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Substrate dependent transport and magnetotransport in manganite multilayer
Physica B 406 (2011) 2270–2272
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Physica B journal homepage: www.elsevier.com/locate/physb
Substrate dependent transport and magnetotransport in manganite multilayer P.S. Vachhani a, P.S. Solanki a, R.R. Doshi a, N.A. Shah b, S. Rayaprol c, D.G. Kuberkar a,n a
Department of Physics, Saurashtra University, Rajkot 360005, India Department of Electronics, Saurashtra University, Rajkot 360005, India c UGC–DAE Consortium for Scientific Research, R-5 Shed, B.A.R.C. Campus, Mumbai 400085, India b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 December 2010 Received in revised form 7 March 2011 Accepted 21 March 2011 Available online 31 March 2011
We report magnetotransport properties of La0.5Pr0.2Sr0.3MnO3 (LPSMO) {5 layers}/La0.5Pr0.2Ba0.3MnO3 (LPBMO) {4 layers} manganite multilayers grown on single crystalline STO (h 0 0) and NGO (h 0 0) substrates using pulsed laser deposition (PLD) technique. An appreciable magnetoresistance (MR) 56% (80 kOe field) at room temperature (RT) is exhibited by the heterostructure deposited on STO substrate having field coefficient of resistance (FCR) 35% (100 Oe) while the multilayer deposited on NGO substrate exhibits MR 61% (80 kOe field) and FCR 18% (5 kOe) at RT. The observed values of temperature coefficient of resistance (TCR) are 3.15% and 2.77% at RT for the multilayers grown on STO and NGO substrates, respectively. A comparison of the field sensitivity of the multilayered structure studied with those reported for LPSMO/Al2O3/LPSMO (FCR 20% at 220 K) and LPSMO/STO film (FCR 13% at 250 K) shows that the multilayer exhibits higher field sensitivity, which can be attributed to the improved LPSMO–LPBMO interfaces. In this communication, the results of the structural, transport and magnetotransport studies on LPSMO/LPBMO multilayered systems have been discussed. & 2011 Elsevier B.V. All rights reserved.
Keywords: Multilayer structure Magnetic materials Sensors Perovskites
1. Introduction Research on cation doped rare earth manganites has been carried out vigorously owing to various physical properties such as insulator–metal (I–M) transition along with paramagnetic– ferromagnetic (PM–FM) transition and colossal magnetoresistance (CMR) exhibited by them [1]. Initially, a large MR was observed at RT in La0.67Ba0.33MnO3 (LBMO) manganite thin films while in the annealed films of La0.67Ca0.33MnO3 (LCMO) three orders of magnitude increase in MR was reported at 77 K [2,3]. Appreciable field sensitivity is exhibited by manganite films and attention is now focused on achieving large tunneling magnetoresistance (TMR) in the multilayered thin film devices for suitable applications such as read/write heads, magnetic random access memories (MRAM), etc. For the use of any TMR device, the thin films should possess high field sensitivity as well as higher operating temperature. TMR device usually consists of a multilayer structure with non-magnetic layer sandwiched between the top and bottom magnetic electrodes (manganite layers). Due to the presence of non-magnetic barrier between two ferromagnetic layers, the operating temperature of the device
n
Corresponding author. Tel.: þ91 281 2588428; fax: þ91 281 2576347. E-mail address: [email protected] (D.G. Kuberkar).
