La0.7Sr0.3MnO3 Thin Films Research Articles

La0.7Sr0.3MnO3 thin films deposited by pulsed laser ablation for spintronic applications

AbstractAmong spintronic materials, mixed‐valence manganite La 0.7Sr0.3MnO3 (LSMO) is widely investigated due to its half‐metal nature. LSMO thin films were grown by pulsed laser deposition (PLD) onto amorphous silica substrates heated at nearly 600 °C. An ArF excimer laser was chosen to induce ablation due to its more energetic photons compared to the other quoted excimer laser sources. Different oxygen pressures were considered in order to study the influence of oxygen on the LSMO optical and electrical properties. In this respect, the visible transparency percentage of the deposited films is found good enough for spin‐OLED applications. The absorption coefficient shows an absorption band tunable as a function of the oxygen content. Its energetic location and evolution with the oxygen content demonstrate it originates from radiative transitions between the spin‐majority bands separated by the Jahn–Teller distortion. All of this lets relate the deposition oxygen pressure to the Mn3+ ion content in each film and interpret electrical data. The 200 and 100 nm thick samples exhibit weak metallic transport behavior at room temperature with a resistivity of 4.8 and 6.9 Ω cm, respectively. Concerning the resistivity response versus temperature, the measured low metal–insulator transition temperature (150 K) is related to the sample structural features as involved by the depositions. Two different transport mechanisms describe the conductivity regime of the deposited samples, namely the small polaron variable range hopping (VRH) and the Arrhenius law.

Thickness Impacts of Vacancy Defects in Epitaxial La0.7Sr0.3MnO3 Thin Films Using Slow Positron Beam

Thickness effects of thin La0.7Sr0.3MnO3 (LSMO) films on (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates were examined by a slow positron beam technique. Doppler-broadening line shape parameter S was measured as a function of thickness and differnt annealing conditions. Results reveal there could be more than one mechanism to induce vacancy-like defects. It was found that strain-induced defects mainly influence the S value of the in situ oxygen-ambience annealing LSMO thin films and the strain could vanish still faster along with the increase of thickness, and the oxygen-deficient induced defects mainly affect the S value of post-annealing LSMO films.

Growth and structural characteristics of perovskite–wurtzite oxide ceramics thin films

Wurtzite ZnO thin films were grown on single-crystal perovskite SrTiO3(STO) (100) substrates at various temperatures. The ZnO/STO thin films thus formed exhibit a preferred (110)-orientation at a growth temperature of 600–700°C. A high growth temperature enhances not only the (110)-texture of ZnO/STO thin films but also the crystalline quality of the film. (La0.7Sr0.3)MnO3 (LSMO) thin films were subsequently grown on ZnO(110)/STO(100) substrates with various thicknesses, and were polycrystalline. A thicker LSMO film has a stronger (00l)-preferred orientation than the thinner one. The lattice distortion of LSMO decreases as the LSMO thickness increases. Magnetization vs. temperature curves show that both crystalline quality and lattice distortion influence the magnetic properties of LSMO thin films. The physical properties of the manganite oxide can be modulated by forming a heterostructure with wurtzite ZnO.

Transport and magnetic properties of epitaxial LSMO thin films grown on MgO single-crystal substrates

Thin epitaxial La0.67Sr0.33MnO3 (LSMO) films were deposited on single crystal MgO substrates. The electrical transport and magnetic properties of the films in the temperature range 4 – 350 K were investigated and strong correlation between them was registered. Magnetoresistance up to 52 % at temperature T = 256 K and magnetic field B = 5 T was achieved. The results obtained indicate that LSMO films with such properties are suitable for application as "barrier" layers in superconducting-ferromagnetic-superconducting heterostructures, but optimization of LSMO film thickness is needed.

