Abstract
The manganites La1-xSrxMnO3 (LSMO), exhibiting a high Curie temperature (Tc), a good canonical double exchange system, and a good colossal magnetoresistance (CMR), have attracted much attention for their magnetic, electrical, and structural properties. The crystal structure, chemical configuration, ferromagnetic property, electrical transport, and nanoscale characterization are investigated in this study. The LSMO thin films were deposited on SiO2(200 nm)/Si(100) substrate by R.F. magnetron sputtering at 6000C in an atmosphere of 5 mtorr with Ar/O2 ratio ranging from 4/1, 2/1 to 1/1, which is fabricated to different preferred orientation. The diversity of ferromagnetotransport is attributed to the alleviation of Jahn-Teller distortion induced by the thermal stress in films having different preferred orientations. And the polycrystalline films of (La0.91,Sr0.09)MnO3 with and without (100)-preferred orientation have spatial inhomogeneities with conducting and insulating domains coexisted in submicrometer scale, which is observed by conductive atomic force microscopy (CAFM). The domains undergo a percolative metal-insulator transition, and the transition temperature (TM-I) observed from CAFM is consistent to the result of magnetoresistance measurement. Different preferred orientation of LSMO thin films with various thickness were also studied. The ferromagnetic property and electrical transport increase with increasing film thickness. It is considered as the result of small deformation of the Mn-O bond length/bond angle by the relaxation of thermal strain. We fabricate the metallic Pt nano-crystals embeded in the LSMO matrix for the enhancement of ferromagnetotransport. The downshift of Curie temperature with LSMO/Pt(NP)/LSMO thin films is due to the magnetic inhomogeneity or spin disorder, which is caused by the addition of Pt nano-crystals in the films. The spin alignment in the normal direction of the films is significantly affected by the insertion of the ultrathin layers of Pt nanocrystals. The sub-layer of Pt nanocrystals provides an easier pathway for electron transport between LSMO grains, and thus the resistivity becomes significantly reduced.