Correlation between temperature dependent

Materials Research Express

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Correlation between temperature dependent dielectric and DC resistivity of Cr substituted barium hexaferrite To cite this article before publication: Sunil Kumar et al 2017 Mater. Res. Express in press https://doi.org/10.1088/2053-1591/aa9a51

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Cr Substituted Barium Hexaferrite Sunil Kumar, Sweety Supriya and Manoranjan Kar

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Correlation between Temperature Dependent Dielectric and DC resistivity of

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Department of physics, Indian Insitute of Technology Patna, Bihta-801103, Patna, India

Abstract: The chromium substituted barium hexaferrite (BaFe12O19) crystallize to the hexagonal symmetry (P63/mmc space group), which has been studied by employing the XRD technique. The XRD analysis is supported by the Raman spectra and, microstructural analysis has been carried out by the FESEM (Field Emission Scanning Electron Microscope) technique. Average particle size is found to be around 85 nm. Two peaks are observed in the temperature versus dielectric constant plots and, these two transition temperatures are identified as Td and Tm. The temperature Td is due to dipole relaxation, whereas Tm is assigned as dielectric phase transition. Both Td and Tm

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increase with the increase in frequency. However, the former one (i.e.Td) increases more rapidly compare to that of later one (i.e. Tm). Both the temperature (Td and Tm) are also well identified in the temperature dependent DC resistivity. All the samples exhibit the negative temperature coefficient of resistance (NTCR) behavior, which reveals the semiconducting behavior of the material. The Mott VRH model could explain the DC electrical conductivity. Both dielectric constant and DC resistivity is well correlated with each other to explain the transport

Introduction:

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properties in Cr3+ substituted barium hexaferrite.

The hexaferrite, not only have enormous commercial impact due to various technical applications that include highdensity memories, credit-card stripes, magnetic bar codes, small motors, and low-loss microwave devices, but also have fascinating magnetic and electric properties [1], which has always under the interest of fundamental research. The hexaferrite has five different sub-categories depending on their physical properties. These are: M-type

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(BaFe12O19), W-type (BaR2Fe16O27), X-type (Ba2R2Fe28O46), Y-type (Ba2R2Fe12O22), and Z-type (Ba3R2Fe24O41). Here, ‘R’ represents divalent, trivalent and tetravalent metal ions [2]. The M-type hexaferrite (BaFe12O19) is a hexagonal magnetoplumbite with space group P63/mmc [3]. The barium hexaferrite has high resistance, chemical stability, saturation magnetization, Curie temperatures and, their coercive field strength can be adjusted for a wide range of applications [4]. The structure is comprised of 64 ions per hexagonal unit cell on 11 distinct basic sites. The 24 Fe3+ ions are distributed on five different crystallographic sites: three octahedral sites (12k, 2a, and 4f2), one

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tetrahedral site (4f1) and one trigonal bipyramidal site (2b). The ferromagnetic structure given by the Gorter model shows three parallel (12k, 2a, and 2b) and two antiparallel (4f1 and 4f2) sites, which are coupled with superexchange interactions through the O2− ions [1-2]. The barium hexaferrite can be used in bulk form in many electrical and electronic devices because of their superior electrical and magnetic properties. Both magnetic and electrical properties of the hexagonal ferrites are strongly dependent on the synthesis conditions and the site

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AUTHOR SUBMITTED MANUSCRIPT - MRX-105636.R1

occupancy of the substituted cations among five Fe3+ different crystallographic sites. For improving the electrical and magnetic properties of barium hexaferrite, a number of studies were carried out on the synthesis methods, and

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cationic substitutions of divalent or multivalent ions and, of their mixture. In general, many cations and various cationic combinations such as Al [4,5], Sc [6,7,8], In [9,10], Mn–Ti [11], Al–Cr [12], Ti [13], Co-Ti [14], Pb [15], Mn–Zn [16], Co-Zr [17], Y [18] etc., are doped in BHF. From the above literature survey, it suggests that the single

doping and also a combination of dopants can be used to control the electrical transport properties of barium

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hexaferrite as well as magnetic properties. However, in recent times, the M-type barium hexaferrite attracts attention

as a multiferroic, i.e. a material which has both magnetic and electric polarization [19, 20]. The dielectric properties of hexaferrite depend on the method of preparation, sintering temperature and chemical composition [21]. A very few single material shows multiferroic properties at room temperature. The coupling between ferroelectric and ferromagnetic orders at ambient conditions is not possible because the conditions that lead to good ferromagnetic properties are opposed to those that lead to good ferroelectric properties [22,23]. The factors that create magnetization (aligned spin of free electrons) and dielectric properties (polarization of atoms) do not tend to coexist. The first multiferroic behavior was discovered by Kimura et al. in single phase Ba 0.5Sr1.5Zn2Fe12O22 hexaferrite at room temperature [24]. Later other group/s also has/has been reported muliferroic properties on single phase

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hexaferrite materials [25]. Chen et al. have been observed large ferroelectricity and strong ferromagnetism in barium hexaferrite ceramics [26]. Recently, Ghahfarokhi et al. studied the magnetic and electric properties of PbFe12O19 hexaferrite [27]. Tokunaga et al. have been studied magnetic and magnetoelectric properties of single crystal Scsubstituted BaFe12-xScxO19 [19]. The above studies show that, M-type hexaferrite has attracted the attention of

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researchers due to its simplest crystalline structure among the hexagonal ferrites and strong ferromagnetism at room temperature. A review paper has been reported by R. C. Pullar in 2012, it is a very good and chronological order of development of ferrite materials, especially on the hexagonal structure (BaFe12O19) [2]. It has been reported the development of ferrite materials from initial stage to today scenario. It has also mentioned the different synthesis method and different cation substitution in the single crystallographic site as well as in both crystallographic sites for the optimization of physical properties to use for technological applications. This review article mentioned the magnetic properties, DC conductivity, microwave applications of barium hexaferrite and multiferroic properties.