Magnetic oxide nanowires with strain-controlled uniaxial magnetic anisotropy direction

While magnetic nanowires generally have a preferential magnetization direction along the wire axis to minimize magnetostatic energy, it is shown here for epitaxial magnetic oxide nanowires that substrate-induced strain can be used to tailor the magnetic easy axis in any direction. La0.67Sr0.33MnO3 (LSMO) nanowires were prepared by pulsed laser deposition of LSMO thin films on NdGaO3 (NGO) substrates of two different orientations [NGO(110)o and NGO(010)o], followed by patterning into arrays of nanowires by laser interference lithography. The uniaxial compressive strain from the substrate induces a strong uniaxial magnetic anisotropy in the LSMO that dominates the anisotropy. Hence, one obtains LSMO nanowires having a magnetic easy axis that can lie in any direction, including perpendicular to the wire axis. In marked contrast, similar nanowires on SrTiO3(001) substrates without significant uniaxial strain exhibit the usual preferential magnetization direction along the wire axis, as dictated by magnetostatic shape anisotropy. The tunable magnetic anisotropy direction is a useful feature for applications of magnetic nanowires in magnetic memory, sensor, and logic devices.

Rotation of the magnetic easy axis in La0.67Sr0.33MnO3 thin film on NdGaO3(112)

The in-plane magnetic anisotropy is studied for pseudocubic {011}pc oriented La0.67Sr0.33MnO3 (LSMO) thin film grown on orthorhombic NdGaO3(NGO)(112)o (the subindices “pc” and “o” indicate the pseudocubic and orthorhombic lattice structure, respectively). The direction of the in-plane remanent magnetization of LSMO thin films with different thicknesses is determined. With increasing film thickness the easy axes rotate and the anisotropy changes from uniaxial to biaxial. This is associated with the increasing symmetry of the LSMO with increasing thickness, starting with a monoclinic LSMO structure at the nonrectangular NGO(112)o surface unit cell of the substrate, developing into an orthorhombic structure at the top part of the thickest films.

Epitaxial growth of La0.67Sr0.33MnO3 on glass by laser molecular beam epitaxy

La067Sr033MnO3 thin films have been deposited by laser molecular beam epitaxy system on glass substrates. The measurement of X-ray diffraction shows that the La067Sr033MnO3 thin film is a good orientation of c axis，and the magnetoresistance values of -378%, -268% and 607% at 88, 220 and 300 K, respectively, under 3 T magnetic field were observed.

Grain Size Dependent Transport and Magnetoresistance Behavior of Chemical Solution Deposition Grown Nanostructured La07Sr03MnO3 Manganite Films

Grain-size dependence of electronic transport and magnetoresistance (MR) properties of nanostructured La0.7Sr0.3MnO3 (LSMO) manganite thin films on LaAlO3 (100) single crystal substrates prepared using Chemical Solution Deposition (CSD) technique have been studied. The LSMO thin films were annealed at temperatures in the range of 700-1000 degrees C for different time intervals [6 h and 12 h] and crystallized as singlephase LSMO. Microstructural studies carried out using AFM show a marginal increase in the grain-size from 50 to 90 nm as the temperature was varied from 700 degrees C to 1000 degrees C respectively. It has been observed that the insulator-metal transition (T(p)) and MR depend on the grain size. In zero applied field, resistivity reduction is approximately 10(3) at 5 K for the films annealed at 700 degrees C [T(p) approximately 341 K] and 1000 degrees C [T(p) approximately 373 K]. MR versus H isotherms reveal that MR enhances in the vicinity of T(p) but decreases at low temperatures. The results obtained from the electronic and magnetotransport studies are in good agreement with the change in surface morphology of the films studied, which shows that the randomly distributed domains are composed of faceted grains. Synthesizing conditions, annealing temperature and time control the growth and alignment of grains into the domains, which cause better conduction at grain interface.

