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Final paper Electrical transport and giant magnetoresistance in
manganite oxide.
Ah.Dhahria,*, M.Jemmalib, E.Dhahria, E.K.Hlilc
a
Laboratoire de Physique Appliquée, Faculté des Sciences de Sfax, BP 1171, Université de
Sfax, 3000, Tunisia. b
Laboratoire des Sciences des Matériaux et de l’Environnement, Faculté des Sciences de
Sfax, BP 1171, Université de Sfax, 3000, Tunisia c
Institut Néel, CNRS et Université J. Fourier, BP 166, 38042 Grenoble, France
Abstract We have investigated the influence of chromium (Cr) doping on the magneto-electrical properties of polycrystalline samples La0.75Sr0.25Mn1-xCrxO3 (0.15≤x≤0.25), prepared by solgel method. Comparison of experimental data with the theoretical models shows that in the metal-ferromagnetic region, the electrical behavior of the three samples is quite well described by a theory based on electron-electron, electron-phonon and electron-magnon scattering and Kondo-like spin dependent scattering. For the high temperature paramagnetic insulating regime, the adiabatic small polaron hopping (SPH) model is found to fit well the experimental curves. Keywords:
Conduction
mechanism,
small
magnetoresistance, percolation theory.
*
E-mail address: [emailprotected]
1
polaron
hopping,
magnetic
materials,
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La0.75Sr0.25Mn1-xCrxO3 (0.15, 0.20 and 0.25)
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Tel: +216 20 20 45 55
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Colossal magnetic resistance (CMR) was discovered in the mixed-valence manganese oxides Re1-xMxMnO3 (Re= rare earth, M =Sr, Ca, Ba) at a transition temperature close to that from a paramagnetic insulator (PMI) to ferromagnetic metal (FMM). This discovery has attracted much attention due to the extraordinary magnetic and electronic properties as well as the promise of the potential technological applications of these materials [1, 2]. So far, two CMR effects have been found in these manganites. They are the intrinsic CMR and extrinsic CMR. The intrinsic CMR is caused by the double exchange (DE) mechanism, which was proposed by Zener [3] in 1951. It is useful to explain the CMR phenomena observed near the Curie temperature (TC) at a relatively high magnetic field (up to several kOe). The extrinsic CMR, which is related to the grain boundaries, can be explained by spin polarized tunneling [4]. The parent compound, ReMnO3 is a charge-transfer (CT) insulator with trivalent manganese in different layers coupled among themselves antiferromagnetically through a superexchange mechanism. But within a layer, these Mn3+ ions are coupled ferromagnetically. When the Re trivalent element is doped by various elements, a proportionate amount of Mn3+ with the
(
electronic configuration 3d 4 , t 23g ↑ e1g ↑, S = 2
(
)
is replaced by Mn4+ with the electronic
)
configuration 3d 3 , t 23g ↑ eg0 ↑, S = 3 / 2 creating holes in the eg band[5]. The holes permit charge transfer in the eg state, which is highly hybridized with the oxygen 2p state. According to Hund’s rule, this charge transfer induces a ferromagnetic coupling between Mn3+ and Mn4+ ions which in turn has a dramatic effect on the electrical conductivity [6, 7]. It is believed that the study of the doping effects at the Mn site by other elements with different valences, electron configuration and ionic radius, is very important because of the crucial role of Mn ions in the CMR materials. The Mn-site doping is an effective way to modify the crucial Mn3+-O2--Mn4+ network [8]. In turn, it remarkably affects the double exchange effect by modifying the interaction between Mn3+/Mn4+ions via O2- ion network, which largely affects their physical properties as well as their CMR. So far, the magnetic ion substitution in the Mn-site and its effect on MR and MC properties has been extensively studied. Among the 3delements, Cr substitution is particularly interesting as Cr3+ is isoelectronic with Mn4+ and is a non-Jahn-Teller ion. In addition, the nature of the magnetic interaction between Cr3+-O2-Mn3+ is known to favor ferromagnetism through superexchange interaction. It is of much 2
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1-Introduction
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interest to know how the presence of a Cr ion in the Mn-site influences the magnetotransport and the MR properties of the material. Some models can explain the transport mechanism in manganites materials. However, most of them are only applied to fit the prominent change of
transport mechanism is explained by 3D Mott’s variable range hopping (VRH) model, small Published on 09 February 2015. Downloaded by Selcuk University on 09/02/2015 11:31:19.
