Structural, transport and magnetotransport properties of Ru-doped La0.5Sr0.5Mn1−xRuxO3 (x = 0.0 & 0.05) manganite

Physica B 520 (2017) 13–20

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Structural, transport and magnetotransport properties of Ru-doped La0.5Sr0.5Mn1−xRuxO3 (x = 0.0 & 0.05) manganite Sadaf Jethvaa, Savan Katbaa, Malay Udeshia, D.G. Kuberkarb,a, a b

MARK

⁎

Department of Physics, Saurashtra University, Rajkot 360005, India Department of Nanoscience & Advanced Materials, Saurashtra University, Rajkot 360005, India

A R T I C L E I N F O

A BS T RAC T

Keywords: Manganite Charge ordered Electrical transport Magnetotransport Resistivity

We report the results of the structural, transport and magnetotransport studies on polycrystalline La0.5Sr0.5Mn1−xRuxO3 (x = 0.0 and 0.05) manganite investigated using XRD and resistivity (with and without field) measurements. Rietveld refinement of XRD patterns confirms the single phasic tetragonal structure for both the samples crystalizing in I4/mcm space group (No. 140). Low-temperature resistivity and MR measurements with H = 0 T & 5 T field show thermal hysteresis which has been attributed to the first order phase transition. The increase in resistivity and decrease in metal – insulator transition temperature (TMI) with Ru – doping concentration in La0.5Sr0.5MnO3 (LSMO) has been understood in the context of superexchange interaction between Mn and Ru ions. The observed upturn in resistivity at low temperature under field has been explained using combined effect of electron – electron (e - e) interaction, Kondo-like spin-dependent scattering and electron – phonon interaction while the variation in resistivity at high temperature (T > Tp) has been explained using adiabatic small polaron hopping model.

1. Introduction The discovery of colossal magnetoresistance (CMR) in hole doped perovskite structured manganites (Ln1−xAxMnO3) (Ln = La, Nd, Pr, Sm etc. and A = Ca, Sr, Ba, Pb, etc.) has attracted the interest of researchers owing to their interesting and interrelated properties such as metal– insulator transition (TMI), Charge Ordering (CO), effect of quenched disorder [1], phase separation [2,3] etc. In the doped manganites, the interplay between magnetism, charge ordering and electronic transport have been studied in detail [4–6]. It is reported that, A – site substitution with divalent ions (generally Sr2+, Ca2+) introduces ferromagnetism and metallicity due to double exchange (DE) mechanism [7] which helps to understand the ferromagnetic (FM) alignment of the t2g electron through the delocalization of eg electron between Mn3+ and Mn4+ ions. A strong Hund's coupling of the eg electron with the t2g core spin is considered as a main driving force for the DE mechanism. The magnetic and transport properties of manganites are believed to be due to the competition between the superexchange (SE) and DE mechanisms [7] resulting in the temperature and field dependent magnetic and electronic transport. Other factors, such as, strong Jahn – Teller (J -T) distortion of Mn3+ ions, doping at B – site, as well as the lattice strain and deformation affecting Mn3+ – O – Mn4+ bond angle and Mn - O bond length play an important role in modifying various