0921-4526/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2011.03.051
decreases. Several investigations are aimed at enhancing the operating temperature of manganite devices [4,5]. The first serious attempt towards fabrication and study of manganite based device was on epitaxial trilayer junction device in the form of [(top electrode) La0.67Sr0.33MnO3]/(insulating layer) SrTiO3/[(bottom electrode) La0.67Sr0.33MnO3] exhibiting a large MR 83% at 4.2 K under small applied field [6]. Markna et al. [7] reported the studies on manganite based device having nanostructural Al2O3 islands sandwiched between two ferromagnetic LPSMO layers. Although this device exhibited MR 77% at 220 K, its operating temperature was quite low as compared to LPSMO film (297 K). Keeping in mind the constraints of using a non-magnetic insulator as the sandwich layer, we have deposited nine layered LPSMO {5}/LPBMO {4} heterostructure on two different substrates, namely single crystalline SrTiO3 (STO) and NdGaO3 (NGO) and compared their transport behavior in the presence of applied magnetic field. Our earlier studies have shown that LPSMO is ferromagnetic while LPBMO is a paramagnetic insulator at 300 K [8,9]. Therefore, instead of using insulating non-magnetic Al2O3 layer between two ferromagnetic layers, we have used LPBMO magnetic layer as the sandwich layer between two LPSMO layers to avoid large lattice mismatch and defects at interface in order to improve the MR at temperature close to RT.
P.S. Vachhani et al. / Physica B 406 (2011) 2270–2272
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2. Experimental details Two well characterized polycrystalline bulk targets of La0.5Pr0.2Sr0.3MnO3 (LPSMO) and La0.5Pr0.2Ba0.3MnO3 (LPBMO) were used for the deposition of consecutive layers of LPSMO and LPBMO in order to fabricate nine layered manganite multilayer using pulsed laser deposition (PLD) technique. A third harmonic (355 nm) of a Q-switched Nd-YAG laser was used for the ablation with energy density 2 J/cm2 on the target surface at a repetition rate of 10 Hz. During the film deposition the substrate temperature was maintained at 650 1C, with oxygen partial pressure 400 mTorr. The devices grown on STO and NGO single crystal substrates were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). Transport and magnetotransport measurements were carried out using standard dc four probe method with and without applied magnetic field up to 80 kOe.
3. Results and discussion
Fig. 2. Temperature dependence of TCR of multilayers grown on (a) STO and (b) NGO [inset: R–T plots of multilayers grown on STO and NGO substrates].
Fig. 1(a) shows the schematic diagram of a LPSMO{5}/(LPBMO) {4} multilayers grown on STO/NGO substrates. The thicknesses of each LPSMO and LPBMO layer were 50 and 20 nm, respectively. The lateral dimensions of the device under study were 10 mm (L) 2.4 mm (B). Fig. 1(b) and (c) shows the XRD patterns of devices under study while the insets of Fig. 1(b) and (c) depict the mismatch between the (1 0 0) peak of LPSMO (50 nm) and the substrate peak, leading to structural strain. The values of structural strain due to the lattice–substrate mismatch are 1.28% and 2.06% for multilayers grown on STO and NGO substrates, respectively. The transport and magnetotransport measurements have been carried out on both the multilayers in the current perpendicular to plane (CPP) mode. The temperature (T) dependence of resistance (R) for both the multilayers is shown in the insets of Fig. 2(a) and (b), respectively. The multilayer grown on STO does not show insulator to metal transition (TIM) up to 300 K while multilayer grown on NGO exhibits TIM at 300 K. At 300 K, the multilayers on STO and NGO exhibit resistances 450 and 700 O, respectively. The overall low resistance of multilayer grown on STO with respect to NGO is possibly due to large lattice–substrate mismatch induced strain in the multilayer grown on NGO as compared to STO. Also, the TIM of the multilayer grown on NGO substrate is low due to larger strain in the film [10]. The values of temperature sensing parameter, important for bolometric applications, have been calculated using the formula TCR %¼
Fig. 3. MR versus. H isotherms for multilayer on (a) STO and (b) NGO substrates and (c) FCR versus. H plots for multilayers grown on STO and NGO substrates.
Fig. 1. (a) Schematic diagram of multilayer grown on STO and NGO. XRD patterns of multilayer grown on (b) STO and (c) NGO substrates [insets: the (0 0 1) film peak and the substrate peak].
