Electrical resistivity studies of Cr doped Mg nano-ferrites

Accepted Manuscript Title: Electrical Resistivity studies of Cr doped Mg Nano-Ferrites Author: M. Raghasudha D. Ravinder P. Veerasomaiah PII: DOI: Reference:

S2352-9245(16)30013-8 http://dx.doi.org/doi:10.1016/j.md.2016.05.001 MD 16

To appear in: Received date: Revised date: Accepted date:

19-4-2015 27-5-2016 28-5-2016

Please cite this article as: M. Raghasudha, D. Ravinder, P. Veerasomaiah, Electrical Resistivity studies of Cr doped Mg Nano-Ferrites, Mater. Discov. (2016), http://dx.doi.org/10.1016/j.md.2016.05.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Title of the article: Electrical Resistivity studies of Cr doped Mg Nano-Ferrites

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Names of the authors:

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M. Raghasudha1*, D. Ravinder2, P. Veerasomaiah1

1

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Affiliation of the author:

Department of Chemistry, University Ccollege of Science, Osmania University, Hyderabad500007, Telangana State, India

Department of Physics, University College of Science, Osmania University, Hyderabad-

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2

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500007, Telangana State, India

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Dr. M. Raghasudha

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Corresponding Author

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E-mail: [email protected] Mobile No. +91-9550083100

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Electrical Resistivity studies of Cr doped Mg Nano-Ferrites M. Raghasudha1*, D. Ravinder2, P. Veerasomaiah1 1

Department of Chemistry, University College of Science, Osmania University, Hyderabad-500007, Telangana State, India 2 Department of Physics, University College of Science, Osmania University, Hyderabad-500007, Telangana State, India

Corresponding author E-mail: [email protected] Mobile:+91-9550083100

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ABSTRACT

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*

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Chromium doped Magnesium nano ferrites with the formula MgCrxFe2-xO4 (0≤x≤1) were prepared using the Citrate-gel method. The electrical resistivity (ρ) was measured in the

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temperature range of 200-7000C and was found to decrease with an increase in temperature ensuring the semiconducting nature of the prepared ferrites. The corresponding activation

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energies for conduction were obtained from the plot of log ρ vs 1000/T for all of the compositions, which display two slopes of separate regions. It was found that the activation

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energy was higher in the paramagnetic region than in the ferromagnetic region. With an

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increase in Cr composition, the electrical resistivity was found to decrease.

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Key words: Nanoferrites; Citrate-gel method; DC electrical Resistivity; Activation Energy; conduction mechanism.

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1. Introduction Soft ferrites are employed in a wide range of electronic applications and have increased significantly in importance over the last few years [1, 2]. Ferrites are semiconductors by

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nature. Semiconducting magnetic oxides are extensively used as thermistors. Electrical properties of ferrites provide information suitable for the selection of these materials for

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specific application and they are widely used in the elucidation of the conduction mechanism

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in semiconductors. Nano-ferrites have greater than 50% iron content and are among the most important materials for applications in telecommunication and high frequency devices.

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Ferrites have high electrical resistivity, low dielectric losses, high permeability, thermal stability and are semiconductor in nature. Electrical resistivity is used to describe the

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conduction mechanism in ferrites [3]. The conduction mechanism involves the exchange of electrons between elements having more than one valence state in the equivalent sites in the

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crystalline lattice. Measuring the current flowing through the circuit and the voltage across

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the sample, the resistivity of the sample is calculated in the Methods section of this paper. High resistivity of ferrites makes them suitable for high-frequency and low loss applications.