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physical properties of the manganites [8] which are controlled by several factors, such as, average ionic radius in A – site < rA > =∑ xi ri , cationic size mismatch σ2 = ∑i (xi ri2−2) where xi , ri and rA are the fractional occupancies, ionic radii of A – site cations and the average ionic radius, respectively [9]. Substitution at A – site with various cations leads to significant change in the average A – site ionic radius of the parent manganite which directly affects the bandwidth of the material [10]. Presently studied La0.5Sr0.5MnO3 (LSMO), is a large one electron bandwidth manganite having TP ~ 270 K, TC ~ 317 K, CE type TN ~ 150 K and charge ordered (CO) temperature (TCO) ~ 220 K [11]. It is interesting to study the effect of Mn – site doping in manganites which directly affects the physical properties, by way of changing the carrier density (n), Mn – O – Mn bond angle and Mn – O bond length. Mn – site doping reduces Mn3+/Mn4+ ratio and suppresses TC and metal-insulator transition (TMI). Rathod et al. have studied the effect of non – magnetic Al – doping at Mn – site on modifications in the structural, transport and magnetotransport behavior of La0.7Ca0.3Mn1−xAlxO3 (LCMAO) manganites [12]. Recently, Krichene et al. have investigated Bi – doping induced structural, magnetic and magnetotransport properties of CO LCMO manganite [13]. Orlova et al. have studied the universal effect of Mn – site doping on charge ordering in La1/3Ca2/3Mn1−xMxO3 (M = Fe, Ga, Cr, Ni, Cu, Ru and Mg) with x = 0.0 – 0.07 [14]. Amongst several possible dopants

Corresponding author at: Department of Nanoscience & Advanced Materials Saurashtra University, Rajkot 360005, India E-mail address: [email protected] (D.G. Kuberkar).

http://dx.doi.org/10.1016/j.physb.2017.06.008 Received 27 March 2017; Received in revised form 29 May 2017; Accepted 2 June 2017 Available online 03 June 2017 0921-4526/ © 2017 Elsevier B.V. All rights reserved.

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Fig. 1. XRD patterns of La0.5Sr0.5Mn1−xRuxO3 (x = 0.0 and 0.05). Inset shows the intense (112) peak of XRD patterns.

Fig. 3. Resistivity (ρ) vs. Temperature (T) plots of (a) R0 and (b) R5 at H = 0 T in both cooling and heating cycle. (Inset of (a) shows enlarged view of ρ - T of R0 below 150 K).

at Mn – site, Ru is the most studied dopant ion, the reason for which has been summarized below– a) Ru exhibit different oxidation states (Ru3+ (t24g , eg1), Ru4+ (t24g , eg0 ) and Ru5+ (t23g , eg0 )) b) All the electronic and transport properties of the Ru-doped manganites depend upon the nature of the exchange interaction between Ru and Mn ions via Oxygen. Ru-Mn exchange interactions exist due to the mixed valency of, both, Mn in Mn3+ (t23g ,eg1) and Mn4+ (t23g ,eg0 ) state and Ru in 3+, 4+ and 5+ valence states. Using Xray photoelectron spectroscopy (XPS) and Electron Spin Resonance (ESR) measurements, Ying et al. have shown that, Ru exhibit +4 valence state with a small fraction of Ru5+ with the interaction between Mn3+ and Ru4+(Ru5+) as FM superexchange rather than DE [15].

Fig. 2. Rietveld refined XRD plots of La0.5Sr0.5MnO3 (R0) and La0.5Sr0.5Mn0.95Ru0.05O3 (R5) samples.

Table 1 Values of Rietveld refined XRD parameters and Crystalline Size (CS) of R0 and R5 samples. Sample

La0.5Sr0.5MnO3 (R0)

La0.5Sr0.5Mn0.95Ru0.05O3 (R5)

a (Å)=b (Å) c (Å) Volume (Å3) Mn-O (Å) Mn-O-Mn Rexp Rwp RB χ2 S CS (μm)

5.4357 7.7410 228.719 1.9331(1) 170.220 21.9 24.9 5.60 1.30 1.14 32.33

5.4526 7.7563 230.601 1.9373(1) 174.9 27.7 31.5 2.34 1.29 1.13 34.173

Raveau et al. have studied Ru doping induced metallicity and ferromagnetism in various manganites, wherein, Mn – site doping has a more pronounced effect on the transport and magnetic properties of manganites as compared to Cr – doped system [16]. Kumaresavanji et al. have explained the transport and magnetic properties of Ru–doped La1.32Sr1.68Mn2−yRuyO7 layered manganite having antiferromagnetically coupled Ru and Mn sublattice [17]. In the present paper, we report the structural, transport and magnetotransport properties on La0.5Sr0.5Mn1−xRuxO3 (x = 0.0, 0.05) manganites. Low-temperature resistivity measurements performed on LSMO at 0 T show thermal hysteresis. In the low-temperature region, 14