(1/R)(dR/dT) 100 for both multilayers and are plotted as a function of T in Fig. 2(a) and (b). The observed maximum TCR values are 3.15% and 2.77% near 300 K for the multilayers grown on STO and NGO, respectively. Fig. 3(a) and (b) shows the MR versus H isotherms for multilayers at 5, 150 and 300 K and field up to 80 kOe. The MR has been calculated using the formula MR¼[(RH–R0)/R0] 100. Both the multilayers show a negative MR at all the temperatures studied. It can be seen that at 150 K, the MR values are 5.3% and 7.7% for multilayer grown on STO and NGO, respectively, which becomes 1.4% and 2.1% at 5 K for the respective multilayers. The small amount of MR observed at lower temperatures suggests negligible substrate dependent modifications in MR. It can also be seen that large MR 56% and 61% at 300 K under 80 kOe is exhibited by the multilayer grown on STO and NGO substrates, respectively, which is due to the intrinsic contribution to MR arising near I–M
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transition ( RT), and can be explained by the Zener double exchange mechanism [11]. The observation of large MR value ( 56% and 61%) at 300 K can be explained as follows—LPSMO exhibits TIM 298 K [7] while LPBMO has TIM 210 K [12]. In the temperature range 210–300 K, LPBMO is in paramagnetic insulator (PMI) state while LPSMO is in ferromagnetic metallic (FMM) state. The conduction between FMM–PMI–FMM layers in this temperature range is due to spin flip scattering at various interfaces, which suppresses net spin polarization of charge carriers and hence results in large MR [13]. However, the effect of substrate on the MR at RT is more pronounced in the multilayer grown on NGO (having large lattice mismatch 2.06%), which may be attributed to the field induced suppression in the lattice disorder and Mn–O–Mn bond disorder at the interface. At temperatures below 210 K, LPBMO becomes FMM due to which the LPSMO–LPBMO interfaces become defect free (magnetic–magnetic) resulting in lower MR. The variation in magnetic field sensing parameter quantified using FCR%¼(1/R)(dR/dH) 100 for both multilayers is plotted as a function of H in Fig. 3 (c). The maximum FCR value observed is 35% at 300 K under 100 Oe for multilayer grown on STO, which decreases to 18% at 5 kOe for multilayer on NGO substrate. The maximum FCR reported in LPSMO/Al2O3/LPSMO heterostructure on STO substrate is 20% at 220 K under 5 kOe field and LPSMO/ STO (50 nm) film possesses 13% at 250 K under 5 kOe [7] while in the presently studied multilayers on STO and NGO substrates, FCR values are comparatively higher. The difference in the FCR values of earlier studied heterostructure [7] and the presently studied multilayered structure can be ascribed to the better structural and chemical stoichiometric similarity between the adjacent manganite layers in LPSMO/LPBMO/LPSMO multilayer as compared to LPSMO/Al2O3/LPSMO heterostructure, which results in the improved interfacial structural and magnetic properties. This, in turn, results in the improvement in field sensitivity of the multilayer under study. The observation of large FCR values under smaller required field in multilayer grown on STO as compared to that on NGO is due to the better interface in STO based multilayer.
4. Conclusions In summary, we have successfully grown LPSMO {5}/LPBMO {4} manganite multilayer on STO and NGO substrates and observed
a large MR at RT and field sensitivity under low applied fields and substrate dependent modifications in the transport and magnetotransport properties. The MR is high in multilayer grown on NGO substrate as compared to that on STO, which can be attributed to the field induced modifications in the substrate–film interface. The multilayer under study shows the large field sensitivity at comparatively higher operating temperatures and under relatively lower applied field as compared to LPSMO/STO film and LPSMO/ Al2O3/LPSMO heterostructure, which makes it suitable for the device applications.
