Manganite Thin Films Research Articles

Manipulating Interface Magnetism in Manganite Thin Film Membranes by Substrate Surface Chemistry

Manipulating Interface Magnetism in Manganite Thin Film Membranes by Substrate Surface Chemistry

Preparation of Atomically Smooth SrTiO₃ Substrates

SrTiO3 has been used as a substrate to grow thin films of materials including high-temperature superconductors such as cuprates, ferromagnetic oxides such as manganites, and ferroelectric oxides such as BaTiO3. The use of SrTiO3 as a substrate for the deposition of manganite thin films provides an excellent template for observing unique effects observed only in ferromagnets, such as the anomalous and planar Hall effects. The as-received SrTiO3 substrates require a process that prepares atomically smooth surfaces for thin film deposition. This study focuses on using ultrasonic cleaning, water annealing, and thermal annealing in air to prepare SrTiO3 substrate surfaces and verifying their smoothness at the atomic scale using atomic force microscopy.

Manganite memristive devices: recent progress and emerging opportunities

Manganite-based memristive devices have emerged as promising candidates for next-generation non-volatile memory and neuromorphic computing applications, owing to their unique resistive switching behavior and tunable electronic properties. This review explores recent innovations in manganite-based memristive devices, with a focus on materials engineering, device architectures, and fabrication techniques. We delve into the underlying mechanisms governing resistive switching in manganite thin films, elucidating the intricate interplay of oxygen vacancies, charge carriers, and structural modifications. This review underscores breakthroughs in harnessing manganite memristors for a range of applications, from high-density memory storage to neuromorphic computing platforms that mimic synaptic and neuronal functionalities. Additionally, we discuss the role of characterization techniques and the need for a unified benchmark for these devices. We provide insights into the challenges and opportunities associated with the co-integration of manganite-based memristive devices with more mature technologies, offering a roadmap for future research directions.

Strained single crystal high entropy oxide manganite thin films

The ability to accommodate multiple principal cations within a single crystallographic structure makes high entropy oxides (HEOs) ideal systems for exploring new composition–property relationships. In this work, the high-entropy design strategy is extended to strained single-crystal HEO-manganite (HEO-Mn) thin films. Phase-pure orthorhombic films of (Gd0.2La0.2Nd0.2Sm0.2Sr0.2)MnO3 were deposited on three different single-crystal substrates: SrTiO3 (STO) (100), NdGaO3 (110), and LaAlO3 (LAO) (100), each inducing different degrees of epitaxial strain. Fully coherent growth of the thin films is observed in all cases, despite the high degree of lattice mismatch between HEO-Mn and LAO. Magnetometry measurements reveal distinct differences in the magnetic properties between epitaxially strained HEO-Mn thin films and their bulk crystalline HEO counterparts. In particular, the bulk polycrystalline HEO-Mn shows two magnetic transitions as opposed to a single one observed in epitaxial thin films. Moreover, the HEO-Mn film deposited on LAO exhibits a significant reduction in the Curie temperature, which is attributed to the strong variation of the in-plane lattice parameter along the thickness of the film and the resulting changes in the Mn–O–Mn bond geometry. Thus, this preliminary study demonstrates the potential of combining high entropy design with strain engineering to tailor the structure and functionality of perovskite manganites.

Relationship between structure and charge/orbital order in epitaxial single layer Ruddlesden–Popper manganite thin films

Relationship between structure and charge/orbital order in epitaxial single layer Ruddlesden–Popper manganite thin films

Boosting ferromagnetism in freestanding electronically phase separated manganite thin films

Boosting ferromagnetism in freestanding electronically phase separated manganite thin films

Scalable and environmentally friendly production of perovskite manganite thin films for neuromorphic applications

A method of producing high-quality thin films of perovskite manganites utilizing citrate-based aqueous chemical solution deposition is presented. The method is applied to the production of thin films of gadolinium calcium manganite, Gd1−xCaxMnO3 (GCMO). The film quality is verified by x-ray diffraction analysis, electron microscopy, and magnetic measurements. Finally, planar memristors are fabricated using GCMO films, demonstrating the material’s ability to exhibit resistive switching. This underscores its potential for future memristor technologies.