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Fig. 5. Resistivity (ρ) vs. Temperature (T) plots under H = 0, 5 and 8 T for (a) R0 and (b) R5. Fig. 4. Resistivity (ρ) vs. Temperature (T) plots during cooling and heating protocols in the presence of 5 T field for (a) R0 and (b) R5. (Inset shows enlarged view around TMI). Table 2 Values of TMI, Tmin and depth of minima (Δρ) of R0 and R5 samples.

field dependent MR shows broad hysteresis. Giri et al. have explained the hysteresis in resistivity and MR in the light of phase separation scenario at low temperature [3]. The reason for large upturn in resistivity minima at low temperature observed in polycrystalline (La0.5Pr0.2)Ba0.3MnO3 manganite have been explained by our group [18] and Lalitha et al. using various theories based on Kondo-like spindependent scattering, electron - electron (e – e) interaction, electron – phonon and electron – magnon scattering [19]. Xu et al. have reported that, the upturn of resistivity could be attributed to the both e – e interaction and weak spin disorder scattering including the spin polarization and grain boundary tunneling [20]. According to Lee et al., the e – e interaction play an important role in the electrical transport behavior at low temperature in mixed-valent manganite and has a T1/2 dependence [21]. In the present case, the upturn in low – temperature resistivity with the application of field, for both the samples, has been explained using e – e interaction, Kondo-like spindependent scattering and electron - phonon interaction. In hightemperature region (T > Tp), the electrical transport properties of samples studied are dominated by the small polaron hopping mechanism. The activation energy (Ea) increases significantly with Ru doping, suggesting that, the Ru substitution on Mn – site strongly restrains the hopping possibility of eg electrons.

Sample

H (T)

TMI (K)

Tmin (K)

Δρ

R0

5 8

158 175

57.302 48.907

0.1556 0.1326

R5

5 8

132 156

67.921 58.38

0.1702 0.1705

2. Experimental details Polycrystalline bulk samples of La0.5Sr0.5MnO3 (R0) and La0.5Sr0.5Mn0.95Ru0.05O3 (R5) were synthesized by conventional solid-state reaction method. The stoichiometric quantities of La2O3, SrCO3, Mn2O3 and RuO2 (all > 99.9% purity) were mixed thoroughly, ground for 4–5 hrs and calcined at 950 °C for 24 hrs. The resulting powders were reground and calcined at 1100 °C for 24 hrs. Final powders were pressed into circular pellets and sintered at 1250 °C for 48 hrs and 1350 °C for 72 hrs with intermediate grinding. The structural characterization was carried out using X–ray diffraction (XRD) measurements at room temperature (RT). Resistivity measurements with zero and different applied magnetic fields were performed by a standard four-probe technique using a commercial cryostat (Oxford Instruments Inc., UK) with the 8 T magnetic field in the temperature 15

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Fig. 7. Temperature dependence of MR% for R0 and R5 at H = 5 and 8 T. Fig. 6. Temperature dependent variation of FC_FW and ZFC_FW resistivity curves at 5 T magnetic field for (a) R0 and (b) R5 samples.