Acknowledgments The experimental facilities provided by Dr. R. Rawat and Dr. V. Ganesan, UGC–DAE CSR, Indore, are thankfully acknowledged. PSS is thankful to CSIR, New Delhi, for the award of Senior Research Fellowship (no. 9/151 (28)/2008-EMR-I). N.A.S. is thankful to UGC, New Delhi, for providing financial support in form of Minor Research Project no. 34-511/2008 (SR). References [1] C.N.R. Rao, B. Raveau, Colossal Magnetoresistance Oxides, Gordon and Breach, London, 1999. [2] R. Von Helmolt, J. Wecker, B. Holzapfel, L. Schultz, K. Samwer, Phys. Rev. Lett. 71 (1993) 2331. [3] Ken-ichi Chahara, Toshiyuki Ohno, Masahiro Kasal, Yuzoo Kozono, Appl. Phys. Lett. 63 (1993) (1990). [4] H.Q. Yin, J.S. Zhou, J.B. Goodenough, Appl. Phys. Lett. 77 (2000) 714. [5] P.S. Vachhani, J.H. Markna, R.J. Choudhary, D.M. Phase, D.G. Kuberkar, Appl. Phys. Lett. 92 (2008) 043506. [6] Yu Lu, X.W. Li, G.Q. Gong, G. Xiao, A. Gupta, P. Lecoeur, J.Z. Sun, Y.Y. Wang, V.P. Dravid, Phys. Rev. B 54 (1996) R8357. [7] J.H. Markna, P.S. Vachhani, R.N. Parmar, D.G. Kuberkar, P. Misra, B.N. Singh, L.M. Kukreja, D.S. Rana, S.K. Malik, Euro. Phys. Lett. 79 (2007) 17005. [8] J.H. Markna, R.N. Parmar, D.S. Rana, Ravi Kumar, P. Misra, L.M. Kukreja, D.S. Rana, S.K. Malik, Nucl. Instrum. Methods B 256 (2007) 693. [9] D.S. Rana, J.H. Markna, R.N. Parmar, D.G. Kuberkar, P. Raychaudhuri, J. John, S.K. Malik, Phys. Rev. B 71 (2005) 212404. [10] M. Petit, M. Rajeswari, A. Biswas, R.L. Greene, T. Venkatesan, L.J. Martı´nezMiranda, J. Appl. Phys. 97 (2005) 093512. [11] C. Zener, Phys. Rev. 82 (1951) 403. [12] J.H. Markna, R.N. Parmar, D.G. Kuberkar, Ravi Kumar, D.S. Rana, S.K. Malik, Appl. Phys. Lett. 88 (2006) 152503. [13] F. Guinea, Phys. Rev. B 58 (1998) 9212.
Contents lists available at ScienceDirect
Physica B journal homepage: www.elsevier.com/locate/physb
Substrate dependent transport and magnetotransport in manganite multilayer P.S. Vachhani a, P.S. Solanki a, R.R. Doshi a, N.A. Shah b, S. Rayaprol c, D.G. Kuberkar a,n a
Department of Physics, Saurashtra University, Rajkot 360005, India Department of Electronics, Saurashtra University, Rajkot 360005, India c UGC–DAE Consortium for Scientific Research, R-5 Shed, B.A.R.C. Campus, Mumbai 400085, India b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 December 2010 Received in revised form 7 March 2011 Accepted 21 March 2011 Available online 31 March 2011
We report magnetotransport properties of La0.5Pr0.2Sr0.3MnO3 (LPSMO) {5 layers}/La0.5Pr0.2Ba0.3MnO3 (LPBMO) {4 layers} manganite multilayers grown on single crystalline STO (h 0 0) and NGO (h 0 0) substrates using pulsed laser deposition (PLD) technique. An appreciable magnetoresistance (MR) 56% (80 kOe field) at room temperature (RT) is exhibited by the heterostructure deposited on STO substrate having field coefficient of resistance (FCR) 35% (100 Oe) while the multilayer deposited on NGO substrate exhibits MR 61% (80 kOe field) and FCR 18% (5 kOe) at RT. The observed values of temperature coefficient of resistance (TCR) are 3.15% and 2.77% at RT for the multilayers grown on STO and NGO substrates, respectively. A comparison of the field sensitivity of the multilayered structure studied with those reported for LPSMO/Al2O3/LPSMO (FCR 20% at 220 K) and LPSMO/STO film (FCR 13% at 250 K) shows that the multilayer exhibits higher field sensitivity, which can be attributed to the improved LPSMO–LPBMO interfaces. In this communication, the results of the structural, transport and magnetotransport studies on LPSMO/LPBMO multilayered systems have been discussed. & 2011 Elsevier B.V. All rights reserved.
