La0.7Sr0.3MnO3 Thin Films Research Articles

Control of Magnetic Shape Anisotropy by Nanopillar Dimensionality in Vertically Aligned Nanocomposites.

Perpendicular magnetic anisotropy forms the foundation of the current data storage technology. However, there is an ever-increasing demand for higher density data storage, faster read-write access times, and lower power consuming storage devices, which requires new materials to reduce the switching current, improve bit-to-bit distributions, and improve reliability of writing with scalability below 10 nm. Here, vertically aligned nanocomposites (VANs) composed of self-assembled ferromagnetic La0.7Sr0.3MnO3 (LSMO) nanopillars in a surrounding ZnO matrix are investigated for controllable magnetic anisotropy. Confinement of LSMO into nanopillar dimensions down to 15 nm in such VAN films aligns the magnetic easy axis along the out-of-plane (i.e., perpendicular) direction, in strong contrast to the typical in-plane easy axis for strained, phase pure LSMO thin films. The dominant contribution to the magnetic anisotropy in these (LSMO)0.1(ZnO)0.9 VAN films comes from the shape of the nanopillars, while the epitaxial strain at the vertical LSMO:ZnO interfaces exhibits a negligible effect. These VAN films with their large, out-of-plane remnant magnetization of 2.6 μB/Mn and bit density of 0.77 Tbits/inch2 offer an interesting strategy for enhanced data storage applications.

Unveiling the red electroluminescence in LSMO-SRO thin film heterostructures

Herein, intense red electroluminescence (674 nm) in a La0.7Sr0.3MnO3(LSMO)-SrRuO3(SRO) thin films heterostructure obtained by RF-magnetron sputtering is reported for the first time. This novel phenomenon may open a new door in the field of optoelectronics and new generation devices based on multiferroic heterostructure. The structural properties were analyzed using grazing incidence x-ray diffraction demonstrating a rhombohedral structure for LSMO with (024) preferential orientation and an orthorhombic structure for SRO films with (121) preferential orientation. Raman and x-ray photoelectron spectroscopy (XPS) results demonstrated a mix of phases present in LSMO thin films. The thickness analysis was performed using scanning electron microscopy (SEM) in cross section and the thickness was found to be 123 nm and 49 nm for LSMO and SRO, respectively. XPS analysis for LSMO revealed that point defects associate to Mn cations and oxygen vacancies modify the total electrical conductivity and due to Mott transitions, suggest a p-type semiconductor behavior. For the SRO film, the XPS analysis demonstrated a change in the stoichiometry of the film surface, which provides a large amount of oxygen vacancies indicating a metal oxide transition with effects that involve multiple degrees of freedom (charge, spin, and lattice). The electrical behavior observed in the heterostructure corresponds to a metal-semiconductor junction showing a Schottky conduction mechanism in positive bias and a space charge limited conduction mechanism in negative bias. The red electroluminescence effect is discussed considering both a radiative recombination process occurred at the interface due to the presence of Mn2+ ions and an energy transfer mechanism assisted by the migration of the high amount of oxygen vacancies present in the interface.

Manipulating the magnetic and electric transport properties of La0.7Sr0.3MnO3 epitaxial thin film through ionic liquid-gated technology

Reversible manipulation of magnetic and electric transport properties by electrical means in perovskite transition metal oxides is of paramount importance in modern condensed matter physics and generates promising application prospects in electronic devices. However, the conventional method of field-effect transistor structure presents a huge limitation due to its poor ability to modulate the exceedingly high carrier density of about 1014−1015 cm−2. In this study, La0.7Sr0.3MnO3 (LSMO) epitaxial thin films with tensile and compressive strain states were obtained by growth on different single-crystal substrates. Compared with the LSMO thin film under tensile strain, the compressed LSMO thin film possesses more oxygen vacancies, a higher resistance and a smaller magnetization. In addition, the structural phases, magnetic and electric transport properties in both LSMO thin films were also manipulated by the ionic liquid-gated method. The LSMO thin film under compressive strain shows easier access to the reversible control of the structural phase and magnetic & electrical transport properties than the LSMO thin film under tensile strain. The synergy of the above capabilities proves an effective and reversible route to manipulate the properties of perovskite transition metal oxides, providing tremendous potential in the design of multiple-state memories, neuromorphic transistors, and other multifunctional devices.