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Also, an extensive search with the help of scientific search engines reveals that, detailed study of magnetic properties and microwave physical properties of barium hexaferrite are reported [28,29]. Similarly, the electrical properties of barium hexaferrite such as dielectric, impedance analysis, DC resistivity are reported [30-36]. However, it needs further study to explore its applications. Especially the correlation between dielectric analysis and DC resistivity study needs to be addressed for better way to understand these materials. Hence, it has been motivated to researchers in recent past to explore the dielectric study as well as DC resitivity on barium hexaferrite. Therefore,

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in this article, the temperature and frequency dependent dielectric constant and its correlation with the crystal structure and DC resistivity has been reported for Cr substituted barium hexaferrite (BaFe12-xCrxO19). The present article may fulfill a little gap in the literature for the dielectric study of this material. The electrical transport properties are investigated through dielectric analysis with frequency as well as temperature variation. It is interesting to note that, two dielectric transition temperatures have been observed in the 300 to 775 K temperature

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range. It is similar to that of a ferroelectric material. The 1st transition temperature named as Td, which is due to dielectric loss, whereas, the 2nd transition temperature is called Tm.. At Tm, the material exhibited a para to

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ferroelectric like transition behavior. This dielectric behavior is comparable to that of ferroelectric bismuth sodium titanate (Bi0.5Na0.5TiO3). First time these two transition temperatures have been reported on temperature versus DC

resistivity study. These two transition temperatures also observed in temperature versus DC resistivity plot. The DC

conduction mechanism could be explained by the Mott’s variable range hopping (VRH) for all the samples. The

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analysis of crystal structure, dielectric analysis, and DC resistivity, have been carried out. Finally, an interesting correlation between DC resistivity and dielectric properties has been reported.

Experimental

The chromium substituted barium hexaferrite (BaFe12-xCrxO19) for x =0.0, 0.5, 1.0, 2.0 and 3.0 were synthesized by following the chemical sol-gel method [2]. The starting chemical such as BaNO3, Cr(NO₃)₃·9H₂O, Fe(NO3).H2O and citric acid are procured from either Merck or Alfa Aesar with >99% purity. The citric acid is used as fuel for reaction. The PH of the aqueous solution is maintained at ~ 7 (greenish color). This aqueous solution was dried with the help of hot plate with magnetic stirrer at the 80 OC for overnight. The synthesized powder was ground and it

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was sintered in two temperatures, i.e. 500 OC and 1000 OC for 2 hours each with ramping rate of 4O C per minute. The crystallinity and crystal structure of the samples were studied by the X-ray diffraction (Rigaku TTRX III diffractometer) technique with CuKα radiation (λ = 1.5418 Å) in the range of 15o to 70o. The measurement of Raman spectra of all samples has been carried out in the backscattering geometry using micro-Raman spectrometer

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(Seki Technotron Corp., Japan) with the 514 nm Argon ion laser line as excitation source by STR 750 RAMAN spectrograph. The Raman spectra measurement was performed on pellet at room temperature and 20x microscope lens was used to focus the laser and collects the scattered light. The morphology and microstructure analysis of the sintered samples have been performed by using Hitachi S-4800 Field Emission Scanning Electron Microscopy (FESEM). The pellets are prepared using KBr press, which is 10 mm diameter and 1mm thickness. The pellets are sintered at 1000 OC for 4 hours to obtain high density. The bulk density of all the sintered pellets was measured by the Archimedes method. The surfaces of pellets were painted by silver paste for electrical measurement. The

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electrical measurements of all the samples have been carried out by N4L Impedance analysis interface (PSM1735 NumetriQ) in the frequency range of 100 Hz–10 MHz and temperature 300 -775 K. To understand the DC electrical transport mechanism of barium hexaferrite and Cr3+ substituted barium hexaferrite, the DC resistivity measurements were carried out by employing the two probe method with the help of high precision Keithley Electrometer (Model

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No. 6517B).

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Result and Discussion: Structural analysis:

BaFe12-xCrxO19

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x=3.00 Yobs Ycalc Yobs-Ycalc

x=1.00

20

30

40

50

2 (Degree)

(2,2,0) (2,1,11) (2,0,14)

(2,0,9)

(2,0,10) (2,1,7) (2,0,11)

an (2,0,5) (2,0,6)

(0,0,8)

(1,0,7) (1,1,4) (2,0,0) (2,0,3)

(1,1,2)

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(1,0,1) (1,0,2) (1,0,3) (1,0,4)

(1,1,0)

x=0.00

(2,1,9)

ICCD No: 00-039-1433

x=0.50

(2,0,12)

Intensity (A.U.)

x=2.00

60

70

Fig. 1. XRD patterns (red) along with the Rietveld analysis patterns (black) of the samples (BaFe12-xCrxO19) x= 0.0, 0.50, 1.0, 2.0, and 3.0. The blue patterns are the difference between observed XRD and the Rietveld analysis

0.8

1.0

BaFe12-xCrxO19

-3

O 12 19

18

3.0

16

2.8

14

2.6

12

2.4

10

2.2

8

2.0

Lattice strain Dielectric constant

1.8 1.2

4Sin

1.4

1.6

20

3.2

1.8

0.0

0.5

1.0 (x) Cr

1.5

6

3

(b)

Dielectric consant (x10 )

BaFe

3.4

(a)

Lattice strain (x10 )

Experimental Data points Linear Fit

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0.054 0.051 0.048 0.045 0.042 0.039 0.036 0.033 0.030 0.027 0.024 0.021 0.6

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hkl cos

patterns. The peaks are indexed to P63/mmc spacegroup in hexagonal symmetry.

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2.0

Fig. 2. (a) Williamson-Hall Plot, βhkl cos θ vs 4 sin θ with a linear fit of BaFe12O19 and (b) The lattice strain and

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dielectric constant with increasing Cr content in barium hexaferrite.