samples measured at 0 T are shown in Fig. 3(a) and (b). Sample R0 exhibits thermal hysteresis in the low-temperature region between heating and cooling cycles which gets suppressed in the 5% Ru-doped sample (R5) (Fig. 3). Thermal hysteresis is also observed in both the samples (R0 and R5) around the metal to insulator transition (TMI) temperature region during cooling and heating protocol under 5 T field (Fig. 4). The thermal hysteresis is a generic feature of a first order phase transition in CO manganite [23,24] which indicates the coexistence of FM and CO phase. The first order phase transition can be suppressed by either doping at B – site or by application of applied magnetic field [24]. To understand the effect of magnetic field on both the samples, temperature dependent resistivity measurements were taken under different applied magnetic fields. Fig. 5(a) and (b) show resistivity versus temperature plots of the R0 and R5 samples under 0 T, 5 T & 8 T. Under H = 0 T field, both the samples show insulating behavior in the entire temperature range. With the application of field, both samples exhibit TMI which shifts towards higher temperature with its value increasing with the applied field (Table 2). An increment in the value of TMI with the application of field for both the samples can be attributed to the enhancement of DE mechanism which favours the FM tendency. With Ru doping, an increase in resistivity and decrease in TMI indicate that, the interaction between Mn and Ru ions is FM superexchange rather than DE [15,17]. Further, an increment in the resistivity with Ru substitution can be understood through the ability of Ru to exist in mixed valence state as Ru4+ and Ru5+. Reported studies using XAS and XPS on La0.7Pb0.3Mn1−xRuxO3 [25] and La0.45Sr0.55Mn0.6Ru0.4O3 [15] samples respectively, reveal the mixed valence state of Ru which favours the condition Mn3+ + Ru5+ ↔ Mn4+ + Ru4+. The presence of Ru5+ results in the decrease in the Mn4+ content and increase in Mn3+ content in accordance with the equation [26].

range of 5 – 300 K. 3. Results and discussions 3.1. Structural property X–ray diffraction (XRD) patterns of R0 and R5 samples are shown in Fig. 1. Rietveld refinement of the XRD data using FULLPROOF Code [22] indicates that, both the samples are single phase and crystallize in tetragonal structure with I4/mcm space group (No. 140) (Fig. 2). Values of structural parameters, cell volume, Mn – O – Mn bond angle, Mn – O bond length and Bragg factors for both the samples obtained from the Rietveld refinement are listed in Table 1. Value of χ2 and S (Goodness of fit) indicate that, fitting of the experimental data and calculated values are in good agreement. Lattice parameters and unit cell volume are found to increase with Ru – doping concentration in LSMO. It can also be seen from Fig. 1 that, the intense (112) peak in XRD pattern shift towards lower 2θ, with Ru – doping, indicating the increment in unit cell volume due to the substitution of larger Ru ion at Mn-site. Crystallite size (CS) calculated using Scherrer's formula (CS = 0.9λ/Bcosθ, where λ = 1.5418 Å is the wavelength of X-ray used, B is the FWHM and θ is the Bragg angle) for both the samples increases with Ru – doping concentration. 3.2. Transport properties To study the effect of Ru doping on LSMO, magnetotransport properties of both the samples were studied within a temperature range ~5 K to 300 K. Temperature dependent resistivity (ρ) plots of both the

2Mn4+ = Ru5+ + Mn3+ 16

(1)

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Fig. 8. MR% vs. H for R0 and R5 (a) – (d) 0 T – 8T – 0 T, (e) and (f) at 0 – 8 T magnetic field at different temperatures.

An increase in the Mn3+ content leads to FM – DE interaction between Mn3+ and Mn4+ ions while Ru4+ and Ru5+ ions also interact ferromagnetically with Mn3+ ion through SE interaction. Observation of thermomagnetic history effect at low temperature below TMI cannot be explained only by the first order phase transition. To acquire more information about this phenomena, the temperature dependent resistivity curves for R0 and R5 samples were obtained under the applied field using two different measurement protocols –

heating during the measurements. Fig. 6 shows the resistivity curves under the ZFC_FW and FC_FW conditions at the 5 T field for both the samples. It can be observed from the Fig. 6 that, the low-temperature resistivity obtained under two measurement protocols tend to bifurcate from each other at low temperature (92 K) for R0 sample while for R5 sample, the bifurcation shift towards lower temperature and gets suppressed. Interestingly, the FC_FW curve remains below the ZFC_FW curve for both the samples. Also, in the case of R5 sample, the ZFC_FW curve crosses the FC_FW curve at a particular temperature (20 K). This crossover may be due to the Ru doping indicating that, the sample remembers history even during heating at the same field which is reflected in the huge bifurcation between ZFC_FW and FC_FW resistivity curves at low temperature. This thermomagnetic history dependent resistivity has been reported in (Nd0.4Gd0.3) Sr0.3MnO3 and Sm0.5Sr0.4MnO3 manganites [2,27]. Giri et al. have found that under low field (~0.1 T), the bifurcation is not prominent and is maximum at 3 T field. With the increase in the applied field, the bifurcation in ρ – T plots decreases and shifts towards lower

