Synthesis, structural, electrical and magnetic studies of La0.5Ca0.45 ...

Journal of Physics and Chemistry of Solids 73 (2012) 925–930

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Synthesis, structural, electrical and magnetic studies of La0.5Ca0.45 xSrxBa0.05MnO3 B. Munirathinam a,n, M. Krishnaiah a, U. Devarajan b, S. Esakki Muthu b, S. Arumugam b a b

Department of Physics, Sri Venkateswara University, Thirupathi, India Centre for High Pressure Research, School of Physics, Bharathidasan University, Trichirapalli, India

a r t i c l e i n f o

abstract

Article history: Received 29 March 2011 Received in revised form 20 December 2011 Accepted 14 February 2012 Available online 24 February 2012

Half doped mixed valence manganite system La0.5Ca0.45 xSrxBa0.05MnO3 (with x ¼ 0.1, 0.2, and 0.3) synthesized through a low temperature nitrate route is systematically investigated in this paper. The electronic transport and magnetic properties are analyzed and compared apart from the study of unit cell structure and composition. The system is found to crystallize only in orthorhombic structure (Pnma) and the electronic phase transitions are observed to be of second order. The charge and orbital ordering have been observed to coexist with ferromagnetism in x ¼0.1 compound. Application of small polaron and variable range hopping models to resistivity data of the system corresponding to high temperature range shows increasing mobility of eg electrons with x, with the later model describing the electronic transport very closely than the former. The temperature dependent magnetization of the compounds shows monotonic increase of paramagnetic to ferromagnetic transition (TC) with x. Ferromagnetism is exhibited for the complete temperature range down from respective TC in contrast to antiferromagnetism usually exhibited by half-doped compounds in the low temperature range. The plots of magnetization versus magnetic field reveal a transition from soft to hard magnetic character for all the compounds as the temperature is lowered. & 2012 Elsevier Ltd. All rights reserved.

Keywords: A. Ceramics B. Chemical synthesis C. X-ray diffraction D. Electrical properties E. Magnetic properties

1. Introduction Half-doped mixed valence manganites RE0.5D0.5MnO3 (RE¼La, Nd, Pr and D¼Ca, Sr, Ba) have been the focus of extensive experimental and theoretical studies in the recent years due to their intriguing electronic and magnetic properties [1]. One of the interesting features of La1–xCaxMnO3, for instance, is the co-existence of ferromagnetic (FM) and anti-ferromagnetic (AFM) phases at x¼0.5 unlike the case of 0.15oxo0.5 for which the ground state is FM metallic due to the double exchange mechanism (DE). The phase coexistence of FM and charged ordered AFM for x¼0.5 is usually attributed to the small energy difference between these competing phases [2]. Studies have shown that the ground state is sensitive to the average size /rAS of A-site cations (La3 þ and Ca2 þ ), hydrostatic pressure, magnetic field, chemical substitutions at Mn site, and A-site ionic radii mismatch (s2) [3,4]. These manganites in general show different types of ground states depending on the dominance of AFM and/or FM interactions, and Jahn–Teller distortions [5]. However, the complex physics behind these is yet to be fully understood and hence the need for further studies. In widely studied half-doped manganites, La0.5Ca0.5MnO3 ˚ is reported to undergo ferromagnetic metallic (/rAS¼1.198 A) (TC 225 K) transition followed by AFM insulating state (TN 150 K);

n

Corresponding author. Tel.: þ91 08623 225711; fax: þ 91 08623 225842. E-mail address: [email protected] (B. Munirathinam).

0022-3697/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2012.02.025

the latter state is linked to the simultaneous ordering of orbital (Jahn– Teller), charge and spin (CE type) [6–8]. In contrast, the compound ˚ is reported to be a La0.5Sr0.5MnO3 with large /rAS (¼1.263 A) ferromagnetic metal with TC 310 K. Although no charge or orbital ordering is reported for this compound, only a weak A-type AFM ordering in addition to ferromagnetic ordering has however been observed [9]. The compound Nd0.5Sr0.5MnO3 with /rAS¼1.236 A˚ is observed to be a charge-ordered insulator (TCO 158 K) and is also seen to exhibit a CE-type AFM spin structure below 150 K. However ˚ is the compound Pr0.5Sr0.5MnO3 with still larger /rAS (¼1.245 A) seen to exhibit an A-type spin structure below its ordering temperature [10,11]. High pressure studies on the charge-ordered Nd0.5Sr0.5MnO3 compound reveal that on application of high pressure A-type AFM state with orbital ordering gets stabilized at the expense of CE-type AFM state [12]. In contrast, the AFM ordering is suppressed rather than enhanced in La0.5 xYxCa0.5MnO3 compound, where the substitution of Y decreases /rAS but increases s2, clearly revealing the influence of the latter factor [13]. The disorder factor s2 is however much reduced for the La0.5Ca0.5 xSrxMnO3 series and is almost constant for x ranging from 0.2 to 0.5. This signifies that this series may be a good candidate to study the effect of /rAS independent of s2 by low level substitution of larger size Ba2 þ ions for Ca2 þ ions. Earlier studies [14] on La0.5Ca0.5 xSrxMnO3 system reveal a non-monotonous variation of TN with increasing Sr concentration up to x¼0.3, attributable to a change in the type of AFM structure.