polaron hopping (SPH) model and by the adiabatic small polaron hopping mechanism in the semiconductor region [9,10]. On the other hand, in the metallic region, the transport mechanism is governed by the single magnon’s scattering contribution, the electron-magnon scattering mechanism, electron–electron and electron–phonon scattering processes [11-13]. In addition, a theoretical percolation model, proposed by Li et al., which is based on phase segregation between metallic and semiconductor regions, is used successfully in the whole temperature range [14].In view of these facts, a lot of efforts have been made to get insights into the effect of Cr3+ on the electrical properties of
La03.+75 Sr02.25+ Mn03.+75−x Crx Mn04.+25O32− (0.15≤
x ≤0.25). These materials show an important magnetoresistance effect near room temperature especially in the x=0.15 sample (MR= 59%, TM-Sc=303K), which gives this compound the possibility of technologic application in the spintronic field at room temperature. The theoretical percolation model has been successfully used to explain the transport mechanism in the whole temperature range.
2-Experiment The microstructure of ceramic materials in general and CMR materials in particular are highly affected by preparation routes and heat treatments. Sol-gel routes are known to produce very high quality, hom*ogeneous and fine particle materials [15]. Bulk polycrystalline samples with compositional formula La0.75Sr0.25Mn1-xCrxO3 (0.15≤x≤0.25) were prepared by the sol-gel process. In this method, the metal nitrates taken in stoichiometric ratio were dissolved in an aqueous solution. Citric acid was added in 1:1 ratio and the pH was adjusted to a value between 6.5 and 7.0 by adding ammonia. After getting a sol on slow evaporation, a gelating reagent-ethylene glycol was added and heated between 160 and 180°C to get a gel. On further heating, this solution yielded a dry fluffy porous mass (precursor), which was calcined at 700°C for 6h. Then the powder was pressed into circular pellets. These pellets were sintered at 900°C in air for 12h. To obtain the metal-insulator transition temperature (TM-Sc) and to study the influence of magnetic field on resistivity, the electrical resistivity and
3
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the ρ-T curves in a finite temperature region (above or below TC). On the one hand, the
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magnetoresistance measurements have been done by standard dc four-probe technique using a closed cycle helium refrigerator cryostat in applied fields of 0T, 2T and 5T over a temperature range 4-400K.
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3.1. Magneto-transport behavior A typical plot of resistivity (ρ) versus absolute temperature (T) in the case of LSMCrx (x=0.15, 0.2 and 0.25) at different fields is shown in figure 1. Change in resistivity around TMSC
is interpreted in the framework of percolative conduction model based on the mixed phase
of itinerant electrons and localized magnetic polarons. From figure 1, we can see that the resistivity at a given temperature is found to decrease with increasing field and that TM-SC values are found to move towards the high temperature side with increasing magnetic field. The observed behavior may be attributed to the fact that the applied magnetic field induces the delocalization of charge carriers, which in turn suppresses the resistivity causing local ordering of the magnetic spins. Due to this ordering, the ferromagnetic metallic state may 1 suppress the magnetic insulating regime. As a result, the conduction electrons ( eg ) are
