A B CA CB A B0 B1 B2 B3 B4 CB A B0 B1 B2 B3 B4 A B0 B1 B2 B3

– – – – 49.96 47.73 – – 51.09 43.06 37.25 24.12 16.51 7.33 – 50.88 46.55 45.2 43.11 40.17 35.85 47.87 50.76 49.58 46.83 45.44

0.62 0.18 0.51 0.52  0.81 0.82 0.84 0.48  0.22  0.16  0.05  0.13 0.01 10.15 0.45  0.23  0.07 0.1  0.15 0.2  0.26 0.12  0.19 0.09  0.24 0.01

0.1 0.64 0.1 0.26 0.35 0.47 0.2 0.19 0.21 0.23 0.21 0.13 0.2 0.1 0.19 0.21 0.21 0.18 0.19 0.13 0.27 0.14 0.23 0.23 0.2 0.1

1.1 0.25 0.34 1.16 0.54 0.85 0.66 0.78 0.54 0.55 1.39 1.32 1.04 0.62 0.6 0.73 0.3 0.6 0.8 1.17 1.23 0.55 0.57 0.25 0.45 0.61

0.28 0.48 0.31 0.69 0.07 0.1 0.52 0.31 0.32 0.04 0.18 0.2 0.13 0.05 0.08 0.32 0.06 0.2 0.23 0.13 0.06 0.31 0.29 0.05 0.12 0.23

– – – – – – – – – 0.11 0.28 0.33 0.21 0.07 – – 0.11 0.28 0.33 0.21 0.07 – 0.18 0.29 0.33 0.2

300 500

700

900

1100

splitting) QS values at the A-sites lie between 0.12 and 0.84 mm/s and B-sites between 0.01 and 0.82 mm/s. The values of IS and QS agree with the corresponding values of spinel ferrites [16,17,25,26]. The change of QS sign is due to the chemical disorder which produces a distribution of electric fields of varying magnitude, direction, sign and symmetry. The relatively high values of IS and QS reveal the fine size nature of the samples [8,9,21]. The hyperfine magnetic field H of Fe þ 3 ions at the A-sites (HA) and average B-sites (HB) are plotted against T as displayed in Fig. 12. It is displayed that HA values are higher than HB values. This may be due to the wideness of B-subspectrum where the average HB becomes little than HA and to concentrated magnetic Fe3 þ ions among the B-sites. It is seen that HB decreases with T to a

Fig. 12. Variation of H at A- and B-sites versus T.

156

M.A. Amer et al. / Journal of Magnetism and Magnetic Materials 401 (2016) 150–158

Fig. 13. Dependence of ΓA and ΓB on T. Fig. 16. The relation between saturation magnetization Ms and T.

Fig. 14. The area ratio of B- to A-sites (B/A) versus T. Table 4 Cation distribution of as-prepared (Ap) and annealed MgFe2O4 nanoferrites. T (°C)

A-site

B-site

Ap 300 500 700 900 1100

Mg0.44Fe0.56 Mg0.38Fe0.62 Mg0.24Fe0.76 Mg0.36Fe0.64 Mg0.36Fe0.64 Mg0.38Fe0.62

Mg0.56Fe1.44 Mg0.62Fe1.38 Mg0.76Fe1.24 Mg0.64Fe1.36 Mg0.64Fe1.36 Mg0.62Fe1.38

minimum value at 700 °C and increases thereafter whereas HA slowly increase to a maximum value at 700 °C and decreases thereafter. This variation may be due to the A–B magnetic super exchange interactions, cation distribution and change in the bond

Fe3 þ –O2  length at A- and B-sites [32,34]. The increase of HB may reflect a ferromagnetic interaction between the magnetic ions within the sublattices. i.e. supertransferred B–B magnetic interactions arising from the presence of a large amount of Fe3 þ magnetic ions at B-site [8,15]. Fig. 13 displays dependence of outermost line width Γ of the magnetic subspectra A and B, ΓA and ΓB, respectively, on T. It is displayed that ΓA and ΓB increase with T and the values of ΓB are higher than ΓA, which may be due to the random distribution of Mg2 þ and Fe3 þ ions among the A-sites as nearest neighbors of Fe3 þ ions at the B-sites. The variation of ΓA proves the concentration of Fe3 þ ions amongst the B-sites. The area ratio of B- to A- sites (B/A) is plotted against T as shown in Fig. 14. It is shown that the area ratio of B/A-sites decreases with T to a minimum value at 500 °C and increases thereafter. This proves that the annealing temperature pushes the Fe3 þ ions to move between the A- and B-sublattices [7–10]. The cation distribution of this system can be estimated using the area under the well resolved A- and B-subspectra and the well-known ionic site preference as given in Table 4. 3.5. The magnetic measurements RT magnetic hysteresis loops for as-prepared and heated MgFe2O4 nanoferrites are depicted in Fig. 15. It is depicted that the hysteresis loops are very narrow which reveals that the samples are soft magnetic materials. The relation between the deduced saturation magnetization Ms and T is depicted in Fig. 16. It is depicted that Ms decreases slowly for T r500 °C and

Fig. 15. RT magnetic hysteresis loops of as-prepared and annealed MgFe2O4 nanoparticle samples.

