MnO3 Films Research Articles

Rapid Color-Switching of MnO2 Hollow-Nanosphere Films in Dynamic Water Vapor for Reversible Optical Encryption.

Drop-casting manganese oxide (MnO2 ) hollow nanospheres synthesized via a simple surface-initiated redox route produces thin films exhibiting angle-independent structural colors. The colors can rapidly change in response to high-humidity dynamic water vapor (relative humidity > 90%) with excellent reversibility. When the film is triggered by dynamic water vapor with a relative humidity of ≈100%, the color changes with an optimal wavelength redshift of ≈60nm at ≈600ms while there is no shift under static water vapor. The unique selective response originates from the nanoscale porosity formed in the shells by randomly stacked MnO2 nanosheets, which enhances the capillary condensation of dynamic water vapor and promotes the change of their effective refractive index for rapid color switching. The repeated color-switching tests over 100 times confirm the durability and reversibility of the MnO2 film. The potential of these films for applications in anti-counterfeiting and information encryption is further demonstrated by reversible encoding and decoding initiated exclusively by exposure to human breath.

Bending Modulated Ultralarge Magnetoresistance in Flexible La0.67Ba0.33MnO3 Thin Film Based Device.

Magnetoresistance based information devices have attracted much attention due to the ability to utilize spins as information carriers. To promote the magnetoresistance-based devices, ultrahigh magnetoresistance ratios are highly desirable for magnetic sensing, memory, and artificial intelligent devices, etc. However, today the magnetoresistance devices are facing the challenge of limited magnetoresistance ratio, low work temperature, or high magnetic field, which calls for proper theories and mechanisms. To address it, we first introduce the flexible bending-controlled magnetoresistance device based on the La0.67Ba0.33MnO3 film. Due to the anisotropic resistance of the La0.67Ba0.33MnO3 film and the nonlinear amplification effect of the Zener diode, the device has exhibited strong magnetoresistive performance (∼8725% at 1 T, 300 K). Combining the assist from mechanical bending and diode, high magnetic field sensitivity with large magnetoresistance ratio (∼1.7 × 104% at 1 T, 300 K) and low work current (∼0.15 mA) is simultaneously achieved at room temperature, which is over 104 times larger than that of the planar La0.67Ba0.33MnO3 film. Based on the above results, we propose one but not the only possible application as tunable multistage switch. Our findings may pave a strategy to develop flexible diode-enhanced magnetoresistance device with ultrahigh magnetoresistance ratios and bending tunable performances.

Current modulations of the metal-insulator phase transition in epitaxial thin films of Pr0.7Sr0.3MnO3

Pr[Formula: see text]Sr[Formula: see text]MnO3 thin films were grown epitaxially on SrTiO3 and LaAlO3 substrates by pulse laser deposition. X-ray diffraction spectra obtained on these films revealed good crystallinity and epitaxy. It was found that the oxygen deficiency and in-plane strain may affect the transport behavior and phase transition near Curie temperature in these Pr[Formula: see text]Sr[Formula: see text]MnO3 films. Also, the resistance and metal-insulator phase transition could be modulated significantly by the applied electric currents. The reduction ratio of the peak resistance reached −38% for a bias current [Formula: see text]A, demonstrating a remarkable electroresistance effect. The results are interpreted based on the spatial inhomogeneity related to the coexisted multi-phases with different electronic and magnetic properties.

Mid-infrared optical response to magnetic field in the La0.65Ba0.35MnO3 film grown by PLD

Optical and magneto-optical properties of the La0.65Ba0.35MnO3/SrTiO3(001) thin film with CMR and the paramagnetic-to-ferromagnetic transition at T = 310 K have been investigated in the infrared spectral range. It is shown that magnetotransmission and magnetoreflection of unpolarized light in the film reach up to 10 % at the magnetic field of 4kOe. The possible physical mechanisms responsible for negative magnetotransmission and positive magnetoreflection in the mid-infrared range are interpreted in the framework of the theory of magnetorefractive effect in manganites. High optical response of the La0.65Ba0.35MnO3 film to an external magnetic field (up to ∼ 25 %/kOe in the magnetoreflection) could be used in the design of optical magnetic field sensor, switches and modulators.

