Sr MnO Research Articles

Extraordinary relative cooling power in the magnetocaloric La0.6Y0.07Ca0.33MnO3-δ

The magnetocaloric effect of La0.6Y0.07Ca0.33MnO3-δ is reported to cover a wide temperature range, including ambient temperature and cryogenic temperature, making it a promising material for magnetic refrigerators. Furthermore, the remarkable cooling power of La0.6Y0.07Ca0.33MnO3-δ is much higher than that of well-known magnetic refrigerants like Gd, (La–Sr)MnO3, (La–Sr)MnO3, (La–Ca–Pb)MnO3, and La1-xCaxMnO3 samples. La0.6Y0.07Ca0.33MnO3-δ can be used as a single magnetic refrigerant in MR at room-temperature and cryogenic temperatures. Consequently, La0.6Y0.07Ca0.33MnO3-δ is recommended as a potential magnetic refrigerant for various applications, including food refrigeration and nitrogen liquefaction.

Point-contact spectroscopy of Leggett modes in superconducting compounds with unconventional pairing

Proximity-coupled nanostructures of conventional superconductors (SCs) and half-metallic ferromagnets (hmFs) are promising candidates as materials with unconventional superconductivity. The interrelated superposition of spin singlet-triplet and frequency even-odd superconducting condensates characterizes the superconducting state in such heterostructures. In a multi-band SC, the collective modes associated with the excitations of the relative phase between superconducting bands without perturbation of the Cooper pairs symmetry (Leggett modes) are allowed. In this report, we present the results of experimental investigations via the point-contact transport measurements of the Leggett-like collective excitations in the superconducting state of the nanocomposite of s-wave two-band superconductor MgB2 and half-metallic ferromagnet (La,Sr)MnO3. Two types of point contacts (PCs) have been used: the nanocomposite-nonmagnetic metal PCs and the nanocomposite–hmF PCs. The conductance equidistant peaks against the background of the gap structure were observed in both types of high-quality point junctions. Their distinctive feature was their period: two times shorter for the nanocomposite–hmF contacts compared to the nonmagnetic metal PCs. We attribute these spin-selective conductance periodic peaks to the relative phase Leggett’s excitations between “parents” MgB2 even-frequency singlet condensates and proximity-induced triplet superconducting condensates. The data obtained on the hmF PCs also demonstrate the features that may indicate a dynamic coupling between even-frequency condensates and odd-frequency gapless superconducting condensates.

Exploring orientation-dependent interface engineering in manganite heterostructures

The crucial role of interface engineering in controlling functionality has been well documented in the (001)-orientated perovskite oxide heterostructures; however, limited attention has been given to other epitaxial orientations. In this study, the (La,Sr)MnO3 heterostructure is selected to present the epitaxial-orientation-dependent interface engineering strategies based on magnetoelectric coupling and oxygen octahedral coupling. When capped by a ferroelectric PbTiO3 layer for interlayer magnetoelectric coupling, the (001) (La,Sr)MnO3 layer exhibits the most significant magnetic modulations compared to (110) and (111) counterparts. This can be attributed to the PbTiO3's out-of-plane polarization that depends on the epitaxial orientations. Also, if considering the interfacial oxygen octahedral structure in terms of epitaxial orientations, the buffer (or cap) layer hosts the most part of interfacial oxygen octahedra and, thus, plays a dominant role in controlling oxygen octahedral coupling of (001)-orientated [or (110)-orientated] perovskite heterostructures. This is consistent with our observations that for the (001) [or (110)] (La,Sr)MnO3 heterostructures, the DyScO3 buffer layer offers the more (or less) effective magnetic modulations compared to the cap one. These findings underscore the orientation-dependent nature of interface engineering in manganite heterostructures as well as in other perovskite heterostructures for tailoring functionalities.

