Influence of the growth parameters on the electronic and magnetic properties of La0.67Sr0.33MnO3 epitaxial thin films

Applied Surface Science 437 (2018) 281–286

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Short Communication

Influence of the growth parameters on the electronic and magnetic properties of La0.67 Sr0.33 MnO3 epitaxial thin films E. Annese a,b,∗ , T.J.A. Mori a , P. Schio a , B. Rache Salles c , J.C. Cezar a a b c

Laboratório Nacional de Luz Síncrotron – Centro Nacional de Pesquisa em Energia e Materiais, CP 6192, 13083-970 Campinas, SP, Brazil Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud, 150 – Urca, Rio de Janeiro, Brazil Instituto de Física, Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, RJ, Brazil

a r t i c l e

i n f o

Article history: Received 4 November 2017 Accepted 18 December 2017 Available online 27 December 2017 Keywords: Magnetism Structure Surface

a b s t r a c t The implementation of La0.67 Sr0.33 MnO3 thin films in multilayered structures in organic and inorganic spintronics devices requires the optimization of their electronic and magnetic properties. In this work we report the structural, morphological, electronic and magnetic characterizations of La0.67 Sr0.33 MnO3 epitaxial thin films on SrTiO3 substrates, grown by pulsed laser deposition under different growing conditions. We show that the fluence of laser shots and in situ post-annealing conditions are important parameters to control the tetragonality (c/a) of the thin films. The distortion of the structure has a remarkable impact on both surface and bulk magnetism, allowing the tunability of the materials properties for use in different applications. © 2017 Elsevier B.V. All rights reserved.

1. Introduction Thin films of manganite perovskites such as La1−x Srx MnO3 have been intensively studied due to their unusual electronic structure and the strong interplay between magnetic ordering and charge transport properties [1]. Their electronic and magnetic properties are mainly determined by the Mn valence, oxygen (non)stoichiometry and surface morphology [1,2]. Because of its high spin polarization (nominally 100% [3–5]), La0.67 Sr0.33 MnO3 (LSMO) is used as component in multilayered structures to investigate, for example, the spin-injection into cuprate superconductors or to probe spin polarization at ferroelectric/ferromagnetic, such as BaTiO3 /Fe, and hybrid organic interfaces [6,7]. Lately, LSMO thin films have been used as a component of hybrid organic–inorganic spin valves [8] and as a spin polarized surface supporting organic thin films [9]. For all these applications it is needed to grow high quality LSMO thin films, i.e. with optimal magnetization and electrical conductivity and smooth surface morphology. Epitaxial LSMO thin films have been deposited on single crystals substrates by techniques such as pulsed laser deposition (PLD) and magnetron sputtering, for instance. Nevertheless, over the years it has been demonstrated that the ideal layer-by-layer growth is in competition with three-dimensional grain formation depending on the growth parameters such as oxygen pressure, substrate temper-

∗ Corresponding author at: Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro, Brazil. E-mail address: [email protected] (E. Annese). https://doi.org/10.1016/j.apsusc.2017.12.164 0169-4332/© 2017 Elsevier B.V. All rights reserved.

ature and target-substrate distance [10,11]. The growing condition that permits pure and stoichiometric LSMO thin films to be grown is very narrow, so that very small changes in the deposition parameters can lead to major changes in the properties of the film. Here, we report on the study of the structural, morphological, electronic and magnetic properties of a series of epitaxial LSMO thin films grown by PLD. We focus on the influence of laser fluence (F) and post-annealing treatment on the properties of LSMO samples. The thin film structure and morphology were determined by X-ray diffraction (XRD) and atomic force microscopy (AFM). The surface electronic and magnetic properties, which are strictly related to the film strain and termination were established by means of X-ray absorption spectroscopy (XAS) through X-ray linear dichroism (XLD) and X-ray magnetic circular dichroism (XMCD) analysis. Standard magnetometry measurements completed the magnetic characterization of the samples. 2. Experimental details The LSMO thin films deposition was carried out by PLD, using a KrF excimer laser (wavelength of 248 nm) and a La0.67 Sr0.33 MnO3 stoichiometric target, at the sample preparation facility of the U11-PGM beamline of the Brazilian Synchrotron Light Laboratory (LNLS). The substrates (2.5 mm × 5 mm SrTiO3 (001) single crystals, STO) were placed at a fixed distance (ds−t ) of ∼46 mm, on an infrared laser heated sample holder. The SrTiO3 (STO) single crystals were prepared ex situ following the same methods described in Ref. [12]. The base pressure before deposition was lower than 1 × 10−7 mbar. For all the samples the temperature during the