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It depends on the method of preparation, types of substituent, sintering duration, and temperature, among other factors [3]. Many researchers have studied the effect of metal ions as substituent on the electrical properties of ferrites. Kolekar et al. have studied the effect of Gd3+ substitution on electrical resistivity in

Cu - Cd ferrites and found that the substitution of Gd has increased the activation energy and also resistivity [4]. Vasambekar et al have studied the electrical properties of chromium substituted Cd-Co ferrites and reported that with an increase in Chromium content the Curie temperature has decreased [5]. It is reported by them that trivalent ions used as substituent occupy B-sites in the lattice and play a vital role in influencing the magnetic and electrical properties of ferrites. Bhaskar et al. have studied the electrical resistivity of Mg-Cu-Zn

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ferrites prepared by the microwave sintering method [6].The study of Cr3+ substituted copper ferrites [7] and Zn2+ substituted Li-Mg ferrites [8,9] are reported in the literature. Among the ferrites, Magnesium Ferrites (MgFe2O4) are soft magnetic ferrites

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crystallizing with the cubic spinel structure. They can be easily magnetized and demagnetized and hence, are used in electromagnets. They are nanocrystalline in nature and possess

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interesting electrical and magnetic properties. Thus, MgFe2O4 shows potential applications in many fields such as semiconductors [10], catalysts [11], gas sensing [12] and drug delivery

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[13, 14].

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It is quite interesting that MgFe2O4 show feeble magnetism even though Mg2+ ions are non-magnetic. This may be due to the inverse spinel structure of Magnesium Ferrites. The

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effect of non magnetic ions such as Zn2+ on various properties of Mg ferrites was studied by H.M. Zaki [15]. In Magnesium ferrites, when Zn2+ substituted for Mg2+, the electrical

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resistivity was decreased as reported by El Hiti [16]. Chand et al. have studied the effect of

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Gd substitution in Magnesium ferrites synthesized by the conventional ceramic method and reported that the resistivity increased with Gd substitution [17].

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Here we check the change in their electrical properties by the substitution of

paramagnetic Cr for iron in Magnesium ferrite. Moreover, DC electrical studies of Cr substituted magnesium ferrites synthesized using the Citrate-gel method have seldom been reported in the literature. Cr3+ ions have strong preference for the octahedral (B) site while Mg2+ ions have preference for both tetrahedral and octahedral sites. With a view to understand the conduction mechanism in the mixed Mg-Cr nano-ferrite system, we have undertaken the study of electrical resistivity as a function of composition and temperature.

2. Materials and methods MgCrxFe2-xO4 nano ferrites (with x=0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) were prepared using the Citrate-gel auto-combustion method with Magnesium Nitrate, Chromium Nitrate, Ferric

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Nitrate, Citric Acid and Ammonia solution as starting materials [18]. The flow chart for the synthesis of the Mg-Cr nano-ferrites is shown below (Figure 1).

Ferric Nitrate Solution

+

+

Citric Acid Solution

+

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Chromium Nitrate Solution

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Magnesium Nitrate Solution

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Mixing and continuous stirring on Magnetic stirrer

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Citrate Nitrate Mixture

Continuous stirring

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pH maintained at 7 by Ammonia addition

Continuous stirring

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Nitrate-Citrate Solution

Stirring and heating from 800C to1000C on hot plate Dry Gel

Heating up to 2000C Auto combustion Burnt ash

Calcination at 5000C for 4 hours and Grinding

Mg-Cr Nano ferrite powder

Figure 1 Flow Chart for the synthesis of Mg-Cr Nano ferrites

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In the process, required quantities of metal nitrates and citric acid were dissolved in distilled water separately. All these solutions were thoroughly mixed on a magnetic stirrer to get a homogeneous solution. Ammonia solution was then added to adjust the pH to 7. To

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remove water molecules, the solution was heated to about 1000C with constant stirring on magnetic hot plate that results in the formation of a viscous gel. On further heating, the

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viscous gel started foaming and underwent a flame less auto combustion reaction that started in the hottest portion of the beaker from the bottom and propagated upwards. The reaction

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completed in minute, resulting in a loose powder. Finally it was subjected to calcination at

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5000C for 4 hours in a muffle furnace to obtain the spinel phase. After cooling, the samples were ground thoroughly to obtain nano-ferrites in the spinel phase.