completely polarized inside the magnetic domains and are easily transferred between the pairs
(
4 3 1 Mn3+ 3d , t 2 g ↑ eg ↑, S = 2
)
(
)
and Mn4+ 3d 3 , t 23g ↑ eg0 ↑, S = 3 / 2 via oxygen. Hence the peak
temperature (TM-Sc) shifts to high temperature side with the application of magnetic field [16]. The percentages of magnetoresistance (MR) of all the samples have been calculated using the relation:
MR ( % ) =
( ρ ( 0, T ) − ρ ( H , T ) ) ×100
(1)
ρ ( 0, T )
Where ρ(0, T) is resistivity under a zero magnetic field, ρ(H, T) is resistivity under an applied field. Figure 2 shows the variation of MR as a function of the temperature at different applied magnetic fields (2 and 5 T). The MR values of all the samples of the present work were calculated over a temperature range 4-450K, and maximum values of MR for each field were also calculated, and are given in table 1. It is interesting to note from table 1 that the samples with low TM-SC exhibit large MR while those with high TM-SC exhibit low MR, and the behavior is in agreement with the universal MR- TM-SC relationship [17]. Our results are as important as earlier results. They even could be better in some cases (table1). 3.2. Electrical transport properties 4
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3-Results and discussion
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First, we discuss electrical resistivity results with zero external magnetic field. Figure 1 shows the temperature dependence of electrical resistivity for LSMCrx samples. Taking the sign of
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exhibit a metallic behavior (
dρ ) as a criterion, we found that samples dT
dρ > 0 ) at a low temperature (TTC, the concentration of the ferromagnetic phase approaches zero. The external magnetic
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References
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[2]Md.M.Seikh, L.Sudheendra, C.N.R.Rao, J.Solid State Chem.177(2004)3633. [3]C.Zener, Phys.Rev.82(1951)403. [4]H.Y.Hwang, S.W.Cheong, N.P.Ong, B.Batlogg, Phys.Rev.Lett.77(1996)2041. [5]K.Cherif, J.Dhahri, E.Dhahri, M.Oumezine, H.Vincent, J.Solid State Chem.163(2002)466471. [6]Z.Xinghua, L.Zhiqing, J.Rare earth2 9(2011)230-234 [7] L.Joshi, S.Keshri, Measurement 44(2011)938-945. [8]J.L.Garcia,_Munoz, C.Frontera, P.Beran, N.Bellido, J.Hernandez-Velasco, C.Ritter, Phys.Rev.B81(2010)014409-014420. [9] Dinesh Varshney, M.W. Shaikh. J. Alloy. Compd, 589 (2014) 558-567 [10]Dinesh Varshney, M.W. Shaikh, I.Mansuri J. Alloy. Compd, 486, (2009) 726-732. [11]M.W. Shaikh, Dinesh Varshney. Mat Sci Semicon Proc 27(2014)418-426. [12]A. Narjis, A. El kaaouachi, G. Biskupski, E. Daoudi, L. Limouny, S. Dlimi, M. Errai, A. Sybous. Mat. Sci. Semicon. Proc. 16 (2013) 1257–1261 [13] D. Varshney, D. Choudhary, M.W. Shaikh and E. Khan. Eur. Phys. J. B 76 (2010) 327– 338. [14] G. Li, H.D. Zhou, S.L. Feng, X.-J. Fan, X.G. Li, J. Appl. Phys. 92 (2002) 1406. [15]P.N.Lisboa, A.W.Mombro, H.Pardo, E.R.Leite, W.A.Ortiz , Solid State Commun.130(2004)31. [16]A.Banerjee, S.Pal, B.K.Chaudhuri, J.Chem.Phys.115(2001)1550-1559. [17] A.P.Ramirez, J.phys: Condens. Matter 9 (1997) 8171. [18] Ah.Dhahri, E.Dhahri,E.K.Hlil, Appl.Phys.A116(2014)2077-2085. [19]S.Jin, T.H.Tiefel, M.McCromack, R.A.Fastnach, R.Ramesh, L.H.Chen, Science 264 (1994) 413.
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[1]L.Hueso,N.D.Mathur, Nature427(2004)303
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[20]M.Auslender, A.E.Karkin, E.Rozenberg, G.Gorodetsky, J.Appl.Phys89(2001)6639. [21]T.Sarkar, B.Ghosh, A.K.Raychaudhuri, T.Chatterji, Phys.Rev.B77(2008)235112.