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growth was (725 ± 25) ◦ C with 0.15 mbar of oxygen pressure in the chamber. After the deposition the samples were annealed on 600 ◦ C at different oxygen pressure conditions. In order to separate the contributions of post-annealing and laser fluence two set of samples were analyzed. Firstly F was varied by changing the laser spot size producing shots of 0.9, 1 and 1.3 J/cm2 . For the second set of samples the fluence and growth temperature were fixed at 1.1 J/cm2 and (725 ± 25) ◦ C, respectively, whilst the annealing time and pressure were changed but the annealing temperature was kept constant. The annealing was 0.5, 1 or 3 h long and oxygen pressure was 103 , 102 and 0.15 mbar. The structural characterization was performed by X-ray diffraction techniques. Some measurements were carried out in a Panalytical X’Pert Pro diffractometer with Cu K˛ radiation, and others at the XRD2 beamline (at LNLS) with a monochromatic beam of energy 8.04 keV. Standard Bragg–Brentano (–2) diffractograms were acquired to verify the out-of-plane crystallinity of the films and to investigate parasitic phases. Rocking curves at the LSMO (002) peak were collected as a figure of merit to evaluate the degree of mosaicity of the epitaxial samples. The X-ray reflectivity curves were acquired in small incidence angles, providing the information about sample thickness and roughness. The reciprocal space maps (RSM) around the asymmetric (103) reflections of LSMO and STO were measured to study the symmetry and in-plane strain. Atomic force microscopy images were taken in a Nanosurf Flex microscope in the tapping mode to study the local topography. The electronic and element-specific surface magnetic properties of the films were characterized by XAS through XLD and XMCD investigations around the L2,3 absorption edges of Mn. The measurements were performed at the U11A-PGM beamline of the LNLS [13], at room temperature using the total electron yield (TEY) mode. The XAS/XLD spectra were acquired in two different geometries, with the light polarization vector either parallel or almost perpendicular to the c crystallographic axis of the films (i.e. ˛ = 0◦ or ˛ = 60◦ , respectively). The difference spectrum I60 − I0 , i.e. the linear dichroic (LD) spectrum, gives a direct insight of the anisotropic character of the empty Mn 3d states. The XAS/XMCD measurements were performed under a fixed magnetic field of 0.5 T applied along the beam direction, and the helicity of the circular polarized light was reversed. XMCD spectra were obtained by making the difference between the absorption spectra for incident photons of both right- and left-handed circular polarizations. The XMCD difference spectrum is proportional to the projection of the sample magnetization vector along the photon propagation direction. To check the in-plane magnetic properties, the experimental geometry was chosen such that the photons impinges on the sample at an angle of 60◦ with respect to the sample normal. In the soft X-ray range, the absorption spectroscopy is surface sensitive as the electrons contributing to the TEY current are generated in the first few nanometers from the surface. The bulk magnetic properties of the samples were characterized, at different temperatures, with a vibrating sample magnetometer (VSM). At each temperature, a full hysteresis loop between 2 and −2 T was measured and the film magnetization was obtained after subtraction of the linear diamagnetic contribution of the substrate.