A study on the kinetic arrest of magnetic phases in nanostructured Nd0.6Sr0.4MnO3 thin films

The Nd0.6Sr0.4MnO3 (NSMO) manganite system exhibits a phase transition from paramagnetic insulating (PMI) to ferromagnetic metallic (FMM) state around its Curie temperature T C = 270 K (bulk). The morphology-driven changes in the kinetically arrested magnetic phases in NSMO thin films with granular and crossed-nano-rod-type morphology are studied. The manganite thin films at low temperatures possess a magnetic glassy state arising from the coexistence of the high-temperature PMI and the low-temperature FMM phases. The extent of kinetic arrest and its relaxation was studied using the ‘cooling and heating in unequal field (CHUF)’ protocol in magnetic and magnetotransport investigations. The sample with rod morphology showed a large extent of phase coexistence compared to the granular sample. Further, with a field-cooling protocol, time-evolution studies were carried out to understand the relaxation of arrested magnetic phases across these morphologically distinct thin films. The results on the devitrification of the arrested magnetic state are interpreted from the point of view of homogeneous and heterogeneous nucleation of the ferromagnetic phase in the paramagnetic matrix with respect to temperature.

Influence of crystallographic orientation on electronic phase separation in manganite thin films

Thin film epitaxy is a powerful method to control the strain and crystallographic orientation of the thin films using epitaxial relationship with the substrate. For colossal magnetoresistive (CMR) manganites thin films, the strong correlation between spin, charge, orbital and lattice degrees of freedom make their physical properties depend sensitively on the choice of substrate. This is especially true when considering the fact that the physical behaviors of manganites are often governed by electronic phase separation (EPS) phenomena, whose physical origin is strongly tied to lattice strain distribution. While many studies have been conducted on the substrate lattice mismatch induced strain effect, research on the substrate crystallographic orientation effect on EPS has received less attention. In this work, using (La2/3Pr1/3)5/8Ca3/8MnO3 (LPCMO) films grown on SrTiO3 (STO) substrate as a protype system, we show that EPS and its associated physical properties are strongly affected by the substrate crystallographic orientations. Specifically, we observed a clear boost of ferromagnetism in (110)-oriented LPCMO thin films with elongated EPS domains. First principles calculations show that the magnetic phase transitions of LPCMO are dominantly influenced by the spin-lattice coupling.

Structural, optical and electrical studies of non-toxic oxide- RMnO3 [R=Y, Er, Yb] hexagonal manganite thin-films

Recently, ferroelectric-photovoltaics have come under the spotlight as a potential class of materials for application in photovoltaic devices. However, the broad bandgap of these ferroelectric-photovoltaic materials causes them to have modest photocurrents[1]. To overcome this challenge hexamanganites can be used to achieve high photovoltaic efficiency as it has a small band gap. Here we present a stable, non-toxic, and cost-efficient hexamanganite RMnO3 [R=Y, Er, Yb] thin films prepared by spray pyrolysis method. The formation of the single phase is confirmed by X-ray diffraction analysis. Morphological studies show grains are uniform and closely packed and the grain size increases with the decrease in ionic radii of rare earth ions. A narrow optical band gap of nearly 1.5 eV is observed for the films. The results of this investigation show that Ultraviolet ray irradiation can be used to tune the bandgap. With a carrier concentration of around 10+14 cm−3, Hall measurements proved that the films are p-type semiconductors. This research illuminates the exploration of stable oxide semiconductors with a small band gap for applications in futuristic solar cells.

Tuning the metal-insulator transition temperature by the controlled generation of oxygen vacancies on La0.7Ca0.3MnO3-x epitaxial thin films

This report presents a study on the effect of the controlled generation of oxygen vacancies on the electronic transport properties of La0.7Ca0.3MnO3-x epitaxial thin films. Oxygen defects cause significant changes in the crystalline structure of mixed-valence manganites and lower the Mn valence, resulting in a shift of the metal-insulator transition to lower temperatures due to modifications in the angles and lengths of Mn-O bonds. Experiments using Polarized Extended X-Ray Absorption Fine Structure Spectroscopy have provided strong evidence that oxygen vacancies are mainly formed in the basal plane of the MnO6 octahedra. The accurate control of oxygen vacancies generation opens possibilities for managing and enhancing the magneto-electronic properties of epitaxial manganite thin films with potential in industrial applications.