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X-ray diffraction (XRD) patterns of (BaFe12-xCrxO19) for x =0.0, 0.5, 1.0, 2.0 and 3.0 along with the Rietveld refinement analysis are shown in figure 1. In the figure black solid line represents the experimentally observed XRD

patterns (Yobs), the red color circle represents the calculated patterns by employing Rietveld refinement (Ycalc) which

are overlapped with observed XRD patterns and, the blue color solid line represents the difference of observed data

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and calculated one (Yobs - Ycalc). All the observed Bragg’s peaks are indexed to P63/mmc space group in hexagonal symmetry [37]. No impurity phases could be traced for the samples with x ≤ 2 within XRD limit. However, small impurity peaks have been observed in the XRD pattern of the x=3 sample and it could be identified as Fe2O3. It is observed that, the impurity peak intensity increases for x≥3 (XRD patterns not shown). Hence, it reveals that the

Cr3+ ions can be incorporated in place of Fe to the lattice sites of hexagonal crystal structure up to 16 % (i.e. x=2). It is important to note that the XRD study has been performed by using a high power XRD machine (16 KW). Hence, the error is expected very low. Due to presence of impurity phase (within XRD limit), the higher doping (x ≥3) has not been considered for further analysis. The obtained lattice parameters and cell volumes are enlisted in the table I. It is observed that these two parameters decrease with the Cr substitution. It could be due to smaller ionic radius of

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the Cr3+ (0.615 Ǻ) compare to that of Fe3+ ion (0.645 Ǻ). The crystallite size and strain factor (due to substitution) were obtained by analyzing the XRD peaks by employing the W-H method and, these values are enlisted in table I. The crystallite sizes are found to be almost same for all the samples. However, the strain factor increases with the increase in Cr substitution, it could be due to lattice strain created by the smaller substituted Cr ion compare to that

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of replaced Fe ions in the crystal lattice.

Table I. The structural parameters, crystallite size, bulk density and particle size of BaFe 12-xCrxO19 (x= 0.0, 0.50, 1.0, and 2.0) samples.

Samples

(W-H method)

Crystal Structure parameters

Microstructure parameters

a=b(Å)

Volume

Density(db)

Particle

(Ǻ3)

(g/cm3)

Size (nm)

c(Å)

Crystallite

Strain

size (nm)

(10-3)

x=0.0

72

1.8

5.8872

23.1738

695.57

4.66

80

x=0.5

73

2.4

5.8870

23.1710

695.52

4.49

79

x=1.0

76

2.8

5.8867

23.1695

695.34

4.44

75

x=2.0

73

3.4

5.8859

23.1688

696.19

4.39

76

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BaFe12-xCrxO19

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a

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Microstructure analysis: BaFe12O19

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Particle density

b

40 50 60 70 80 90 100 110 120 130 140 Particle Size (nm)

Fig. 3. FE-SEM Micrographs of (BaFe12-xCrxO19) with x= (a) 0.0, (b) 0.5, and, (c) histogram of BHF (x=0).

The typical FESEM micrographs are shown in figure for BaFe12-xCrxO19 (x= 0.0 and 0.5). It is interesting to note that the grains are uniformly distributed. A histogram for BaFe12O19 micrograph is shown in 3 (c). The particle sizes are

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distributed from 40-130 nm. However, the average particle size of the pure BHF is about 87 nm. All other samples also have similar particle distribution. The average particle size obtained from FESEM micrograph is little higher than that of XRD analysis (crystallite size). It could be due to the larger crystallite size of the sample which is limit

Raman analysis:

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size calculation from the XRD peak broadening.

(613)

(524)

(466)

(412)

(332)

(284)

(208)

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Intensity (A. U.)

(181)

BaFe12-xCrxO19

(682) (707)

of the XRD technique to calculate the crystallite size [38]. Hence, it is assumed that there may be error in crystallite

x=2.0 x=1.0

x=0.5

x=0.0

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150 225 300 375 450 525 600 675 750 825 Raman Shift (cm-1)

Fig. 4. Raman spectra of BaFe12-xCrxO19 for x= 0.0, 0.50, 1.0 and 2.0 at room temperature.

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TABLE II. The observed Raman shift and assignment to crystal site and symmetry for BaFe12-xCrxO19 (x= 0.0, 0.50, 1.0 and 2.0) sample. Symmetry

BaFe12O19

BaFe11.5Cr0.5O19

BaFe11Cr1O19

BaFe10Cr2O19

181

179

174

172

209

284

281

332

330

466

524

613

413

465

203

278

325

408

463

324

402

461

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412

205

an

208

522

610

Assigned

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Raman Shift (cm-1) Peaks

517

609

500

608

E1g

E1g E1g

A2g

A1g

A1g

E1g

A1g

Polyhedra

Whole spinel block

Whole spinel block

Octahedrahedral Octahedrahedral (12 k) Octahedrahedral (12k) dominated Octahedrahedral (2a) Octahedrahedral (2a) Octahedrahedral (4f2)

680

676

672

A1g

Bipyramid (2b)

707

704

697

689

A1g

Tetrahedral (4f1)

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682

The structural analysis of BaFe12-xCrxO19 for x =0.0, 0.50, 1.0, and 2.0 samples have been carried out by using the XRD as well as the Rietveld analysis. Due to the impurity detection limitation of XRD technique, Raman spectra of the samples have been measured. The Raman spectroscopy is one of the advanced experimental technique for

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characterization of bulk material as well as the nanomaterial. The Raman scattering in vibrational or rotational mode is responsive only when the derivative of polarizability is non-zero. It utilizes the advantages of vibration or rotation of the molecules, which are the unique signature for the material. The 64 atoms in the unit cell of barium hexaferrite give rise to 189 optical modes, which can be characterized according to the D 6h factor group of the crystal by using group theory analysis. According to group theory and D6h symmetry, the 42 Raman active modes

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(11A1g+14E1g+17E2g) have been predicted for the M-type hexagonal symmetry at room temperature with space group P63/mmc [39-41]. The Raman spectra of BaFe12-xCrxO19 for x =0.0, 0.50, 1.0, and 2.0 samples have been recorded by using Argon ion laser (λ=514 nm) with 2 mW power in the frequency range of 150 cm-1 to 800 cm-1 at

7


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the room temperature which are shown in figure 4. There are 10 modes are clearly observed in the figure 4 and, all the observed 10 peaks in the spectra for all the samples are similar to that of single phase BaFe12O19. No other additional peak/s has/has been observed which reveals the absence of impurity in the material for x≤2. It well

supports to the XRD analysis. The observed peaks in the Raman spectra are assigned to different crystal symmetry

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and crystallographic sites of barium hexaferrite enlisted in table II, Which is similar to that of earlier results reported by Kreisel et al [42]. The observed peaks are shifted towards lower wave number, which is known as red shift. It is due to less atomic mass of Cr (51.991 amu) compare to that of Fe (55.845 amu). It is interesting to note that the intensity in the Raman spectra decreases with the increase of Cr substitution in the barium hexaferrite. It could be due to the increase of lattice strain in the samples with increase in Cr in barium hexaferrite. The lattice strain has been obtained from the XRD pattern analysis and listed in the table I and, it is found that the lattice strain increases with the increase of Cr substitution in the sample. The above discussion reveals that the Raman spectra and XRD analysis are well supports to each other.