Effect of annealing temperature on resistive switching behavior of Al/ La0.7Sr0.3MnO3 /LaNiO3 devices

La0.7Sr0.3MnO3 (LSMO)/LaNiO3 (LNO) thin films were deposited successively on Si single crystal by the sol-gel method. The bipolar resistive switching (RS) behavior was studied in Al/LSMO/LNO devices. Obvious current hysteresis was observed, the set (reset) voltage and resistance ratio were modulated by the annealing temperature of LSMO thin films. At the annealing temperature of 750 °C, good endurance and retention performance were obtained in the memory device. According to the fitting results of I–V curves, based on Schottky emission model, the conduction mechanisms of Al/LSMO/LNO devices were discussed. Our results may give a valuable insight on developing perovskite-type rare earth manganese oxide.

Mechanical tuning of room temperature magnetism in flexible manganite/mica heterostructures

Flexible materials have attracted increasing attention due to their potential application in wearable or implantable circuits and systems. Here, the La0.67Sr0.33MnO3 (LSMO) thin films have been grown on single crystalline mica substrates and the impact of mechanical strain on the magnetic properties is investigated through varying external mechanical bending. The in-plane saturated magnetic moment decreases firstly with increasing radius of curvature (ROC) and then increases after attaining a minimum value of MS = 187 emu/cm3 at ROC = 3.0 mm. The nonmonotonous dependence of magnetic moment on ROC can be attributed to the mechanical bending-triggered lateral tensile strain, which can not only enhance the Jahn-Teller splitting and reduce the double-exchange interaction, but also enable the neighboring ferromagnetic domain switching in the LSMO films. Moreover, the out-of-plane magnetic anisotropy can also be reinforced by exerting mechanical tensile strain. Meanwhile, the superior mechanical antifatigue character is found in the LSMO/mica structures. These flexible LSMO thin films with highly tunable magnetism and excellent mechanical durability exhibit promising prospect in designing stable flexible spintronic devices and wearable sensors.

Tunable magnetic and magnetotransport properties in locally epitaxial La0.67Sr0.33MnO3 thin films on polycrystalline SrTiO3, by control of grain size

La0.67Sr0.33MnO3 (LSMO) thin films have been grown by pulsed laser deposition on SrTiO3 using combinatorial substrate epitaxy (CSE) approach, i.e. polycrystalline substrates with micrometer-size grains. The crystallographic domains size of those polycrystalline substrates can be controlled between 2 and 45 µm depending on the annealing temperature during synthesis. Each grain of the substrate acts as a single crystalline growth template promoting local epitaxy with a reproduction of the substrate grain structure in the thin film. Therefore, a fine-tuning of the substrate grain metrics and high crystalline quality of locally epitaxial LSMO film, allows to combine the advantages of polycrystalline, i.e. the presence of low field magnetoresistance (LFMR) and the possibility to use very thin films, with a pronounced magnetic shape anisotropy. For this, the magnetic and transport properties of the films are showing a strong influence with varying grain metrics of the substrate. High Curie temperatures, important values of the LFMR and anisotropy for optimized substrate grain metrics with the relative orientation of the magnetic field to the film plane underline the high quality of the films and the advantage of the CSE approach. The obtained LSMO thin films may have an interest for high-resolution low field magnetic sensors application.

