MnO3 Thin Films Research Articles

Strain-Induced Domain Structure and Its Impact on Magnetic and Transport Properties of Gd0.6Ca0.4MnO3 Thin Films.

The evolution of lattice strain on crystallographic domain structures and magnetic properties of epitaxial low-bandwidth manganite Gd0.6Ca0.4MnO3 (GCMO) films have been studied with films on different substrates: SrTiO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, SrLaAlO3, and MgO. The X-ray diffraction data reveals that all of the films, except the films on MgO, are epitaxial and have an orthorhombic structure. Cross-sectional transmission electron microscopy (TEM) shows lattice mismatch-dependent microstructural defects. Large-enough tensile strain can increase oxygen vacancies concentration near the interface and can induce vacancies in the substrate. In addition, a second phase was observed in the films with tensile strain. However, compressive strain causes dislocations in the interface and a mosaic domain structure. On the other hand, the magnetic properties of the films, including saturation magnetization, coercive field, and transport property depend systematically on the substrate-induced strain. Based on these results, the choice of appropriate substrate is an important key to obtaining high-quality GCMO film, which can affect the functionality of potential device applications.

Colossal crystalline anisotropic magnetoresistance in A-type antiferromagnetic film

A colossal crystalline anisotropic magnetoresistance (CAMR) is observed in an epitaxial A-type antiferromagnetic Pr0.5Sr0.5MnO3 (PSMO) thin film, which is 1600% at 20 K under the magnetic field of 50 kOe. This colossal CAMR is associated with an anisotropic switching process between low and high resistivity states. Based on the symmetry of angular dependence of the CAMR, we attribute the origin to the strong anisotropic magnetostriction in PSMO. Our results explored a potential utilization of an A-type antiferromagnetic thin film for CAMR based spintronic devices.

Unraveling hausmannite (Mn3O4) thin films surface structure by X ray linear dichroism

There is an urgent need to understand the relationship between oxide thin-film surface plane and its electronic properties because of its key role in molecular adsorption and surface reactivity as requested in optimal applications of magnetism to catalysis. The present work intends to resolve this open issue by investigating the surface structure and electronic properties of Mn3O4 thin films. To this end, well-defined Mn3O4 (110) and (001) surfaces were prepared and their electronic properties were explored by X-ray linear dichroism, XLD (the search light effect). The Mn3O4 thin films were extensively prepared on distinct noble metal substrates (Au(111), Cu (111), Ag (001)) with the aim of disentangling the film’s electronic structure and their corresponding film strain from their free surface, bulk, and interface contribution. Our experiments revealed the sensitivity of the 3d orbital occupancy and their intensity ratio (dx2−y2/d3z2−r2) to the surface orientation. The variation of relative 3d occupation as a function of strain was quantified by using the XLD sum rules. These results reveal important aspects for the identification and further engineering of well-defined crystallographic surfaces in several fields of applications.

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.

Electro−Photo Double Control of Resistive Switching in Electron‐Doped La0.9Hf0.1MnO3 Films

Electron‐doped La0.9Hf0.1MnO3 thin films are epitaxially integrated onto 0.7Pb(Mg1/3Nb2/3)O3−0.3PbTiO3 single‐crystalline ferroelectric substrates to construct multiferroic heterostructures. By applying a light field and not just changing temperature, the relative magnitude of the electric‐field‐generated lattice strain effect and interfacial charge effect is identified to be controllable. Moreover, the electric field can enhance the photoresistance effect by 26%. This, accompanied by light‐tunable electroresistance effect, intimate interaction between the electric‐field‐generated and light‐generated effects is demonstrated. Herein, a route to achieve low‐power multifield (light and electric field) control of electronic transport in electron‐doped perovskite manganites is provided.

