- Email: [email protected]
YBCO heterostructures by pulsed laser deposition technique
Nuclear Instruments and Methods in Physics Research B 212 (2003) 539–544 www.elsevier.com/locate/nimb
Synthesis of good quality LCMO/YBCO heterostructures by pulsed laser deposition technique S.K. Wanchoo a,*, J. Jasudasan b, V.C. Bagwe b, A.D. Thakur b, U.D. Vaishnav b, S.P. Pai b, A.M. Narsale a, R. Pinto b a
Department of Physics, University of Mumbai, Santacruz (E), Mumbai 400 098, Maharashtra, India b Tata Institute of Fundamental Research, Mumbai 400 005, India
Abstract Deposition of multilayers of La0:7 Ca0:3 MnO3 –YBa2 Cu3 O7d offers great challenges and opportunities for future spin-based device applications. Pulsed laser deposition is a well-established and unique tool for making such highly stoichiometric, nearly single crystal-like epitaxial films. Here we discuss the synthesis of multi-component La0:7 Ca0:3 MnO3 –YBa2 Cu3 O7d oxide thin films and their heterostructures, which were grown in situ by sequential deposition of LCMO and YBCO thin films on Æ0 0 1æ LaAlO3 substrate using a pulsed laser deposition (PLD) system. We discuss the growth of these thin-film multi-layers, from the device applications point of view. The micro-structural properties, continuity and texture of the films were studied by using XRD, AFM and SEM. The good interface quality of these films was established using the secondary ion mass spectroscopy technique. Transport measurements on the individual layers of these heterostructures were carried out using a low temperature four-probe measurement setup. A Quantum design SQUID magnetometer was used to carry out the magnetization measurements on these multilayers, which display excellent superconducting and ferromagnetic properties of the heterostructures. 2003 Elsevier B.V. All rights reserved. PACS: 74.25.Ha; 74.76.)w; 74.80.Dm Keywords: Heterostructures; Multilayers; Spintronics; Cationic inter-diffusion
1. Introduction The possible application of spin-injection devices in the field of ‘‘spintronics’’ has received a lot of attention of the researchers in the recent
* Corresponding author. Tel.: +91-22-2652-8835; fax: +9122-2652-9780. E-mail address: sunilkwanchoo@rediffmail.com (S.K. Wanchoo).
past. Such devices can be realized from superconductor–ferromagnet (F/S) heterostructures. Such heterostructures have received a lot of attention because of their rich physics and potential applications. Development of such heterostructures with the constituent layers having identical crystal structure and exhibiting superconducting and magnetic properties in the alternate layers is the most important requirement. Moreover these heterostructures must possess clean and sharp interfaces. If we are able to understand and control
0168-583X/$ - see front matter 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0168-583X(03)01841-X
540
S.K. Wanchoo et al. / Nucl. Instr. and Meth. in Phys. Res. B 212 (2003) 539–544
the quality and sharpness of the interface then these heterostructures could also lead to novel spin-based devices. These devices are said to be based on spin-polarized transport across the half-metallic ferromagnet and high temperature superconductor (F/S) heterostructures. The halfmetallic nature of the hole doped rare earth manganites of the form R1x Ax MnO3 (R ¼ rare earth, A ¼ bivalent cation) provide a reserve of spin-polarized electrons, which can be utilized in unconventional devices. La0:7 Ca0:3 MnO3 is a wellstudied CMR manganite with a degree of polarization close to unity, which also has a good structural compatibility with high temperature superconductors such as YBa2 Cu3 O7d . Hence, La0:7 Ca0:3 MnO3 /YBa2 Cu3 O7d heterostructures have become attractive for spin injection studies. A number of experiments have been reported on these heterostructures (F/S) [1,2]. However most of these studies heavily rely on a sandwiched insulating layer, which is deposited to avoid any cationic inter-diffusion across the interface. But in such studies the possibility of joule heating cannot be entirely ruled out during transport measurements. Therefore F/S barrierless heterostructures with sharp interfaces, exhibiting ferromagnetism and superconductivity in alternate layers are highly desired. Though there have been a few reports [3] on such heterostructures, to the authorÕs best knowledge conclusive study of the cationic inter-diffusion across the interface has not been carried out so far. Most of the F/S based injection experiments [4] have been mainly based on trilayers of (ferromagnet–insulator–superconductor) F–I–S on single crystal substrates. The insulating layer in these studies has been used to avoid the inter-layer cationic diffusion. Pulsed laser deposition (PLD) is a unique method for growing highly stoichiometric, nearly single crystal-like materials in the form of epitaxial films and heterostructures. Multi-component La0:7 Ca0:3 MnO3 –YBa2 Cu3 O7d oxide thin film heterostructures can be easily grown in situ by sequential deposition of La0:7 Ca0:3 MnO3 and YBa2 Cu3 O7d thin films by this technique. In this work an effort has been made to synthesize good quality F/S bylayers with tailored superconducting and ferromagnetic properties. The synthesis and
characterization of good quality F/S heterostructures is discussed here.