3. Results and discussion 3.1. Crystalline structure and surface morphology The structural properties of the samples were evaluated by XRD techniques. Fig. 1(a) shows the representative –2 scan of LSMO (F = 1 J/cm2 ) measured with the scattering vector orthogonal to the STO (001) planes in the range of 20–80◦ . Only peaks corresponding to the planes of STO and LSMO indexed (00L) are distinguished,

Fig. 1. LSMO/STO(001), i.e. LSMO film grown with fluence of 1 J/cm2 : (a) –2 scan in the range of 20–80◦ ; (b) azimuthal scan, i.e. rotation around surface normal, at asymmetric (103) reflections.

Table 1 In-plane (a, b) and out-of-plane (c) lattice parameters determined by X-ray diffraction experiments for LSMO films grown. Out-of-plane (zz ) and in-plane (xx ) strain values for LSMO films are reported in percent. A bulk value of 3.88 A˚ is used to calculate the strain of the LSMO films. Fluence (J/cm2 )

˚ a, b (A)

˚ c (A)

c/a

xx (%)

zz (%)

FWHM (◦ )

1.3 1.0 0.9

3.905 3.904 3.905

3.860 3.856 3.877

0.989 0.988 0.993

0.64 0.62 0.64

−0.51 −0.62 −0.08

0.17 0.17 0.23

Fig. 2. (a)–(b) XRD diffratograms of LSMO/STO(001) as a function of thickness, laser fluences and post-annealing oxygen pressure; (c) XRR pattern of a representative sample (dots) and its fit (continuous line), the sample was grown with 2000 pulses which corresponds to a thickness of ∼27 nm. For the fit we used as parameters the density of LSMO and STO: 8.250 and 5.110 g/cm3 , respectively, and obtained a roughness of 0.6 nm for the LSMO surface. The measurements of panel (b) were made with monochromatic synchrotron X-ray source at XRD2, LNLS. A vertical line is used as guide line to indicate the 2 position of the STO (002) and both bulk and strained LSMO (002) peaks.

confirming that the LSMO film c-axis is along the out-of-plane orientation. Fig. 1(b) displays the azimuthal angle () scans acquired by keeping the detector at the position of the asymmetric (103) reflection of LSMO (STO) whilst rotating . The absence of spurious features in the –2 and  scans confirms the epitaxial growth of the LSMO film on STO with the LSMO a, b and c-axes parallel to the substrate ones. Therefore, all the samples showed a unique phase, as well as similar cube-on-cube epitaxy relationship. We measured rocking curves at the LSMO (002) peak (not shown), whose FWHM are reported in Table 1. The very small FWHM of the rocking curves, together with the results shown in Fig. 1, point out the good structural quality of the LSMO films. In Fig. 2 we report –2 scans zoomed in the region of the (002) peaks of STO and LSMO, (a) as a function of the thickness, (b) laser fluencies and post-annealing parameters, respectively. The samples

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Fig. 3. Reciprocal space maps around the LSMO (103) reflection of 90 nm thick film as a function of fluence: 1.3 (a), 1 J/cm2 (b) and 0.9 J/cm2 (c).