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B. Munirathinam et al. / Journal of Physics and Chemistry of Solids 73 (2012) 925–930

A very recent study of the same system using neutron diffraction [15] confirms the suppression of charge-ordered state beyond x¼ 0.3 and the decline of CE-type AFM ordering with the increase of x. In this paper, we first deal with the synthesis of La0.5Ca0.5 xSrxBa0.05MnO3 (with x¼0.1, 0.2 and 0.3) compounds by low temperature nitrate route (in contrast to solid state reaction routes followed in the earlier studies) and then study the effects of above substitution on electronic transport and magnetic properties. It is to be noted that in this system, the variation of s2 with x is observed to be negligibly small as compared to that of /rAS and in fact reduces after x¼0.2. High temperature electrical properties are studied using standard resistivity models such as small polaron and variable range hopping. The electrical parameters arising out of these studies are discussed and compared. Low temperature resistivity minimum is observed for x¼ 0.1 and x ¼0.2 samples and resistivity data corresponding to low temperature range has been fitted using the model r(T)/r(300 K) ¼a b ln(T) cT1/2 þdT2. In addition, magnetization (M) has been studied by varying both temperature and magnetic field strength.

2. Experimental Details The polycrystalline powder samples of La0.5Ca0.45 xSrxBa0.05 MnO3 were synthesized through low temperature nitrate route [16]. 1 M solutions of 99.9% pure chemicals La(NO3)3 6H2O, Ca(NO3)2 4H2O, Ba(NO3)2, Sr(NO3)2, and Mn(CH3COO)2 4H2O were prepared individually using distilled water. These solutions were further used to prepare mixed solutions of specific ratio required for each composition. The solution of each composition was then slowly dried at 80 1C and the resulting solid pulp was calcined first at 700 1C. These black powder samples were then ground thoroughly in a mortar and again calcined in air for 14 h at 900 1C. Around one gram of each powder thus prepared was then mixed with few drops of polyvinyl alcohol and pressed into pellet of diameter 11 mm using a pellet making machine and sintered in air at 900 1C for another 14 h. The XRD patterns of all the samples were recorded using PANalytical X’pertPro diffractometer with Cu-Ka radiation ˚ in angular steps of 0.021. The temperature dependent (l ¼1.5406 A) electrical resistivity of pellets was measured by the conventional four probe technique using a closed cycle He-cryostat. A programmable current source was used to apply constant current and the resulting voltage was measured with a voltmeter. The magnetization measurement of the compounds was carried out using Physical Property Measurement System (PPMS) with a magnetic field of strength 1 T in the temperature range of 2–300 K. The magnetic hysteresis behavior was also studied in the ferromagnetic domain of each compound for different temperatures by varying the field strength from 5000 Oe to þ5000 Oe.

3. Structural, SEM and EDS results The X-Ray diffraction (XRD) patterns of La0.5Ca0.45 xSrx Ba0.05MnO3 compounds have been recorded in the angular range of 101 to 801 (Fig. 1). The diffraction patterns confirm that the compounds are crystallized in single phase and could be indexed to orthorhombic structures (space group Pnma), as observed in the case of parent compound La0.5Ca0.5MnO3 [2], using XRDA software with a maximum error of 70.009 A˚ in the estimation of lattice parameters. It can be seen from Table 1 that the cell volume increases with x, consistent with the fact that bigger Sr2 þ and Ba2 þ ions are substituted at Ca2 þ sites [15]. The lattice parameters b and c are observed to increase with x, while a is seen

Fig. 1. X-ray diffraction patterns of La0.5Ca0.45 xSrxBa0.05MnO3 powder compounds for x¼ 0.1, 0.2 and 0.3.