Ferroelectric SrMnO3 Thin Film Grown on (110)‐Oriented PMN‐PT Substrate

Exploring the unique physical properties of oxide perovskites necessitates their growth on diverse single‐crystal substrates. The thin‐film growth of perovskite SrMnO3 (SMO) has been a particular focus of research due to its emerging room‐temperature multiferroicity. Herein, the epitaxial thin films of (110)‐oriented SMO are grown on the piezoelectric (110)‐oriented (1–x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN‐PT) substrate. The effects of the thickness and oxygen annealing on the crystal structure, stoichiometry, and ferroelectric properties of the SMO thin film are systematically investigated. The tensile strain produced by the lattice mismatch between the bulk SMO and the PMN‐PT substrate causes an expansion of the c‐lattice parallel to the in‐plane direction of the substrate. The films show larger a‐, b‐, and c‐lattice parameters than the bulk material, resulting in volume expansion of the unit cell. This lattice expansion is attributed to the generation of oxygen vacancies driven by the reduced formation energy caused by the high elastic strain. Piezoelectric force microscopy reveals that the SMO film contains domains with strain‐mediated in‐plane and vacancy‐mediated out‐of‐plane polarization. Furthermore, the piezoelectric response of the PMN‐PT substrate effectively modulates the biaxial tensile strain in the SMO film, offering a potential strategy for controlling the crystal structure and ferroelectric properties of SMO.

Dielectric Spectroscopy of Non-Stoichiometric SrMnO3 Thin Films

The dielectric properties of non-stoichiometric SrMnO3 (SMO) thin films grown by molecular beam epitaxy were systematically investigated. Especially, the effects of cation stoichiometry-induced diverse types and densities of defects on the dielectric properties of SMO films were revealed. Two anomalous dielectric relaxation behaviors were observed at different temperatures in both Sr-rich and Mn-rich samples. High-temperature dielectric relaxation, resulting from a short-range Mn-related Jahn–Teller (JT) polaron hopping motion, was reinforced by an enhancement of JT polaron density in the Sr-rich film, which contained abundant SrO Ruddlesden–Popper (R-P) stacking faults. However, an excessive number of disordered Sr vacancy clusters in Mn-rich thin film suppressed the hopping path of JT polarons and enormously weakened this dielectric relaxation. Thus, The Sr-rich film demonstrated a higher dielectric constant and dielectric loss than the Mn-rich film. In addition, low-temperature dielectric relaxation may be attributed to the polarization/charge glass state.

Effect of Sm doping on structure, dielectric properties and microwave absorption performance of SrMnO3

In this work, Sr1-xSmxMnO3(x = 0,0.5) powders were prepared by solid-state reaction method. The effects of Sm doping on structure, electromagnetic properties and microwave absorption performance of SrMnO3 were systematically investigated by experimental characterizations and first-principles calculations. It is found that the doping of Sm transforms the hexagonal structure P63/mmc of SrMnO3(SMO) into an orthorhombic phase Pnma of Sr0.5Sm0.5MnO3 (SSMO) at room temperature. Sm doping and the increase of Mn3+ content induce the lattice distortion, resulting in octahedral torsion and the Mn–O–Mn bond angle towards 180°. Furthermore, doping introduces additional oxygen vacancies and defects in SMO, significantly enhancing various polarizations within the system. As a result, there is a substantial improvement in the microwave absorption capability of the doped sample. Compared to undoped SMO, SSMO performs excellent microwave absorbing properties in the higher frequency band and the value of reflection loss has increased by 29.47 dB at the optimal matching thickness.

Manipulation of Spin-Orbit Torque in Tungsten Oxide/Manganite Heterostructure by Ionic Liquid Gating and Orbit Engineering.

Spin-orbit coupling (SOC) is the interaction between electron's spin and orbital motion, which could realize a charge-to-spin current conversion and enable an innovative method to switch the magnetization by spin-orbit torque (SOT). Varied techniques have been developed to manipulate and improve the SOT, but the role of the orbit degree of freedom, which should have a crucial bearing on the SOC and SOT, is still confusing. Here, we find that the charge-to-spin current conversion and SOT in W3O8-δ/(La, Sr)MnO3 could be produced or eliminated by ionic liquid gating. Through tuning the preferential occupancy of Mn/W-d electrons from the in-plane (dx2-y2) to out-of-plane (d3z2-r2) orbit, the SOT damping-like field efficiency is nearly doubled due to the enhanced spin Hall effect and interfacial Rashba-Edelstein effect. These findings not only offer intriguing opportunities to control the SOT for high-efficient spintronic devices but also could be a fundamental step toward spin-orbitronics in the future.