The transport properties and large magnetoresistance effect in Pr0.7Sr0.3MnO3 film on SrTiO3

The transport properties and large magnetoresistance effect in Pr0.7Sr0.3MnO3 film on SrTiO3

La0.7Na0.3−xKxMnO3 (x = 0.2): A thermistor film that exhibits high-sensitivity at room temperature

A high-sensitivity thermistor La0.7Na0.3−xKxMnO3 (x = 0.2) film with a perovskite structure was fabricated and studied. The results show that the film displayed excellent adaptation and clear interfaces with the SrTiO3 substrate. Under the combination of Jahn–Teller effect and double exchange mechanism, the temperature coefficient of resistivity (TCR) of the La0.7Na0.1K0.2MnO3 film reached 10.86% K−1 at 296.98 K. Compared with the conventional VO2 and nickel–manganite-based film materials, the La0.7Na0.1K0.2MnO3 film with high TCR values at room temperature exhibited tunable metal–insulation transition temperature and more sensitive thermal properties. Consequently, the La0.7Na0.1K0.2MnO3 film can substantially improve the detection sensitivity of uncooled infrared bolometers as thermistor materials.

MnO2 Films deposited on CuO nanomaterials as electrode materials for supercapacitors

In this paper, CuO/MnO2 composites with different morphology were successfully fabricated by simple and economical electrodeposition and successive ionic layer adsorption and reaction (SILAR) method as electrode materials for supercapacitors (SCs). The spherical and wheat-shaped CuO/MnO2 composites were obtained by changing the deposition voltage. The wheat-shaped CuO/MnO2 composite electrodes exhibited better electrochemical performance than the spherical. Its areal capacitance is up to 261.4 mF/cm2 at a current density of 1 mA/cm2 in 1 M Na2SO4 electrolyte and the capacitance retention reaches 90% after 1000 charge-discharge cycles. The symmetric aqueous SCs was then assembled with wheat-shaped CuO/MnO2 as positive and negative electrode materials respectively. The SCs exhibited not only outstanding specific capacitance of 152.7 mF/cm2 at 1 mA/cm2, but also good cycling stability of 74.2% after 500 charge-discharge cycles. Furthermore, its operating voltage window reaches 1.6 V, which results in an outstanding energy density of 54.3 μWh/cm2 and a power density of 5040 μW/cm2. This strategy of changing the morphology of materials by changing the deposition voltage provides an ideal scheme for improving the properties.

Enhanced magnetoresistance and electroresistance at high temperature in a nano-matrix manganite

Magnetoresistance (MR) is highly exploitable to future spintronics devices, such as random-access memory, magnetic sensors, and spin-based neuromorphic electronics. Conventionally the enhanced MR in manganite always companies a sacrifice of Curie temperature, which limits its widespread application potential. Here we report a high-temperature survived MR in a La0.67Sr0.33MnO3 (LSMO) film grown on a piezoelectric substrate. The lattice mismatch between the film and substrate creates a self-assembled nano-matrix with two types of nanoscale matrices, namely [001]- and [101]-orientated LSMO magnetic domains. In this structure, the MR can reach -67% at even 350 K. Furthermore, the resistance of LSMO is electric-field-tunable to multiple resistance states by electrically modulating the biaxial strain imposed by the underlying piezoelectric substrate, an additional ∼14.2% electroresistance (ER) can be obtained. The achievements of high-temperature substantial MR and its electrical tunability in the nano-matrix manganite are of use to future multi-state memory devices in both spintronics and straintronics.

Core-level binding energy shifts between interior, terrace and edge atoms in MnO(001) thin films

Understanding the physical origin of core-level photoemission line shapes can offer valuable information about the chemical and physical properties of surfaces. For instance, in a large number of transition metals oxides, changes in the line shape allow the accurate determination of their oxidation states and cation site symmetry. Yet, despite this importance, experimental investigations on core-level shifts have been much neglected in recent years. In order to provide further evidence of the physical relevance, we have, in this contribution, introduced a new aspect of interior-, terrace- and edge- atom core-level binding energy shifts to describe monolayers of MnO(001) films grown on an Au(111) substrate. By this means we were able to distinguish the line shape contributions related to different types of atomic sites. We show that their relative intensities and energy shifts are able to provide information about the relative amount of under coordinated atoms on the surface and, thus give insights into their catalytic properties. Our findings reveal the importance of a detailed surface science characterization to provide the correct interpretation of distinct photoemission line shapes when considering thin film samples as well as nanostructures in general.