Table 1 Structural and EDS parameters of La0.5Ca0.45 xSrxBa0.05MnO3 compounds. (Note: As oxygen content could not be determined due to instrument limitation, corresponding percentage is not included in EDS results. The calculated atomic percentage values are given in brackets.) Structural and EDS parameters

La0.5Ca0.45 xSrxBa0.05MnO3 x ¼0.1

x ¼0.2

x ¼0.3

˚ a (A)

5.490

5.476

5.463

˚ b (A) ˚ c (A)

7.723

7.739

7.766

V (A˚ 3) /rAS (nm) t s2 (nm2) 10 5

5.450

5.478

5.485

231.076

232.126

232.716

0.123 0.934 4.5

0.124 0.939 4.8

0.125 0.943 4.8

Atomic percentage obtained (calculated) La (%) 28.355 (25.00) Ca (%) 15.000 (17.50) Sr (%) 2.185 (5.00) Ba (%) 3.040 (2.50) Mn (%) 51.430 (50.00)

27.425 (25.00) 12.460 (12.50) 5.710 (10.00) 2.950 (2.50) 51.455(50.00)

26.010 (25.00) 7.590 (7.50) 11.695 (15.00) 3.690 (2.50) 50.855 (50.00)

to decrease with x-value. The analysis of atomic percentage of elements of EDS data shows that La and Ca are exchanged in a closely linear manner as intended. However the percentage of Ba and Mn are found marginally in excess while that of Sr are observed to be lower than the expected values for the compounds. The approximate minimum particle size for x ¼0.1 sample is measured to be around 150 nm and that of x ¼0.2 and 0.3 samples is found to be around 250 nm from SEM photographs of the respective pellets (Fig. 2(a), (b) and (c)).

4. Electronic transport studies The resistivity behavior of pellets is studied in the temperature range from 4 K to 300 K. The resistivity ratio r(T)/r(300 K) of the samples as a function of temperature during cooling phase is plotted in Fig. 3. The compounds display insulator or semiconductor-like property in the paramagnetic region and do not show for the most part any metallic behavior even in the ferromagnetic region which is expected for double-exchange ferromagnetic interaction. This behavior is usually attributed to the smaller


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Fig. 3. Temperature dependent resistivity of La0.5Ca0.45 xSrxBa0.05MnO3 series during cooling phase.

Fig. 2. (a) SEM image of x ¼0.1 sample. (b) SEM image of x¼ 0.2 sample. (c) SEM image of x ¼0.3 sample.

width (W) of one electron eg band [14]. In contrast to the first order transitions reported for La0.5Ca0.5 xSrxMnO3 compounds, the nature of phase transitions of the present compounds is found to be of second order as the transitions are observed to be reversible and not hysteretic upon cooling and warming (Fig. 4).

The exhibition of an insulating behavior with steep rise in resistivity by x ¼0.1 compound as the temperature is lowered is observed to be similar to that of La0.5Ca0.5MnO3 compound that displays an insulating behavior with a sharp increase in resistivity at about 155 K [17]. Further an insulator to metal transition (TIM) is observed at 70 K followed by metal to insulator transition (TMI) at 38 K (Fig. 3) as the temperature of x ¼0.1 compound is decreased. With further increase of Sr concentration to obtain x¼0.2 compound, resistivity shows drastic fall. However like the case of x¼0.1 insulator to metal and metal to insulator transitions are observed at slightly higher temperatures (TIM ¼78 K and TMI ¼48 K) for x¼ 0.2. With x¼0.3, resistivity shows marginal fall as compared to x ¼0.2, suggesting that the increase in /rAS due to the substitution of larger ions (Sr2 þ and Ba2 þ ) for smaller Ca2 þ ions cause an increase of one electron (eg) bandwidth W as well as double exchange ferromagnetic interactions. The increasing value of tolerance factor (t) with x is also observed to be in line with this behavior. For the calculation of /rAS and t (Table 1), nine-fold coordination is assumed for A-site ions [18]. The steep increase in resistance by a factor of about 20 for x¼0.1 compound may be due to charge ordering behavior. The corresponding transition temperature of 199 K is determined from the minimum of d(ln r)/dT. The absence of such steep increase of resistivity for x ¼0.2 and 0.3 compounds reveals possible suppression of charge ordering attributable to the increasing value of /rAS. This fact is observed to be in line with the reported observation that charge ordering may be suppressed for /rAS values of about 0.124 nm and beyond [15]. These results also indicate possible competition between double exchange and super-exchange interactions, with the former becoming dominant by the increase of /rAS and W. The smaller and decreasing value of s2 with the increase of x (Table 2) reveals negligible influence in affecting both electronic transport as well as magnetic transitions of present compounds. There is also a reported observation that for a fixed hole concentration and /rAS, the charge ordering is not very sensitive to size mismatch between A-site cations [19]. 4.1. Resistivity behavior in the high temperature domain The electrical resistivity of manganites generally exhibit strong temperature dependence in the high temperature range. Standard models such as small polaron and variable range hopping (VRH)