2.0

5 4

(a)

1.5 1.0

Tm

Td

0.5 0.0

300 360 420 480 540 600 660 720 780

3

BaFe11.5Cr0.5O19 Tm

(b)

2

Td 1 0 300 360 420 480 540 600 660 720 780

Temprature K 21 18

1 KHz 10 KHz 100 KHz 500 KHz 1 MHz

BaFe10Cr2O19

Tm

3

15

'x10

17 Tm 1 KHz BaFe11Cr1O19 16 10 KHz 15 100 KHz 14 500 KHz 13 1 MHz 12 11 Td 10 (c) 9 8 7 6 5 4 3 2 1 0 300 360 420 480 540 600 660 720 780

12 9

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3

Temprature K

'x10


3

2.5

BaFe12O19

'x10

'x10

3

3.0


dM

3.5

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Dielectric analysis:

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(d)

Td

6 3 0 300 360 420 480 540 600 660 720 780

Temprature K

Temprature K

Fig. 5. The temperature variation of the dielectric properties of (BaFe12-xCrxO19) for x= (a)0.0, (b)0.50, (c)1.0, and (d) 2.0 at different selected frequencies.

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Figures 5(a-d) depicts the temperature dependence of dielectric constants at different selected frequencies of

(BaFe12-xCrxO19) for x= (a) 0.0, (b) 0.50, (c) 1.0, and (d) 2.0. There are two transition peaks appeared in the temperature dependent dielectric constants of all the samples. One peak is below 500 K and another one is above 𝑑𝜀 ′ 𝑑𝑡

| versus T at the maxima of the peak |

𝑑𝜀 ′

| → 0. The 1st

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500 K. The peak positions were obtained from the curve |

𝑑𝑡

peak temperature appears in the range of 340 to 450 K. The second peak is marked as ferroelectric to paraelectric like phase transition temperature, which appears at ~700 K in pure barium hexaferrite sample. According to the literature, the barium hexaferrite is not a ferroelectric material because, it does not have the permanent dipole, but when apply the electric field to the sample large number of the dipole is created due to inter ionic hopping’s via oxygen and, it behaves like a strong ferroelectric material [8]. The entire temperature range 300 K to 775 K is divided into the three regions and compare with a model, which is shown in figure 6 for BaFe12O19. It is already reported, that the dielectric constant increases with increasing temperature (thermal activation energy) [43-44]. From

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the literature survey, it is reveals that, the polar nano regions are formed due to the compositional disorder in the crystal structure due to mismatch of ionic radii of different atoms [45]. As in present samples, various ions with different ionic radii (Cr3+ and Fe3+) are present in the crystal sites, which leads to the formation of nanosize domain polarization (basically called as nano polar-region) and hence, affect the dielectric behavior of the samples. In the

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region I, the nano-polar region would be frozen at the lower temperature, but the dielectric constant increases with the increase in temperature. The increasing temperature is as much as high to initiate the bigger polar region converted into the nano-polar region in the samples for minimizing the thermal energy. Hence, during the formation of nano-polar region, the dielectric constant starts to decrease, which is clearly observed in the figure 5(a-d) with the region II [46]. Due to this effect, the 1st peak (Td) is observed, which not a phase transition, but it is a relaxor type behavior of the sample. After minimizing the energy of the system, the dielectric constant increases again with increasing temperature, and attained very high dielectric constant due to the presence of large number of nano-Polar domains. In the nano-polar domain, the electric dipoles are required very less energy to be polarized. So, the high

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dielectric constant is observed between region II and region III. Finally, the increasing temperature is that much higher, the ordered electric dipoles become a disorder due to excess of thermal energy, and dielectric constant suddenly decrease. The above transition assign by the 2nd peak temperature, which indicate the ferroelectric to paraelectric like phase transition (Tm). It is well comparable with the earlier report [47]. The region III is for the paraelectric nature of the samples. The proposed model is depicted in figure 6, which explains the physical

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phenomena of dielectric versus temperature in 300 K to 775 K, and the results are comparable to the bismuth sodium titnate (Ba0.5Na0.5TiO3) physical phenomena in the same temperature range (300 K to 775 K). In between these two transition peaks, it shows antiferroelectric type behavior, which is similar to the ferroelectric materials (BNT, BTO, PZT etc.) [45,48,49]. Both Td and Tm increase with the increase in frequency. The Td varies more rapidly with the frequency compare to that of Tm.

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Page 9 of 17

One cannot ignore the magnetic phase transition (Para-ferromagnetic transition) of barium hexaferrite,

which appears around 720K. Also another magnetic transition is observed above 400K. Both the magnetic transition temperatures are comparable to TM and Td (reported in the present study) respectively. Hence, the electrical

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polarization can be correlated with the magnetic phase transitions in the barium hexaferrite which needs further studies by temperature depended magnetization and crystal structure. However, it is beyond the scope of the present article and is our future research problem. Also it is worth to note that, barium hexaferrite exhibits multiferroic

1.4

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properties [24-26]. BaFe12O19

10 KHz

'x10

3

1.2 1.0 0.8 Region I 0.6

Region II Region III

0.4 0.2 0.0

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300 360 420 480 540 600 660 720 780 840 900

Temprature K

Fig. 6 Model for explaining the temperature dependant dipole characteristic in the samples. It is also explained the

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two dielectric transition and its behaviour like BNT pure ferroelectric materials.