˚ were aligned by taking the STO (002) peak position (d001 = 3.905 A) as reference. It is important to note that these LSMO samples were grown with a fixed fluence F = 1.3 J/cm2 , but different thicknesses manifest the same diffraction peak position (Fig. 2(a)). The diffractogram of the thinnest sample (∼7.5 nm) does not show a clear peak, this is likely to be due to the very low sample volume which does not allow one to measure the diffraction peaks with reasonable acquisition times with the experimental geometry used. The upper curves of Fig. 2(b) show the (002) peak of LSMO for the different fluencies. The c parameter of relaxed bulk LSMO is 3.88 A˚ [14] and corresponds to 2 of ∼46.67◦ as indicated by a guide to the eyes in Fig. 2. As the misfit between LSMO and STO is small, it is known to grow pseudomorphically, without lattice parameter relaxation up to critical thickness of 100 nm [15]. In the case of LSMO/STO, tetragonal deformation presents a contracted c-axis and an in-plane tensile strain. For lower fluence (0.9 J/cm2 ) the LSMO presents the bulk lattice parameter, while it decreases for intermediate fluence of 1 J/cm2 and then increases for fluence of 1.3 J/cm2 . Assuming a Poisson ratio of 0.35, a fully strained LSMO/STO film ˚ which corresponds to a 2 of would have a c parameter of 3.853 A, ∼47.13◦ , also indicated in Fig. 2. The 2 of the sample with intermediate F = 1 J/cm2 , matches well this value of a fully strained film. The post-annealing pressure and duration also influence the structural properties of the sample, as shown in Fig. 2(b). LSMO films annealed with pO2 = 102 mbar during a shorter time (1 h) show a contraction along the [001] axis. If the oxygen pressure is further reduced to 0.15 mbar the contraction becomes even more pronounced. Note that these samples display a lattice parameter smaller than expected for a strained pseudomorphic LSMO film. We infer that the collapse of the LSMO structure is associated to an oxygen deficiency in the crystal structure. In Fig. 3(a)–(c) we show the reciprocal space maps (Qx , Qz ) acquired around the reflections (103) of the STO (stronger peak at lower Qz in the plots) and LSMO (peak at higher Qz ), for F varying from 1.3 to 0.9 J/cm2 . The Qz position of LSMO with lowest F is close to the STO one, in agreement with the –2 results. Similar values of c parameter were extracted from –2 and RSM measurements and are reported in Table 1. The c-axis of the LSMO films with F = 1.3 and 1 J/cm2 is strongly contracted with respect to the bulk, which is in agreement with the presence of a tensile strain. The LSMO peak position for each sample is at the same Qx value of the substrate corroborating that LSMO is pseudomorphic with the STO substrate ˚ Hence, the a, b-lattice parameters of the film modify with (3.905 A). respect to the bulk values to adjust to the substrate, causing an inplane stress. The contraction of the c-axis leads to a remarkable distortion of the unit cell as indicated by the c/a ratio (Table 1). The surface morphology of the samples was imaged by AFM. Topographic images are reported in panels (a)–(d) of Fig. 4. The images do not reveal neither regular terraces nor steps from the

Fig. 4. (a and b) AFM topographic images for samples grown with F = 1.3 J/cm2 and varying the thickness from 90 to 7.5 nm. (c and d) 90 nm LSMO thick film grown with F = 1.1 J/cm2 and pO2 = 102 and 10−2 mbar, respectively. All images are 1.5 ␮m × 1.5 ␮m.

substrate. The samples present a quasi-2D layer-by-layer growth mode and a roughness (rms) of 0.8 nm (0.4 nm) for 7.5 nm (90 nm) thick films, values comparable to the LSMO unit cell. The roughness was estimated from 1.5 ␮m × 1.5 ␮m squared areas of AFM images. The morphology of the LSMO films is slightly affected by the post-annealing conditions (pO2 and duration): all the samples of the second set (Fig. 4(c) and (d)) showed a rms better than 0.3 nm. Therefore, the LSMO film structure and morphology strongly affect the electronic and magnetic properties of the LSMO thin film, as it is discussed in the next sections. 3.2. Electronic structure In LSMO, Mn ions appear in the mixed-valence state (Mn3+ and Mn4+ ) and are located at the center of an oxygen octahedron, with 6-fold coordination. For the stoichiometric oxide, the proportions of Mn ions in the valence states 3+ and 4+ are proportional to the La and Sr content, respectively [1]. The Mn orbital is split into t2g and eg as shown in Fig. 5. The intra-atomic correlations cause the parallel alignment of the electron spins in Mn3+ and Mn4+ ions and the corresponding exchange energy is ∼2.5 eV, being larger than

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Fig. 5. Expected Mn 3+ and Mn 4+ electronic configurations for relaxed LSMO (left panels) and under tensile strain (right panel).

