Growth and Magnetic Properties of La 0.65 Pb 0.35 MnO 3 Films
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INTRODUCTION Since the discovery [1] of the large magnetoresistance (MR) in La,..A.MnO3 (A=dopant), the attention was focused on Sr and Ca doped manganites [2-4], because of both potential technological applications and basic condensed-matter physics studies. On the other hand, these type of materials exhibit a wide range of imperfectly understood, structure, magnetic and
electronic properties. The Lal.,PbMnO 3 systems have received much less attention, although single crystal samples were successfully grown and studied [5-9]. More recently, several papers [10-131 reported that Lal-,Pb1 MnO 3 thin film exhibited large magnetoresistance. In this paper, we report results of fabrication and characterization of Lao.65Pbo.35MnO 3 films made by RF magnetron sputtering process. SAMPLE PREPARATION AND CHARACTERIZATION LaPb.35 MnO3 films were deposited by RF magnetron sputtering method. The targets were made of from very homogeneous powders that were prepared by citric acid sol-gel process. The targets were pre-sintered in 900°C for 12 hours (form a stable phase) and then sintered at 1000°C for 24 hours (form a dense target). The deposition system was pumped down to a base pressure of 10i7 torr and then filled with a mixture of 20% oxygen and 80% argon up to a pressure of 23 mtorr during the sputtering. The target-substrate distance was around 2 inches. Films with a thickness of 1000 A were deposited when on-axis sputtering was carried out at a RF power of 15 Watts (at 13.6 MHz) for 1.5 hours. The temperature of LaAlO 3 substrates was
75 Mat. Res. Soc. Symp. Proc. Vol. 602 © 2000 Materials Research Society
heated between 200 and 300'C during the deposition. The as-prepared films were subsequently annealed, first at 650'C for 10 hours (in Ar), then at 850'C for 2hours (in Ar), and last, at 650'C for 10 hours (in 21 psi 02). X-ray diffraction patterns were measured by using a Rigaku X-ray difractometer with Cu Ka radiation. DC magnetization and resistance in a four-probe configuration were carried out using a SQUID quantum magnetometer. X-ray photoemission spectroscopy was undertaken with the Mg-Ka line (1253.6 eV). Energy distribution curves of the elemental core levels were acquired with an hemispherical electron analyzer (PHI Model 10-360). The surface morphology and magnetic domain structure were characterized by a scanning probe microscope (Digital Instrument Dimension 3000). RESULTS AND DISCUSSIONS The best films have been deposited using an optimum substrate (single crystal LaA10 3), kept at a temperature between 200 to 300'C. Higher deposition temperature resulted in a random orientation of the films. The as-prepared films were amorphous, and the perovskite phase was formed after annealing in oxygen. Figure 1 shows the magnetization versus temperature curves (in a field of IT) for a Ilim thick La0 65Pbo35MnO 3 film sintered at different temperatures for 10 hours. Magnetization and Curie temperature are very low for the film annealed at 700'C. Microstructure measurements indicate that the films have not crystallize
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