1. The sample was cooled from RT to 5 K in a zero magnetic field and data were taken during heating cycle at particular magnetic field: ZFC_FW 2. The sample was cooled from RT to 5 K under particular magnetic field and data were taken during heating cycle at the same magnetic field: FC_FW During all the above measurement protocols, the current was kept at 0.1 mA for R0 sample and 1 mA for R5 samples to avoid thermal 17

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Fig. 7 shows the variation of MR% as a function of temperature under 5 and 8 T fields for both the samples. It can be observed from the plots that; both the samples show large negative magnetoresistance at a low temperature which decreases with increasing temperature. Also, MR increases with the application of a field in both the samples which can be attributed to the suppression in the scattering of charge carriers. Interestingly, MR% in Ru – doped LSMO is higher than that of undoped sample indicating that, the Ru – substitution results in the marginal variation in MR. The field dependent MR at different temperatures were obtained during heating the samples in a thermally demagnetized state after cooling them from RT to the desired temperature in zero magnetic field. From the MR versus H curves, we observe that, at 5 K, both the R0 and R5 samples show thermal hysteresis under isothermal sweeping of the magnetic field in a cycle from 0T to 8 T and 8 T–0 T which becomes weak at 25 K [Fig. 8(a) – (d)]. Beyond 25 K, there is no irreversibility in magnetic hysteresis observed [Fig. 8(e) – (f)]. To understand the observed MR behavior as well as the thermomagnetic history dependence of magnetotransport, the phase separation scenario has been invoked. With the application of the applied magnetic field, the phase fraction of low resistive metallic phase increases and the insulating phase decreases which give rise to the negative MR [2]. 3.2.1. Resistivity behavior under low temperature (T < TP) The emergence of (i) Metal-insulator transition with the application of applied magnetic field and (ii) appreciable resistivity upturn at low temperature with applied field has been attributed to the melting of CO phase and competition between various interactions such as e – e, electron-phonon, and Kondo-like spin dependent scattering at lowtemperature region [30–37]. In the present study, resistivity upturn behavior has been observed under 5 T and 8 T applied fields, with a distinct minimum temperature (Tmin) at which the resistivity increases with decrease in temperature. Under application of magnetic field, Tmin shifts towards lower temperature and hence exhibit strong field dependence [Inset of Fig. 5(a) and (b)]. In order to quantify the effect of magnetic field, depth of Tmin ρ −ρ represented by Δρ, calculated using equation ∆ρ = 5Kρ Tmin , is found Tmin to decrease with increase in applied field (Table 2), where, ρ5K and ρTmin represent the resistivity minimum at 5 K and Tmin respectively. Earlier reports to understand the cause of the observed resistivity minimum at low temperature involves the analysis and fittings of the experimental data using different theoretical models such as, Coulomb blockade [31], Kondo effect [32] or e – e interaction effect [32,33], electron-phonon interaction [20]. According to Coulomb blockade effect, the low-temperature resistivity varies as exp (√Δ/T) in the low-temperature region. Kondo effect is generally observed in diluted magnetic alloys [34] due to the scattering from a magnetic impurity in a non-magnetic lattice which gets suppressed in the presence of a higher magnetic field. According to e-e interaction, the upturn in resistivity is due to the quantum interference effect [35]. In addition, the resistivity upturn at low temperature has been observed in different divalent doped manganites in the absence of external magnetic field [36,37]. In order to understand the origin of field dependent resistivity upturn at low temperature in the sample under study, the experimental data was analyzed and fitted using combined e – e interaction, Kondolike spin-dependent scattering and electron–phonon interaction using the following equation –

Fig. 9. Low-temperature resistivity fittings of (a) R0 and (b) R5 at H= 5 T & 8 T using the Eq. (3).