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The X-ray diffraction patterns of the ferrites under investigation confirmed the formation of a homogeneous single phase cubic spinel structure with a crystallite size ranging

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from 7-23nm [18]. The calcined powders (at 5000C, for 4 hours) were ground and circular

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pellets (diameter-13mm and thickness-2mm) were made using polyvinyl alcohol as a binder by exerting a pressure of 5tons for 1-2 minutes. These samples were finally sintered at 4000C

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for 5 hours and then slowly cooled to room temperature. To have a uniformly smooth surface, the circular pellets were carefully polished. Then the pellets were then coated with a thin layer of silver paste to have good electrical contact for the electrical measurements. The sample was placed between two electrodes in the sample holder and kept inside

the furnace maintaining the required temperature with the help of a temperature controller. The electrical resistance of the sample was measured in the temperature range of 2000C to 7000C using two probe method with a temperature increment of 100C. From the values of Resistance (R), thickness (h), and area of cross section of the sample (A), the electrical resistivity ρ was calculated using the relation (1) ..

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The densities (ρ) of the prepared samples was measured from the Archimedes principle and were tabulated in table 1. The following expression gives the relationship between DC electrical resistivity (ρ) and

∆E

kBT

(3)

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ρ = ρ∞e

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temperature (T in Kelvin) and is termed the Arrhenius relation [19].

where ρ∞ is the resistivity extrapolated to T=∞, kB is the Boltzmann constant, T is the

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absolute temperature and ∆E is the Activation energy needed for the hopping of an electron from one ion to the other neighboring ion of the same element with the different valence

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state, which gives rise to conduction in materials.

Drift mobility (µd) of the sample was measured using the following relation [20]

1 ηeρ

M

µd =

(4)

d

where ‘e’ is the charge of an electron, ‘ρ’ is the DC electrical resistivity and ‘η’ is the

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concentration of charge carriers that can be calculated from the following relation [21]

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η=

N a ρ s PFe M

(5)

where ‘M’ is the molecular weight of the sample, ‘Na’ is the Avogadro number, ‘ρs’ is the sintered density and ‘PFe’ is the number of iron atoms in the chemical formula of the ferrites.

3. Results and Discussion

3.1. Effect of temperature on D.C. Electrical Resistivity The effect of temperature on the D.C. electrical resistivity of all the samples was studied using two probe method techniques in the temperature range of 2000C -7000C. From figure 2 it is clear that the calculated resistivity from relation 1 decreased with increasing temperature. This fact reveals the semiconducting nature of the prepared ferrites. This could be ascribed to

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the increase in the drift mobility of electric charge carriers which are thermally activated with increasing temperature.

x=0.0 x=0.1 x=0.3 x=0.5 x=0.7 x=0.9 x=1.0

0.9 0.8 0.7

cr

0.5 0.4

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7

ρx10 ohm-cm

0.6

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1.0

0.3 0.2

an

0.1 0.0 -0.1

450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100

M

Temperature T (K)

Figure 2 Variation of Electrical Resistivity (ρ) of MgCrxFe2-xO4(x=0.0 to 1.0) with temperature

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The calculated resistivity of various compositions of the Mg-Cr nano-ferrite system at

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specific temperatures 300K (Room Temperature), 570K, 670K and 770K were tabulated in

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table 1. It is clear from table 1 that the room temperature resistivity is very high (77.90 x106 Ωcm at 300K of pure MgFe2O4) and is decreasing with increasing temperature (0.63 x106 Ωcm at 770K of pure MgFe2O4).

Table 1 Resistivity ‘ρ’ of MgCrxFe2-xO4 (x=0.0 to 1.0) ferrite system at various temperatures

Composition

Resistivity x 106 (Ωcm)

300K

570K

670K

770K

MgFe2O4

77.90

23.41

3.92

0.63

MgCr0.1Fe1.9o4

61.77

12.02

1.11

0.18

MgCr0.3Fe1.7o4

60.55

6.90

0.57

0.09

MgCr0.5Fe1.5o4

53.17

3.88

0.34

0.05

MgCr0.7Fe1.3o4

38.13

1.88

0.15

0.03

MgCr0.9Fe1.1o4

34.14

0.73

0.05

0.01

MgCrFeO4

22.49

0.31

0.04

0.009

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There is no change in the crystal structure of the ferrite samples with the substitution of Chromium in Magnesium ferrites as was clear from XRD studies from our earlier publication.