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Viret et al. [20] (for optimally doped manganites), which basically describes the hopping transport, where the carriers are localized by random magnetic potential (arising due to Hund’s coupling between localized Mn t2g ion cores and spins of eg electrons) and that the hopping probability may be modified by the mutual spin orientations of the two sites. The value of characteristic temperature (To) is obtained from the fit of VRH model with resistivity data. The confinement or the localization length (1/a) of carriers may be calculated using the following formula: 1=a ¼ ð18U m V=½ð1yÞfgkB T o Þ1=3

ð2Þ

here Um ( 2 eV) is the magnitude of the potential [20] and V is the unit cell volume per Mn ion. (1 y) is the probability that the eg orbital at the Manganese site receiving hopping electron is unoccupied, f ¼0.5 is a geometric factor relating the wave function of the hopping electron and g is the probability that an unoccupied manganese orbital can actually accept an electron. The carrier hopping energy Ev in this model may be written as Fig. 4. Temperature dependent resistivity behavior during cooling and warming of La0.5Ca0.35Sr0.1Ba0.05MnO3 compound.

Ev ¼ 3VU m =½4pR3 ð1yÞjg

ð3Þ

where R is the hopping distance at a temperature (T) given by Table 2 Electronic transport and magnetic transition parameters of La0.5Ca0.45 xSrx Ba0.05MnO3 compounds. Electrical and Magnetic parameters

Low temperature results a b c (K 1/2) d (K 2) 10 4 Small polaron model results A (Om) 10 3 EP (eV) VRH model results To (K) 106 ˚ 1/a (A) ˚ at 300 K R (A) Ev (eV) at 300 K Magnetic parameters TC (K) Retentivity at 160 K (emu/g) Coercive field at 160 K (Oe)

La0.5Ca0.45 xSrxBa0.05MnO3 Samples x¼ 0.1

x ¼0.2

x¼0.3

27.60 0.3 0.7 7.4

8.66 0.2 0.2 1.3

5.72 0.10

12.81 0.08

168 0.08

11.84 2.54

3.26 3.90

2.38 4.34

13.42

14.97

0.09

0.07

272 4.34 90.96

276 5.80 68.99

– – –

15.38 0.06

R ¼ ð9VU m =½8pakB Tð1yÞjgÞ1=4

ð4Þ

The VRH model is observed to give a good fit to the resistivity data of all samples [in the temperature range approximately from 150 K to 300 K for x ¼0.1; 170 to 300 K for x ¼0.2 and 180 K to 300 K for x ¼0.3] as compared to small polaron model [from 185 K to 300 K for x ¼0.1 and 200 K to 300 K for x¼0.2 and x¼0.3]. This is clearly revealed in the comparative fit of these models as illustrated in Fig. 5 for x ¼0.1 compound, suggesting that the conduction may be readily described by variable range hopping of eg carriers specifically in the temperature ranges indicated above for the compounds. The value of g has been assumed to be 0.5 for all the compounds. The localization lengths have been calculated using the values of To obtained from the fit (Table 2). The decreasing value of To with the increase of x reveals suppression of Jahn–Teller (JT) distortion or the orbital ordering. In other words electron delocalization is enhanced as x is increased from 0.1 to 0.3 and the same is reflected in the increase of (1/a) by a factor of about 1.7.