Strain-induced phase transition at the surface of epitaxial La0.65Sr0.35MnO3 films

The strong coupling between lattice, electron and spin systems in perovskite manganites along with symmetry breaking at interfaces could lead to inherently different electronic and structural phases at the surface of thin manganite films. To study whether the surface reconstruction can be tuned by epitaxy strain, we employed Surface-Enhanced Raman Spectroscopy (SERS) on La0.65Sr0.35MnO3 (LSMO) thin films epitaxially grown on LaAlO3 substrates. A moderate compressive strain (ε < 1 %) did not change the surface state as compared to that found in unstrained LSMO/MgO(200) films. In contrast, a strong in-plane compressive strain (2 < ε < 3.4 %) stabilizes a novel phase at the surface, characterized by a unique SERS spectrum, which reveals a phase transition at T* = 220 K accompanied by an anomalously strong hardening of the Jahn-Teller mode.

Effects of electric field and light on resistivity switching of Eu0.7Sr0.3MnO3 thin films.

Based on the excellent piezoelectric properties of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) single crystals, a hole-doped manganite film/PMN-PT heterostructure has been constructed to achieve electric-field and light co-control of physical properties. Here, we report the resistivity switching behavior of Eu0.7Sr0.3MnO3/PMN-PT(111) multiferroic heterostructures under different in-plane reading currents, temperatures, light stimuli and electric fields, and discuss the underlying coupling mechanisms of resistivity change. The transition from the electric-field induced lattice strain effect to polarization current effect can be controlled effectively by decreasing the in-plane reading current at room temperature. With the decrease of temperature, the interfacial charge effect dominates over the lattice strain effect due to the reduced charge carrier density. In addition, light stimulus can lead to the delocalization of eg carriers, and thus enhance the lattice strain effect and suppress the interfacial charge effect. This work helps to understand essential physics of magnetoelectric coupling and also provides a potential method to realize energy-efficient multi-field control of manganite thin films.

Polarization-dependent photoinduced metal–insulator transitions in manganites

In correlated oxides, collaborative manipulation on light intensity, wavelength, pulse duration and polarization has yielded many exotic discoveries, such as phase transitions and novel quantum states. In view of potential optoelectronic applications, tailoring long-lived static properties by light-induced effects is highly desirable. So far, the polarization state of light has rarely been reported as a control parameter for this purpose. Here, we report polarization-dependent metal-to-insulator transition (MIT) in phase-separated manganite thin films, introducing a new degree of freedom to control static MIT. Specifically, we observed giant photoinduced resistance jumps with striking features: (1) a single resistance jump occurs upon a linearly polarized light incident with a chosen polarization angle, and a second resistance jump occurs when the polarization angle changes; (2) the amplitude of the second resistance jump depends sensitively on the actual change of the polarization angles. Linear transmittance measurements reveal that the origin of the above phenomena is closely related to the coexistence of anisotropic micro-domains. Our results represent a first step to utilize light polarization as an active knob to manipulate static phase transitions, pointing towards new pathways for nonvolatile optoelectronic devices and sensors.

Enhanced temperature coefficient of resistance in nanostructured Nd0.6Sr0.4MnO3 thin films

Manganite thin films are promising candidates for studying strongly correlated electron systems. Understanding the growth and morphology-driven changes in the physical properties of manganite thin films is vital for their applications in oxitronics. This work reports the morphological, structural, and electrical transport properties of nanostructured Nd0.6Sr0.4MnO3 thin films fabricated using the pulsed laser deposition technique. Scanning electron microscopy imaging of the thin films revealed two prominent surface morphologies: a granular and a crossed-nano-rod-type morphology. From X-ray diffraction and atomic force microscopy analysis, we found that the observed nanostructures resulted from altered growth modes on the terraced substrate surface. Furthermore, investigations on the electrical-transport properties of thin films revealed that the films with crossed-nano-rod morphology showed a sharp resistive transition near the metal-to-insulator transition. Also, an enhanced temperature coefficient of resistance (TCR) of up to one order of magnitude was observed compared to the films with granular morphology. Such enhancement in TCR% by tuning the morphology makes these thin films promising candidates for developing oxide-based temperature sensors and detectors.

Characterization of pristine bismuth manganite thin films deposited on glass substrates by spray pyrolysis technique

The multiferroic Bismuth Manganite (BiMnO3) material which has wide application in memory device. The effect of solute and annealing temperature on spray pyrolyzed pure phase BiMnO3 was studied in detail. The deposited thin films showed the polycrystalline nature with bismuth oxide and manganese oxide impurity phases. The salt considered for the manganese source has effect on obtaining bismuth manganite phase and the annealing temperature has effect on the crystalline nature of the film. The needle like surface morphology was noticed from the deposits. The variation of energy band gap noticed with used solutes and annealing temperature due to change in chemical reaction during deposition and crystallinity respectively. The least energy band gap of 1.81 eV was observed by optimizing the deposition parameters. The blue emission and different defect related peaks are observed in photoluminescence. This work helps in developing prominent material for optoelectronic application.