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3.2. Effect of Cr composition on D.C. Resistivity With the increase in the Cr concentration in the Mg-Cr ferrite system from 0.0 to 1.0 it is

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observed that the DC electrical resistivity at room temperature i.e. 300K was found to decrease from 77.90 x106 to 22.49 x 106 Ω-cm as indicated in table 1 and as apparent from

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figure 3. The variation in resistivity of all the ferrite compositions at temperatures 570K,

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670K and 770K were calculated and are summarized in table 1. From the table, it is clear that the resistivity has decreased from 0.63x 106 to 0.009 x 106 Ω-cm at 770K with the increase in

M

Cr concentration from 0.0 to 1.0.

The observed variations in resistivity with composition can be explained by Verwey’s

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hopping mechanism [22]. According to Verwey, the electronic conduction in ferrites is

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mainly due to hopping of electrons between the ions of the same element present in more than one valence state (Fe2+ and Fe3+ ions), distributed randomly over crystallographically

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equivalent lattice sites [23]. The probability of hopping depends upon two factors viz., the separation between the ions involved in hopping and the activation energy. It is a known fact that Cr3+ ions have strong octahedral (B) site preference. Hence, with an increase in Cr content, Fe3+ ions are partially replaced by Cr3+ ions at B-sites while Mg ions partially occupy A-sites and B-sites. As a consequence, an increase in Cr3+ ion substitution (at B site) decreases Fe3+ ions in the B site. It is observed from table 2 that the activation of hopping (Ea) has decreased with an increase in Cr content, resulting in the migration of some Fe ions from A-site to B-site to substitute the decrease in Fe ions at B-sites. Thus, the extent of electron exchange between Fe2+ and Fe3+ increase. Consequently, the resistivity decreases with the increase in Cr concentration in Mg-Cr nano ferrite system.

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80

300 K

Resistivity ρ (ohm-cm)

70

60

50

30

20 0.2

0.4

0.6

Cr Composition (x)

0.8

1.0

cr

0.0

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40

Figure 3 Variation of resistivity with composition at Room temperature (300K) of MgCrxFe2-xO4(x=0.0 to 1.0)

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3.3. Activation Energy of hopping

Arrhenius plots (log ρ vs 1000/T) of various compositions of the Mg-Cr nano ferrites

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were shown in the figure 4. From the slope of the Arrhenius plots, activation energies were calculated using the formula

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Ea = 2.303 x kB x 103 x slope (eV) where kB =Boltzmann Constant = 8.602 × 10-5 eV/K

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A change in slope is observed in the resistivity curve of the plot dividing the curve into two regions corresponding to ferrimagnetic region and paramagnetic region. From the figure, it is

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observed that the variation of resistivity is linear up to a temperature where a kink occurs, which represents the transition temperature known as Curie temperature (Tc). It shows a change of magnetic ordering from ferrimagnetism to paramagnetism upon the conductivity process in ferrites. The plots are hence divided into two regions. The region of plot below Tc is called the ferrimagnetic region while above Tc, is called the paramagnetic region. The calculated activation energies of all the compositions were summarized in table 2. It is clear from the table that the activations energies in the paramagnetic region (Ep) are higher than those in the ferrimagnetic region (Ef) and are in good agreement with the theory of Irkhin and Turov [24]. According to this theory for magnetic semiconductors, the activation energy in the paramagnetic state (Ep) should be greater than the activation energy in the ferrimagnetic

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region (Ef). This is because the ferrimagnetic state is an ordered one while the paramagnetic state is disordered one [25]. Hence, the charge carriers need more energy for the conduction in the paramagnetic state as compared to the ferrimagnetic state.

