Study On The Structures, Magnetic And Transport Properties Of Several Perovskite Manganese Oxide Thin Films

Doped perovskite manganites have been a topic in the field of condensed matter physics and material science due to its abundant physical and chemical properties, such as ferromagnetic and colossal magnetoresistance effect. Studies on functional thin film are of vital importance for fabrication of functional device. In this paper, microstructure, magnetotransport properties and magnetism of several rare earth doped manganite thin films were studied. The results were as follows:Firstly, we studied the magnetic and transport properties of Pr0.7Sr0.3Mn03(36nm)/Lao.5Cao.5Mn03(x nm)/Pr0.7Sro.3MnO3(36nm)(PSMO/LCMO/PSMO) trilayers deposited on (001)-oriented single crystal MgO by pulsed laser deposition. The results showed that strain relaxation status of trilayers were determined by bulk strain and Jahn-Teller (JT) strain together. The mechanism for strain relaxation in trilayers is different from that for tetragonal distortion. The roughness of the surface and interface in the trilayers varied with respect to the thickness of LCMO layer, indicating that the roughness was related to the mismatch strain relaxation in the film. Surface status, interdiffusion and the competition between bulk strain and Jahn-Teller (JT) strain played an important role in the magnetotransport and magnetic properties. Moreover, transport properties of trilayers are associated with enhancement of volume fraction of ferromagnetic clusters of LCMO spacer with charge ordering and magnetic phase separation. Interestingly, exchange bias (EB) was not observed in PSMO/LCMO/PSMO trilayers. The enhancement of volume fraction of ferromagnetic clusters, strain distribution and interface structure probably lead to the disappearance of EB in trilayers.Secondly, we studied the structural and magnetotransport properties of [Pro.7Sr0.3Mn03(x nm)/Lao.5Cao.5Mn03(4.8nm)]2o superlattices deposited on (001)-oriented single crystal MgO by pulsed laser deposition. Superlattices showed remarkable ferromagnetism at110K. Interestingly, asymmetrical stress at the PSMO/LCMO interface lead to enhanced magnetoresistance effect at wide temperature range, which suggested that asymmetrical stress would be helpful to decrease the temperature sensitivity of magnetoresistance.Thirdly, conventional x-ray diffraction and grazing incidence x-ray diffraction techniques were applied to characterize the strain relaxation of Lao.5Ba0.5MnO3(LBMO) films deposited on (001)-oriented single crystal SrTiO3(STO) substrates by pulsed laser deposition The thickness of these films ranged from12nm to96nm. The results indicated that the lattice strain of LBMO films began to relax when the film thickness was less than12nm. When the thickness increased to about43nm, LBMO film was in fully-strain relaxed state. It was discovered that Jahn-Teller (JT) strain played an important role in LBMO/STO system, and the mechanism for strain relaxation is the same as that for tetragonal distortion. In addition, surface and interface structure of film changed due to the contamination at air/LBMO interface and a sublayer between LBMO layer and the STO substrate, respectively.Finally, Pr0.7Sr0.3MnO3films with (100),(110) and (111) oriention were deposited on (001)-oriented single crystal sapphire (α-Al2O3) substrates by pulsed laser deposition. We studied magnetic and transport properties of these films and found ferromagnetism at room temperature and enhanced magnetoresistance effect at a wide temperature range. These characters would be helpful for practical development of related electronics device.