MnO3 Thin Films Research Articles

Crystalline symmetry controlled magnetic switching in epitaxial (111) La0.7Sr0.3MnO3 thin films

Mixed-valence manganite thin films are attractive for spintronic devices. Crystalline orientation is a promising route to tailor switching mechanisms, as magnetization reversal depends on the magnetic anisotropy. Here, magnetic properties of (111)-oriented La0.7Sr0.3MnO3 thin films are elucidated by correlating macroscopic and local properties. The coercive field is an order of magnitude lower than (001)-oriented La0.7Sr0.3MnO3. Locally, a 6-fold magnetic anisotropy is observed, while macroscopically, an isotropic response is prevailing. This local coupling between the symmetry of the (111)-facet and magnetization governs the domain reversal process, demonstrating that symmetry offers a route to control magnetic properties for spintronic devices.

Reversible oxygen vacancies doping in (La0.7,Sr0.3)MnO3 microbridges by combined self-heating and electromigration

Combination of electric fields and Joule self-heating is used to change the oxygen stoichiometry and promote oxygen vacancy drift in a freestanding (La,Sr)MnO3 thin film microbridge placed in controlled atmosphere. By controlling the local oxygen vacancies concentration, we can reversibly switch our (La,Sr)MnO3-based microbridges from metallic to insulating behavior on timescales lower than 1 s and with small applied voltages (<5 V). The strong temperature gradients given by the microbridge geometry strongly confine the motion of oxygen vacancies, limiting the modified region within the free-standing area. Multiple resistive states can be set by selected current pulses that determine different oxygen vacancies profiles within the device. Qualitative analysis of device operation is also provided with the support of finite element analysis.

Effect of low magnetic fields on the morphology and electrochemical properties of MnO2 films on nickel foams

Nanostructured MnO2 films have been deposited on nickel foams by a hydrothermal synthesis route under a low magnetic field. It was shown that even though the magnetic field was weak (at a level of several millitesla), it induced substantial change in the nanostructures and electrochemical properties of the MnO2 films. The as-prepared MnO2 thin films were largely amorphous and had a spherical superstructure composed of thin nanoflakes. The size of the microspheres decreased and, accordingly, the specific surface area increased with increasing magnetic field’s strength. A probable formation mechanism for the nanostructures of MnO2 was proposed that the weak magnetic field enhanced the nucleation rate, and modified subsequent growth and aggregation processes, which all had a significant influence on the morphology and electrochemical performance of the MnO2 electrodes. The optimal MnO2 electrode synthesized under the low magnetic fields had a specific capacitance of 493.0Fg−1 at 2.0Ag−1 and a retention ratio of 95.6% over 1000 cycles. Therefore, low magnetic fields may be an economic and effective tool in hydrothermal synthesis of MnO2 electrodes for high-performance supercapacitors.

A study of optothermal and AC impedance properties of Cr-doped Mn3O4 sprayed thin films

Chrome-doped Mn3O4 thin films were grown on the glass substrates by the spray pyrolysis technique at 350°C. XRD diffraction and Raman spectroscopy analysis revealed that all samples have tetragonal spinel structure with a preferred orientation along the direction (101). Absorption coefficient has been measured using both transmission and mirage effect. The band gap energy decreases from 2.2 to 1.9eV with Cr content while Urbach energy value increases from 354 to 473meV. Also, thermal conductivity was evaluated. Finally, physical properties have been evaluated and discussed in terms of alteration of the band gap edges, electrical patterns and mirage effect.

Structural, magnetic and magnetodielectric properties of the Mn3O4 thin films epitaxially grown on SrTiO3 (001) substrates

The (001)-orientated Mn3O4 thin films were fabricated on Nb-doped SrTiO3 (001) substrates by a pulsed laser deposition method, and the structural, magnetic, and magnetodielectric properties were investigated. We found that the as-prepared thin film is tetragonal with biaxial compressive strain in the film plane. The orientation relationship in the film plane is Mn3O4 [100] || SrTiO3 [110]. Compared with the single crystals, the paramagnetic–ferrimagnetic transition temperature TN is greatly increased due to the in-plane compressive strain. At TN, a sharp drop in the dielectric constant was observed. Under a magnetic field, the dielectric constant shows a negative field-direction dependent response around TN. Our experiments indicated the strong coupling between the strain, lattice, spin, and orbital degrees of freedom in the epitaxial Mn3O4 thin films.