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Table 2 Sintered density (ρs), resistivity (ρ), Charge carrier concentration (η), drift mobility(µd), Activation energy (Ep, Ef and ∆E) and Curie temperature (Tc) of MgCrxFe2-xO4(x=0.0 to 1.0) Cr Composition X=0.1

X=0.3

X=0.5

ρs (gm/cc)

2.212

2.199

2.179

2.166

ρ at 770K x106 Ω-cm

0.633

0.18

0.09

η x 1022

1.326

1.325

µd at 770K x10-8(cm2/V-s)

0.26

0.60

Ep(ev)

0.984

0.884

Ef (ev)

0.907

0.827

∆E=Ep-Ef (ev)

0.087

X=1.0

2.154

2.142

2.109

0.03

0.013

0.009

1.325

1.326

1.325

1.35

2.74

5.24

14.26

22.61

0.703

0.678

0.659

0.643

0.626

0.650

0.630

0.659

0.604

0.593

0.053

0.048

0.042

0.039

0.033

710

701

694

680

670

d

1.326

M

an

0.05

1.327

te

0.057

781

X=0.9

720

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Curie Temperature (Tc)K

X=0.7

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X=0.0

cr

Parameter

8.0

x=0.0 x=0.1 x=0.3 x=0.5 x=0.7 x=0.9 x=1.0

7.5 7.0 6.5

log ρ (ohm-cm)

6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5

0.9

1.0

1.1

1.2

1.3

1.4

1.5 -1

1.6

1.7

1.8

1.9

2.0

1000/T (K )

Figure 4 Compositional variation of DC electrical resistivity (log ρ) with inverse temperature (1000/T) of MgCrxFe2-xO4(x=0.0 to 1.0)

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Thus, it indicates that the process of conduction in ferrites is influenced by the change in magnetic ordering. Similar results were reported in the case of a number of mixed ferrites such as Zn-Ni [26], Ni-Al [27] and Li-Ti [28].

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0.09

Activation Energy Ea

0.08

cr

0.07

0.06

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0.05

0.04

0.0

0.2

0.4

an

0.03 0.6

0.8

1.0

Composition (x)

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Figure 5 Variation of Activation of energy of hopping with Cr composition of MgCrxFe2-xO4(x=0.0 to 1.0)

The value of activation energy decreased from 0.087 to 0.033ev with an increase in Cr

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concentration from 0.0 to 1.0 (figure 5). It may be justified due to the decrease in resistivity

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DC electrical resistivity.

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with the increase in Cr concentration because activation energy behaves in the same way as

3.4 Curie temperature

The Curie temperature determined from resistivity plots shows a decreasing trend with increase in Cr3+ content as clear in table 2 and figure 6. This fact can be explained on the basis of the number of magnetic ions present in the two sub-lattices and their mutual interactions. As the concentration of Cr3+ ions increases at the octahedral site, the Fe3+ ions are replaced. As a result, AB interaction of the type Fe3+(A) - O2- - Fe3+(B) weakens. The Curie temperature is determined by an overall strength of the AB exchange interaction. Hence, the successive increase of Cr content in Magnesium ferrite that weakens the Fe3+(A) O2- -Fe3+(B) interaction results in a decrease of Curie temperature. Similar behavior was

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observed in the Al substituted Ni Ferrite system synthesized by the wet chemical coprecipitation method [27]. 780

Curie Temperature - Tc (K)

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760

740

cr

720

680

660 0.2

0.4

0.6

0.8

1.0

an

0.0

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700

Cr composition(x)

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Figure 6 Variation of Curie temperature of MgCrxFe2-xO4 with composition

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3.5 Drift mobility

The drift mobility for all the samples of the Mg-Cr nano-ferrite system has been calculated

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using relations 4 and 5. It is observed that the drift mobility has increased from 0.26x 10-8 to

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22.6 x10-8 cm2/Vs at 770K with a corresponding increase in Cr concentration from 0.0 to 1.0 (figure-7). It can be seen that the samples having higher resistivity have low mobility and vice versa. The plot of drift mobility (µd) vs Temperature (T) (figure-8) helps in understanding the temperature dependence of drift mobility. From the the figure-8, it is observed that mobility increases by increasing the temperature. The calculated values of drift mobility (µd) and charge carrier concentration (η) at different temperatures using relations 4 and 5 indicate that there is no change in the carrier concentration but that there is a change in the mobility of the charge carriers with an increase in temperature. This suggests that, it is the change in charge carrier mobility rather than the change in carrier concentration that is responsible for the variation of resistivity with temperature in the mixed Mg-Cr nano ferrite

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system. Hence, as the temperature increases, the charge carriers start hopping from one site to another resulting in an increase in the drift mobility and a decrease in the resistivity of the ferrite system. A similar behavior of variation of drift mobility with composition was

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reported in the mixed ferrite systems Ni-Zn [29], and Zr-Mg [30].