Novel and high-performance (La,Sr)MnO3 based composite cathodes for intermediate-temperature solid oxide fuel cells

Novel and high-performance (La,Sr)MnO3 based composite cathodes for intermediate-temperature solid oxide fuel cells

An investigation of Cr vaporization from SUS430 metallic interconnect and deposition on (La,Sr)MnO3 cathode of intermediate temperature solid oxide fuel cells

In solid oxide fuel cells (SOFCs), chromium deposition and poisoning of metallic interconnect is one of the most important issues in the electrochemical activity and stability of the cathode for the oxygen reduction reaction (ORR). In this paper, the chromium evaporation characteristics, oxide scale growth, and deposition of chromium on the ORR on (La,Sr)MnO3 (LSM) cathode are studied at 700–800 °C for SUS430 alloy interconnect material in the intermediate-temperature solid oxide fuel cells. The chromium vaporization rate is measured using the transpiration technique and the surface morphologies, and cross-sections of oxide scales are examined by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The results indicate that chromium volatilization is correlated with the composition and morphology of the oxide scale, the Cr volatilization process presents two stages according to the structural evolution of the oxide scale. In addition, deposition and poisoning of Cr species released from metallic interconnect on the LSM cathode are studied and the formation of MnCr2O4 phase on the LSM backbone degrades the ORR electrochemical activity, causing the increase of overpotential of the cathode. The results obtained give insight into the mechanism of the Cr poisoning effect in intermediate-temperature.

Magnetic Refrigeration: An Environment-friendly Cooling Technology

Magnetic Refrigeration: An Environment-friendly Cooling Technology

Dimensionality engineering dependence of vertical magnetization shift and magnetic anisotropy evolution in manganite superlattices

The manganite superlattices consisting of a ferromagnetic La0.7Sr0.3MnO3 (LSMO) metal and a G-type antiferromagnetic SrMnO3 (SMO) insulator have been investigated in this work. Two very intriguing effects have been observed in these LSMO/SMO superlattices. The first one is the coexistence of the robust exchange bias and the evident vertical magnetization shift in the thicker superlattices. The second is the magnetic anisotropy variation from planar to perpendicular with increasing SMO layer thickness. These two novel phenomena have been confirmed by the electric transport anisotropy measurements and the microscopic magnetic domain switching images. Moreover, the X-ray linear dichroism experiments and first-principle calculations have revealed the orbital reconstruction dependence on the SMO layer thickness. It is noteworthy that the vertical magnetization shift and perpendicular magnetic anisotropy are usually observed in intrinsic out-of-plane magnetic easy axis materials such as SrRuO3-based heterostructures. However, the spins within LSMO films preferably orient towards the in-plane direction. Therefore, a new microscopic method for vertical magnetization shift and magnetic anisotropy manipulation has been developed, enabling the discovery of emergent phenomena as well as the control of the magnetic properties.

Influence of electronic transport on electrochemical performance of (Cu,Mn)3O4 solid oxide fuel cell cathodes

Alkaline Earth free spinel oxides provide a potential benefit over Sr-doped perovskite-based materials commonly used as electrodes in high-temperature electrochemical energy conversion devices, e.g., solid oxide fuel cells (SOFCs). Sr-segregation is a known issue leading to performance degradation. In this study, CuxMn3-xO4 (x = 1, 1.2, and 1.5) porous electrodes were examined as SOFC cathodes using electrochemical impedance spectroscopy to investigate the oxygen reduction reaction (ORR) kinetics in relation to the material's intrinsic conductivity, the extrinsic electrode structure, and the cell test design. Similar to the electronic conducting (La,Sr)MnO3 SOFC cathodes, the ORR kinetics of CuxMn3-xO4 spinel electrodes was governed by the oxygen adsorption and diffusion at the particle surface as well as the charge transfer at the triple phase boundaries. The overall electrode polarization resistance was highly dependent on contact density with the metallic current collector, active material particle connectivity, electrode thickness, and the intrinsic electronic materials conductivity. We describe the importance of effective electronic charge transport parallel to the electrode surface in maximizing the electrochemically active electrode volume and enhancing electrode performance. We discuss an approach to optimize cell and electrode design with respect to active materials properties. This aspect is critical to ensure reliable evaluation of new materials, since laboratory-scale button-cells typically exhibit a high degree of electrode microstructure (e.g. porosity, thickness) and electrical contact density variation from sample to sample.