Table 2 Coercive field and Mr /Ms at 300 K and lowest temperature for representative LSMO samples. F = fluence, d = thickness, post-annealing: pO2 oxygen partial pressure, t = time.

Fig. 6. XAS and XLD spectra of LSMO thin films (a) as a function of film thickness at fixed F 1.3 J/cm2 and (b) vs. F. All measurements were performed at room temperature. XAS spectra were measured with the electric field of the light parallel (˛ = 0◦ ) or almost perpendicular to the c axis of the sample (˛ = 60).

3 ↑ e1 ↑) occupation and the crystal field splitting. Mn3+ has 3d4 (t2g g 3 ↑ e0 ) configuration. The total spin S = 2, whereas Mn4+ has 3d3 (t2g g first unoccupied 3d orbitals of Mn are dx2 −y2 and dz2 , whose energy position depends on the distance and position of the neighboring oxygen atoms. The electronic properties are strictly related to the LSMO structure. In particular a tensile strain (c/a < 1) lowers dx2 −y2 with respect to dz2 , whereas the compressive strain (c/a > 1) does the opposite. On the other hand, the termination of the LSMO film at the free surface with a MnO2 plan can suppress the degeneracy of dx2 −y2 and dz2 orbitals of the Mnm+ by pushing up the dx2 −y2 orbitals. In the case of termination with a LaSrO layer, the Mn ions of the topmost MnO2 have the octahedral oxygen coordination complete and no further effect on the alignment of d orbitals. We obtained the information about the electronic configuration of the Mn atom by measuring X-ray absorption at Mn L2,3 edges which probes the unoccupied states at Mn sites [12,16,17]. Fig. 6 shows the XAS (top panels) and XLD (bottom panels) spectra of the LSMO samples as a function of the thickness (a) and the laser fluence (b). Mn L3 XAS spectra present features at ∼639 eV (Ia ) and at 639.7 eV (Ib ), which are attributed to Mn3+ and Mn4+ , respectively [18]. XAS spectral shape is similar for all samples but for the ∼90 nm thick film grown with the highest F, whose Ia is more prominent. Stoichiometry evaluation through X-ray photoemission (not shown) confirms that the samples grown with F = 1.3 J/cm2 present the correct ratio of La/Sr = 2 and therefore the expected content of Mn3+ in the sample, whereas the samples with lower F show a ratio of ∼1, i.e. higher content of La and an imbalance of the Mnm+ atoms. The different La/Sr ratio in LSMO films may be at the origin of the XAS lineshape. Furthermore, the absence of a well

Sample (F; d; pO2 ; t) (J/cm2 ; nm; mbar, h)

Hc (mT) @ 300 K

Hc (mT) Low T

Mr /Ms

Mr /Ms

@ 300 K

@ low T

0.9; 90; 103 ; 0.5 1.3; 90; 103 ; 0.5 1.3; 7.5; 103 ; 0.5 1.1; 90; 102 ; 3 1.1; 90; 102 ; 1 1.1; 90; 0.15; 1

1.8 5 6.3 0.8 2 0

9.7 (10 K) 9 (10 K) 9.7 (10 K) 0.8 (100 K) 3 (100 K) 3 (100 K)

0.3 0.34 0.14 0.04 0.18 0

0.55 (10 K) 0.7 (10 K) 0.3 (10 K) 0.2 (100 K) 0.45 (100 K) 0.31 (100 K)