Epitaxial (110)-oriented La0.7Sr0.3MnO3 film directly on flexible mica substrate

Manufacture and characterizations of perovskite-mica van der Waals epitaxy heterostructures are a critical step to realize the application of flexible devices. However, the fabrication and investigation of the van der Waals epitaxy architectures grown on mica substrates are mainly limited to (111)-oriented perovskite functional oxide thin films up to now and buffer layers are highly needed. In this work, we directly grew La0.7Sr0.3MnO3 (LSMO) thin films on mica substrates without using any buffer layer. By the characterizations of x-ray diffractometer and scanning transmission electron microscopy, we demonstrate the epitaxial growth of the (110)-oriented LSMO thin film on the mica substrate. The LSMO thin film grown on the mica substrate via van der Waals epitaxy adopts domain matching epitaxy instead of conventional lattice matching epitaxy. Two kinds of domain matching relationships between the LSMO thin film and mica substrate are sketched by Visualization for Electronic and STructural Analysis software and discussed. A decent ferromagnetism retains in the (110)-oriented LSMO thin film. Our work demonstrates a new pathway to fabricate (110)-oriented functional oxide thin films on flexible mica substrates directly.

Dislocation Defect Layer-Induced Magnetic Bi-states Phenomenon in Epitaxial La0.7Sr0.3MnO3(111) Thin Films.

La0.7Sr0.3MnO3 (LSMO) is one of the most fascinating strongly correlated oxides in which the spin polarization and magnetic property are sensitive to strain, especially in the (111)-oriented LSMO. In the paper, epitaxial LSMO(111) thin films with different thicknesses were prepared, and they showed continuous dislocation defect arrays with thickness greater than 45 nm. Then, the thick LSMO(111) films were divided into a double-layer structure with two slightly different oriented cells. The LSMO(111) films present a stronger lattice-spin coupling, thus the double-layer structure triggers an obvious magnetic heterogeneity phenomenon (magnetic bi-states) by the way of creating a double-mode ferromagnetic resonance (FMR) spectrum. Therefore, the nanostructures, especially the ordered structure defects, may trigger enriched physical phenomena and offer new forms of spin coupling and device functionality in strain-sensitive strongly correlated oxide systems.

Evidence of Mn-Ion Structural Displacements Correlated with Oxygen Vacancies in La0.7Sr0.3MnO3 Interfacial Dead Layers.

The properties of half-metallic manganite thin films depend on the composition and structure in the atomic scale, and consequently, their potential functional behavior can only be based on fine structure characterization. By combining advanced transmission electron microscopy, electron energy loss spectroscopy, density functional theory calculations, and multislice image simulations, we obtained evidence of a 7 nm-thick interface layer in La0.7Sr0.3MnO3 (LSMO) thin films, compatible with the formation of well-known dead layers in manganites, with an elongated out-of-plane lattice parameter and structural and electronic properties well distinguished from the bulk of the film. We observed, for the first time, a structural shift of Mn ions coupled with oxygen vacancies and a reduced Mn valence state within such layer. Understanding the correlation between oxygen vacancies, the Mn oxidation state, and Mn-ion displacements is a prerequisite to engineer the magnetotransport properties of LSMO thin films.

Manipulation of microwave magnetism in flexible La0.7Sr0.3MnO3 film by deformable ionic gel gating

The flexible La0.7Sr0.3MnO3 (LSMO) film shows good mechanical stretchability and property stability under bending states, which makes it a candidate material for flexible electronics and spintronics devices. Here the microwave magnetism of flexible LSMO thin film has been manipulated effectively by the ionic gel (IG) gating process. A reversible and non-volatile magnetoelectric (ME) coefficient of 50 Oe/V was observed using electron paramagnetic resonance (ESR) technology at the flat multilayer structure. This ME coupling is caused by the electrons hopping between Mn3+ and Mn4+ ions under the interfacial electric double layer. When the membranes were bent to a radius of curvature of 15 mm, a larger ME coefficient of 67 Oe/V was also observed, which indicating that this flexible structure can work effectively under mechanical deformation. This work demonstrates the voltage control of magnetism for flexible correlated materials and paves a way towards wearable low-power devices based on flexible manganite films.