2. Experimental details All the bulk targets used for the present work have been synthesized using the standard solidstate reaction method. Pulsed laser deposition technique was employed to grow the LCMO/ YBCO heterostructure on (0 0 1) LaAlO3 (LAO) single-crystal substrates. An excimer laser was used to grow these heterostructures with a wavelength of 248 nm and a repetition rate of 10 Hz. Both the targets were mounted on the multi-target carrousel target holders and the same can be rotated using automated motor control. LAO substrate was mounted on the heater with the help of conducting silver paste for better thermal conductivity. Due to the crystallographically compatible nature of these oxides we have used identical deposition conditions (after optimizing the same) for the in situ growth of both the two oxide layers. These heterostructures were deposited at a substrate temperature of 800 C. Oxygen partial pressure of 400 mTorr for LCMO and 250 mTorr for YBCO were maintained during their growth, respectively. Laser fluence of 2.5 J/cm2 was used for ablating the targets. The superconducting transition temperature was established by using a homemade ac susceptibility measurement setup. Surface morphology of as grown thin films has been probed using the atomic force microscope. The phase pure nature of the films was established by powder X-ray diffraction technique. YBCO/LCMO bilayers were prepared by sequentially depositing YBCO and LCMO onto LAO substrates. To carry out the resistivity measurements using a homemade resistivity measurement setup, films were patterned using UV photolithography technique. Contact pads of gold were patterned using UV photolithography after depositing a gold film on the sample by pulsed laser deposition technique. Another sister sample, which was grown in the same run, was used to carry out the resistivity measurements on the bottom LCMO layer. The top YBCO layer was patterned into a prototype
S.K. Wanchoo et al. / Nucl. Instr. and Meth. in Phys. Res. B 212 (2003) 539–544
device structure. Patterning the YBCO layer became necessary, as we wanted to carry out the resistivity measurements on the bottom LCMO layer in the LCMO/YBCO bilayer. In order to ensure the complete removal of the top YBCO layer on either side of the microbridge the YBCO layer was slightly over etched so that the bottom LCMO layer was fully exposed on both the sides of the microbridge. Using the same method as used for YBCO layer four gold pads were deposited on the LCMO layer two on either side of the YBCO microbridge. The interface of the LCMO/YBCO heterostructures was characterized using secondary ion mass spectroscopy technique (SIMS). In order to establish the interface quality a depth profiling was carried out using a Cameca 34f SIMS machine. In this measurement Oþ 2 was used for ionization at a current of 50 nA and at an effective incidence angle of 42. Finally an analysis zone of 33 lm diameter was used in the center of the erosion zone of 150 lm · 150 lm to carry out the depth profiling. Further, a quantum design superconducting quantum interference device (SQUID) magnetometer was used to probe the magnetic properties of the YBa2 Cu3 O7d layer. Thickness of the constituent layers was measured by using a surface Profilometer (Sloan Dektak) and was found to be (LCMO) and 1500 A (YBCO), respec1000 A tively.