Low Field Magnetocaloric Properties in Potassium-Doped (La, Sr)MnO3 Manganese Oxides

Low Field Magnetocaloric Properties in Potassium-Doped (La, Sr)MnO3 Manganese Oxides

Stress analysis and Q-factor of free-standing (La,Sr)MnO3 oxide resonators

Stress analysis and Q-factor of free-standing (La,Sr)MnO3 oxide resonators

Changeable electroresistance in Pt/Pb(Zr,Ti)O3/(La,Sr)MnO3 tunnel junctions and memristive properties for synaptic plasticity emulation

Ferroelectric tunnel junctions (FTJs) are promising candidates for the next-generation memory technologies. The electroresistance mechanism, however, has been reported not only from the polarization-modulation of barrier profiles. Electrical migration of charged defects has also been observed as a possible origin for the resistive switching. Here, we achieve two kinds of electroresistance behaviors in Pt/Pb(Zr,Ti)O3/(La,Sr)MnO3 tunnel junctions by introducing oxygen vacancies in the Pb(Zr,Ti)O3 barrier. The oxygen vacancies are observed by x-ray photoelectron spectroscopy, and their effects on the widely adopted piezoresponse force microscopy characterizations of ultrathin ferroelectric films have been analyzed by AC voltage-dependent hysteresis loops. For the Pt/Pb(Zr,Ti)O3/(La,Sr)MnO3 device that is modulated by the polarization reversal, a counterclockwise resistance–voltage (R–V) relationship is observed due to the tunneling between high and low barriers, whereas the R–V hysteresis loop is changed to clockwise with the existence of oxygen vacancies, in which conductive filaments are formed in the Pb(Zr,Ti)O3 barrier. However, such an ionic electroresistance is not stable during repetitive switching. Further investigation on memristive behaviors is, thus, performed on the ferroelectric-controlled Pt/Pb(Zr,Ti)O3/(La,Sr)MnO3 tunnel junctions. An excellent linearity is achieved in continuous resistance change owing to the nucleation-limited-switching mode of domain switching in the Pb(Zr,Ti)O3 barrier, giving rise to spike-timing-dependent plasticity behaviors for the Hebbian rule of learning and memory. These results provide insight into the distinguishing of ferroelectric and ionic contributions in electroresistance of FTJ devices, facilitating deep understanding of nonvolatile resistive memories.

Interfacial engineering manipulation of magnetic anisotropy evolution via orbital reconstruction in low-dimensional manganite superlattices

Control of magnetic anisotropy in low-dimensional systems is of paramount importance in terms of their fundamental and technological perspectives. La0.7Sr0.3MnO3 (LSMO) is a ferromagnetic half-metal with a high Curie temperature and many efforts have been made to control its magnetic anisotropy. However, the relationship between the evolution of the magnetic anisotropy orientation and the electronic structure of low-dimensional LSMO still remains poorly understood. Here, the high-quality superlattices comprised of LSMO and SrMnO3 (SMO) layers are synthesized with a compatible structure at the atomic scale. Their magnetic anisotropy is gradually varied from planar to perpendicular by increasing the SMO thickness, and the special fourfold magnetic anisotropy is also observed at the intermediate superlattice thickness. The evolution of the magnetic anisotropy in these systems is confirmed by the electronic transport and magnetic measurements. Moreover, X-ray linear dichroism measurements and first-principles calculations reveal the interfacial orbital reconstruction with the in-plane to out-of-plane magnetic reorientation transition. Therefore, a new microscopic method for magnetic anisotropy manipulation is developed in the present study, enabling discovery of novel phenomena as well as control of the magnetic properties.