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[23]G.Venkataiah, P.Venugopal Reddy, solid State Commun.136 (2005)114. [24] L.Li, K.Nishimura, M.Fujii, K.Mori, solid State Commun.144 (2007)10. [25]A.Urushibara,Y.Moritomo,T.Arima, A.samitsu, G.Kido,Y.Tokura, Phys.Rev.B51(1995)14103. [26]P.T.Phong, N.V.Khiem, N.V.Dai, D.H.Manh, L.V.Hong, N.X.Phuc, J. Magn. Magn. Mater. 321(2009)3330-3334. [27]M.Viret, L.Ranoo, J.M.D.Coey, Phys.Rev.B55(1997)8067-8070. [28] Mohammed Wasim Shaikh, Dinesh Varshney Mater. Chem. Phys 134 (2012) 886-898. [29]V.Sen, N.Panwar, G.L.Bhalla, S.K.Aguarwall, J.Phys.Chem.Solids.68(2007)1685. [30]G.J.Snyder, R.Hiskers, S.Dicarolis, M.R.Beasley, T.H.Geballe, Phys. Rev. B53 (1996)14434-14444. [31 ] M.Ziese, Phys.Rev.B68(2003)132411. [32]J.B.Goodenough, J.S.Zhou, Nature 386(1997)229. [33] A.Banerjee, S.Pal, S.Bhattacharya, B.K.Chaudhuri, J.Appl.Phys.91(2002)5125 [34] E. Dagotto, T. Hotta, A. Moreo, Phys. Rep. 344 (2001) 1. [35] G. Li, H.D. Zhou, S.L. Feng, X.-J. Fan, X.G. Li, J. Appl. Phys. 92 (2002) 1406. [36] M. Pattabiramana, G. Rangarajana, P. Murugaraj, Solid State Commun, 132 (2004) 7. [37]Young Sun, Wei Tong, Xiaojun Xu, and Yuheng Zhang. Appl. Phys. 78(2001) 5. [38]F. Elleuch , M. Triki , M. Bekri , E. Dhahri, E.K. Hlil. J. Alloy. Compd 620 (2015) 249– 255. [39] M. Khlifi, E. Dhahri, E.K. Hlil. J. Alloy. Compd 587 (2014) 771–777. [40] N. Kallel ,K. Frohlich, S. Pignard, M. Oumezzine, H. Vincent . J. Alloy. Compd 399 (2005) 20–26.
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[22]E.Rozenberg, M.Auslender, I.Felner, G.Gordetsky, J.Appl.Phys.88(2000)094407.
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[41] W. Cheikh-Rouhou Koubaa, M.Koubaa,A. Cheikhrouhou. J. Alloy. Compd. 453 (2008)
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42–48
13
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Tables caption Table.1.Comparison
of
the
values
of
magnetoresistance
of
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Table.2.The best fit parameters obtained from the experimental resistivity data of the metallic behavior (below TM-Sc). Table.3.Fitting
parameters
of
the
small
polaron
model
for
La0.75Sr0.25Mn1xCrxO3(0.15≤x≤0.25). Table.4. Obtained parameters corresponding to the best fit to the Eq. 9 of the experimental data of La0.75Sr0.25Mn1xCrxO3 (0.15≤x≤0.25) at 0, 2, and 5 T.
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La0.75Sr0.25Mn1xCrxO3(0.15≤x≤0.25) compounds (this work) with earlier results.
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Table 1 Samples
TM-Sc (K)
MR(%) around TM-Sc
References
La0.75Sr0.25Mn0.85Cr0.15O3
303
59
This work
La0.75Sr0.25Mn0.8Cr0.2O3
264
65
This work
La0.75Sr0.25Mn0.75Cr0.25O3
231
74
This work
La 0.67Sr0.33Mn0.9Cr0.1O3
340
30
[37]
Pr0.5□0.1Sr0.4MnO3
211
25
[38]
La0.8Ca0.2MnO3
250
48
[39]
La0.7Sr0.3Mn0.9Sn0.1O3
225
11
[40]
La0.7 Sr0.1Ag0.2MnO3
245
30
[41]
15
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for 5T field
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Sample code
µoH(T)
ρ0(Ω.cm)
LSMCr0.15
LSMCr0.20
LSMCr0.25
ρ2(×10-6Ω.cm/K2)
ρ9/2(×10-11Ω.cm/K2)
ρe(Ω.cm/K1/2)
ρs(Ω.cm)
ρp(×10-6Ω.cm/K5)
0.28861 20
5.7492
0.20219
0.1833
7.6442
2
0.26752 19.5316
3.3578
0.04115
1.3233
2.6696
5
0.25631 19.3256
1.626
0.03439
0.26295
1.7457
0,63169 12,8976
8.4965
0.4452
0.22168
4.57
2
0,62457 11.6573