DC conduction mechanism: 32

ln DC(m)

24

Td

pte

20 16


28

Tm

12 8 4

1.4

1.6

40

BaFe12-xCrxO19

X =0.0 X =0.5 X =1.0 X =2.0

1.8

2.0

2.2

2.4

2.6

BaFe12-xCrxO19

35 30 25 T= 303 K

20 15

2.8

3.0

-1

10 0.0

0.5

1.0

1.5

2.0 2.5 (x) Cr

3.0

3.5

4.0

ce

1000/T (K )

Fig. 7 (a) DC resistivity (natural log (ln) has taken for clarity) versus Temperature (1000/T) of (BaFe12-xCrxO19) x= 0.0, 0.50, 1.0 and 2.0 and, (b) the DC resistivity at 303 K with the increases of Cr 3+ concentration in the sample.

The DC electrical resistance was measured by two probe method using Keithley 6517B in the temperature range

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Page 10 of 17

300-775 K. The DC electrical resistivity (ρ) was calculated by using the

𝜌=

𝑅𝐴 𝑡

standard formula,

(R is the resistance, t is the thickness of the sample and A = (πr2) is the area of the electrode in contact with the

10

Page 11 of 17

pt

sample). The natural log of electrical DC resistivity versus 1000/T(K-1) temperature of (BaFe12-xCrxO19) for x= 0.0, 0.50, 1.0 and 2.0 are shown in figure 7 (a). The two anomalies were observed in the temperature dependent DC resistivity curve, which is also observed from dielectric constant versus temperature plot and discussed in the

previous section. These two anomalies are defined as two transitions with peaks at (Td and Tm) similar to that of

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dielectric analysis. DC resistivity increases with the increase in Cr3+ concentration in the barium hexaferrite as shown in figure 7 (b). It is worth to note that the room temperature DC resistivity of BaFe 12O19 is 1.6x105 Ω-m,

which increases up to 1.6x105 to 4.3x1012 Ω-m for the BaFe10Cr2O19 sample. From the figure 7 (a), it is observed that the electrical resistivity decreases with the increase in temperature. It reveals that all the samples show semiconducting nature with negative temperature coefficient of resistance (NTCR) behavior. The electrical conduction mechanism in ferrite materials is explained by the Verwey’s hopping mechanism [43]. According to Verwey’s hopping mechanism, hopping process takes place between two metal ions via an oxygen atom of the same element in more than one valence state, distributed randomly over crystallographic sites such as; Fe2+ ↔ Fe3+ + e-. The Cr3+ ions have 3 up spin arrangement. Due to this spin alignment of Cr3+ ions, it has more affinity to be

an

substituted in Fe3+ crystallographic sites, which has up spin alignment. Hence, the Cr3+ ions substituted to that of octahedral and bipyramidal sites (Fe3+ ions) of 12k, 2a and 2b in barium hexaferrite. Hence, Fe3+ ion reduces in the sample, which leads the decrease of hopping between Fe2+ ↔ Fe3+. This causes the increase in resistivity with the increase in chromium substitution in BHF. However, the hopping probability depends on the activation energy and

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the number of charge carriers present at the octahedral sites. The probability of hopping also depends on the potential barrier (activation energy for hopping) and the distance between the ions [50,51]. Hence, different models has been taken into account to explain the electrical transport behavior of disordered magnetic semiconductors. The analysis of electrical charge mobility in magnetic semiconductor material received attention by experimentally as

ce

pte

well as theoretically.

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11


Td

12 10

III

II

Re

Tm

Region I BaFe11Cr1O19

Td

Tm

6 0.19

0.20

dM

I gio n II Re

9

Region II

0.21 0.22 [T(K)]-1/4

(d)

25

Region I

BaFe10Cr2O19

Td

20

15 12

Experimental VRH model fit



30

(c)

an


21 18

0.23

0.22 0.21 [T(K)]-1/4

0.20

0.23

Region II

15 10

gio nI II

4 0.19

24

gio n

gio nI

6

Region II

Re

8

Re



Region I

BaFe12O19

pt

16 14

19 Experimental (b) 18 VRH model fit 17 Region I 16 15 BaFe11.5Cr0.5O19 14 Td 13 12 11 10 Region II 9 8 7 Tm 6 0.19 0.20 0.21 0.22 0.23 [T(K)]-1/4

(a)

us cri


18

0.19

Tm

0.20

0.21 0.22 [T(K)]-1/4

0.23

FIG. 8. The DC resistivity of (a) BaFe12O19, (b) BaFe11.5Cr0.5O19, (c) BaFe11Cr1O19, and (d) BaFe10Cr2O19, solid lines

pte

are VRH model curves.

TABLE III. The residual resistivity (ρ0) and Mott characteristic temperature (To) for BaFe12-xCrxO19 (x= 0.0, 0.50, 1.0 and 2.0) sample.

Samples

VRH model parameters ρo (Ωcm)

To(x1010 K)

Region I

Region II

Region I

Region II

x=0.0

2.61x10-58

7.40x10-20

17.40

0.389

x=0.5

3.19x10

-62

-21

22.60

0.389

x=1.0

845x10-79

1.22x10-22

58.70

0.709

x=2.0

-97

-27

74.34

1.61

ce

BaFe12-xCrxO19

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Page 12 of 17

8.17x10

3.43x10

1.65x10

12

Page 13 of 17

pt

TABLE IV. The density of states N(EF), average hoping distance (Rh), hopping energy (Eh) in both the regions of BaFe12-xCrxO19 (x= 0.0, 0.50, 1.0 and 2.0) sample.