Strong tailoring magnetocaloric effect in highly (001)-oriented La0.7Sr0.3MnO3 thin films

In this work, we simulated the dependence of magnetization versus temperature for highly (001)-oriented La0.7Sr0.3MnO3 (LSM) thin film prepared under several oxygen growth pressures to predict magnetocaloric effect (MCE). The results reveal that MCE of highly (001)-oriented LSM thin films is strongly tunable with oxygen growth pressure during preparation. Furthermore, the MCE of these films is enhanced with increasing oxygen growth pressure during preparation. The comparison of MCE parameters for (001)-oriented LSM thin films and some published works has been done, showing that these films are considerably larger and comparable with some MCE parameters of these published works. It is suggested that (001)-oriented LSM thin films can be used as a function material of MR that cools at cryogenic and room temperatures.

Electro-thermal and optical characterization of an uncooled suspended bolometer based on an epitaxial La0.7Sr0.3MnO3 film grown on CaTiO3/Si

The electro-thermal and optical properties of a bolometer based on an La0.7Sr0.3MnO3( LSMO) thin film with a detection area of 100 × 100 µm2 are presented. The LSMO thin film was epitaxially grown on CaTiO3/Si and patterned using a two-step etching process of ion-beam etching in argon and of reactive-ion etching in SF6, in order to etch LSMO/CaTiO3 and Si, respectively. The voltage-current (V–I) characteristics of the bolometer were measured in vacuum from 240 K to 415 K. From the V–I characteristics and a thermal model of the bolometer, the electrical responsivity was determined and compared to the optical responsivity measured with a laser diode at 635 nm. The noise equivalent power (NEP) as a function of frequency was measured by dividing the spectral noise power density by the optical responsivity. At 300 K and a bias current of 80 µA, the NEP was 2.3 × 10−11 W · Hz−1/2 in the 20–200 Hz modulation frequency range and the response time was 1.3 ms. The obtained NEP value without any absorbing layer or antennas, combined with the low value of the response time, are a very promising step towards the use of such LSMO-based bolometers for IR or THz detection.

Effects of Oxygen Modification on the Structural and Magnetic Properties of Highly Epitaxial La0.7Sr0.3MnO3 (LSMO) thin films

La0.7Sr0.3MnO3, a strong semi-metallic ferromagnet having robust spin polarization and magnetic transition temperature (TC) well above 300 K, has attracted significant attention as a possible candidate for a wide range of memory, spintronic, and multifunctional devices. Since varying the oxygen partial pressure during growth is likely to change the structural and other physical functionalities of La0.7Sr0.3MnO3 (LSMO) films, here we report detailed investigations on structure, along with magnetic behavior of LSMO films with same thickness (~30 nm) but synthesized at various oxygen partial pressures: 10, 30, 50, 100, 150, 200 and 250 mTorr. The observation of only (00 l) reflections without any secondary peaks in the XRD patterns confirms the high-quality synthesis of the above-mentioned films. Surface morphology of the films reveals that these films are very smooth with low roughness, the thin films synthesized at 150 mTorr having the lowest average roughness. The increasing of magnetic TC and sharpness of the magnetic phase transitions with increasing oxygen growth pressure suggests that by decreasing the oxygen growth pressure leads to oxygen deficiencies in grown films which induce oxygen inhomogeneity. Thin films grown at 150 mTorr exhibits the highest magnetization with TC = 340 K as these thin films possess the lowest roughness and might exhibit lowest oxygen vacancies and defects. Interpretation and significance of these results in the 30 nm LSMO thin films prepared at different oxygen growth pressures are also presented, along with the existence and growth pressure dependence of negative remanent magnetization (NRM) of the above-mentioned thin films.