541
3. Results and discussions This paper presents the results of a systematic study of the electric, magnetic and interface properties of bilayer heterostructure made form epitaxially in situ grown LCMO and YBCO thin films. The main issue we are addressing here is the quality of the interface and ferromagnetic and superconducting properties of the constituent layers. Fig. 1 shows a typical X-ray diffraction pattern of a LCMO/YBCO heterostructure. The pattern shows most of the reflections along the (0 0 l) direction suggesting the epitaxial c-axis oriented growth of both LCMO and YBCO layers and indicates that these bilayers have preferred orientation with the crystal c-axis perpendicular to the plane of the substrate. Fig. 2 shows the temperature dependence of resistance as a function of temperature for LCMO/YBCO bilayers. Fig. 2(a) shows the resistivity curve as measured on the top YBCO layer. Fig. 2(b) shows the resistivity curve for the LCMO/YBCO heterostructure. It can be seen from the graph that the metal–insulator transition temperature of the LCMO layer is 250 K. Here at this temperature there is no contribution of the top YBCO microbridge apart from adding few hundred ohms to the overall resistance of the bilayer. However as we go down to 82 K the resistance of the sample drops almost to zero. This is because the top microbridge is now
Fig. 1. X-ray diffraction pattern for LCMO/YBCO heterostructure.
542
S.K. Wanchoo et al. / Nucl. Instr. and Meth. in Phys. Res. B 212 (2003) 539–544 250
3
YBCO Layer
2.5
Arb Units
Resistance ohms
200 150
2
(a)
1.5 1
Tp
0.5 0
100
0
50
100
150
200
250
300
(b)
Temperature K
Tc
50
LCMO/YBCO bilayer
0 0
50
100
150 200 Temperature K
250
300
Fig. 2. R versus T for F/S bilayers. (a) Resistivity curve as measured for the top YBCO layer. (b) Resistivity curve as measured for the LCMO/YBCO heterostructure.
superconducting and the current sees a resistance less path and shorts through the microbridge. This drop clearly indicates the superconducting nature of the microbridge. Hence at 250 K LCMO layer shows a clear ferromagnetic behavior while as at 82 K since the resistance of the YBCO microbridge drops to zero and the same conclusively indicates the superconductivity in the microbridge. Hence the four-probe measurements clearly indicate that the LCMO/YBCO heterostructure essentially displays both ferromagnetism and superconductivity in the alternate layers. The four-probe data though does not show any effect of YBCO on LCMO as the metal–insulator transition is found to be equal to that of a single layer of LCMO, which was grown for comparison. However the superconducting transition temperature Tc of YBCO does show a decrease from standard 90 K to 86 K. In order to probe this decrease we have carried out secondary ion mass spectroscopy studies on these heterostructures to characterize the sharpness of the interface between LCMO and YBCO. Fig. 3 shows the SIMS profiles for LCMO/YBCO heterostructures. The quality of LCMO–YBCO interface is very important. The interface quality depends primarily on the surface roughness of LCMO layer and on the possible inter-diffusion of cations at the interface during YBCO growth. Atomic force microscopy showed
the LCMO roughness (determined partly due to . We the twinned LAO substrate) to be 200 A evaluated the cationic inter-diffusion using secondary ions mass spectroscopy (SIMS). Shown in Fig. 3 are the SIMS profiles of a LCMO–YBCO interface (YBCO on top). If we account 200 A due to surface roughness in the 400 A inter-diffused layer (SIMS), we see only a nominal inter on each side of the junction, diffusion of 100 A except for diffusion of Cu into the LCMO layer. Longer diffusion of Cu into the LCMO layer does not appear to affect the spin carrier density as the Tp was found to be 250 K. This clearly indicates that the minimal diffusion of Cu does not affect the properties of LCMO. We believe that the interdiffused Cu may be sitting at the grain boundaries and does not have any impact on the LCMO properties. Therefore it is clear that due to the loss inter-diffused layer, of Cu and also due to a 100 A the Tc of YBCO shows a decrease of 4 K. Fig. 4 shows the M versus H hysteresis loop for La0:7 Ca0:3 MnO3 /YBa2 Cu3 O7d heterostructures carried out at 40 K (well below the Tc of YBa2 Cu3 O7d ). The plot clearly demonstrates the excellent display of superconducting ordering in these heterostructures at 40 K. Therefore the magnetic properties of the superconducting layer are found to be excellent in case of La0:7 Ca0:3 MnO3 /YBa2 Cu3 O7d heterostructures.