Effect of thickness variation on the physical properties of La0.85Te0.15MnO3 thin films grown on LaAlO3 (001) by pulsed laser deposition

We report the effect of thickness on the structural, morphological, transport and magnetic properties of perovskite oxide La0.85Te0.15MnO3 thin films grown on LaAlO3 (001) single crystal substrate by pulsed laser deposition. We have observed that the transport and magnetic properties of the films depend on the film thickness, surface morphology, and epitaxial strain. The films were characterized by x-ray diffraction that confirms that the films have good crystalline quality, single phase and c-axis orientation. The Atomic force microscopic (AFM) results show that surface roughness and average grain size increase with film thickness. The resistivity measurements show an insulator to metal transition that correlates well with the magnetic ordering temperature. X-ray photoemission spectroscopy measurements suggests that Te ions are in the Te4+ state, while the Mn ions stay in the Mn2+ and Mn3+ valence states.

Development of nano fiber MnO2 thin film electrode and cyclic voltammetry behavior modeling using artificial neural network for supercapacitor application

This paper deals with the fabrication of MnO2 supercapacitor and modeling of cyclic voltammetery using Artificial Neural Network (ANN). Nano fiber MnO2 (NF-MnO2) films synthesized on stainless steel substrate by adopting potentiodynamic technique from an aqueous manganous sulfate monohydrate (MnSO4·H2O) and surface morphology have characterized using field emission scanning electron microscope (FE-SEM). The electrochemical characterizations have studied with the help of cyclic voltammogram, from which the maximum specific capacitance was estimated to be 392Fg−1. The present investigation further involves modeling of supercapacitor performance using artificial neural network (ANN) approach. The said ANN model based on the multilayer perceptron concept and model is scripted in MATLAB. The Levenberg–Marquart back propagation algorithm (BP) and the sigmoid activation function are used to improve the performance of ANNs. The intelligent model shows the satisfactory performance with the error rate 1.24%, 1.03%, 0.87%, 1.17%, and 1.28% for electrodeposited MnO2 samples.

English

We present the structural, interface, surface morphological and transport characteristics of La0.7Sr0.3MnO3 (LSMO) thin film on Si (001) substrate. X-ray reflectivity of the La0.7Sr0.3MnO3 thin film confirms the presence of silicon oxide at the interface and a dead layer below the LSMO film layer. Reflectivity data also supports the granular growth of La0.7Sr0.3MnO3 islands, causing voids on the La0.7Sr0.3MnO3 film surface as observed from atomic force microscopy studies. From current-voltage measurements, Shottky behaviour is observed for La0.7Sr0.3MnO3 on Si (001) substrate. In comparison to La0.7Sr0.3MnO3 film on Si (001), normal p-n junction behaviour is observed when SnO2 is introduced in between La0.7Sr0.3MnO3 layer and Si (001) substrate. Observed transport properties of La0.7Sr0.3MnO3 on Si are discussed phenomenologically in the presence of intermediate layers.

Improvement in the long-term stability of parameters of encapsulated magnetic field sensors based on La[sbnd]Sr[sbnd]Mn[sbnd]O thin films

The effectiveness of different approaches used for improvement of stability of colossal magnetoresistance-B-scalar magnetic field sensors made from polycrystalline manganite La0.83Sr0.17MnO3 thin films were considered. We show that the ageing process of sensors can be accelerated by annealing the films in Ar atmosphere at 75–125°C and covering them by hot melt adhesive (polyethylene). Ageing kinetics of electrical resistance and magnetoresistance (MR) were investigated as well as the influence of hot melt adhesive. Despite of increased resistance only small changes of the MR and the temperature coefficient of resistance were observed. The obtained results are explained by the oxygen release, displacement or redistribution which takes place most probably in grain boundaries of polycrystalline manganites. Based on the obtained results optimal conditions for the stabilization of encapsulated sensors parameters were found resulting in the resistance drift less than 1.5% per year.