Asymmetric spin dependent scattering at the interfaces of Si/La0.7Sr0.3MnO3/ZnO heterostructures

A ferromagnetic 120 Å thick La0.7Sr0.3MnO3 (LSMO) film grown on (001)Si using the sputtering deposition technique demonstrates a large positive in-plane magnetoresistance (MR) at 10 K, in the field window of ±0.084 kG to±0.405 kG, although the bulk LSMO exhibits negative MR. Around the coercive field (∼179 G), the positive MR becomes ∼ 11%. The positive MR of the LSMO thin film is explained by the charge transfer driven localized strong antiferromagnetic coupling at the Si−LSMO interface, which favors the reduction of the Curie temperature TC of LSMO compared to that of its bulk value. The construction of the interface on the top surface of LSMO with ZnO thin films further reduces TC ∼ 30 K and the positive MR decreases to ∼ 1% for 45° oriented in-plane current with the in-plane field. The coupling through Mn−O−Zn at the LSMO−ZnO interface preserves the charge state, and the weak exchange coupling at the (La/Sr)O−ZnO interface reduces the spin-dependent scattering process under the field and thereby, the negative MR. The reduced TC and in-plane low-field MR at 10 K of a series of Si/LSMO/ZnO are the same irrespective of the ZnO thickness, which confirms their interfacial origin. The presence of interfacial spin disorder at the Si−LSMO interface is further confirmed from the increase in resistance at low temperatures, which is explained by the Kondo like effect and quantum interference effect. Our investigations show that the technologically important interfacial magnetic coupling and magnetoresistance could be achieved and manipulated by the selective interfacial exchange coupling.

Ferromagnetic Resonance of Single-Crystalline La0.67Sr0.33MnO3 Thin Film Integrated on Silicon

Integration of high-quality multifunctional oxide thin films in silicon technology promises a wide range of potential applications in low loss spintronic devices such as sensors, detectors, data storage media, and so on. However, the heteroepitaxial growth of functional complex oxides on silicon substrates has been proved challenging, which limits the development of semiconductor-based spintronic devices. In this work, epitaxial single-crystalline La0.67Sr0.33MnO3 (LSMO) thin films have been integrated on silicon substrates by epitaxy and transfer carried out at room temperature. The microwave magnetisms of the LSMO thin films transferred on silicon substrates have been investigated under multiple directions of magnetic field by ferromagnetic resonance. The transferred LSMO thin films on silicon substrates preserve the microwave magnetic characteristics of the primary as-grown LSMO thin films. Our results demonstrate that the epitaxy and transfer method has enormous potential in future spintronic applications of functional oxide devices compatible with semiconductor technology without thermal damage.

Surface modification of Sr-doped LaMnO3 coating by spray drying on Ni-rich LiNi0.8Mn0.1Co0.1O2 cathode material for lithium-ion batteries

Abstract Sr-doped LaMnO3 with a composition of La0.7Sr0.3MnO3 (LSMO) was introduced as coating material to modify the surface of layered oxide Ni-rich LiNi0.8Mn0.1Co0.1O2 (NMC) cathode material though a spray-drying method. For the spherical hierarchical NMC secondary particles prepared by co-precipitation, each grain is covered by a uniform LSMO thin film. The LSMO material with superior conductivity functions as a protective layer from interface side reactions also to avoid the additional impedance contributed by the coating shell. The NMC@LSMO composite exhibits superior rate capability and excellent cycling stability especially at high temperature. The specific capacity is 190.3 and 128.6 mAh g−1 at 0.1 and 10 C, respectively. After 100 cycle times at a current density of 1 C under 55 °C, the NMC@LSMO can delivers a capacity of 166.5 mAh g−1 with a retention ratio of 89.7%. The evenly coating by a simple technology, superior capability and cycling stability at elevated temperature demonstrate potential for up-scaling to industrial quantities.