An investigation of chemical and electrochemical conversion of SILAR grown Mn3O4 into MnO2 thin films

Manganese oxide is an interesting material for electrochemical properties. It is well known that Mn3O4 (spinel) can be electrochemically converted to MnO2 (birnessite) via the electrochemical route during cyclic voltammetry (CV) cycling in aqueous Na2SO4 solution. Herein, the novel way is represented for the growth of highly adherent and compact Mn3O4 thin films by using successive ionic layer adsorption and reaction (SILAR) method. As grown Mn3O4 thin films are converted into MnO2 after chemical treatment by hydrochloric acid (HCl) via a disproportionate reaction. Mn3O4 thin films are converted into MnO2 by both chemical and electrochemical paths. During chemical conversion, at acidic pH, the crystal water insertion (H3O+) in Mn3O4 crystal provides the necessary driving force to transform it into MnO2 crystal. During electrochemical transformation, the specific capacitance was found to increase from 72 (1st CV cycle) to 393 F/g (1600th CV cycle). On the other hand, the specific capacitance was increased from 72 to 258 F/g through chemical transformation. Electrochemical and chemical conversion leads to ~5.5 and ~3.5 fold, respectively, improved supercapacitive performance than pristine Mn3O4 thin films. Both chemical and electrochemical conversion routes are extremely useful to recycle battery waste for supercapacitor applications.

The structural, optical, and self-cleaning properties of Mn3O4/SnO2 Multilayer Thin Films, deposited via Spray Pyrolysis Technique

Due to the wide applications of self-cleaning surfaces in various industries such as textile, automotive, construction, agriculture, optics, marine and aerospace industries, the development of self-cleaning coating production methods in a simple and inexpensive way has been considered by researchers. In this paper, Tin oxide (SnO2) and Manganese (II, III) oxide (Mn3O4) were prepared via sol–gel procedure. Next, (Mn3O4/ SnO2) double-layers were deposited using spray pyrolysis system on glass substrates. According to AFM images of Mn3O4 thin films, grains are tightly packed, entirely compressed and without crack. AFM images of SnO2 films indicated that the width of grain was about 242.8 nm and RMS roughness was about 25.85 mm. These images for bilayer demonstrated that the grain width was about 130-220 nm and root-mean-square thickness was about 20 mm. The SnO2 and Mn3O4 films, and SnO2/Mn3O4 bilayer showed a direct optical band gap and hydrophilicity with water contact angle of 75◦, 31◦, and 70◦ respectively. Due to the importance and various applications of hydrophilic surfaces, in this research, thin layers of metal oxide were produced in a very simple way, among which the thin layer of Mn3O4 has good hydrophilicity.

The effect of stress on the magnetic properties of sol–gel-derived Pr0.9Ca0.1MnO3 thin films

The effect of stress on the magnetic properties of sol–gel-derived Pr0.9Ca0.1MnO3 thin films

Vertical strain tuning and perpendicular magnetic anisotropy in La0.5Ca0.5MnO3 vertically aligned nanostructured thin films by the application of high magnetic fields

Epitaxial La0.5Ca0.5MnO3 (LCMO) thin films with vertically aligned nanostructures (VANs) have been achieved with the application of high magnetic fields in pulsed laser deposition processing. More interestingly, the microstructures, vertical strain, and perpendicular magnetic anisotropy (PMA) in the LCMO VAN films can be systematically manipulated by changing the applied high magnetic field strength. With increasing the high magnetic field, an increase in growth rate and a decrease in nanocolumn dimension are observed in the LCMO VAN films, which can be attributed to the enhanced suppression effect on adatom mobility and surface diffusion. Different from the LCMO planar-structured films, the intrinsic stress behaviors associated with vertical interfaces and grain boundaries instead of substrate strain in the LCMO VAN films are dominant in vertical strain evolution, indicating an out-of-plane compressive state, which is highly correlated with the growth rate and nanocolumn dimension. A core-shell model based on phase separation is proposed to understand the nanoscale size effect on magnetic properties in the LCMO VAN films. A tunable and enhanced PMA effect in the LCMO VAN films is also demonstrated. The results suggest that the application of a high magnetic field in pulsed laser deposition processing is a practicable route to achieve tunable VANs, and manipulate physical properties in manganite films.