Keywords: Multilayer structure Magnetic materials Sensors Perovskites
1. Introduction Research on cation doped rare earth manganites has been carried out vigorously owing to various physical properties such as insulator–metal (I–M) transition along with paramagnetic– ferromagnetic (PM–FM) transition and colossal magnetoresistance (CMR) exhibited by them [1]. Initially, a large MR was observed at RT in La0.67Ba0.33MnO3 (LBMO) manganite thin films while in the annealed films of La0.67Ca0.33MnO3 (LCMO) three orders of magnitude increase in MR was reported at 77 K [2,3]. Appreciable field sensitivity is exhibited by manganite films and attention is now focused on achieving large tunneling magnetoresistance (TMR) in the multilayered thin film devices for suitable applications such as read/write heads, magnetic random access memories (MRAM), etc. For the use of any TMR device, the thin films should possess high field sensitivity as well as higher operating temperature. TMR device usually consists of a multilayer structure with non-magnetic layer sandwiched between the top and bottom magnetic electrodes (manganite layers). Due to the presence of non-magnetic barrier between two ferromagnetic layers, the operating temperature of the device
n
Corresponding author. Tel.: þ91 281 2588428; fax: þ91 281 2576347. E-mail address: [email protected] (D.G. Kuberkar).
0921-4526/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2011.03.051
decreases. Several investigations are aimed at enhancing the operating temperature of manganite devices [4,5]. The first serious attempt towards fabrication and study of manganite based device was on epitaxial trilayer junction device in the form of [(top electrode) La0.67Sr0.33MnO3]/(insulating layer) SrTiO3/[(bottom electrode) La0.67Sr0.33MnO3] exhibiting a large MR 83% at 4.2 K under small applied field [6]. Markna et al. [7] reported the studies on manganite based device having nanostructural Al2O3 islands sandwiched between two ferromagnetic LPSMO layers. Although this device exhibited MR 77% at 220 K, its operating temperature was quite low as compared to LPSMO film (297 K). Keeping in mind the constraints of using a non-magnetic insulator as the sandwich layer, we have deposited nine layered LPSMO {5}/LPBMO {4} heterostructure on two different substrates, namely single crystalline SrTiO3 (STO) and NdGaO3 (NGO) and compared their transport behavior in the presence of applied magnetic field. Our earlier studies have shown that LPSMO is ferromagnetic while LPBMO is a paramagnetic insulator at 300 K [8,9]. Therefore, instead of using insulating non-magnetic Al2O3 layer between two ferromagnetic layers, we have used LPBMO magnetic layer as the sandwich layer between two LPSMO layers to avoid large lattice mismatch and defects at interface in order to improve the MR at temperature close to RT.
P.S. Vachhani et al. / Physica B 406 (2011) 2270–2272
2271
2. Experimental details Two well characterized polycrystalline bulk targets of La0.5Pr0.2Sr0.3MnO3 (LPSMO) and La0.5Pr0.2Ba0.3MnO3 (LPBMO) were used for the deposition of consecutive layers of LPSMO and LPBMO in order to fabricate nine layered manganite multilayer using pulsed laser deposition (PLD) technique. A third harmonic (355 nm) of a Q-switched Nd-YAG laser was used for the ablation with energy density 2 J/cm2 on the target surface at a repetition rate of 10 Hz. During the film deposition the substrate temperature was maintained at 650 1C, with oxygen partial pressure 400 mTorr. The devices grown on STO and NGO single crystal substrates were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). Transport and magnetotransport measurements were carried out using standard dc four probe method with and without applied magnetic field up to 80 kOe.
3. Results and discussion
Fig. 2. Temperature dependence of TCR of multilayers grown on (a) STO and (b) NGO [inset: R–T plots of multilayers grown on STO and NGO substrates].