M.A. Amer et al. / Journal of Magnetism and Magnetic Materials 401 (2016) 150–158

157

values of K are affected by the variation of both Hc and Ms with T, as well as the effect of increasing R and spin canting. Therefore the surface spins also affect the magnetization and anisotropy energy [31,32]. K points to the anisotropy energy sources as magnetocrystalline, shape and surface anisotropies [31,32]. The deduced values of coercivity Hc, remanent magnetization Mr, squareness (Mr/Ms) are presented in Table 5. It is presented that Hc, K and Mr /Ms do not depend on T, whereas that nB decreases to a minimum value at 500 °C and increases thereafter. The variation of nB may be due to variation of Ms, spin canting angle as well as the increased A–B super-exchange magnetic interactions [15].

4. Conclusion

Fig. 17. Dependence of Ms on (a) crystallite size R and (b) porosity P.

Table 5 The coercivity Hc, remanent magnetization Mr, squareness (Mr/Ms), crystal anisotropy constant K and magneton number nB. T (°C)

HC (G)

Mr (emu/g)

Mr/Ms

K (erg/Gauss)

nB (μB)

AP 300 500 700 900 1100 Error

32.525 82.977 39.431 13.654 143.5 184.67 7 0.002

0.0206 0.0391 0.0264 0.0453 1.3273 4.0194 7 0.0001

0.0038 0.0083 0.0055 0.0054 0.101 0.2353 70.0001

182.36 409.6 195.15 119.04 1964.75 3286.36 70.002

0.193 0.17 0.17 0.3 0.471 0.612 70.002

increases sharply thereafter. Variation of Ms may ascribe to the motion of magnetic Fe3 þ ions between the A- and B-sites which affects the A–B magnetic superexchange interaction, increase in the crystallite size R and improve in the crystallization process as T increases. The increase of Ms proves that the average magnetic domain size of the nanoparticle is increased and the spins become more aligned with the direction of the applied magnetic field. The increase in R leads to decrease of canting the spins at the particle surface which causes increase in Ms [36–38]. The correlation between Ms and both crystallite size R and porosity P is seen Fig. 17 which confirms the dependence of Ms on R and P. It is obvious that Ms increases with increase of R and decreases with increase of P. The values of anisotropy constant (K) and magneton number (nB) can be determined by the equations [39]:

Hc =

0.96K M × Ms , nB = Ms 5585

The calculated values of K and nB are given in Table 5. The

Heating MgFe2O4 nanoparticle samples led to increasing the crystallite size R. This proves that we can obtain fine nanoparticles by synthesizing the materials using the coprecipitation method and can control their size by the heating treatment. Seven absorption bands were observed in the IR spectra and assigned to their corresponding bonds. The theoretical and experimental density, strain and trend of stiffness constant C12 were increased against T, whereas the porosity, oxygen parameter, specific surface area, distortion parameter, positions of IR absorption bands ν1 and ν2, force constants, Debye temperature and stiffness constant C11 were decreased and the lattice constant and parameters did not show dependence on T. Mössbauer spectra revealed that the samples for T r500 °C are paramagnetic and other samples are ferrimagnetic materials. They proved that the hyperfine magnetic fields and line widths of the magnetic pattern at the A- and B-sites and fractional area ratio were affected by T, where the cation distributions were estimated. The magnetic hysteresis loops proved that the samples are soft magnetic. Their coercivity, squareness and crystal anisotropy constant showed independence on T, whereas their saturation magnetization Ms, remnant magnetization and magneton number showed dependence and Ms proved dependence on R.

Acknowledgment The authors thank Tanta University for supporting the current research project under the code number 01-13-05.

References [1] A. Manikandan, R. Sridhar, S. Arul Antony, S. Ramakrishna, J. Mol. Struct. 1076 (2014) 188. [2] B. Viswanathan, V.R.K. Murthy, Ferrite Materials Science and Technology, Narosa Pub. House, New Delhi, 1990. [3] J.Z. Mesomi, T. Moyo, T.B. Doyle, J. Magn. Magn. Mater. 310 (2007) 2534. [4] A. Surendiran, S. Sandhiya, S.C. Pradhan, C. Adithan, Indian J. Med. Res. 130 (2009) 689. [5] G.A. Mansoori, T. Rohani.Bastami, A. Ahmadpour, Z. Eshaghi, Annu. Rev. Nano Res. 2 (2008). [6] L. Filipponi, D. Sutherland, European Commission Directorate-General for Research and Innovation Industrial Technologies (NMP) Programme B-1049 Brussels, 2013. [7] E. Ranjith Kumar, R. Jayaprakash, Sanjay Kumar, J. Magn. Magn. Mater. 351 (2014) 70. [8] M.A. Amer, T.M. Meaz, A.G. Mostafa, H.F. El-Ghazally, Mater. Sci. Semicond. Process. 36 (2015) 49. [9] M.A. Amer, T.M. Meaz, A.G. Mostafa, H.F. El-Ghazally, Mater. Sci. Semicond. Process. 32 (2015) 68. [10] S.S. Jonit, M. Aziz, R. Sundari, UMTAS, 2011. [11] M.M. Hessien, Z.I. Zaki, Q. Mohsen, Int. J. Mater. Sci. 1 (2011) 30. [12] M.J. Iqbal, Z. Ahmad, T. Meydan, Y. Melikhov, J. Appl. Phys. 111 (2012) 33906. [13] S.S. Khot, N.S. Shinde, B. Ladgaonkar, B.B. Kale, S.C. Watawe, Int. J. Adv. Eng. Technol. 1/4 (2011) 422. [14] M.K. Rendale, S.D. Kulkarni, V. Puri, Arch. Appl. Sci. Res. 3/5 (2011) 491.