defined Ia feature for thinner films has already been observed in Ref. [18]. The Mn L2,3 XLD spectra provide direct information about the character of the empty Mn 3d orbitals: positive LD spectra indicate a majority of out-of-plane empty 3d states, whereas negative LD is related to a majority of in-plane empty states [17]. The XLD spectra in the bottom panels of Fig. 6 show an average negative dichroic signal for all the samples that indicate a majority of in-plane empty states. This is compatible with the structural characterization that made it clear the presence of a tensile strain and c/a ratios lower than unity. The overall negative LD also suggests a LaSrO type termination, since the lowest unoccupied orbital is of dx2 −y2 type [12]. 3.3. Magnetic properties Fig. 7 shows hysteresis curves of selected LSMO samples as a function of F (a, b), thickness (c, d) and post-annealing condition (e, f), measured along the [100] in-plane directions by VSM. All samples present ferromagnetic behavior, although different coercive field (Hc ), remanent (Mr ) and saturation magnetization (Ms ). In Table 2 we report Hc and Ms and the ratio Mr /Ms at 10, 100 and 300 K. Hc increases while lowering temperature, reaching a maximum Hc of ∼9 mT for all LSMO at 10 K. The decreasing of Hc with the temperature is mainly due to magnetization reversal mechanisms, coherent reversal or domain wall motion [19,20]. LSMO films (>30 nm) present a small variation of Hc with temperature, indicating an almost single domain formation. As for the thinner film, the Hc increase is related to a non-uniformity of the film which results in a domain size distribution with different critical temperature. The hysteresis loop obtained for LSMO (1.3 J/cm2 , 90 nm) with the applied field parallel to the (001) crystal direction is almost square shaped with remanent magnetization in the easy direction of 70% of the saturation value at low temperature. On the other hand, the hysteresis loop of the thinnest LSMO films showed a smaller Mr /Ms ratio tending to a Langevin-like shape. The magnetization reversal in the sample grown with the lowest F shows a two-step process: at low field the magnetization partially reverses in a sharp process at a field of the order of mT and then progressively

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Fig. 7. Isothermal magnetization curves of LSMO epitaxial films, measured at 300 K (a, c, e), 10 K (b, d) and 100 K (f), with magnetic field along the LSMO film surface (maximum magnetic field of |1.75| T, but displayed for up to |0.5| T). M–H curves measured as a function of F (a, b), thickness (c, d) and post-annealing conditions. The diamagnetic contribution to the magnetization (not shown) was attributed to the substrate and has been subtracted. The curve was normalized to Ms .

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increases while the field increases up to a saturation magnetization two orders of magnitude higher. We associate the high field behavior to domain wall pinning at structural defects, such as misfit dislocations and surface roughness created by strain release mechanism. LSMO films prepared with different post-annealing conditions display Mr /Ms < 0.2 (<0.45) at room temperature (100 K) and in some cases the disappearance of Hc . We infer that the density of structural defects increases in the case of low F and postannealing conditions with low content of oxygen and affects the magnetization properties of the film. Structural defects would lead to a distribution of pinning energies and to a multi domain state at zero magnetic field. It is critical to study the surface/interfacial magnetic properties of LSMO thin films in order to optimize their use in multilayer devices. In order to obtain surface sensitive magnetic information, we used XMCD in TEY mode which is sensitive to the first nanometers from the surface of the material. These results can then be compared with the bulk magnetization data. Fig. 8(a) and (b) show the XAS (top panel) and XMCD (bottom panel) spectra taken at the resonant Mn L2,3 edges at 300 K. The absence of peak position shift and the similar multiplet features but the Ia feature of the LSMO film (1.3 J/cm2 ; 90 nm), suggest similar mixed Mn valence in all samples (in agreement with the XAS measured with linear polarized X-rays). The large dichroism (∼20%) at the Mn edge is expected for the highly spin-polarized ferromagnetic LSMO and is consistent with magnetometry at room temperature. The XMCD signal, which is proportional to Ms in a fully satured film, presents different extent as a function of LSMO film preparation. XMCD signal per atom decreases to ∼10% in the film grown with F = 0.9 J/cm2 (Fig. 8(a)) and in the thinnest film ∼7.5 nm (Fig. 8(b)). We observe a drastic reduction of the XMCD signal for the sample post-annealed at oxygen pressure smaller than 1 bar. XMCD signal was measured at 0.5 T and is proportional to M(0.5 T)/Ms that is 87% of Ms in this LSMO film. Therefore, the reduced XMCD signal may be due to the magnetic field (lower than 2 T) and can be connected to the different structure of each film. Moreover, XAS/XMCD acquired in TEY mode probes only a few nanometers from the surface.