Sensitive electric field control of first-order phase transition in epitaxial multiferroic heterostructures

Strongly correlated electron materials that exhibit rich phase transition and multiple phase separation have shown many fascinating properties. Using these properties in the electronic device will require the ability to control their phase transition and phase separation behaviours. In this work, we report a sensitive electric field control of first-order phase transition in epitaxial (011)-Nd0.5Sr0.5MnO3/0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 (PMN-PT) heterostructure. The pristine film shows phase separation character with the penetration of the ferromagnetic metallic phase into the charge and orbital ordered antiferromagnetic insulating phase, and this was revealed by the XMCD and XLD investigation. The (011)-oriented PMN-PT piezoelectric single crystal adopted can exert anisotropic in-plane tensile strains on the epitaxial Nd0.5Sr0.5MnO3 film when applying the electric field. The coaction of the electric field-induced strain and polarization effects of the PMN-PT piezoelectrics enable the efficient manipulation of orbital ordering and the coupled electronic and magnetic phase transitions. Accordingly, a small +1.6 kV cm−1 electric field can recover the first-order metal-insulator transition which was inhibited in the pristine heterostructure, increase the transition temperature by 56 K and the maximum resistance change reaches 7033%. Furthermore, the electric field demonstrated non-volatile control of magnetization, and the magnetoelectric coefficient reaches 1.89 × 10−7 s m−1 at 200 K. This work indicates that choosing the piezoelectric substrate with appropriate electric-field-induced strain opens a route to designing functional electronic devices where the tunable macroscopic properties derive from strongly interacting degrees of freedom present in the manganite.

Self-Powered Resistance-Switching Properties of Pr0.7Ca0.3MnO3 Film Driven by Triboelectric Nanogenerator.

As one of the promising non-volatile memories (NVMs), resistive random access memory (RRAM) has attracted extensive attention. Conventional RRAM is deeply dependent on external power to induce resistance-switching, which restricts its applications. In this work, we have developed a self-powered RRAM that consists of a Pr0.7Ca0.3MnO3 (PCMO) film and a triboelectric nanogenerator (TENG). With a traditional power supply, the resistance switch ratio achieves the highest switching ratio reported so far, 9 × 107. By converting the mechanical energy harvested by a TENG into electrical energy to power the PCMO film, we demonstrate self-powered resistance-switching induced by mechanical movement. The prepared PCMO shows excellent performance of resistance switching driven by the TENG, and the resistance switch ratio is up to 2 × 105, which is higher than the ones ever reported. In addition, it can monitor real-time mechanical changes and has a good response to the electrical signals of different waveforms. This self-powered resistance switching can be induced by random movements based on the TENG. It has potential applications in the fields of self-powered sensors and human-machine interaction.

Asymmetric ground states in La0.67Sr0.33MnO3/BaTiO3 heterostructures induced by flexoelectric bending

Misfit strain delivered from single-crystal substrates typically modifies the ground states of transition metal oxides, generating increasing interest in designing modern transducers and sensors. Here, we demonstrate that magnetotransport properties of La0.67Sr0.33MnO3 (LSMO) films were continuously tuned by uniaxial strain produced by a home-designed bending jig. The electrical conductivity and Curie temperature of LSMO films are enhanced by bending stresses. The resistivity of u-shape bended LSMO decays three times faster than that of n-shape bended LSMO as a response to the same magnitude of strain. The asymmetric magnetic states in uniaxially strained LSMO are attributed to the dual actions of Jahn–Teller distortion and strain gradient mediated flexoelectric fields in an adjacent ferroelectric layer. These findings of multi-field regulation in a single material provide a feasible means for developing flexible electronic and spintronic devices.

