We report on tunneling magnetoresistance (TMR) experiments that demonstrate the existence of a significant spin polarization in Co-doped (La, Sr)TiO(3-delta) (Co-LSTO), a ferromagnetic diluted magnetic oxide system (DMOS) with high Curie temperature. These TMR experiments have been performed on magnetic tunnel junctions associating Co-LSTO and Co electrodes. Extensive structural analysis of Co-LSTO combining high-resolution transmission electron microscopy and Auger electron spectroscopy excluded the presence of Co clusters in the Co-LSTO layer and thus, the measured ferromagnetism and high spin polarization are intrinsic properties of this DMOS. Our results argue for the DMOS approach with complex oxide materials in spintronics.
Electron energy-loss spectroscopy is used to map composition and electronic states in epitaxial La 2/3 Ca 1/3 MnO 3 films grown on SrTiO 3 ͑001͒ and ͑110͒ substrates. It is found that in partially relaxed ͑110͒ films cationic composition and valence state of Mn 3+/4+ ions are preserved across the film thickness. In contrast, in fully strained ͑001͒ films, the Ca/La ratio gradually changes across the film, being La rich at film/substrate interface and La depleted at free surface; Mn valence state changes accordingly. These observations suggest that a strongly orientation-dependent adaptative composition mechanism dominates stress accommodation in manganite films and provides microscopic understanding of their dissimilar magnetic properties. ͒ / STO/ LSMO system but found a weak decrease in the Mn valence near the interfaces, attributed to a transfer of electrons from STO to LSMO. It has been observed that in LCMO films grown on LaAlO 3 substrates, which are under compressive strain, the La 3+ ions migrate toward the top layer surface. 9 Little attention was received, so far, by the chemistry and electronic structure of ͑110͒ LCMO films, reported to display enhanced magnetic properties when compared to their ͑001͒ counterparts. 10,11 In this work, we report detailed transmission electron microscopy ͑TEM͒ and EELS analyses of epitaxial LCMO layers grown simultaneously on ͑001͒ and ͑110͒ STO substrates.The ͑001͒ and ͑110͒ LCMO layers were grown by rf sputtering at 800°C, at 330 mtorr, with an O 2 / Ar pressure ratio of 1 4 and a growth rate of ϳ0.4 nm/ min. After growth, in situ annealing was performed at 800°C for 1 h in O 2 atmosphere at 350 torr. 10 The magnetic properties of these films have been previously studied. 10,11 both magnetization ͓Fig. 1͑a͔͒ and Curie temperature of the ͑110͒ films are much larger than those of their ͑001͒ counterparts. LCMO films, when grown on ͑001͒ and ͑110͒ STO substrates, have identical ͑tensile͒ lattice mismatch ͑ϳ1.1%͒. However, whereas in-plane orthogonal directions ͓100͔ and ͓010͔ of ͑001͒ films are equivalent, ͓001͔ and ͓110͔ directions are not equivalent a͒ Electronic mail: sestrade@el.ub.es.FIG. 1. ͑Color online͒ ͑a͒ Magnetization vs field curves in the −1 -20 kOe range for ͑001͒ LCMO ͑squares͒ and ͑110͒ LCMO ͑triangles͒ 80 nm films measured at 10 K. Magnetic field was applied in-plane of the samples, being parallel to ͓100͔ direction for the ͑001͒ films and to ͓001͔ direction for the ͑110͒ film. Inset: Normalized XRR spectra from ͑001͒ ͑squares͒ and ͑110͒ ͑triangles͒ 85 nm films. ͑b͒ g = ͑1-10͒ and ͑c͒ g = ͑011͒ two beam images of ͓110͔ LCMO/STO in PV geometry.
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