S.K. Wanchoo et al. / Nucl. Instr. and Meth. in Phys. Res. B 212 (2003) 539–544
543
. (2150 s in the time Fig. 3. SIMS profiles of a typical YBCO/LCMO heterostructure. The full scale of the x-axis corresponds to 3954 A .) axis correspond to an etch crater depth of 3416 A
Fig. 4. M–H hysteresis loop recorded for La0:7 Ca0:3 MnO3 /YBa2 Cu3 O7d heterostructure at 40 K.
4. Conclusions In conclusion, we have fabricated good quality LCMO–YBCO heterostructures (YBCO on top) in situ by PLD on LAO substrates. Measurements showed that Tc of YBCO layer on top of LCMO
layer is equal to 82 K The Tp of the bottom LCMO layer was found to be 250 K. Contribution of due to surface roughness (as seen by 100 A due to inter-diffusion (as verAFM) and 100 A ified by SIMS) does not seem to affect the material properties of LCMO. The LCMO/YBCO
544
S.K. Wanchoo et al. / Nucl. Instr. and Meth. in Phys. Res. B 212 (2003) 539–544
heterostructure displays both superconductivity and ferromagnetism simultaneously. Acknowledgements The authors wish to thank M. NeumannSpallart for useful discussions and F. Jomard for carrying out SIMS measurements and S. Kathua for helping in SQUID measurements.
References [1] V.A. VasÕko, V.A. Larkin, P.A. Kraus, K.R. Nikolaev, D.E. Grupp, C.A. Nordman, A.M. Goldman, Phys. Rev. Lett. 78 (1997) 1134. [2] P. Raychaudhuri, S. Sarkar, P.K. Mal, A.R. Bhangale, R. Pinto, J. Phys.: Condens. Matter 12 (2000) 9933. [3] H.C. Yang, J.Y. Lin, H.E. Horng, Chin. J. Phys. 36 (1998) 388. [4] N.-C. Yeh, R.P. Vasquez, C.C. Fu, A.V. Samoilov, Y. Li, K. Vakiki, Phys. Rev. B 60 (1999) 10522.
Synthesis of good quality LCMO/YBCO heterostructures by pulsed laser deposition technique S.K. Wanchoo a,*, J. Jasudasan b, V.C. Bagwe b, A.D. Thakur b, U.D. Vaishnav b, S.P. Pai b, A.M. Narsale a, R. Pinto b a
Department of Physics, University of Mumbai, Santacruz (E), Mumbai 400 098, Maharashtra, India b Tata Institute of Fundamental Research, Mumbai 400 005, India
Abstract Deposition of multilayers of La0:7 Ca0:3 MnO3 –YBa2 Cu3 O7d offers great challenges and opportunities for future spin-based device applications. Pulsed laser deposition is a well-established and unique tool for making such highly stoichiometric, nearly single crystal-like epitaxial films. Here we discuss the synthesis of multi-component La0:7 Ca0:3 MnO3 –YBa2 Cu3 O7d oxide thin films and their heterostructures, which were grown in situ by sequential deposition of LCMO and YBCO thin films on Æ0 0 1æ LaAlO3 substrate using a pulsed laser deposition (PLD) system. We discuss the growth of these thin-film multi-layers, from the device applications point of view. The micro-structural properties, continuity and texture of the films were studied by using XRD, AFM and SEM. The good interface quality of these films was established using the secondary ion mass spectroscopy technique. Transport measurements on the individual layers of these heterostructures were carried out using a low temperature four-probe measurement setup. A Quantum design SQUID magnetometer was used to carry out the magnetization measurements on these multilayers, which display excellent superconducting and ferromagnetic properties of the heterostructures. 2003 Elsevier B.V. All rights reserved. PACS: 74.25.Ha; 74.76.)w; 74.80.Dm Keywords: Heterostructures; Multilayers; Spintronics; Cationic inter-diffusion
1. Introduction The possible application of spin-injection devices in the field of ‘‘spintronics’’ has received a lot of attention of the researchers in the recent
* Corresponding author. Tel.: +91-22-2652-8835; fax: +9122-2652-9780. E-mail address: sunilkwanchoo@rediffmail.com (S.K. Wanchoo).