Samples

Region I

Region II

Rh (Ǻ)

Eh (eV)

N(EF) (eV

)x1023

(300 K)

(300 K)

1

x=0.0

6.15

40

1.47

x=0.5

4.73

77

1.69

x=1.0

1.82

98

1.99

x=2.0

0.79

121

2.44

BaFe12-xCrxO19

N(EF) (eV m

-

3

Rh (Ǻ)

Eh (eV)

m-3)x1025

(500 K)

(500 K)

2.75

24.7

0.56

2.32

25.8

0.63

1.50

28.0

0.66

0.66

35.0

0.81

-

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-1

The electrical charge mobility can be understood by the Mott Variable range hopping (VRH) model. The hopping

an

takes place between occupied to non-occupied localized states. It is assumed that, the localized state in the present case are distributed in the material which creates uneven defect states distributions. Hence, the Mott-VRH model can be employed to understand the charge transport phenomena in this material. Further, the substitution may leads to more uneven distribution. The Motts variable range model is defined as[52], 𝑇

1

𝜌(𝑇) = 𝜌𝑜 exp⁡( 𝑜 )4

(1)

dM

𝑇

Here, ρ0 is the residue resistivity, T0 is the Mott characteristic temperature, which is expressed in terms of density of state in the Fermi level N(EF) and T is the measuring temperature. The DC resistivity versus temperature plots are shown in Figure 8 (a–d) along with the theoretical curve generated by the Mott VRH model. The y-axis and the xaxis are taken as ln ρ and T(1/4) respectively. There are three regions in the curve, which are region I, region II and region III as shown in the figure 8 (a-d). It is observed that, there are two peaks: one (Td) is in between region I and region II and other (Tm) is in between region II and region III. A careful analysis reveals that the strength of

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transition at Tm is weaker compare to Td. However, the Td and Tm values are comparable to that of dielectric measurement which is discussed earlier. Hence, it is worth to note that, the temperature dependent DC conductivity and dielectric are similar to each other in Cr substituted barium hexaferrite. Hence, the above observation and analysis opens a window to understand the electrical properties of barium hexaferrite. It is interesting to note that the Tm is close to that of para to ferromagnetic transition temperature of barium hexaferrite.

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The regions I and II have been analyzed by employing the VRH model. The residual resistivity (ρ0) and Mott characteristic temperature (To) are calculated by employing 3-D VRH model, which are enlisted in table III. All the parameters (ρo and To) increase with the increase in Cr concentration in the region I but in region II it decreases. It is concluded that the transport properties of Cr doped barium hexaferrite could be understood by the 3D VRH model. Also, it is worth noting that the hopping distance and energy is different in two regions. The Mott’s

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characteristic temperature (To) is represented as[52],

13


18

(2)

𝐾𝑏 𝑇𝑁(𝐸𝐹 )𝑎3

pt

𝑇𝑜 =

Where a is the localization length. The mean hopping length (Rh) and mean hopping energy (Eh) can be expressed at a given temperature T as[52], 3

𝑇

8

𝑇

1

𝑅ℎ (𝑇) = 𝑎( 𝑜 )4 3

4

1

(3)

us cri

1

𝐸ℎ (𝑇) = 𝑘𝑏 𝑇 4 𝑇𝑜 4

(4)

The density of states N(EF), Rh (300 K) and Eh (300 K) has been calculated by using equations (2-4) and, all the obtained parameters are enlisted in table IV. For this calculation, the localization length taken as 1Ǻ from the earlier report by P. Brahma et.al [53]. The density of states and average hopping distance increase with the increase in chromium concentration in barium hexaferrite. Similarly the hopping energy is also increase with the increase in Cr

an

content in the samples. The average hopping distance is linearly decrease with the increase in temperature. The average hopping distance is almost comparable to the average bond length in the barium hexaferrite. The hoping energy is linearly increasing with the increase in temperature, which is typical phenomena in the ferrite materials.. Conclusion:

The BaFe12-xCrxO19 (M-type hexaferrite) has been prepared by the sol-gel method. Analysis of XRD patterns of all

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the by employing the Rietveld refinement technique reveals that the samples crystallize to hexagonal symmetry (P63/mmc space group). The dielectric constant increases with the chromium content in the sample due to strain created in hexagonal symmetry by substitution of chromium. The two transition temperatures have been observed in temperature dependent dielectric as well as DC resistivity plots. These two transition temperatures are identified as dipole relaxation (Td) and para-ferroelectric like transition temperature (Tm). More interesting that the Tm is comparable to that of para-ferromagnetic transition temperature of barium hexaferrite. The temperature variation of DC electrical conductivity can be well understood by employing the Mott variable range hopping model in two

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different temperature ranges. The electrical conduction mechanism can be explained by assuming hopping mechanism between Fe3+/Cr3+ and Fe3+ /Fe2+sites. The density of state and average hopping distance increases with the increase in Cr concentration. Also, it is interesting to conclude that the hopping energy increases with the increase in Cr concentration in barium hexaferrite. All the samples exhibit the negative temperature coefficient of resistance behavior which reveals the semiconducting nature of the material. The electrical resistivity increases with

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the increase in Cr concentration in BaFe12-xCrxO19. Reference [1] S. E. Rowley, T. Vojta, A. T. Jones, E. Baggio Saitovitch, W. Guo, J. Oliveira, B. E. Watts, F. D. Morrison and J. F. Scott, N. Lindfield, “Quantum percolation phase transition and magnetoelectric dipole glass in hexagonal ferrites”, Physical Review B, 96 (2017) 020407-6. [2] R. C Pullar, Hexagonal Ferrites “A Review of the Synthesis, Properties and Applications of Hexaferrite Ceramic”, Progress in Materials Science, 57(7) (2012) 1191-1334. [3] S. R. Janasi, D. Rodrigues, F. J. G. Landgraf, and M. Emura, “Magnetic properties of coprecipitated barium ferrite powders as a function of synthesis conditions”, IEEE Trans. Magn., 36 (5) (2000) 3327-3329.