Double-Site Substitution of Ce into (Ba, Sr)MnO3 Perovskites for Solar Thermochemical Hydrogen Production

Solar thermochemical hydrogen production (STCH) is a renewable alternative to hydrogen produced using fossil fuels. While serial bulk experimental methods can accurately measure STCH performance, screening chemically complex materials systems for new promising candidates is more challenging. Here we identify double-site Ce-substituted (Ba,Sr)MnO3 oxide perovskites as promising STCH candidates using a combination of bulk synthesis and high-throughput thin film experiments. The Ce substitution on the B-site in 10H-BaMnO3 and on the A-site in 4P-SrMnO3 lead to 2-3x higher hydrogen production compared to CeO2, but these bulk single-site substituted perovskites suffer from incomplete reoxidation. Double-site Ce substitution on both A- and B-site in (Ba,Sr)MnO3 thin films increases Ce solubility and extends the stability of 10H and 4P structures, which is promising for their thermochemical reversibility. This study demonstrates a high-throughput experimental method for screening complex oxide materials for STCH applications.

The role of etching anisotropy in the fabrication of freestanding oxide microstructures on SrTiO3(100), SrTiO3(110), and SrTiO3(111) substrates

The release process for the fabrication of freestanding oxide microstructures relies on appropriate, controllable, and repeatable wet etching procedures. SrTiO3 (STO) is among the most employed substrates for oxide thin films growth and can be decomposed in HF:water solution. Such a process is strongly anisotropic and is affected by local defects and substrate cut-planes. We analyze the etching behavior of SrTiO3 substrates having (100), (110), and (111) cut-planes during immersion in a 5% HF:water solution. The etching process over the three substrates is compared in terms of pitting, anisotropy, macroscopic etch rate, and underetching effects around HF-resistant (La,Sr)MnO3 thin film micropatterns. The release of targeted structures, such as the reported (La,Sr)MnO3 freestanding microbridges, depends on the substrate crystallographic symmetry and on the in-plane orientation of the structures themselves along the planar directions. By comparing the etching evolution at two different length scales, we distinguish two regimes for the propagation of the etching front: an intrinsic one, owing to a specific lattice direction, and a macroscopic one, resulting from the mixing of different etching fronts. We report the morphologies of the etched SrTiO3 surfaces and the geometries of the underetched regions as well as of the microbridge clamping zones. The reported analysis will enable the design of complex MEMS devices by allowing to model the evolution of the etching process required for the release of arbitrary structures made of oxide thin films deposited on top of STO.

Temperature-dependent periodicity halving of the in-plane angular magnetoresistance in La0.67Sr0.33MnO3 thin films on LaAlO3

Strain-engineering is used as a tool to alter electronic and magnetic properties like anisotropy energy. This study reports the different angle-dependent magnetoresistance properties of the strain-engineered La0.67Sr0.33MnO3 (LSMO) thin films, grown on LaAlO3, compared to their bulk analogs. Upon increasing temperature, a symmetry change from fourfold [cos(4θ)] to twofold [cos(2θ)] is observed in the angle-dependent resistance measurements. This systematic study with increasing temperature allows us to define three distinct temperature-dependent phases. The fourfold symmetric signal originates from magnetocrystalline anisotropy, whereas the twofold symmetric signal is believed to be the conventional anisotropic magnetoresistance. Our observations show that strain-engineering creates the possibility to manipulate the anisotropy, which, for example, can ultimately lead to observations of noncollinear quasi-particles like skyrmions in single layer thin films of LSMO.

Imaging the formation and surface phase separation of the CE phase

The CE phase is an extraordinary phase exhibiting the simultaneous spin, charge, and orbital ordering due to strong electron correlation. It is an ideal platform to investigate the role of the multiple orderings in the phase transitions and discover emergent properties. Here, we use a cryogenic high-field magnetic force microscope to image the phase transitions and properties of the CE phase in a Pr0.5Ca0.5MnO3 thin film. In a high magnetic field, we observed a clear suppression of magnetic susceptibility at the charge-ordering insulator transition temperature (TCOI), whereas, at the Néel temperature (TN), no significant change is observed. This observation favors the scenario of strong antiferromagnetic correlation developed below TCOI but raises questions about the Zener polaron paramagnetic phase picture. Besides, we discoverd a phase-separated surface state in the CE phase regime. Ferromagnetic phase domains residing at the surface already exist in zero magnetic field and show ultra-high magnetic anisotropy. Our results provide microscopic insights into the unconventional spin- and charge-ordering transitions and revealed essential attributes of the CE phase, highlighting unusual behaviors when multiple electronic orderings are involved.