past. Such devices can be realized from superconductor–ferromagnet (F/S) heterostructures. Such heterostructures have received a lot of attention because of their rich physics and potential applications. Development of such heterostructures with the constituent layers having identical crystal structure and exhibiting superconducting and magnetic properties in the alternate layers is the most important requirement. Moreover these heterostructures must possess clean and sharp interfaces. If we are able to understand and control
0168-583X/$ - see front matter 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0168-583X(03)01841-X
540
S.K. Wanchoo et al. / Nucl. Instr. and Meth. in Phys. Res. B 212 (2003) 539–544
the quality and sharpness of the interface then these heterostructures could also lead to novel spin-based devices. These devices are said to be based on spin-polarized transport across the half-metallic ferromagnet and high temperature superconductor (F/S) heterostructures. The halfmetallic nature of the hole doped rare earth manganites of the form R1x Ax MnO3 (R ¼ rare earth, A ¼ bivalent cation) provide a reserve of spin-polarized electrons, which can be utilized in unconventional devices. La0:7 Ca0:3 MnO3 is a wellstudied CMR manganite with a degree of polarization close to unity, which also has a good structural compatibility with high temperature superconductors such as YBa2 Cu3 O7d . Hence, La0:7 Ca0:3 MnO3 /YBa2 Cu3 O7d heterostructures have become attractive for spin injection studies. A number of experiments have been reported on these heterostructures (F/S) [1,2]. However most of these studies heavily rely on a sandwiched insulating layer, which is deposited to avoid any cationic inter-diffusion across the interface. But in such studies the possibility of joule heating cannot be entirely ruled out during transport measurements. Therefore F/S barrierless heterostructures with sharp interfaces, exhibiting ferromagnetism and superconductivity in alternate layers are highly desired. Though there have been a few reports [3] on such heterostructures, to the authorÕs best knowledge conclusive study of the cationic inter-diffusion across the interface has not been carried out so far. Most of the F/S based injection experiments [4] have been mainly based on trilayers of (ferromagnet–insulator–superconductor) F–I–S on single crystal substrates. The insulating layer in these studies has been used to avoid the inter-layer cationic diffusion. Pulsed laser deposition (PLD) is a unique method for growing highly stoichiometric, nearly single crystal-like materials in the form of epitaxial films and heterostructures. Multi-component La0:7 Ca0:3 MnO3 –YBa2 Cu3 O7d oxide thin film heterostructures can be easily grown in situ by sequential deposition of La0:7 Ca0:3 MnO3 and YBa2 Cu3 O7d thin films by this technique. In this work an effort has been made to synthesize good quality F/S bylayers with tailored superconducting and ferromagnetic properties. The synthesis and
characterization of good quality F/S heterostructures is discussed here.
2. Experimental details All the bulk targets used for the present work have been synthesized using the standard solidstate reaction method. Pulsed laser deposition technique was employed to grow the LCMO/ YBCO heterostructure on (0 0 1) LaAlO3 (LAO) single-crystal substrates. An excimer laser was used to grow these heterostructures with a wavelength of 248 nm and a repetition rate of 10 Hz. Both the targets were mounted on the multi-target carrousel target holders and the same can be rotated using automated motor control. LAO substrate was mounted on the heater with the help of conducting silver paste for better thermal conductivity. Due to the crystallographically compatible nature of these oxides we have used identical deposition conditions (after optimizing the same) for the in situ growth of both the two oxide layers. These heterostructures were deposited at a substrate temperature of 800 C. Oxygen partial pressure of 400 mTorr for LCMO and 250 mTorr for YBCO were maintained during their growth, respectively. Laser fluence of 2.5 J/cm2 was used for ablating