Table 3 Values of low-temperature resistivity fitting parameters for R0 and R5 samples obtained from Eq. (3). Sample

H (T)

ρ0 (Ω cm)

ρe (Ω cm K−1/2)

ρs (Ω cm K−1)

ρp (Ω cm Kn)

R0

5 8

27.3637 20.6082

0.0482 0.0255

1.7584 1.4533

3.01775E−10 1.74039E−10

R5

5 8

808.2218 609.3069

0.6461 0.4947

52.2446 40.3032

5.85555E−9 7.39313E−9

temperature under application of high magnetic field [2]. In our case, we have taken the similar measurements at 5 T field and observed appreciable bifurcation in ρ – T data at ZFC_FW and FC_FW conditions even at high field for R0 sample which gets suppressed with Ru doping (R5 sample) which can be attributed to the kinetic arrest of electronic phase which gives low resistive metallic state when the sample is field cooled [2,3,23]. Bifurcation between ZFC_FW and FC_FW in resistivity plots is also an indication of the first order phase transition as reported earlier [27–29] which has been further confirmed through isothermal MR vs H measurements. MR% of both the samples were calculated using the relation –

MR% =

ρH − ρ0 ×100% ρ0

ρ = ρ0 + ρe T − ρs ln T + ρp T 5

(3)

where ρ0 represents the residual resistivity, ρe T is e–e interaction term while ρs ln T represents the contribution due to Kondo-like spin dependent scattering and ρp T 5 term is due to electron–phonon interaction which represents the phonon scattering in the low temperature region. Fig. 9 shows the experimental results and theoretical fittings of

(2) 18

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(a)

Fig. 10. Plots of fitting ln (ρ/T) vs. T−1 resistivity data for (a) R0 and (b) R5 at (T > Tp) using adiabatic small polaronic hopping model.

ρ – T data using Eq. (3) at low temperature under H = 5 T & 8 T fields for, both, R0 and R5 samples. The solid line in the Fig. 9 clearly indicates the best fit to the Eq. (3). It is observed from Table 3 that, the fitting parameters are found to increase with Ru – doping concentration and decrease with increasing magnetic field. This may be due to the suppression of different scattering mechanisms in the presence of magnetic field. In the present case, resistivity upturn is observed even under 8 T field which suggests the combined effect of e – e, Kondo-like spin-dependent scattering and electron-phonon scattering mechanisms responsible for the occurrence of low temperature resistivity minimum.

hopping), KB is the Boltzmann's constant and ρ0 is the residual resistivity coefficient term described by ρ0 = 2KBT/3ne2a2 v where, e is the electronic charge, n is the density of charge carriers, a is the site to site hopping distance and v is the longitudinal phonon frequency. From the fitting of (ln(ρ/T) vs. T−1) plots using SPH model (Fig. 10) the obtained value of activation energy (Ea) decreases with increase in field while increases with Ru doping concentration (Table 4). It is belived that, the value of Ea increases with lattice distortion and the strong Jahn–Teller electron – phonon coupling resulting in the increase in tendency of electrons to become localized [39]. The present behavior shown in Fig. 10 suggests a strong correlation between the lattice constant and Ea [39] wherein Ru doping in LSMO, results in the increment in unit cell volume and lattice parameters (Table 1). In addition, observed increment in the activation energy and resistivity with Ru – doping indicate the weakening of ferromagnetic order in R5 sample [Fig. 5(b)].