280 5.90 48.79

models have been applied and compared in fitting the resistivity data of samples. It is known that in the polaron transport, conduction takes place by thermally assisted hopping and polarons hop only to nearest neighbors. In the adiabatic regime of this model, where the electron motion is assumed to be much faster than that of lattice vibrations, the activation energy Ep for hopping and the temperature independent constant A are obtained (Table 2) from the fit of data using the following small polaron equation: lnðr=TÞ ¼ lnðAÞ þ Ep =kB T

ð1Þ

Mott’s model of variable range hopping of carriers involves carrier hopping to states of nearly equal energy, located at random distances in the lattice due to the randomness in the potential. Though Mott’s model predicts correctly the temperature dependence of resistivity [r ¼ rN exp(To/T)1/4, rN is a constant], it has been found to be inadequate due to the requirement of very large randomness in the potential to predict the observed localization in this kind of materials. The potential is considerably reduced in the magnetic localization model proposed by

Fig. 5. Fit of VRH model for To50 K and T4165 K and small polaron model for the high temperature region with the resistivity data of x¼ 0.1 compound. Inset shows fit of the resistivity model r(T)/r(300 K) ¼a bT1/2–c ln(T) þ dT2 in the low temperature range.


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4.2. Resistivity behavior in the low temperature domain The observation of resistivity minimum for x ¼0.1 and x¼ 0.2 compounds and the subsequent insulating behavior as the temperature is further reduced are seen to be similar to that reported in a number of materials in the recent years [21–23]. Various models have been proposed to explain this anomalous behavior at low temperature [24–26]. For the present samples following model has been found to fit the resistivity data (correlation coefficient r¼ 0.999 for x¼ 0.1 and r ¼0.996 for x¼0.2). Apart from dT2, contributions from Kondo-like scattering (blnT) and correlated electron–electron interaction (cT1/2) in a weakly disordered system [27] are included in this model.

rðTÞ=rð300 KÞ ¼ ab lnðTÞcT 1=2 þ dT 2

ð5Þ

The Kondo effect originally observed in dilute magnetic alloys has been attributed to the interaction between localized spins of magnetic impurities and conduction electrons. As the present compounds have ferromagnetic behavior at low temperatures one may treat the electrical transport behavior as Kondo-like [28,29] and the parameter b is then affected by the intensity of the spin scattering. It is to be noted that the resistivity minimum has been reported to be suppressed by the external magnetic field indicating possible contribution of spin dependent scattering to resistivity at low temperature [24]. The best fit parameters are given in Table 2. It can also be seen from the inset of Fig. 5 for x¼ 0.1 compound that theoretical and experimental points match well indicating that Eq. (5) might be explaining well the observed anomalous resistivity behavior at low temperature. An attempt is also made to fit the resistivity corresponding to low temperature ( o50 K) semiconductor-like region of x¼ 0.1 compound to both VRH and small polaron models. As in the high temperature region, the former model was found to fit the data well (r ¼0.994 for the temperature range of 4–43 K) as compared to the later model (r ¼0.975) for the temperature range 4–31 K. The fit of VRH model for both low and high temperature semiconductor-like regions is illustrated for x¼ 0.1 compound in Fig. 5. The characteristic temperature for this compound is found to be 0.013 K and the activation energy is calculated to be 0.53 meV indicating high mobility of eg carriers in the lower temperature range.

5. The temperature dependent magnetic behavior The magnetization measurement of compounds was carried out with a magnetic field of strength 1 T in the temperature range of 2–300 K. The temperature dependent behavior of magnetization of La0.5Ca0.45 xSrxBa0.05MnO3 compounds is shown in Fig. 6. At high temperatures, the compounds are paramagnetic insulators and upon cooling, all of them exhibit ferromagnetic ordering. The paramagnetic to ferromagnetic transitions (TC) have been determined by differentiation of magnetization with respect to temperature (dM/dT) and noting the temperature corresponding to inflection point (Table 2). Unlike the reported intriguing magnetic behavior [14,15,18] of other Lanthanum based half doped manganites such as La0.5Ca0.5MnO3 and La0.5Ca0.5 xSrx MnO3, the present compounds have been found to exhibit ferromagnetism for the complete measured range of temperature down to 2 K starting from respective transition temperatures (TC) and no AFM character is explicitly revealed by the magnetization of compounds. This behavior is in line with the reported role of Ba doping in half doped compounds in suppressing antiferromagnetism even at lower level of concentration of Ba (x 0.1) [30] as compared to Sr doped compounds in which the CE-type antiferromagnetism is suppressed only at higher concentration of Sr

Fig. 6. Magnetization behavior of La0.5Ca0.45 xSrxBa0.05MnO3 compounds in the temperature range of 2–300 K.