8.4792
0.2364
0.67357
4.374
5
0.62183 10.5746
5.9099
0.20897
0.283
1.9499
0.91437 7.6973
12.176
0.6821
0.10187
7.4878
2
0.83888 7.0698
6.9099
0.5482
0.19168
5.2957
5
0.71051 5.8952
4.4068
0.50879
0.04594
2.6123
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Table 2
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Table 3
Sample code
µ0H(T)
ρα(×10-6Ω.cm)
Ea(meV)
R2
LSMCr0.15
22.9
61.29
99.95
2
23.1
54.57
99.92
5
29
22.93
99.97
11.9
102.25
99.95
2
12.1
93.88
99.96
5
22.4
82.09
99.96
7.82
242.42
99.98
2
7.42
225.14
99.93
5
9.44
200.16
99.94
LSMCr0.2
LSMCr0.25
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Table 4:
Sample code
LSMCr0.15
LSMCr0.20
LSMCr0.25
0T
2T
5T
0T
2T
5T
0T
2T
5T
ρ0 (Ω.cm)
0.28855
0.26755
0.25630
0.63171
0.62458
0.62186
0.91439
0.83891
0.7104
ρ2 (××10-6 Ω.cm/K2)
21
19.5322
19.3258
12.8973
11.6572
10.5751
7.6971
7.0696
5.8949
ρα (10-6Ω.cm)
22.86
23.22
29.01
11.95
12.16
22.38
7.79
7.45
9.51
3.3576
1.6261
8.4966
8.4789
5.9011
12.174
6.9012
4.4072
ρ9/2(××10-11 Ω .cm/K2) 5.7491 ρe (Ω.cm/K1/2)
0.20201
0.04117
0.03441
0.4456
0.2361
0.20898
0.6823
0.5484
0.5088
ρs (Ω.cm)
0.1831
1.3236
0.26299
0.22167
0.67360
0.2833
0.10191
0.19172
0.0459
ρp (×10-13 Ω .cm/K5)
7.6446
2.6693
1.7461
4.5731
4.3762
1.9511
7.4882
5.2963
2.6133
EA/kB (K)
711.26
633,28
266,10
1186,60
1089,47
952,65
2813,27
2612,74
2322,8
Uo/kB (K)
3065
3088
3122
2040
2194
2288
1412
1759
1772
TCmod(K)
320
324
329
277
283
287
236
241
245
R2 (%)
99.96
99.98
99.94
99.93
99.97
99.98
99.93
99.98
99.97
18
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Figure captions Figure.1. Temperature dependence of resistivity ρ(T) under different magnetic field for LSMCrx (x=0.15 and x=0.25).
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x=0.25) samples under different magnetic field applied. Figure.3 Theoretical fit of low temperature resistivity data for LSMCrx (x=0.15 and x=0.25). Symbols are the experimental results and the bold solid line in these plots represents the best fit of experimental data in the metallic regime, below TM-Sc with Eq.(2)
ρ (T ) = ρ0 + ρeT 1/ 2 − ρ s ln T + ρ pT 5 + ρ 2T 2 + ρ9 / 2T 9 / 2 Figure.4. Theoretical fit of high temperature resistivity data for LSMCrx (x=0.15 and x=0.25). Figure.5. The temperature dependence of resistivity for LSMCrx (x=0.15 and x=0.25) under various magnetic fields 0, 2 and 5T. Symbols are the experimental data and solid lines are the resistivity calculate using Eq. 9 corresponding to the parameters indicated in table 3. Figure.6. the temperature dependence of ferromagnetic phase volume fraction f (T) for LSMCrx (x=0.15 and x=0.25) under applied magnetic fields 0, 2 and 5T.
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Figure.2. Magnetoresistance plotted vs. temperature for LSMCrx (x=0.15, x=0,20 and
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Figure 1
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Figure 2
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Figure 3
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Figure 4
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Figure 6
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Magnetoresistance plotted vs. temperature for La0.75Sr0.25Mn0.75Cr0.25O3 sample under different magnetic field.
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DOI: 10.1039/C4DT03662J