3.2.2. Resistivity behavior at high temperature (T > TP) The variation of resistivity at high temperature (T > Tp), can be understood using the adiabatic small polaronic hopping (SPH) model [38] given by the equation –

ρ = ρ0 Texp (Ea / KB T )

(4)

where Ea is the activation energy (the potential barrier for polaron 19

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Table 4 Fitting parameters obtained from Eq. (4) for R0 and R5 samples. Sample

R0 R5

Value of Ea (meV) 0T

5T

8T

79 82.57

65.23 75.43

62.08 70.85

4. Conclusion In conclusion, we have investigated the structural, transport and magnetotransport properties of polycrystalline La0.5Sr0.5Mn1−xRuxO3 (x = 0.0 and 0.05) manganites using XRD and resistivity measurements. The structural study shows that, both the samples possess tetragonal structure with I4/mcm space group (No. 140) with the unit cell volume increasing with Ru-doping concentration in LSMO. Temperature dependent resistivity below 150 K and under the 0 T and 5 T fields and MR below 25 K show thermal hysteresis which may be attributed to the first order phase transition. Observation of field induced suppression in resistivity and shifting of TMI towards higher temperature and its value increases with the field has been attributed to the enhancement in DE mechanism which favours the FM tendency. The increase in resistivity and activation energy (Ea) while a decrease in TMI with Ru doping in LSMO indicates that, Ru substitution at Mn – site strongly restrains the hopping possibility of eg electrons thereby favouring the FM superexchange rather than double exchange. Acknowledgements Authors are thankful to UGC–DAE CSR, Indore for financial support in the form of [Ref No. CSR-IC-BL-54/CRS-171/2016-17/ 835]. Dr. Rajeev Rawat UGC – DAE CSR, Indore is thankfully acknowledged for providing resistivity measurements. Sadaf Jethva is thankful to UGC - MANF, New Delhi, for the award of Maulana Azad National Fellowship for Minority students [Award Letter No. MANF2014-15-MUS-GUJ-33765]. Savan Katba is thankful to UGC, New Delhi for BSR Meritorious Fellowship [No. F.7-156/2007(BSR)]. References [1] E. Dagotto, Nanoscale Phase Separation and Colossal Magnetoresistance, Springer, Berlin, 2002. [2] S.K. Giri, T.K. Nath, An investigation of low-temperature electronic phase arrest in Sm0.55Sr0.45MnO3 phase separated manganite, J. Appl. Phys. 115 (2014) 053902. [3] S.K. Giri, T.K. Nath, Evidence of glassy ferromagnetic phase and kinetic arrest of electronic phase in Sm0.35Pr0.15Sr0.5MnO3 manganites, J. Magn. Magn. Mater. 324 (2012) 2277. [4] R. von Helmolt, J. Wecker, B. Holzapfel, L. Schultz, K. Samwer, Giant negative magnetoresistance in perovskite like La2/3Ba1/3MnOx ferromagnetic films, Phys. Rev. Lett. 71 (1993) 2331. [5] K. Khazeni, Y.X. Jia, L. Lu, V.H. Crespi, M.L. Cohen, A. Zettl, Effect of pressure on the magnetoresistance of single crystal Nd0.5Sr0.36Pb0.14MnO3−δ, Phys. Rev. Lett. 76 (1996) 295. [6] A. Urushibara, Y. Moritomo, T. Arima, G. Kito, Y. Tokura, Insulator-metal transition and giant magnetoresistance in La1−xSrxMnO3, Phys. Rev. B 51 (1995) 14103. [7] C. Zener, Interaction between the d-Shells in the Transition Metals. II. Ferromagnetic compounds of manganese with perovskite structure, Phys. Rev. 82 (1951) 403. [8] H.Y. Hwang, S.W. Cheong, P.G. Radaelli, M. Marezio, B. Batlogg, Lattice effects on the magnetoresistance in doped LaMnO3, Phys. Rev. Lett. 75 (1995) 914. [9] (a) L.M. Rodriguez-Martinez, J.P. Attfield, Cation disorder and the metal-insulator transition temperature in manganese oxide perovskites, Phys. Rev. B 58 (2426) (1998);

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