Probing charge transport in manganite film through switching parameters

We have investigated the bipolar resistive switching of Y0.95Ca0.05MnO3 (YCMO) thin film on Si substrate using pulsed laser deposition. Simulation of Mn L3,2 near-edge X-ray absorption fine structure has been executed by CTM4XAS to corroborate the presence of a mixed-valence state of Mn ions and oxygen vacancies. The charge transport in the film is described by the space charge limited mechanism. Murgatroyd and space charge limited mechanism relations are used to calculate the mobility and other switching parameters at high resistance state. With a decrease in the switching layer (near to positively biased electrode) thickness, better resistive switching was observed. This work indicates that the localized switching thickness and temperature strongly affect the resistive switching of the YCMO film.

Tuned AFM–FM coupling by the formation of vacancy complex in Gd0.6Ca0.4MnO3 thin film lattice

The effect of in situ oxygen and vacuum annealings on the low bandwidth manganite Gd1−x Ca x MnO3 (GCMO) thin film with x = 0.4 was investigated. Based on the magnetic measurements, the AFM–FM coupling is suppressed by the vacuum annealing treatment via destroying the double exchange interaction and increasing the unit cell volume by converting the Mn4+ to the Mn3+. Consequently, resistance increases significantly compared to pristine film. The results are explained by a model obtained from the positron annihilation studies, where the vacuum annealing increased the annihilation lifetime in A and B sites due to the formation of vacancy complexes V A,B–V O, which was not the case in the pristine sample. The positron annihilation analysis indicated that most of the open volume defects have been detected in the interface region rather than on the subsurface layer and this result is confirmed by detailed x-ray reflection analysis. On the other hand, the effect of oxygen annealing on the unit cell volume and magnetization was insignificant. This is in agreement with positron annihilation results which demonstrated that the introduction of oxygen does not change the number of cation vacancies significantly. This work demonstrates that the modification of oxygen vacancies and vacancy complexes can tune magnetic and electronic structure of the epitaxial thin films to provide new functionalities in future applications.

Extended phase diagram of La1–x Ca x MnO3 by interfacial engineering* *Project supported by the National Key Research and Development Program of China (Grant Nos. 2016YFA0401003, 2017YFA0403502, and 2020YFA0309100), the National Natural Science Foundation of China (Grant Nos. 11974326, 12074365, 11804342, U2032218, and 51872278), the Fundamental Research Funds for the Central Universities, China (Grant Nos. WK2030000035 and WK2340000102), and Hefei

The interfacial enhanced ferromagnetism in maganite/ruthenate system is regarded as a promising path to broaden the potential of oxide-based electronic device applications. Here, we systematically studied the physical properties of La1−x Ca x MnO3/SrRuO3 superlattices and compared them with the La1−x Ca x MnO3 thin films and bulk compounds. The La1−x Ca x MnO3/SrRuO3 superlattices exhibit significant enhancement of Curie temperature (T C) beyond the corresponding thin films and bulks. Based on these results, we constructed an extended phase diagram of La1−x Ca x MnO3 under interfacial engineering. We considered the interfacial charge transfer and structural proximity effects as the origin of the interface-induced high T C. The structural characterizations revealed a pronounced increase of B–O–B bond angle, which could be the main driving force for the high T C in the superlattices. Our work inspires a deeper understanding of the collective effects of interfacial charge transfer and structural proximity on the physical properties of oxide heterostructures.

Prototype Design of a Domain-Wall-Based Magnetic Memory Using a Single Layer La0.67Sr0.33MnO3 Thin Film.