the targets. The superconducting transition temperature was established by using a homemade ac susceptibility measurement setup. Surface morphology of as grown thin films has been probed using the atomic force microscope. The phase pure nature of the films was established by powder X-ray diffraction technique. YBCO/LCMO bilayers were prepared by sequentially depositing YBCO and LCMO onto LAO substrates. To carry out the resistivity measurements using a homemade resistivity measurement setup, films were patterned using UV photolithography technique. Contact pads of gold were patterned using UV photolithography after depositing a gold film on the sample by pulsed laser deposition technique. Another sister sample, which was grown in the same run, was used to carry out the resistivity measurements on the bottom LCMO layer. The top YBCO layer was patterned into a prototype
S.K. Wanchoo et al. / Nucl. Instr. and Meth. in Phys. Res. B 212 (2003) 539–544
device structure. Patterning the YBCO layer became necessary, as we wanted to carry out the resistivity measurements on the bottom LCMO layer in the LCMO/YBCO bilayer. In order to ensure the complete removal of the top YBCO layer on either side of the microbridge the YBCO layer was slightly over etched so that the bottom LCMO layer was fully exposed on both the sides of the microbridge. Using the same method as used for YBCO layer four gold pads were deposited on the LCMO layer two on either side of the YBCO microbridge. The interface of the LCMO/YBCO heterostructures was characterized using secondary ion mass spectroscopy technique (SIMS). In order to establish the interface quality a depth profiling was carried out using a Cameca 34f SIMS machine. In this measurement Oþ 2 was used for ionization at a current of 50 nA and at an effective incidence angle of 42. Finally an analysis zone of 33 lm diameter was used in the center of the erosion zone of 150 lm · 150 lm to carry out the depth profiling. Further, a quantum design superconducting quantum interference device (SQUID) magnetometer was used to probe the magnetic properties of the YBa2 Cu3 O7d layer. Thickness of the constituent layers was measured by using a surface Profilometer (Sloan Dektak) and was found to be (LCMO) and 1500 A (YBCO), respec1000 A tively.
541
3. Results and discussions This paper presents the results of a systematic study of the electric, magnetic and interface properties of bilayer heterostructure made form epitaxially in situ grown LCMO and YBCO thin films. The main issue we are addressing here is the quality of the interface and ferromagnetic and superconducting properties of the constituent layers. Fig. 1 shows a typical X-ray diffraction pattern of a LCMO/YBCO heterostructure. The pattern shows most of the reflections along the (0 0 l) direction suggesting the epitaxial c-axis oriented growth of both LCMO and YBCO layers and indicates that these bilayers have preferred orientation with the crystal c-axis perpendicular to the plane of the substrate. Fig. 2 shows the temperature dependence of resistance as a function of temperature for LCMO/YBCO bilayers. Fig. 2(a) shows the resistivity curve as measured on the top YBCO layer. Fig. 2(b) shows the resistivity curve for the LCMO/YBCO heterostructure. It can be seen from the graph that the metal–insulator transition temperature of the LCMO layer is 250 K. Here at this temperature there is no contribution of the top YBCO microbridge apart from adding few hundred ohms to the overall resistance of the bilayer. However as we go down to 82 K the resistance of the sample drops almost to zero. This is because the top microbridge is now
Fig. 1. X-ray diffraction pattern for LCMO/YBCO heterostructure.
542
S.K. Wanchoo et al. / Nucl. Instr. and Meth. in Phys. Res. B 212 (2003) 539–544 250
3
YBCO Layer
2.5
Arb Units
Resistance ohms
200 150
2
(a)
1.5 1
Tp
0.5 0
100
0
50
100
150
200
250
300
(b)
Temperature K
Tc
50
LCMO/YBCO bilayer
0 0
50
100
150 200 Temperature K
250
300
Fig. 2. R versus T for F/S bilayers. (a) Resistivity curve as measured for the top YBCO layer. (b) Resistivity curve as measured for the LCMO/YBCO heterostructure.