Intriguing photo-control of exchange bias in BiFeO3/La2/3Sr1/3MnO3 thin films on SrTiO3 substrates

To date, electric fields have been widely used to control the magnetic properties of BiFeO3-based antiferromagnet/ferromagnet heterostructures through application of an exchange bias. To extend the applicability of exchange bias, however, an alternative mechanism to electric fields is required. Here, we report the photo-control of exchange bias in BiFeO3/La2/3Sr1/3MnO3 thin films on an SrTiO3 substrate. Through an ex situ pulsed laser deposition technique, we successfully synthesized epitaxial BiFeO3/La2/3Sr1/3MnO3 thin films on SrTiO3 substrates. By measuring magnetoresistance under light illumination, we investigated the effect of light illumination on resistance, exchange bias, and coercive field in BiFeO3/La2/3Sr1/3MnO3 thin films. After illumination of red and blue lights, the exchange bias was sharply reduced compared to that measured in the dark. With increasing light intensity, the exchange bias under red and blue lights initially decreased to zero and then appeared again. It is possible to reasonably explain these behaviors by considering photo-injection from SrTiO3 and the photo-conductivity of La2/3Sr1/3MnO3. This study may provide a fundamental understanding of the mechanism underlying photo-controlled exchange bias, which is significant for the development of new functional spintronic devices.

Effect of epitaxial strain on small-polaron hopping conduction in Pr0.7(Ca0.6Sr0.4)0.3MnO3 thin films

We investigated the epitaxial strain effect on the small-polaron hopping conduction properties in Pr0.7(Ca,Sr)0.3MnO3 (PCSMO) films. An increase in the carrier localization, as evidenced by the enhancement of the small-polaron activation energy EA in the high temperature region, was obtained by increasing the epitaxial lattice strain in either the tensile or compressive strained film. Furthermore, it was found that the magnitude of EA, and thus the carrier localization, strongly depends on the sign of the lattice strain, which explains the diverse percolative transport behaviors in PCSMO films with different types of strains. Meanwhile, similar dependencies on the strain of the films were also obtained for the electron-phonon interaction, characterized by the calculated small-polaron coupling constant. Our results reveal that the type of lattice strain plays a crucial role in determining the degree of localization of charge carriers and the electron-phonon coupling strength, which is important for understanding the lattice strain-induced various novel properties related to phase separation and percolation behaviors.

Flexible all-solid-state MnO2 thin films based symmetric supercapacitors

Flexible energy storage devices gained lot of substantial research interest in the recent decade as their special features and potential applications in different portable electronic devices such as smart sensors, actuators, mobiles, flexible touch screens and electronic newspapers, etc. Therefore, to develop such devices, the flexible electrode and electrolytes with desired mechanical and electrochemical properties are required. In present article, porous nanostructured MnO2 thin films are prepared directly on flexible stainless steel substrate through chemical bath deposition (CBD) method. Further, flexible all-solid-state thin film symmetric supercapacitors (FASSTF-SSCs) have been fabricated using identical MnO2 electrodes with carboxymethyl cellulose- Na2SO4 (CMC-Na2SO4) gel electrolyte. Our results, demonstrate that 0.7μm thick FASSTF cell exhibits specific capacitance of 145Fg−1 with specific energy of 16Whkg−1 and excellent cycling stability after 2500 cycles. In addition, we have presented demonstration of lighting of two light emitting diodes (LEDs) for 135s which finally confirms the potential applicability of MnO2 based solid-state symmetric cells for high-performance flexible energy storage devices.

Tuning the orbital ordering in La0.7Sr0.3MnO3 thin films in all-oxide hybrids

This work presents a systematic characterization including x-ray diffractometry, SQUID magnetometry and x-ray absorption spectroscopy on all-oxide ferromagnetic/ferroelectric heterosystem BaTiO3/La0.7Sr0.3MnO3/SrTiO3(001) fabricated by pulsed-laser deposition. The key aspect of this study is to provide accurate information about differences in electronic and structural properties in LSMO thin films as a function of the oxygen pressure during BTO growth. X-ray absorption spectroscopy experiments at the Mn L3,2 edge have revealed the conservation of mixed valency configuration of the LSMO films near the interface while tuning the oxygen pressure of overlayer BTO growth. The existing ions favor an in-plane eg orbital ordering, reducing the in-plane strain and promoting room temperature ferromagntism in the LSMO film. Furthermore, diffraction experiments showed that the out-of plane lattice parameter of BTO reduces with increasing oxygen pressure consistent with the x-ray linear dichrosim at Ti edge showing less tetragonal symmetry, although the chemical environment of the Ti ions was not changed notably. We demonstrated a way to control magnetic properties and orbital ordering in LSMO thin films while optimizing the ferroelectric properties of BTO overlayer films, which are promising results in terms of magnetoelectric applications using functional heterosystems.