12000

x=0.0 x=0.1 x=0.3 x=0.5 x=0.7 x=0.9 x=1.0

20

15

10

-8

6000

4000

5

an

2000

us

µd x 10-10 (cm2/V-s)

8000

2

µ x 10 (cm /V-s)

10000

0

cr

25

0

0.0

0.2

0.4

0.6

0.8

1.0

500

600

700

800

Temperature(T) K

900

1000

M

Composition

Figure 7 Variation of Drift mobility (µd) with Cr content of MgCrxFe2-xO4(x=0.0 to 1.0) at 770K

d

Conclusions

Figure 8 Variation of Drift mobility (µd) of MgCrxFe2-xO4(x=0.0 to 1.0) with temperature

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MgCrxFe2-xO4 (x = 0.0 to 1.0) nano ferrite samples show semiconducting behavior with DC electrical resistivity ρ decreasing on increasing the temperature. Room temperature resistivity

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for a ferrite sample is very high and decreases with an increase in temperature. For MgFe2O4, the room temperature resistivity is 77.90 x106 Ωcm which decreased to 0.63x106 Ωcm at 770K. The DC electrical resistivity ρ, activation energies for electrical conduction (Ep, Ef and ∆E) and the curie temperature Tc of the ferrites under investigation were found to decrease as the Cr concentration increases. With increase in Cr composition electrical resistivity (ρ) of the ferrite samples were found to decrease from 0.6333x106 Ωcm to 9.26x103 Ωcm at 770K, which is explained by the Verwey conduction mechanism. The activation energy of hopping (∆E) was found to decrease from 0.087 to 0.033ev with an increase in Cr composition. All these changes are favorable for electronic applications. The

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resistivity values of all the prepared ferrites are of the order of 106 Ωcm which make them desirable for MLCI applications Acknowledgement

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The authors are thankful to Prof. K.M. Jadhav, department of physics, Dr. B.A.M. University, Aurangabad, Maharashtra, India for providing the lab facility for the electrical measurements.

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References

[1] Vermaa, M.I. Alama, R. Chatterjee, T.C. Goelb, R.G. Mendirttac, J. Magn. Magn. Mater. 300

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(2006) 500.

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[2] A. Goldmann, Handbook of Modern Ferromagnetic Materials, Kulwer Academic Publishers, Boston, USA, 1999. [3] A.K.M. Akther Hossaina, S.T. Mahmuda, M. Sekib, T. Kawaib, H. Tabata, J. Magn. Magn. Mater. 312 (2007) 210.