superconducting and the current sees a resistance less path and shorts through the microbridge. This drop clearly indicates the superconducting nature of the microbridge. Hence at 250 K LCMO layer shows a clear ferromagnetic behavior while as at 82 K since the resistance of the YBCO microbridge drops to zero and the same conclusively indicates the superconductivity in the microbridge. Hence the four-probe measurements clearly indicate that the LCMO/YBCO heterostructure essentially displays both ferromagnetism and superconductivity in the alternate layers. The four-probe data though does not show any effect of YBCO on LCMO as the metal–insulator transition is found to be equal to that of a single layer of LCMO, which was grown for comparison. However the superconducting transition temperature Tc of YBCO does show a decrease from standard 90 K to 86 K. In order to probe this decrease we have carried out secondary ion mass spectroscopy studies on these heterostructures to characterize the sharpness of the interface between LCMO and YBCO. Fig. 3 shows the SIMS profiles for LCMO/YBCO heterostructures. The quality of LCMO–YBCO interface is very important. The interface quality depends primarily on the surface roughness of LCMO layer and on the possible inter-diffusion of cations at the interface during YBCO growth. Atomic force microscopy showed
the LCMO roughness (determined partly due to . We the twinned LAO substrate) to be 200 A evaluated the cationic inter-diffusion using secondary ions mass spectroscopy (SIMS). Shown in Fig. 3 are the SIMS profiles of a LCMO–YBCO interface (YBCO on top). If we account 200 A due to surface roughness in the 400 A inter-diffused layer (SIMS), we see only a nominal inter on each side of the junction, diffusion of 100 A except for diffusion of Cu into the LCMO layer. Longer diffusion of Cu into the LCMO layer does not appear to affect the spin carrier density as the Tp was found to be 250 K. This clearly indicates that the minimal diffusion of Cu does not affect the properties of LCMO. We believe that the interdiffused Cu may be sitting at the grain boundaries and does not have any impact on the LCMO properties. Therefore it is clear that due to the loss inter-diffused layer, of Cu and also due to a 100 A the Tc of YBCO shows a decrease of 4 K. Fig. 4 shows the M versus H hysteresis loop for La0:7 Ca0:3 MnO3 /YBa2 Cu3 O7d heterostructures carried out at 40 K (well below the Tc of YBa2 Cu3 O7d ). The plot clearly demonstrates the excellent display of superconducting ordering in these heterostructures at 40 K. Therefore the magnetic properties of the superconducting layer are found to be excellent in case of La0:7 Ca0:3 MnO3 /YBa2 Cu3 O7d heterostructures.
S.K. Wanchoo et al. / Nucl. Instr. and Meth. in Phys. Res. B 212 (2003) 539–544
543
. (2150 s in the time Fig. 3. SIMS profiles of a typical YBCO/LCMO heterostructure. The full scale of the x-axis corresponds to 3954 A .) axis correspond to an etch crater depth of 3416 A
Fig. 4. M–H hysteresis loop recorded for La0:7 Ca0:3 MnO3 /YBa2 Cu3 O7d heterostructure at 40 K.
4. Conclusions In conclusion, we have fabricated good quality LCMO–YBCO heterostructures (YBCO on top) in situ by PLD on LAO substrates. Measurements showed that Tc of YBCO layer on top of LCMO
layer is equal to 82 K The Tp of the bottom LCMO layer was found to be 250 K. Contribution of due to surface roughness (as seen by 100 A due to inter-diffusion (as verAFM) and 100 A ified by SIMS) does not seem to affect the material properties of LCMO. The LCMO/YBCO
544
S.K. Wanchoo et al. / Nucl. Instr. and Meth. in Phys. Res. B 212 (2003) 539–544
heterostructure displays both superconductivity and ferromagnetism simultaneously. Acknowledgements The authors wish to thank M. NeumannSpallart for useful discussions and F. Jomard for carrying out SIMS measurements and S. Kathua for helping in SQUID measurements.
References [1] V.A. VasÕko, V.A. Larkin, P.A. Kraus, K.R. Nikolaev, D.E. Grupp, C.A. Nordman, A.M. Goldman, Phys. Rev. Lett. 78 (1997) 1134. [2] P. Raychaudhuri, S. Sarkar, P.K. Mal, A.R. Bhangale, R. Pinto, J. Phys.: Condens. Matter 12 (2000) 9933. [3] H.C. Yang, J.Y. Lin, H.E. Horng, Chin. J. Phys. 36 (1998) 388. [4] N.-C. Yeh, R.P. Vasquez, C.C. Fu, A.V. Samoilov, Y. Li, K. Vakiki, Phys. Rev. B 60 (1999) 10522.