(x 0.4). However it is difficult to rule out low concentration of antiferromagnetic clusters as low temperature neutron diffraction pattern revealing weak A-type AFM superlattice reflections has been reported for La0.5Ca0.5 xSrxMnO3 though the magnetization has not revealed such behavior [15]. The absence of AFM ordering signature in Fig. 6 may be attributed to the dominant influence of ferromagnetic interactions over antiferromagnetic contribution. It is to be noted that TC increases monotonically from 272 K (x ¼0.1) to 280 K (x¼ 0.3) and this trend is in agreement with the reported magnetization studies on similar compounds [14,15]. This behavior of TC suggests an increase in FM interactions with /rAS. The ferromagnetic charge ordered phase for x ¼0.1 compound may plausibly be due to an inhomogeneous mixture of ferromagnetic and charge ordered AFM regions on a very small scale as reported for La0.5Ca0.5MnO3 compound [31] using electron microscopy techniques. There are also results which show that charge ordering occurs not only in regions with no net magnetization (AFM) but also can occur in ferromagnetic regions [32]. In this sense the conventional models (by Zener, Anderson and Hasegawa, and Goodenough) [5] fail to predict such a charge ordered ferromagnetic phase. For instance studies by Zuo and Tao [33] have revealed diffuse charge order reflections in La2/3Ca1/3MnO3 both above and below its Curie temperature confirming that charge ordered modulations are not restricted to AFM phase and can be observed in ferromagnetic and paramagnetic phases as well. The general increase of ferromagnetic ordering with the increase of /rAS found for x¼0.2 and x¼ 0.3 compounds appears to disrupt both charge and orbital orderings in these compounds, thus widening the one electron bandwidth. There is however a reduction of magnetization observed in the low temperature region for x¼0.3 as compared to that of x ¼0.2 compound amounting to a maximum of about 5% at 2 K, attributable to possible domain wall pinning effects [34]. The magnetic hysteresis behavior in the ferromagnetic domain was recorded at four different temperatures (290 K, 230 K, 160 K and 2 K) in the measured range of temperature. As expected, the hysteresis behavior is absent in the paramagnetic region corresponding to 290 K. The area enclosed by the hysteresis loop in the ferromagnetic domain is observed to increase with the decrease of temperature, attaining maximum at 2 K (Fig. 7) for all the compounds. This behavior clearly reveals the increasing hardening of magnetization as the temperature is lowered. While the magnetization retentivity increases with x, the behavior of

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of x¼0.1 (as compared to x ¼0.1 and 0.2 compounds) as the temperature of the corresponding pellet is lowered, attributable to charge ordering behavior. However in respect of magnetic behavior, the trend is contrastingly different for LCSBMO as compared to that of LCSMO; the magnetization of former compounds shows PM to FM transitions (TC) first and thereafter pure FM character is observed for temperature range down to 2 K, whereas that of the latter shows first PM to FM transition followed by FM to AFM transition as the temperature is lowered. This turn around in magnetic behavior may be attributed to the low level substitution of bigger size Ba2 þ ions. The study of temperature dependent magnetic hysteresis of all the three compounds reveals hardening of magnetization behavior with decrease of temperature. The electrical conduction in the high temperature region is clearly favoured by variable range hopping of eg carriers.

Acknowledgments Fig. 7. Increasing hardening behavior of magnetization with decreasing temperature for La0.5Ca0.25 Sr0.2Ba0.05MnO3 compound. The saturation magnetization values for a magnetic field of strength 5000 Oe are 14.24 emu/g at 290 K, 38.97 emu/g at 230 K, 47.60 emu/g at 160 K and 53.15 emu/g at 2 K.

The authors SA, ESM, and UD would like to thank DST and UGC, New Delhi, for financial support. References

Fig. 8. Comparative hardening of magnetization for La0.5Ca0.45 xSrxBa0.05MnO3 compounds at 160 K. The saturation magnetization values at 5000 Oe are 40.59 emu/g for x ¼0.1, 47.60 emu/g for x¼ 0.2 and 48.20 emu/g for x ¼0.3.

coercive field is observed to be opposite (Table 2). The comparison of magnetic hysteresis of compounds at 160 K is shown in Fig. 8.

6. Conclusion Our studies of half-doped manganite compounds La0.5Ca0.45 x SrxBa0.05MnO3 (LCSBMO) are consistent with the previous studies on La0.5Ca0.5 xSrxMnO3 (LCSMO) in respect of structural, and electronic transport properties in the sense they show similar trend in the variation of following quantities as x is increased from x¼0.1–0.3: (a) Increasing volume of unit cell, (b) increasing electrical conductivity, and (c) increasing magnetic transition temperatures (TC) apart from the steep increase in the resistivity

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