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te

d

M

[4] C. B. Kolekar, P. N. Kamble, A. S. Vaingankar, Ibid, 38(1994) 211. [5] P. N. Vasambekar, C. B. Kolekar, A. S. Vaingankar, J. Mater. Sci. Mater. Electronics. 10(1999) 667. [6] A. Bhasker, B. Rajnikanth, S.R. Murthy, J. Magn. Magn. Mater. 283(2004) 109. [7] Y. C. Venudhar. J.Alloys & Compd. 370 (2004)17. [8] M.A. Ahmed, E. Ateia, L. M. Salah, A.A. El-Gamal, Mater.Phys.Chem.92 (2005)310. [9] A. Verma, O. P. Thakur, C. Prakash, T.C. Goel, R.G. Mendiratta, Mater. Sci. & Eng.B 116(2005) 1. [10] P.V. Reddy, R. Satyanarayana, T.S. Rao , J. Mater. Sci. Lett. 3(1984) 847. [11] YH. Lee, GD. Lee, SS. Park, SS. Hong. React. Kinet. Catal. Lett. 84(2005) 311. [12] Y. Shimizu, H. Arai, T. Seiyama, Sens. Actuators. 7(1985) 11. [13] A. Goldmann, Modern Ferrite Technology, Van Nosttrand Reinhold, New York, 1990, 71. [14] N.S. Chen, X.J. Yang, E.S. Liu, J.L. Huang, Sens. Actuators B, 66(2000)178. [15] H.M. Zaki , Physica B. 404 (2009) 3356. [16] M. A. El Hiti, J. Magn. Magn. Mater. 136(1994) 138. [17] J. Chand, M. Singh, J. Alloys Compd. 486(2009)376. [18] M. Raghasudha, D. Ravinder, P. Veerasomaiah, Adv. Mat. Lett. 4(2013)910. [19] J. Smit, H.P.J. Wijn, Ferrites, John Wiley, New York, 1959, 233. [20] M.U. Islam, M.A. Chaudhry, T. Abbas, U. Umar, Mater. Chem. Phys. 48 (1997) 227. [21] N.F. Mott, E.A. Davis, Electronic Processes in Non-crystalline Material, Oxford, London, 1979. [22] E.J. Verwey, J.H. De Boer, Recueil des Travaux Chimiques des Pays-Bas, 55 (1936) 531. [23] A. Lakshman, P.S.V. Subba Rao, B.P. Rao, K.H. Rao, J. Phys. D: Appl. Phys. 38 (2005) 673.

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16 [24] Y.P. Irkhin, E.A. Turov, Sovt. Phys. JEPT 33 (1957) 673. [25] V.K. Lakhani, K.B. Modi, J. Phys. D: Appl. Phys. 44 (2011) 245403. [26] M. El-shabasy, J. Magn. Magn. Mater. 172 (1997) 188.

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[27] S.M. Patange, Sagar E. Shirsath, K.S. Lohar, S.S. Jadhav, Nilesh Kulkarni, K.M. Jadhav, Physica B 406 (2011) 663. [28] R. Manjula, V.R.K. Murthy, J. Sobhanadri, J. Appl. Phys. 59 (1986) 2929.

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[29] Muhammad Ajmal, Asghari Maqsood, Mater. Sci. Engg. B 139 (2007) 164.

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te

d

M

an

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[30] Muhammad Javed Iqbal, Mah Rukh Siddiquah, J. Magn. Magn. Mater. 320 (2008) 845.

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Electrical Resistivity studies of Cr doped Mg Nano Ferrites M. Raghasudha1*, D. Ravinder2, P. Veerasomaiah1 1

Department of Chemistry, University college of Science, Osmania University, Hyderabad-500007, Telangana State, India 2 Department of Physics, University college of Science, Osmania University, Hyderabad-500007, Telangana State, India *

cr

ABSTRACT

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Corresponding author E-mail: [email protected] Mobile:+91-9550083100

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Chromium doped Magnesium nano ferrites with the formula MgCrxFe2-xO4 (0≤x≤1) were prepared using Citrate-gel method. The electrical resistivity (ρ) was measured in the

an

temperature range of 200-7000C and was found to decrease with increase in temperature ensuring the semiconducting nature of the prepared ferrites. The corresponding activation

M

energies for conduction were obtained from the plot of log ρ vs 1000/T for all the compositions that show a straight line with two slopes. It was found that the activation energy

d

was higher in paramagnetic region than in ferromagnetic region. With increase in Cr

te

composition the electrical resistivity was found to decrease.

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Key words: Nanoferrites; Citrate-gel method; DC electrical Resistivity; Activation Energy; conduction mechanism. 1.0

0.8 0.7

0.5 0.4

7

ρx10 ohm-cm

0.6

x=0.0 x=0.1 x=0.3 x=0.5 x=0.7 x=0.9 x=1.0

0.3

12000

x=0.0 x=0.1 x=0.3 x=0.5 x=0.7 x=0.9 x=1.0

10000

8000

µd x 10-10 (cm2/V-s)

0.9

6000

4000

0.2

2000

0.1 0.0

0 -0.1 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100

Temperature T (K)

500

600

700

800

Temperature(T) K

900

1000

Variation of Electrical Resistivity (ρ) and Drift mobility of MgCrxFe2-xO4(x=0.0 to 1.0) with temperature

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