4. Conclusions In conclusion, we present the ability to prepare LSMO films of well defined magnetic properties and morphology. All preparation conditions end up in epitaxial LSMO films that differs in the c/a lattice ratio. The structural LSMO mismatch with the substrate is at the

Fig. 8. XAS and XMCD spectra of LSMO thin films (a) at fixed F = 1.3 J/cm2 and as a function of number of pulses (i.e. film thickness), (b) vs. F and (c) vs. post-annealing conditions. All measurements were performed at room temperature and with applied magnetic field of 0.5 T.

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basis of its electronic configuration that reflects aMnm+ oxidation state compatible with the film termination (mainly LaSrO,) and film morphology. Although ferromagnetic, LSMO films present different Ms , Hc , Mr parameters depending on the film strain and thickness. An almost single domain structure was observed for thick films, whereas non-uniform size distribution of the magnetic domain is observed in the film of thickness ∼7.5 nm. The reduction of oxygen exposition in the post-annealing of the LSMO films results in a collapse of the LSMO structure, i.e. decreasing of c-axis and an increase of defects that modify the magnetic response of the film at zero applied magnetic field. By discriminating the correct parameters of growth and post-annealing conditions, we achieved an LSMO film quality promising for the realization of multi structure device that make the spin as exchange channel. Acknowledgements This work was supported by FAPESP (Project No. 2012/511982). Some of the XRD measurements were performed at the XRD2 beamline of the LNLS/CNPEM under Project No. 20160908, and the XAS experiments were carried out at the U11-PGM beamline under Project No. 20160126. The authors thank the LNNano/CNPEM for XRD/XRR and AFM facilities, and the Instituto de Física/UFRJ for the VSM measurements. P.S. and E.A. thank FAPESP for financial support (Project No. 2012/18397-1 and Project No. 2015/12312-2, respectively). References [1] A.-M. Haghiri-Gosnet, J.-P. Renard, CMR manganites: physics, thin films and devices, J. Phys. D: Appl. Phys. 36 (8) (2003) R127 http://stacks.iop.org/00223727/36/i=8/a=201. [2] M. Koubaa, A.M. Haghiri-Gosnet, R. Desfeux, P. Lecoeur, W. Prellier, B. Mercey, Crystallinity, surface morphology, and magnetic properties of La0.7 Sr0.3 MnO3 thin films: an approach based on the laser ablation plume range models, J. Appl. Phys. 93 (9) (2003) 5227–5235, http://dx.doi.org/10.1063/1.1566093. [3] R.A. de Groot, F.M. Mueller, P.G.v. Engen, K.H.J. Buschow, New class of materials: half-metallic ferromagnets, Phys. Rev. Lett. 50 (1983) 2024–2027, http://dx.doi.org/10.1103/PhysRevLett.50.2024. [4] J.-H. Park, E. Vescovo, H.-J. Kim, C. Kwon, T. Ramesh, R. Venkatesan, Direct evidence for a half-metallic ferromagnet, Nature 392 (6678) (1998) 794–796, http://dx.doi.org/10.1038/33883. [5] M. Bowen, M. Bibes, A. Barthélémy, J.-P. Contour, A. Anane, Y. Lemaître, A. Fert, Nearly total spin polarization in La2/3 Sr1/3 MnO3 from tunneling experiments, Appl. Phys. Lett. 82 (2) (2003) 233–235, http://dx.doi.org/10.1063/1.1534619. [6] S. Majumdar, S. van Dijken, Pulsed laser deposition of La1−x Srx MnO3 : thin-film properties and spintronic applications, J. Phys. D: Appl. Phys. 47 (3) (2014) 034010 http://stacks.iop.org/0022-3727/47/i=3/a=034010.

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