Fig. 1(a) shows the schematic diagram of a LPSMO{5}/(LPBMO) {4} multilayers grown on STO/NGO substrates. The thicknesses of each LPSMO and LPBMO layer were 50 and 20 nm, respectively. The lateral dimensions of the device under study were 10 mm (L) 2.4 mm (B). Fig. 1(b) and (c) shows the XRD patterns of devices under study while the insets of Fig. 1(b) and (c) depict the mismatch between the (1 0 0) peak of LPSMO (50 nm) and the substrate peak, leading to structural strain. The values of structural strain due to the lattice–substrate mismatch are 1.28% and 2.06% for multilayers grown on STO and NGO substrates, respectively. The transport and magnetotransport measurements have been carried out on both the multilayers in the current perpendicular to plane (CPP) mode. The temperature (T) dependence of resistance (R) for both the multilayers is shown in the insets of Fig. 2(a) and (b), respectively. The multilayer grown on STO does not show insulator to metal transition (TIM) up to 300 K while multilayer grown on NGO exhibits TIM at 300 K. At 300 K, the multilayers on STO and NGO exhibit resistances 450 and 700 O, respectively. The overall low resistance of multilayer grown on STO with respect to NGO is possibly due to large lattice–substrate mismatch induced strain in the multilayer grown on NGO as compared to STO. Also, the TIM of the multilayer grown on NGO substrate is low due to larger strain in the film [10]. The values of temperature sensing parameter, important for bolometric applications, have been calculated using the formula TCR %¼
Fig. 3. MR versus. H isotherms for multilayer on (a) STO and (b) NGO substrates and (c) FCR versus. H plots for multilayers grown on STO and NGO substrates.
Fig. 1. (a) Schematic diagram of multilayer grown on STO and NGO. XRD patterns of multilayer grown on (b) STO and (c) NGO substrates [insets: the (0 0 1) film peak and the substrate peak].
(1/R)(dR/dT) 100 for both multilayers and are plotted as a function of T in Fig. 2(a) and (b). The observed maximum TCR values are 3.15% and 2.77% near 300 K for the multilayers grown on STO and NGO, respectively. Fig. 3(a) and (b) shows the MR versus H isotherms for multilayers at 5, 150 and 300 K and field up to 80 kOe. The MR has been calculated using the formula MR¼[(RH–R0)/R0] 100. Both the multilayers show a negative MR at all the temperatures studied. It can be seen that at 150 K, the MR values are 5.3% and 7.7% for multilayer grown on STO and NGO, respectively, which becomes 1.4% and 2.1% at 5 K for the respective multilayers. The small amount of MR observed at lower temperatures suggests negligible substrate dependent modifications in MR. It can also be seen that large MR 56% and 61% at 300 K under 80 kOe is exhibited by the multilayer grown on STO and NGO substrates, respectively, which is due to the intrinsic contribution to MR arising near I–M
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P.S. Vachhani et al. / Physica B 406 (2011) 2270–2272
transition ( RT), and can be explained by the Zener double exchange mechanism [11]. The observation of large MR value ( 56% and 61%) at 300 K can be explained as follows—LPSMO exhibits TIM 298 K [7] while LPBMO has TIM 210 K [12]. In the temperature range 210–300 K, LPBMO is in paramagnetic insulator (PMI) state while LPSMO is in ferromagnetic metallic (FMM) state. The conduction between FMM–PMI–FMM layers in this temperature range is due to spin flip scattering at various interfaces, which suppresses net spin polarization of charge carriers and hence results in large MR [13]. However, the effect of substrate on the MR at RT is more pronounced in the multilayer grown on NGO (having large lattice mismatch 2.06%), which may be attributed to the field induced suppression in the lattice disorder and Mn–O–Mn bond disorder at the interface. At temperatures below 210 K, LPBMO becomes FMM due to which the LPSMO–LPBMO interfaces become defect free (magnetic–magnetic) resulting in lower MR. The variation in magnetic field sensing parameter quantified using FCR%¼(1/R)(dR/dH) 100 for both multilayers is plotted as a function of H in Fig. 3 (c). The maximum FCR value observed is 35% at 300 K under 100 Oe for multilayer grown on STO, which decreases to 18% at 5 kOe for multilayer on NGO substrate. The maximum FCR reported in LPSMO/Al2O3/LPSMO heterostructure on STO substrate is 20% at 220 K under 5 kOe field and LPSMO/ STO (50 nm) film possesses 13% at 250 K under 5 kOe [7] while in the presently studied multilayers on STO and NGO substrates, FCR values are comparatively higher. The difference in the FCR values of earlier studied heterostructure [7] and the presently studied multilayered structure can be ascribed to the better structural and chemical stoichiometric similarity between the adjacent manganite layers in LPSMO/LPBMO/LPSMO multilayer as compared to LPSMO/Al2O3/LPSMO heterostructure, which results in the improved interfacial structural and magnetic properties. This, in turn, results in the improvement in field sensitivity of the multilayer under study. The observation of large FCR values under smaller required field in multilayer grown on STO as compared to that on NGO is due to the better interface in STO based multilayer.