Environmental TEM Study of Electron Beam Induced Electrochemistry of Pr0.64Ca0.36MnO3 Catalysts for Oxygen Evolution

Environmental transmission electron microscopy (ETEM) studies offer great potential for gathering atomic scale information on the electronic state of electrodes in contact with reactants. It also poses big challenges due to the impact of the high energy electron beam. In this article, we present an ETEM study of a Pr0.64Ca0.36MnO3 (PCMO) thin film electrocatalyst for water splitting and oxygen evolution in contact with water vapor. We show by means of off-axis electron holography and electrostatic modeling that the electron beam gives rise to a positive electric sample potential due to secondary electron emission. The value of the electric potential depends on the primary electron flux, the sample’s electric conductivity and grounding, and gas properties. We present evidence that two observed electrochemical reactions are driven by a beam induced electrostatic potential of the order of a volt. The first reaction is an anodic oxidation of oxygen depleted amorphous PCMO which results in recrystallization of the oxide. The second reaction is oxygen evolution which can be detected by the oxidation of a silane additive and formation of SiO2–y at catalytically active surfaces. The quantification of beam induced potentials is an important step for future controlled electrochemical experiments in an ETEM.

Thickness-dependent charge ordering state in Bi0.4Sr0.28Ca0.32MnO3 thin films under the anisotropic strain

We have achieved clear charge ordering (CO) state in Ca doped Bi0.4Sr0.6−xCaxMnO3 (BSCMO) films on (110)-orientated SrTiO3. The BSCMO film's CO transition temperature (TCO) was tuned to room temperature (RT) by optimum doping Ca (x = 0.32). Asymmetric x-ray reciprocal space mapping was used to determine the structure evolution of the films with thickness, in detail, under the anisotropic stress in films. We found that the CO phase only appears in thicker films, accompanied by an unique distortion in structure, in which twin-domains structure occurs with the [110] axis slightly tilting toward [1–10] and [−110] directions. The results demonstrate the effects of anisotropic stress on the structure and electronic phases in BSCMO films as thickness increases. Our works are valuable for allowing a RT study in the CO film and further operation of the devices for a practical use.

Target effects on electrical properties and laser induced voltages of La0.72Ca0.28MnO3 thin films prepared by pulsed laser deposition

La0.72Ca0.28MnO3 thin films were deposited on untilted and 15° tilted LaAlO3 (100) single crystalline substrates by pulsed laser deposition. The polycrystalline targets used in the deposition process were synthesized by sol–gel and coprecipitation methods, respectively. The structure, electrical transport properties and surface morphology of the targets and films were studied. It is found that, compared with coprecipitation method, the sol–gel target has more homogeneous components and larger density and grain size, thus the higher insulator–metal transition temperature and larger temperature coefficient of resistivity. The thin film prepared by sol–gel target has a uniform grain size and higher quality. The metal–insulator transition temperature is higher and the laser induced voltage signal is larger. Preparing the target by sol–gel method can largely improve the properties of corresponding thin films in pulsed laser deposition process.

Synthesis of mesoporous La0.7Sr0.3MnO3 thin films for thermoelectric materials

Mesoporous La0.7Sr0.3MnO3 (LSMO) films were prepared to determine the potential for applications within thermoelectric materials. The mesoporous structure induces a decrease in thermal conductivity due to increased phonon scattering, and an increase in the Seebeck coefficient due to an increased specific surface area. An increase in surface area induces an increase in oxygen vacancies which results in band narrowing and a filled Mn 3d state with the electron-combined oxygen. As a result, the mesoporous LSMO film showed an increased Seebeck coefficient and a reduced thermal conductivity but, in addition, showed a greatly increased electrical resistivity with the filled Mn 3d states. This abnormally large increase in electrical resistivity resulted in a reduced figure of merit for the LSMO film even after the introduction of a mesoporous structure. An effect of the applied mesoporous structure on the thermoelectric properties was shown to be varied due to a change in the amount of oxygen defects in the LSMO with a perovskite structure.