Binder-less fabrication, some surface studies, and enhanced electrochemical performance of Co, Cu-embedded MnO2 thin film electrodes for supercapacitor application

We report the fabrication of nanocystalline MnO2 thin film-based electrode on a predeposited indium tin oxide (ITO) film on the glass substrate, using a binderless and simple two-electrode electrofabrication approach. Effects of Co and Cu incorporation on microstructural and electrochemical performance of the electrode were optimally and extensively investigated. The experimental results for the optimum fabrication conditions for Co@MnO2 and Cu@MnO2 and pure MnO2 thin film-based electrode samples showed uniqueness in microstructural features, degrees of crystallinity and roughness, and high electrochemical energy storage performance. Co@MnO2 film electrode exhibited remarkable specific capacitance (1068 Fg-1) and areal capacity (25.78 mAh cm−2) as against other electrode films (Cu@MnO2 and pure MnO2) which exhibited specific capacitances 837 and 438 F g−1 and areal capacities 10.6 and 4.9 mAh cm−2, respectively. Exceptional stabilities were also recorded for the composite samples (87.2% and 84.4% for Cu@MnO2 and Co@MnO2 thin film electrodes, respectively) against the pure MnO2 film electrode sample (77.8%), after 2000 cycles. In addition, the short time constants (1.27 s and 1.31 s) were respectively realized for the fabricated Co@MnO2 and Cu@MnO2 electrode films as against the pure MnO2 electrodes (4.35 s). These features observed in the composite electrode samples demonstrated an exhibition of faster ion response and higher rate capability by the samples. Moreover, the incorporation of Co into the MnO2 electrode material relatively improved the supercapacitive activeness by enhancing the charge transition and transport.

High-performance complementary electrochromic energy storage device based on tungsten trioxide and manganese dioxide films

In this work, we have selected a representative pseudocapacitive material of manganese dioxide (MnO2) film as the complementing electrode of tungsten trioxide (WO3) film to construct a smart electrochromic energy storage device (EESD), with the aim to simultaneously provide the optical modulation and energy storage performance. WO3 and MnO2 films have been respectively synthesized via simple hydrothermal and electrodeposition methods to achieve desirable matched performance. For the constructed EESD, an obvious optical contrast (38.63% at 633 nm), fast switching times (tb/tc = 9.37/5.19 s), high coloration efficiency (85.36 cm2·C−1), satisfactory specific capacitance (10.69 mF·cm−2 at the discharge current density of 0.1 mA·cm−2) as well as excellent cycle stability (initial capacitance retention rate of 95.90% after 1000 charge/discharge cycles) have been derived. After charging, the obtained EESD could light up an LED bulb or an LCD screen, showing high promising application prospect in energy storage.

CTAB controlled electrochemical deposition of manganese dioxide with enhanced performance in aqueous Zn-ion battery

The collapse and dissolution of the structure of the MnO2 positive electrode in the cycle process is mainly caused by the volume expansion during the phase transition process, which leads to the extrusion of the adjacent parts of the electrode and poor cycle performance. To overcome this issue, morphology of MnO2 films were controlled by adding various concentrations of surfactant Hexadecyl trimethyl ammonium Bromide (CTAB) in the electrolytic cell through changing the current distribution characteristics between substrate and solution. The obtained MnO2 nanofilm materials prepared with different concentrations of surfactant were compared from the aspects of surface morphology, specific capacity and cyclic stability. The morphology and structure of the prepared MnO2 were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer Emmett and Teller (BET). As expected, MnO2 with its unique crystal structure exhibited excellent cycling and superior performance (311.2 mAh g−1 at 0.1 A g−1, 177.6 mAh g−1 at 5 A g−1, 125% capacity retention after 4000 cycles at 5 A g−1). This capacity retention was among the highest reported so far for MnO2-based cathode materials for Zn-ion batteries. The excellent electrochemical performance may be due to its unique nanostructure, which provides enough space for the volume expansion and proper structure for the re-deposition of MnO2. This work provides an new sight to develop long-circulation MnO2 electrodes for aqueous Zn ion batteries by designing an advantageous master structure dynamics.

Anomalous anisotropic spin-wave propagation in thin manganite films with uniaxial magnetic anisotropy

Manipulation of the spin-wave coherent length is highly desirable to overcome intrinsic damping and to improve functionalities of magnonics materials and devices. In this work, based on angle-resolved propagating spin-wave spectroscopy and micro-focused Brillouin light scattering, we report a giant anisotropy of spin wave propagation in a 20 nm-thick La0.67Sr0.33MnO3 film grown on a NdGaO3 substrate. Vanishing of such anisotropic features in reference experiments where the La0.67Sr0.33MnO3 film is grown on SrTiO3 suggests that the anisotropic spin-wave propagation might be originated from different lattice mismatches of the LSMO film with these two substrates. Interestingly, the decay length and the relaxation time of spin waves are found to be largest when the wavevector is along the [110] crystalline orientation, which is neither at easy nor hard axis related to the in-plane uniaxial magnetic anisotropy. This suggests the possibility of individual control of the magnetic anisotropy and spin-wave anisotropy via strain engineering. Our discovery may enrich the material systems for anisotropic spin wave behavior and promote strain engineering and optimization of versatile magnonic devices.