Structural and Electrical Properties of Nd-Doped (La,Sr)MnO3 Bulk Ceramics

Structural and Electrical Properties of Nd-Doped (La,Sr)MnO3 Bulk Ceramics

Enhancing Surface Chemical Stability of LiMn2 O4 Cathode by Strontium Enrichment at Grain Boundaries.

LiMn2 O4 (LMO) cathodes suffer from limited cycle life, resulting from Mn dissolution and side reactions between electrode and electrolyte. In this study, Sr-modified LMO is prepared by using a simple strategy. The nature and position of large-radius Sr ions are investigated, alongside their influence on the structural stability of the bulk. SrMnO3 (SMO) is found to be enriched at grain boundaries of LMO, with Mn-O-Sr bonds forming at the SMO/LMO interface. Furthermore, stable SMO alleviates the migration of Mn ions in LMO associated with structural integrity and suppresses side reactions between the electrode and electrolyte. The modified LMO cathodes maintain their structural integrity and display improved rate performance and cycling stability under harsh conditions. Remarkably, the discharge capacity of a Sr-modified LMO||Li half-cell maintains 94.8 % at 25 °C and 79.6 % at 55 °C after 500 cycles. Consequently, enrichment of strontium at grain boundaries presents a promising strategy for developing cathodes for long-term use.

Experimental realization of strain-induced room-temperature ferroelectricity in SrMnO3 films via selective oxygen annealing

Antiferromagnetic-paraelectric SrMnO3 (SMO) has aroused interest because of the theoretical strong coupling between the ferroelectric and ferromagnetic states with increasing epitaxial strain. In strained SMO films, the <110> polarized state and polar distortions have been observed, although high leakage currents and air degradation have limited their experimental verification. We herein provide a conclusive demonstration of room-temperature ferroelectricity and a high dielectric constant (εr = 138.1) in tensile-strained SMO by securing samples with insulating properties and clean surfaces using selective oxygen annealing. Furthermore, a paraelectricity and low dielectric constant (εr = 6.7) in the strain-relaxed SMO film have been identified as properties of the bulk SMO, which directly proves that the ferroelectricity of the tensile-strained SMO film is due to strain-induced polarization. We believe that these findings not only provide a cornerstone for exploring the physical properties of multiferroic SMO but also inspire new directions for single-phase multiferroics.

Faster Diffusion of Oxygen Along Dislocations in (La,Sr)MnO3+δ Is a Space‐Charge Phenomenon

AbstractIn displaying accelerated oxygen diffusion along extended defects, (La,Sr)MnO3+δ is an atypical acceptor‐doped perovskite‐type oxide. In this study, 18O/16O diffusion experiments on epitaxial thin films of La0.8Sr0.2MnO3+δ and molecular dynamics (MD) simulations are combined to elucidate the origin of this phenomenon for dislocations: Does diffusion occur along dislocation cores or along space‐charge tubes? Transmission electron microscopy studies of the films revealed dislocations extending from the surface. 18O penetration profiles measured by secondary ion mass spectrometry indicated (slow) bulk diffusion and faster diffusion along dislocations. Oxygen tracer diffusivities obtained for temperatures 873 ≤ T [K] ≤ 973 were over two orders of magnitude higher for dislocations than for the bulk. The activation enthalpy of oxygen diffusion along dislocations, of (2.95 ± 0.21) eV, is surprisingly high relative to that for bulk diffusion, (2.67 ± 0.13) eV. This result militates against fast diffusion along dislocation cores. MD simulations confirmed no accelerated migration of oxide ions along dislocation cores. Faster diffusion of oxygen along dislocations in La0.8Sr0.2MnO3+δ is thus concluded to occur within space‐charge tubes in which oxygen vacancies are strongly accumulated. Reasons for and the consequences of space‐charge zones at extended defects in manganite perovskites are discussed.