Study of Coercivity-enhanced Ruthenium-doped La0.67Sr0.33MnO3 Thin Films for Pseudo Spin Valve Devices

ABSTRACTThis investigation focused on the study of La0.67Sr0.33MnO3 (LSMO) thin films with 5 atomic percent Ru-doping (LSMRO). Specifically, we fabricated epitaxial LSMO and LSMRO thin films on LaAlO3 (LAO) (001) substrates by pulsed laser deposition. Resistance- temperature measurement results showed that the Curie temperature (Tc) of LSMRO thin film deposited under an oxygen ambient pressure of 150 mTorr at 830 °C was above room temperature. Hysteresis measurements and anisotropic magnetoresistance (AMR) results confirmed that coercivity of the optimized LSMRO films, as compared with that of LSMO films, can be greatly increased at low temperatures. The study successfully demonstrated the coercivity enhancement effect of Ru-doping on LSMO thin films deposited on LAO substrates.

Magneto-optical properties of La0.7Sr0.3MnO3 thin films with perpendicular magnetic anisotropy

We report the magneto-optical (MO) properties of compressively strained La0.7Sr0.3MnO3 (LSMO) thin films epitaxially grown on a LaAlO3 substrate. The magnetic force microscope images show the stripe magnetic domains, characteristic of films with the perpendicular magnetic anisotropy (PMA). The optical reflectance and transmittance of the samples were measured over a broad energy range from the far infrared through the ultraviolet. To extract the optical constants of the films, we analyzed all of the layers of this thin-film structure using a Drude-Lorentz model. From the parameters obtained, we compute the optical constants, such as frequency-dependent optical conductivity and the diagonal components of the dielectric tensor. Moreover, the MO polar Kerr spectra of the samples were measured in an applied magnetic field of 1.5T between 0.74 and 5.8eV. The off-diagonal components of the dielectric tensor were then calculated by analyzing Kerr rotation, ellipticity, and the determined diagonal elements of the dielectric tensor. These functions yield information about the spin-dependent electronic structures of the LSMO thin films. We observed several MO-active transitions above 2eV. These bands arise from the Mn-d(t2g) to Mn-d(eg) in the majority-spin channel and the onset of O-2p to Mn-d(eg) and O-2p to Mn-d(t2g) transitions in the minority-spin channel, in accord with the band-structure calculations. Most interestingly, their peak position and intensity are dependent on the film thickness, suggesting possible applications for tailoring MO responses in these PMA thin films.

Low-noise La0.7Sr0.3MnO3 thermometers for uncooled bolometric applications

We report measurements of the temperature coefficient of the resistance (TCR) and the low-frequency noise of epitaxial La0.7Sr0.3MnO3 (LSMO) thin films deposited on SrTiO3 (STO) and (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates. An x-ray-diffraction study showed that the films were (001) oriented. A normalized Hooge parameter of 9×10−31m3 was measured at 300K in the case of a 10-μm-wide, 575-μm-long line patterned in the 200-nm-thick film grown on STO substrate. This value is among the lowest reported values for manganites and close to values measured in standard metals and semiconductors. The corresponding noise equivalent temperature (NET) was constant in the 300–340K range and equal to 6×10−7KHz−1∕2 at 10Hz and 150μA for a 10-μm-wide, 575-μm-long line patterned in a 200-nm-thick LSMO film. This very low NET value is comparable to the best published results for manganites and was even found to be lower than the NET of other uncooled thermometers such as amorphous semiconductors, vanadium oxides, or semiconducting YBa2Cu3O6+σ. This can easily be explained by the lower noise level of epitaxial manganites thin films compared to others. The results show that despite a TCR of only 0.017K−1 at 300K, and thanks to a very low-noise level, LSMO thin films are real potential material for uncooled thermometry and bolometry.

Evidence forMn2+ions at surfaces ofLa0.7Sr0.3MnO3thin films

We present a detailed investigation of the valence of manganese sites at the surface of colossal magnetoresistance La0.7Sr 0.3MnO3 (LSMO) thin films by x-ray absorption spectroscopy (XAS). The XAS Mn L-edge spectra of epitaxial LSMO films usually show a peak or shoulder at 640 eV. Differences in the intensity of this feature are commonly attributed to slight changes in the Mn3+/Mn4+ ratio or the crystal field strength. By comparison of different XAS spectra of LSMO thin films with the known multiplet structure of Mn2+ in a cubic crystal field, we assign this 640-eV feature to Mn2+ ions. XAS with increased surface sensitivity, combined with photon energy-dependent photoelectron spectroscopy measurements of the Mn(3s) exchange splitting, show that the Mn2+ species are mainly located at the surface. The Mn2+ scenario indicates significant modification of the LSMO surface with respect to the bulk properties that should be taken into account in all the charge and spin tunneling and injection experiments. © 2005 The American Physical Society.