4. Conclusions In summary, we have successfully grown LPSMO {5}/LPBMO {4} manganite multilayer on STO and NGO substrates and observed
a large MR at RT and field sensitivity under low applied fields and substrate dependent modifications in the transport and magnetotransport properties. The MR is high in multilayer grown on NGO substrate as compared to that on STO, which can be attributed to the field induced modifications in the substrate–film interface. The multilayer under study shows the large field sensitivity at comparatively higher operating temperatures and under relatively lower applied field as compared to LPSMO/STO film and LPSMO/ Al2O3/LPSMO heterostructure, which makes it suitable for the device applications.
Acknowledgments The experimental facilities provided by Dr. R. Rawat and Dr. V. Ganesan, UGC–DAE CSR, Indore, are thankfully acknowledged. PSS is thankful to CSIR, New Delhi, for the award of Senior Research Fellowship (no. 9/151 (28)/2008-EMR-I). N.A.S. is thankful to UGC, New Delhi, for providing financial support in form of Minor Research Project no. 34-511/2008 (SR). References [1] C.N.R. Rao, B. Raveau, Colossal Magnetoresistance Oxides, Gordon and Breach, London, 1999. [2] R. Von Helmolt, J. Wecker, B. Holzapfel, L. Schultz, K. Samwer, Phys. Rev. Lett. 71 (1993) 2331. [3] Ken-ichi Chahara, Toshiyuki Ohno, Masahiro Kasal, Yuzoo Kozono, Appl. Phys. Lett. 63 (1993) (1990). [4] H.Q. Yin, J.S. Zhou, J.B. Goodenough, Appl. Phys. Lett. 77 (2000) 714. [5] P.S. Vachhani, J.H. Markna, R.J. Choudhary, D.M. Phase, D.G. Kuberkar, Appl. Phys. Lett. 92 (2008) 043506. [6] Yu Lu, X.W. Li, G.Q. Gong, G. Xiao, A. Gupta, P. Lecoeur, J.Z. Sun, Y.Y. Wang, V.P. Dravid, Phys. Rev. B 54 (1996) R8357. [7] J.H. Markna, P.S. Vachhani, R.N. Parmar, D.G. Kuberkar, P. Misra, B.N. Singh, L.M. Kukreja, D.S. Rana, S.K. Malik, Euro. Phys. Lett. 79 (2007) 17005. [8] J.H. Markna, R.N. Parmar, D.S. Rana, Ravi Kumar, P. Misra, L.M. Kukreja, D.S. Rana, S.K. Malik, Nucl. Instrum. Methods B 256 (2007) 693. [9] D.S. Rana, J.H. Markna, R.N. Parmar, D.G. Kuberkar, P. Raychaudhuri, J. John, S.K. Malik, Phys. Rev. B 71 (2005) 212404. [10] M. Petit, M. Rajeswari, A. Biswas, R.L. Greene, T. Venkatesan, L.J. Martı´nezMiranda, J. Appl. Phys. 97 (2005) 093512. [11] C. Zener, Phys. Rev. 82 (1951) 403. [12] J.H. Markna, R.N. Parmar, D.G. Kuberkar, Ravi Kumar, D.S. Rana, S.K. Malik, Appl. Phys. Lett. 88 (2006) 152503. [13] F. Guinea, Phys. Rev. B 58 (1998) 9212.