Magnetic field-free, nonvolatile magnetic memory with low power consumption is highly desired in information technology. In this work, we report a current-controllable alignment of magnetic domain walls in a single layer La0.67Sr0.33MnO3 thin film with the threshold current density of 2 × 105 A/cm2 at room temperature. The vector relationship between current directions and domain-wall orientations indicates the dominant role of spin-orbit torque without an assistance of external magnetic field. Meanwhile, significant planar Hall resistances can be readout in a nonvolatile way before and after the domain-wall reorientation. A domain-wall-based magnetic random-access memory (DW-MRAM) prototype device has been proposed.

Electrical properties and stability of low temperature annealed (Zn,Cu) co-doped (Ni,Mn)3O4 spinel thin films

ABSTRACT Toward the development of infrared (IR) detectors, nickel–manganite-based thin films were initially prepared from (Ni0.2Mn2.8–x Cu x )Cl2 (0.010 ≤ x ≤ 0.040) solutions using the liquid flow deposition (LFD) method. The influence of Cu on the negative temperature coefficient of resistance (NTCR) characteristic of the films annealed at 400°C was investigated. It was found that the incorporation of Cu can effectively enhance electrical conductivity; however, it degrades both the thermal sensitivity and stability of the nickel–manganite films. The investigation was extended by further modifying the composition with Zn. The results revealed that by co-doping Cu with a proper amount of Zn the temperature coefficient of resistance (TCR) could be tailored, while a relatively low resistivity (ρ) of the final products was retained. Specially, when 0.01 mol Zn was added to a precursor solution containing 0.025 mol Cu, the resulting specimen possessed a TCR = 2.82% K–1 and a ρ = 820 Ω (measured at RT). More importantly, compared to Zn-free films, the (Zn,Cu) co-doped compositions showed much improved electrical stability, with an aging coefficient (ΔR/R) as low as 4.6%, after aging at 150°C in air for 500 h. The results suggest that the (Zn,Cu) co–doped (Ni,Mn)3O4 thin films have a promising application in IR detectors.

Using spin coating method to prepare near room-temperature TCR of La0.7Ca0.205Sr0.095MnO3 films for uncooled infrared bolometers

La0.7Ca0.205Sr0.095MnO3 (LCSMO) thin films were grown on LaAlO3 (100) substrates via facile spin coating at different sintering temperatures (Ts; Ts = 750, 900, 1100, and 1300 °C). The crystal structures of the films were detected by X-ray diffraction. The distortion of MnO6 octahedral was analyzed by Fourier transform infrared spectroscopy, while the surface morphology was observed using atomic force microscopy. In addition, the concentrations of itinerant electron and Mn3+/Mn4+ pairs were determined by X-ray photoemission spectroscopy. The electrical performance was analyzed using double exchange interaction, Jahn–Teller effect, and phenomenon percolation model. In general, the electrical properties of the films improved by increasing Ts. The peak temperature coefficient of resistivity (TCR) enhanced from 1.9% K−1 at 210.5 K (for Ts = 750 °C) to 11.1% K−1 at 276.8 K (for Ts = 1300 °C). These LCSMO films with optimized electrical properties exhibited a peak TCR temperature close to room temperature (290–300 K), making these films potential candidates for the uncooled infrared bolometers.

Reliable glucose sensing properties of electrodeposited vertically aligned manganese oxide thin film electrode

In this work, vertically aligned nanosheets of manganese oxide (MnO2) were deposited on stainless steel (SS) substrate via binder free anodic electrodeposition method. The MnO2 films were characterized with X-ray diffraction, energy dispersive X-ray spectroscopy, field emission scanning electron microscopy and X-ray photoelectron spectroscopy to study the crystal structure, elemental composition, morphology and chemical state. Further, the films were explored as an electrode for electrochemical detection of glucose by cyclic voltammetry and i–t amperometric techniques using three electrode system. The sensitivity of 4341 µA mM−1 cm−2 at working potential of 0.5 V/SCE was shown by MnO2 electrode with wide linear range of 50 µM–1.2 mM having lower detection limit of 0.53 µM. This result points that the vertically aligned nanosheets of MnO2 thin film can be a promising candidate for enzymeless glucose sensing.