158

M.A. Amer et al. / Journal of Magnetism and Magnetic Materials 401 (2016) 150–158

[15] M.A. Amer, T. Meaz, M. Yehia, S.S. Attalah, F. Fakhry, J. Alloy. Compd. 633 (2015) 448. [16] S. Yan, J. Geng, L. Yin, E. Zhou, J. Magn. Magn. Mater. 277 (2004) 84. [17] D.H. Bobade, S.M. Rathod, M.L. Mane, Physica B 407 (2012) 3700. [18] M.A. Amer, S.A. Saafan, S.M. Attia, Eur. Phys. J.: Appl. Phys. 35 (2006) 201. [19] H.N. Oh, B.J. Evans, Phys. Rev. B14 (1976) 2965. [20] G. Dixit, J. Pal Singh, R.C. Srivastava, H.M. Agrawal, J. Magn. Magn. Mater. 324 (2012) 479. [21] P.P. Hankare, R.P. Patil, U.B. Sankpal, S.D. Jadhav, I.S. Mulla, K.M. Jadhav, B. K. Chougule, J. Magn. Magn. Mater. 321 (2009) 3270. [22] S.M. EL-Sayed, T.M. Meaz, M.A. Amer, H.A. El Shershaby, Part. Sci. Technol. 32 (2014) 39. [23] V. Kumar, Y. Ali, R.G. Sonkawade, A.S. Dhaliwal, Nucl. Instrum. Methods Phys. Res. B 287 (2012) 10. [24] S.S. Ata-Allah, A. Hashhash, J. Magn. Magn. Mater. 307 (2006) 191. [25] Anu Rana Vinod Kumar, M.S. Yadav, R.P. Pant, J. Magn. Magn. Mater. 320 (2008) 1729. [26] N. Rezlescu, E. Rezlescu, F. Tudorache, P.D. Popa, J. Optoelect, Adv. Mater. 6/2 (2004) 695. [27] S.M. Patange, S.E. Shirsath, K.S. Lohar, S.G. Algude, S.R. Kamble, N. Kulkarni, D. R. Mane, K.M. Jadhav, J. Magn. Magn. Mater. 325 (2013) 107.

[28] S.M. Patange, Sagar E. Shirsath, S.P. Jadhav, V.S. Hogade, S.R. Kamble, K. M. Jadhav, J. Mol. Struct. 1038 (2013) 40. [29] S.A. Mazen, S.F. Mansour, E. Dhahri, H.M. Zaki, T.A. Elmosalami, J. Alloy. Compd. 470 (2009) 294. [30] P.P. Hankare, V.T. Vader, N.M. Patil, S.D. Jadhav, U.B. Sankpal, M.R. Kadam, B. K. Chougule, N.S. Gajbhiye, Mater. Chem. Phys. 113 (2009) 233. [31] A.M. Cojocariu, M. Soroceanu, L. Hrib, V. Nica, O.F. Caltun, Mater. Chem. Phys. 135 (2012) 728. [32] E.R. Kumar, R. Jayaprakash, J. Magn. Magn. Mater. 348 (2013) 93. [33] A.B. Gadkari, T.J. Shinde, P.N. Vasambekar, J. Magn. Magn. Mater. 322 (2010) 3823. [34] S. Hajarpour, Kh Gheisari, A. Honarbakhsh Raouf, J. Magn. Magn. Mater. 329 (2013) 165. [35] M.A. Amer, Phys. Status Solidi (B) 237/ (2) (2003) 459. [36] K.K. Bamzai, G. Kour, B. Kaur, M. Arora, R.P. Pant, J. Magn. Magn. Mater. 345 (2013) 255. [37] K.S.A. Kumar, R.N. Bhowmik, Mater. Chem. Phys. 146 (2014) 159. [38] S.A. Saafan, T.M. Meaz, E.H. El-Ghazzawy, M.K. ElNimr, M.M. Ayad, M. Bakr, J. Magn. Magn. Mater. 322 (2010) 2369. [39] R.C. Kambale, P.A. Shaikh, S.S. Kambale, Y.D. Kolekar, J. Alloy. Compd. 478 (2009) 599.