Trade-off between areal capacitance and optical transmittance of highly transparent MnO2 electrodes for supercapacitors

In this study, the capacitive performance of ultrathin-film manganese oxide (MnO2) electrodes for transparent supercapacitors is investigated. The highest transmittance reported so far, 99.1% at a 550 nm wavelength, is achieved with an areal capacitance of 1.6 mF/cm2. The thickness and resulting optical transparency of the MnO2 films can easily be controlled by changing the concentration of the precursor sols in the sol–gel-derived coating process. The thinnest electrode shows the highest transmittance and specific capacitance of 576 F/g. The relationship between the transmittance, optical conductivity and areal capacitance of the electrodes is also investigated. The largest capacitive figure of merits, FoMc, of 62.7 cm2/F is obtained for the thinnest electrode. Deconvolution of the capacitive elements indicates that the surface capacitive element is dominant for the ultrathin electrodes, whereas the contribution of the diffusion-controlled insertion element grows rapidly as the electrode thickness increases.

Optimization of temperature coefficient of resistivity of La0.7Ca0.2-xSrxK0.1MnO3 films by Sr at room-temperature

Optimization of temperature coefficient of resistivity of La0.7Ca0.2-xSrxK0.1MnO3 films by Sr at room-temperature

Linearly shifting ferromagnetic resonance response of La0.7Sr0.3MnO3 thin film for body temperature sensors.

Human body temperature not only reflects vital signs, but also affects the state of various organs through blood circulation, and even affects lifespan. Here a wireless body temperature detection scheme was presented that the temperature was extracted by investigating the out-of-plane (OP) ferromagnetic resonance (FMR) field of 10.2 nm thick La0.7Sr0.3MnO3 (LSMO) film using electron paramagnetic resonance (EPR) technique. Within the range of 34–42 °C, the OP FMR field changes linearly with the increasing or decreasing temperature, and this variation comes from the linear responses of magnetization to the fluctuant temperature. Using this method, a tiny temperature change (< 0.1 °C) of organisms can be detected accurately and sensitively, which shows great potential in body temperature monitoring for humans and mammals.

Angle-dependent AC susceptibility, low-field magnetoresistance and switching behaviour of La0.66Sr0.34MnO3/YSZ(001) films

The La0.66Sr0.34MnO3 (LSMO) films with thickness 200–330 nm have been grown at 750 °C on lattice-mismatched (001)-plane oriented yttria-stabilized zirconia (YSZ) using radio frequency magnetron sputtering technique. The films demonstrated columnar growth structure characterized by coexistance of grains with the averaged diameter of about 50 nm and well defined crystallographic orientations of a pseudocubic LSMO lattice, namely, (001)LSMO[110]//(001)YSZ[100] and (110)LSMO[110;100]//(100)YSZ[100]. Alternating current (AC) magnetic susceptibility, χ(H) ∼ dM/dH, and magnetoresistance, MR(H), of the films were measured at 78 and 295 K with DC magnetic field (H) applied either in-plane or out-of-plane. Unusually sharp peaks at H = ±HSW and clearly defined switching behaviour have been indicated at 78 K in both the χ(H) and MR(H) plots. The HSW values were found to increase with the out-of-plane angle, α, according to the relationship HSW = HSW0/cosα (HSW0 = 4.0 and 1.4 kA/m at 78 and 295 K, respectively) while negligible variation of HSW has been indicated by varying direction of H in a film plane. The investigations revealed close correlation between χ(H) and low-field magnetoresistance. The observed angle-dependent peak-like χ(H) anomalies have been explained assuming magnetization reversal of the multigrain films governed by interparticle interaction and pinning of magnetic domains at grain boundaries. Unusual pit-like anomaly of the transverse biased susceptibility (TS) indicated at H = ±HSW has been explained in a framework of the TS theory developed for isolated uniaxal ferromagnetic particles assuming coexistance of grains with several fixed easy axis orientations in a film plane.