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 17

14

Page 15 of 17

ce

pte

dM

an

us cri

pt

[4] A. Arora, S. B. Narang, K. Pubby, “Effect of thickness on microwave absorptive behavior of La-Na doped CoZr barium hexaferrites in 18.0–26.5 GHz band”, Journal of Magnetism and Magnetic Materials, 423 (2017) 441–446. [5] S. M. E. Sayed, T. M. Meaz, M. A. Amer, H. A. E. Shersaby, “Magnetic behavior and dielectric properties of aluminum substituted M-type barium hexaferrite”, Physica B: Condensed Matter, 426 (2013) 137-143. [6] K. Praveena, R. Sandhya, M. Bououdina, M. P. Reddy, S. Katlakunta and S. Srinath, “Structural, magnetic, and electrical properties of microwave-sintered Cr3+ doped Sr hexaferrites”, Journal of Electronic Materials, 44 (2015) 524-531. [7] A. M. Balbashov, V. Yu. Ivanov, A. A. Mukhin, L. D. Iskhakova, Yu. F. Popov, G. P. Vorob and M. E. Voronchikhina, “Magnetic and magnetoelectric properties of M-type substitution hexaferrites TScxFe12 − xO19 (T = Ba, Sr)”, JETP Letters, 101 (2015) 489–496. [8] Y. Tokunaga, Y. Kaneko, D. Okuyama, S. Ishiwata, T. Arima, S. Wakimoto, K. Kakurai, Y. Taguchi, and Y. Tokura, “Multiferroic M-type hexaferrites with a room-temperature conical state and magnetically controllable spin helicity”, Phys. Rev. Lett., 105 (2010) 257201-4. [9] S. V. Trukhanov, A. V. Trukhanov, V. O. Turchenko, V. G. Kostishin, L. V. Panina, I. S. Kazakevich and A. M. Balagurov, “Magnetic Ordering in BaFe{11.9}In{0.1}O{19} Hexaferrite”, J Low Temp Phys, 186 (2017) 44–62. [10] V. Yu. Ivanov, A. M. Balbashov, A. A. Mukhin, L. D. Iskhakova, and M. E. Voronchikhina, “Magnetic and magnetoelectric properties of substituted M-type SrScxFe12–xO19 hexaferrites”, Journal of Experimental and Theoretical Physics, 124 (2017) 604–611. [11] C. Singh, S.B. Narang, M. Jaroszewski,V. Bhikan, and P. Kaur, “Schottky–Richardson, Poole–Frenkel, and Space Charge Limited Current Mechanisms in M‐Type Sr(MnTi)xFe(12‐2x)O19 Ferrite”, J. Am. Ceram. Soc., 99 (2016) 3639–3644. [12] R.C. Alange, Pankaj P. Khirade, Shankar D. Birajdar, Ashok V. Humbe, K.M. Jadhav, “Structural, magnetic and dielectrical properties of Al–Cr Co-substituted M-type barium hexaferrite nanoparticles”, Journal of Molecular Structure, 1106 (2016) 460-467. [13] A.I. Ghoneim, M.A. Amer, T.M. Meaz, S.S. Attalah, Physica B, 507 (2017) 1–12. [14] S. B. Narang, K. Pubby, C. Singh, “Thickness and Composition Tailoring of K and Ka Band Microwave Absorption of BaCoxTixFe(12-2x)O19 Ferrites”, Journal of Electronic Materials, 46 (2017) 718–728. [15] A. Haq, M. Tufail and M. Anis-ur-Rehman, “Structural, Electrical, and Magnetic Properties of BaFe 12-xPbxO19 Hexaferrite”, J Supercond Nov Magn, 30 (2017) 2991-2995. [16] A. Baykal, M. Demir, B. Unal,·H. Sozeri, M. S. Toprak, “Synthesis characterization and dielectric properties of BaFe10(Mn2+Zn2+Zn2+)O19 hexaferrite”, J Supercond Nov Magn, 29 (2016) 199–205. [17] P. Kaur, S. K. Chawla, S. S. Meena, S. M. Yusuf, S. B. Narang, “Synthesis of Co-Zr doped nanocrystalline strontium hexaferrites by sol-gel auto-combustion route using sucrose as fuel and study of their structural, magnetic and electrical properties”, Ceramics International, 42 (2016) 14475–14489 [18] I. A. Auwal, B.Unal, A. Baykal, U. Kurtan, M. D. Amir, M. Sertkol, A. Yildiz, “Electrical and Dielectric Properties of Y3+ Substituted Barium Hexaferrites”, J Supercond Nov Magn, 30 (2017) 1813–1826. [19] T. Kaur, J. Sharma, S. Kumar, A. K. Srivastava, “Optical and Multiferroic Properties of Gd-Co Substituted Barium Hexaferrite”, Crystal Research and Technology 52, (2017) 1700098-8. [20] G. Tan and X. Chen, “Structure and multiferroic properties of barium hexaferrite ceramics”, J. Magn. Magn. Mater., 327 (2013) 87-90. [21] Y. Liu, Y. Li, H. Zhang, D. Chen, and Q. Wen, “Study on magnetic properties of low temperature sintering MBarium hexaferrites”, Journal of Applied Physics, 107 (2010) 09A507-3. [22] P. Kumar, N. Shankhwar, A. Srinivasan and M. Kar, “Oxygen octahedra distortion induced structural and magnetic phase transitions in Bi1- xCaxFe1- xMnxO3 ceramics” Journal of Applied Physics, 117 (2015) 19410315. [23] P. Kumar, A. Gaur, R. K. Kotnala, “Magneto-electric response in Pb substituted M-type barium-hexaferrite”, Ceramics International 43 (2017) 1180–1185. [24] T. Kimura, G. Lawes and A. P. Ramirez, “Electric polarization rotation in a hexaferrite with long-wavelength magnetic structures”, PRL, 94 (2005) 137201-4. [25] A. V. Trukhanov, S. V. Trukhanov, V. G. Kostishin, L. V. Panina,I. S. Kazakevich, V. A.Turchenko, V. V. Kochervinskii, M. M. Salem, and D. A. Krivchenya, “Multiferroic properties and structural features of M-type Al-substituted barium hexaferrites”, Physics of the Solid State, 59 (2017) 737–745. [26] G. Tan, X. Chen, “Structure and multiferroic properties of barium hexaferrite ceramics”, J. Magn. Magn. Mater., 327 (2013) 87–90.