Temperature dependent transport characteristics of La0.9Sr0.1MnO3 / SrNb0.002Ti0.998O3 device

We report detailed investigations on device functioning capabilities of La0.9Sr0.1MnO3 (LSMO) manganite thin film fabricated on SrNb0.002Ti0.998O3 (SNTO) substrate. The LSMO / SNTO structure has been verified using XRD ϕ–scan measurement. We interpret the device capabilities by investigating the temperature dependent current–voltage (I–V) characteristics. To understand the linearity – nonlinearity nature and temperature effect, current ratio for specific voltages has been identified. Logarithmic scale variation in forward bias current with applied voltages has been studied at different temperatures. For the identification of backward diode behaviour possibility, I–V characteristics at typical temperatures have been studied for forward and reverse currents, simultaneously. The theoretical model fits supporting conduction mechanism in the device understudy has also been investigated for the typical I–V characteristics. The field effect configuration based variation in junction resistance of LSMO / SNTO structure with temperature under applied different junction electric fields and temperature dependent variation in electroresistance (ER) have been recorded to interpret the conduction processes undergoing in the device understudy.

The optical properties of strontium manganite thin films prepared by novel phototreatment technique

SrMnO3 thin films were successfully prepared by spin coating the viscous solution obtained from the autocombustion synthesis. To ensure the transformation of the precursor solution into the manganite phase, conventional thermal treatment and novel phototreatment were applied. The thermal treatment resulted in stable hexagonal SrMnO3, while phototreatment yielded cubic SrMnO3 phase which is usually not stable at ambient conditions. The optical properties of the prepared materials were measured revealing the optical gaps of 1.5 eV for thermally treated material and about 1.3 – 1.4 eV for the phototreated samples. Comparison with ab initio result shows a higher theoretical value of 1.9 eV, ascribed to high exciton binding energy. Since these values are similar to the optical gap (1.48 eV) of widely studied formamidium lead iodide thin films, SrMnO3 thin films are promising candidates for active layers in inorganic perovskite solar cells.

Thermionic emission assisted charge conduction mechanisms across LaMnO3 / La0.7Ca0.3MnO3 interface of manganite thin film structure

In the present communication, temperature dependence of resistive switching (RS) behavior across chemically grown LaMnO3/La0.7Ca0.3MnO3 (LMO/LCMO) interface have been discussed by employing various theoretical approaches and mechanisms. Temperature dependent RS behavior of LMO/LCMO interface highlights impactful switching between high resistance state (HRS) and low resistance state (LRS) under reverse bias mode through an active role of depletion region. Trapping–detrapping processes assisted charge conduction has been identified as a source of RS nature of LMO/LCMO interface. Thermionic emission model and space charge limited conduction (SCLC) mechanism have been employed to understand the charge conduction and charge transport across LMO/LCMO interface. Present structure of Ag/LMO/LCMO/Ag has also been investigated for possible retention and endurance behaviors under different external parameters which verify the stability, reliability, reproducibility, non–volatile nature and applicability of LMO/LCMO interface.

Hierarchically Engineered Manganite Thin Films with a Wide-Temperature-Range Colossal Magnetoresistance Response.

Colossal magnetoresistance is of great fundamental and technological significance in condensed-matter physics, magnetic memory, and sensing technologies. However, its relatively narrow working temperature window is still a severe obstacle for potential applications due to the nature of the material-inherent phase transition. Here, we realized hierarchical La0.7Sr0.3MnO3 thin films with well-defined (001) and (221) crystallographic orientations by combining substrate modification with conventional thin-film deposition. Microscopic investigations into its magnetic transition through electron holography reveal that the hierarchical microstructure significantly broadens the temperature range of the ferromagnetic-paramagnetic transition, which further widens the response temperature range of the macroscopic colossal magnetoresistance under the scheme of the double-exchange mechanism. Therefore, this work puts forward a method to alter the magnetic transition and thus to extend the magnetoresistance working window by nanoengineering, which might be a promising approach also for other phase-transition-related effects in functional oxides.