Free-standing La0.7Sr0.3MnO3 suspended micro-bridges on buffered silicon substrates showing undegraded low frequency noise properties

We report on the microfabrication process of free-standing suspended micro-bridges made of La0.7Sr0.3MnO3 (LSMO) thin films of thicknesses in the range of 10–100 nm. LSMO films were epitaxially grown on either SrTiO3 or CaTiO3 buffer layers on silicon substrates by reactive molecular beam epitaxy. The micro-bridges were patterned using standard UV photolithography then etched by ion beam and released using reactive ion etching of silicon in SF6. LSMO suspended micro-bridges 2 and 4 µm wide and of length ranging from 50 to 200 µm could be fabricated with a high fabrication yield (of about 85% as evaluated over 100 fabricated suspended micro-bridges) without degrading the electrical transport properties and in particular the low frequency noise level, as attested by the normalized Hooge parameter. The latter was measured in the 0.55–7.50 × 10−30 m3 range at 300 K, which is comparable to those measured in non-suspended high quality epitaxial LSMO thin films. This fabrication process could be useful for bolometer fabrication where thermal isolation is needed, or for any microelectromechanical systems devices making use of epitaxial functional oxides.

Integration of sputter-deposited multiferroic CoFe2O4–BiFeO3 nanocomposites on conductive La0.7Sr0.3MnO3 electrodes

The structure, magnetic and ferroelectric properties of sputtered epitaxial CoFe2O4-BiFeO3 (CFO-BFO) nanocomposite thin films grown on La0.7Sr0.3MnO3 (LSMO) layers on (001) oriented SrTiO3 (STO) substrates and on STO-buffered Si are described. The as-grown LSMO thin films were smooth and poorly conductive but the resistivity was reduced and the surfaces roughened after annealing. Cosputtered CFO and BFO on STO formed vertically aligned nanostructures consisting of epitaxial spinel CFO pillars within a perovskite BFO matrix, but the rough surface of the annealed LSMO film promoted additional CFO pillar orientations. A reorientation of the CFO magnetic easy axis to an in-plane direction occurred as the LSMO became thicker due to changes in the strain state of the CFO pillars. The LSMO underlayer enabled the ferroelectric response of the BFO to be measured. Nanocomposites were grown onto LSMO/SrTiO3/Si which provides a path towards large scale integration of electrically contacted nanocomposites on Si.

Multifunctional La0.67Sr0.33MnO3 (LSMO) Thin Films Integrated on Mica Substrates toward Flexible Spintronics and Electronics.

Integrating oxide thin films on flexible substrates is a critical step toward future applications of multifunctional oxides for flexible electronics and spintronic devices. As a demonstration, multifunctional La0.67Sr0.33MnO3 (LSMO) thin films have been deposited on flexible mica substrates. The crystallinity and microstructure of the films have been characterized to show the good epitaxial quality of the films. The LSMO thin films on mica present excellent ferromagnetic and magnetoresistance properties (such as saturation magnetization Ms of 125-400 emu/cm3 at 10 K and a high MR value of ∼45% at 5 K under 1 T for the 50 mTorr deposited sample), which is even better than the ones on conventional rigid single-crystal oxide substrates. More interestingly, no deterioration of the properties is observed under mechanically bending condition, which demonstrates the good mechanical stretchability and property stability of the LSMO thin films on mica. The demonstration of functional oxides integrated on flexible mica substrates paves a route toward future flexible spintronics and electronics.

Epitaxial La0.7Sr0.3MnO3 thin films on silicon with excellent magnetic and electric properties by combining physical and chemical methods

ABSTRACTHalf-metallic ferromagnetic La0.7Sr0.3MnO3 (LSMO) represents an appealing candidate to be integrated on silicon substrates for technological devices such as sensors, data storage media, IR detectors, and so on. Here, we report high-quality epitaxial LSMO thin films obtained by an original combination of chemical solution deposition (CSD) and molecular beam epitaxy (MBE). A detailed study of the thermal, chemical, and physical compatibility between SrTiO3 (STO)/Si buffer layers and LSMO films, grown by MBE and CSD, respectively, enables a perfect integration of both materials. Importantly, we show a precise control of the coercive field of LSMO films by tuning the mosaicity of the STO/Si buffer layer. These results demonstrate the enormous potential of combining physical and chemical processes for the development of low-cost functional oxide-based devices compatible with the complementary metal oxide semiconductor technology.