Microstructure and magnetic properties of strained La0.7Sr0.3MnO3 thin films

The lattice deformation of dense strained La0.7Sr0.3MnO3 (LSMO) films is shown to control the easy direction of the magnetization. Optimized pulsed laser deposited conditions allow the fabrication of dense LSMO thin films which present an exceptional flatness with a peak–valley roughness (Rp–v) of 1 Å, associated to epitaxial grains as large as 1 μm. Electron microscopy coupled with x-ray diffraction have been used to study the unit cell distortion of both tensile and compressive dense LSMO films as a function of the thickness. No relaxation of the lattice distortion imposed by substrate has been observed in the thickness range 10–60 nm. The Curie temperature is not significantly affected by the nature of the substrate: a TC of 350 K is observed for both SrTiO3 (STO) and LaAlO3 (LAO) substrates, i.e., close to the bulk material (369 K). In contrast, the easy direction of magnetization depends on the substrate. For tensile films deposited on the STO substrate, the unit cell is elongated along the film’s plane (ain-plane=3.905 Å) with a reduced perpendicular parameter (cperp=3.85 Å): an easy direction of magnetization M in the plane of the film is observed. For compressive films deposited on LAO substrate, the situation is reversed with a unit cell elongated along the direction of growth (cperp=4.00 Å and ain-plane=3.79 Å) and an easy axis for M along this perpendicular out-plane direction. It is thus demonstrated that the larger cell parameter, ain-plane for films deposited on STO and cperp for films deposited on LAO, is fully correlated to the direction of the easy magnetization.

The role of strain in low-field magnetotransport properties of manganite thin films

AbstractStrain-induced large low-field magnetoresistance has been observed in very thin Pr0.67Sr0.33MnO3 films1. To better understand the role of strain in the low-field magnetotransport properties of manganite thin films, we have studied and compared very thin (3-20 nm) Pr0.67Sr0.33MnO3 (PSMO), La0.67Ba0.33MnO3 (LBMO), La0.67Sr 0.33MnO3 (LSMO) and La0.67Ca0.33MnO3 (LCMO) films grown on different substrates, such as LaAlO3(001) (LAO), NdGaO3(110) (NGO), and SrTiO3(001) (STO). Due to the lattice mismatch between the films and the substrates ranging from -2.6% to +1%, different strains can be imposed to the films. We have found that: (1) large low-field magnetoresistance(LFMR) behaviors are observed in PSMO, LCMO and LSMO thin films on LAO substrates when a magnetic field is applied perpendicular to the film plane, but the maximum LFMR is the largest in PSMO and LCMO samples; (2) most of the films grown on STO substrates show positive MR when a magnetic field is applied perpendicular to the film plane, and when the field is parallel to the film plane all films show negative MR regardless of the substrates; (3) the large low-field MR is strongly dependent on the film thickness and the composition of the manganites. The anomalous low-field MR effect will be discussed based on strain-induced magnetic anisotropy and domain rotation and movement.

Lattice Distortions and Domain Structure in Epitaxial Manganite Thin Films

AbstractLattice distortions, be they in the form of chemical and hydrostatic pressure in bulk or lattice mismatch between film and substrate, have significant effects on the transport as well as the magnetic properties of colossal magnetoresistance (CMR) materials. We summarize here our results on tensilely and compressively strained La0.7Sr0.3MnO3 (LSMO) thin films that indicate the important role of lattice distortions due to the lattice mismatch between the film and substrate. The strain due to lattice distortions can be used to tune the magnetic domain structure, magnetization, magnetic anisotropy and magnetotransport of LSMO thin films.