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


15


ce

pte

dM

an

us cri

pt

[27] S. E. Mousavi Ghahfarokhi, Z.A. Rostami, I. Kazeminezhad, “Fabrication of PbFe 12O19 nanoparticles and study of their structural, magnetic and dielectric properties”, J. Magn. Magn. Mater., 399 (2016) 130–142. [28] J. Qiu, M. Gu and H. Shen, “Microwave absorption properties of Al- and Cr-substituted M-type barium hexaferrite” Journal of Magnetism and Magnetic Materials, 295 (2005) 263–268. [29] J. Qiu, Y. Wang and M. Gu, “Effect of Cr substitution on microwave absorption of BaFe 12O19” Materials Letters, 60 (2006) 2728–2732. [30] A. S. Mikheykin, E. S. Zhukova, V. I. Torgashev, A. G. Razumnaya, B. P. Gorshunov, A. S. Prokhorov, A. E. Sashin, A. A. Bush, Y. I.Yuzyuk, and M. Dressel, “Lattice anharmonicity and polar soft mode in ferromagnetic M-type hexaferrite BaFe12O19 single crystal” Eur. Phys. J. B, 87 (2014) 1-9. [31] M. Micica, K. Postava, M. Vanwolleghem, T. Horak, J. F. Lampin, and J. Pistora, “Terahertz material characterization for nonreciprocal integrated optics” Proc. of SPIE, 9516 (2015) 9516151-10. [32] Ashima, S. Sanghi, A. Agarwal, Reetu, N. Ahlawat, and Monica, “Structure refinement and dielectric relaxation of M-type Ba, Sr, Ba-Sr,and Ba-Pb hexaferrites” Journal of Applied Physics, 112 (2012) 014110-10. [33] R. Tang, H. Zhou, R. Zhao, J. Jian, H. Wang, M. Fan, W. Zhang, H. Wang, H. Yang and J. Huang, J. Phys. D: Appl. Phys., 49 (2016) 115305-6. [34] H. B. Cao, Z. Y. Zhao, M. Lee, E. S. Choi, M. A. McGuire, B. C. Sales, H. D. Zhou, J. Q. Yan, and D. G. Mandrus, “High pressure floating zone growth and structural properties of ferromagnetic quantum paraelectric BaFe12O19” APL Materials, 3 (2015) 062512. [35] S. P. Shen, Y. S. Chai, J. Z. Cong, P. J. Sun, J. Lu, L. Q. Yan, S. G. Wang, and Y. Sun, “Magnetic-ion-induced displacive electric polarization in FeO bipyramidal units of (Ba,Sr)Fe 12O19 hexaferrites” Physical Review B 90 (2014)180404-10. [36] E. S. Zhukova, A.S. Mikheykin, V.I. Torgashev, A. A. Bush, A. E. Sashin, A.S. Prokhorov, M. Dressel, B. P. Gorshunov, Y. I. Yuzyuk, “Crucial influence of crystal site disorder on dynamical spectral response in artificial magnetoplumbites” Solid State Sciences 62 (2016) 13-21. [37] ICDD No: 00-039-1433, International Centre for Diffraction Data (ICDD). [38] B. D. Culity, Elements of X-Ray Diffraction, 3rd edition, Prentice Hall, Upper Saddle River, NJ 07458, USA, 2001 [39] J. Kreisel, G. Lucazeau, and H. Vincent, “Raman Spectra and Vibrational Analysis of BaFe 12O19 Hexagonal Ferrite”, J. Solid State Chem., 137 (1998) 127-137. [40] N. Hien, K. Han, X. B. Chen, J. C. Sur, S. Yang, “Raman scattering studies of spin‐waves in hexagonal BaFe12O19,” J. Raman Spectrosc., 43 (2012) 2020–2024. [41] J. Kreisel, G. Lucazeau and H. Vincent, Raman Study of Substituted Barium Ferrite Single Crystals, BaFe122xMexCoxO19 (Me = Ir, Ti), Journal of Raman Spectroscopy, 30 (1999) 115-120. [42] W. Y. Zhao, P. Wei, X. Y. Wu, W. Wang, and Q. J. Zhang, “Lattice vibration characterization and magnetic properties of -type barium hexaferrite with excessive iron”, Journal of Applied Physics, 103 (2000) 063902-5. [43] S. Supriya, S. Kumar, and M. Kar, “Correlation between AC and DC transport properties of Mn substituted cobalt ferrite”, Journal of Applied Physics 120 (2016) 215106-13. [44] S. Kumar, S. Supriya, and M. Kar, “Effect of Sintering Temperature on Electrical Properties of BHF Ceramics Prepared by Modified Sol-Gel Method”, Materials today: proceedings, 4 (2017) 5517-5524. [45] Y. Hiruma, H. Nagata, and T. Takenaka, “Detection of morphotropic phase boundary of (Bi0.5 Na 0.5)TiO 3–Ba(Al0.5Sb0.5)O 3 solid-solution ceramics”, Applied Physics Letters, 95 (2009) 052903-3. [46] X. Liu, H. Fan, J. Shi and Q. Li, “Origin of anomalous giant dielectric performance in novel perovskite: Bi 0.52+ 3+ xLaxNa0.5-xLixTi1− yMyO3 (M= Mg ,Ga )”, Scientific Reports, 5 (2015)12699-11. [47] G. L. Tan and W. Li “Ferroelectricity and Ferromagnetism of M-Type Lead Hexaferrite” J. Am. Ceram. Soc., 98 (2015) 1812–1817. [48] M. Valeriy, Ishchuk, L. G. Gusakova, N. G. Kisel, N. A. Spiridonov, and V. L. Sobolev, “Zr‐Substituted (Na 0.5Bi0.5)1‐xBa xTiO3‐Based Solid Solutions”, J. Am. Ceram. Soc., 99 (2016) 1786-1891. [49] N. W. Moore, H. J. B. Shaklee, M. A. Rodriguez, and G.L. Brennecka, “Optical anisotropy near the relaxor-ferroelectric phase transition in lanthanum lead zirconate titanate”, Journal of Applied Physics, 114 (2013) 053515-7. [50] S. Supriya, S. Kumar, and M. Kar, “Enhancement of Impedance by Chromium Substitution and Correlation with DC Resistivity in Cobalt Ferrite”, J. Mater Sci: Mater Electron, 28 (2017)10652-10673. [51] T. Rahman, M. Vargas, C.V. Ramana, “Structural characteristics, electrical conduction and dielectric properties of gadolinium substituted cobalt ferrite”, Journal of Alloys and Compounds. 617 (2014) 547–562.

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[52] S. Ravi, Manoranjan Kar, Study of magneto-resistivity in La1−xAgxMnO3 compounds, Physica B, 348 (2004) 169–176. [53] P. Brahma, S. Banerjee, S. Chakraborty and D. Chakravorty, “Small polaron and bipolaron transport in antimony oxide doped barium hexaferrites”, Journal of Applied Physics, 88 (2000) 6526-2628.

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17