Highly orientated growth and characterization of La0.7Sr0.3MnO3 thin films with different orientations on SrTiO3 substrates by chemical solution deposition method

La0.7Sr0.3MnO3 (LSMO) thin films were successfully prepared on (100), (110), and (111) oriented SrTiO3 substrates by chemical solution deposition method. The structural, magnetic, and magnetotransport properties were systematically studied. X-ray diffraction θ-2θ and ϕ-scan measurements results show that all the films have perfect crystalline orientation and in-plane alignment. Both the Curie temperature and metal-insulator transition temperature are almost the same for all the three orientations, about 339 K. The magnetoresistance value (MR value, defined as (RM − R0)/R0 × 100%, where RM and R0 are the resistivity with and without applied magnetic field) for the films reaches maximum near the Curie temperature. Both the magnetization and MR value for (100) direction LSMO are the largest, and meanwhile for (111) direction are the smallest. The saturation magnetization decreases approximately proportional to T2 at low temperature (T < Tc/2) for all the oriented film. Inversely, the resistivity increases proportional to T2 in the same temperature range, which can be attributed to the electron-electron scattering.

Strain modulated large magnetocaloric effect in Sm0.55Sr0.45MnO3 epitaxial films

Epitaxial Sm0.55Sr0.45MnO3 thin films were deposited on LAO (001), LSAT (001), and STO (001) single crystalline substrates by pulsed laser deposition technique to investigate the correlation between the substrate induced film lattice strain and magnetocaloric effect (MCE). The film on LAO substrate (S_LAO), which is under compressive strain, undergoes ferromagnetic → paramagnetic transition at TC ∼ 165 K. The films on STO (S_STO) and LSAT (S_LSAT) substrates are under tensile strain and have TC ∼ 120 K and 130 K, respectively. At T < TC, the zero field cooled and field cooled magnetization curves of all the films show huge bifurcation. In case of S_STO and S_LSAT films, hysteresis is also observed between field cooled cooling and warming cycle in magnetization versus temperature measurement at low magnetic field similar to first order-like magnetic phase transition. No signature of first order magnetic phase transition has been observed in the case of S_LAO film. Most interestingly, both normal (i.e., negative ΔSM) and inverse (i.e., positive ΔSM) MCE around TC and above Tp, respectively, for S_STO and S_LSAT films have been observed with maximum value of MCE ∼ 10 J kg−1 K−1. The S_STO film also exhibits a large relative cooling power of 142 J/kg for a magnetic field change of 1 T. Our findings of substrate-induced strain modulated large MCE in epitaxial Sm0.55Sr0.45MnO3 films have been well explained through the substrate induced film lattice strain, and it may be useful for active magnetic refrigerant materials.

Liquid flow deposited spinel (Ni,Mn)3O4 thin films for microbolometer applications

A liquid flow deposition (LFD) technique was initially used for the fabrication of single-component Mn3O4 thin films onto Si wafer substrates at a range of substrate temperatures of 30–80°C, with the introduction of an oxidizing reagent (H2O2). As a result, solid thin films were well formed from an aqueous solution. An X-ray diffraction (XRD) analysis showed typical characteristics of hausmannite Mn3O4 with a spinel tetragonal phase. Field-emission scanning electron microscopy (FE-SEM) observations revealed nano-sized grains arranged uniformly on a dense and smooth surface for all of the as-deposited films. On the other hand, the LFD method was then extended to prepare two-component nickel–manganite films according to the binary chemical composition of NixMn3−xO4 with x=0.02–0.2. The as-grown nickel–manganite films showed a surface with a good quality with a spherical bead-like architecture when x≤0.10, while a conversion from spherical grains into highly porous nanowalls in the microstructure was noted in films when x≥0.12. These results signify that it is possible to fabricate various multi-component manganite-oxide thin films at a low temperature. In addition, the dependences of the room-temperature electrical resistivity (ρ) and the temperature coefficient of resistance (TCR) on the Ni substitution level (x) were investigated on films annealed at 400°C.