Magnetic properties and colossal magnetoresistance of La(Ca)MnO3 materials doped with Fe

Spin Effects in Optimizing Electrochemical Applications

Efficient electrocatalyst development is crucial for addressing global energy challenges, and recent advances have highlighted the significant role of electron spin-a fundamental property of electrons-in influencing catalytic processes. Regulating the spin states of active sites has emerged as a powerful strategy to enhance catalytic performance. In response to growing interest in spin-induced electrocatalysis, this review offers a comprehensive examination of the impact of spin states on electrocatalytic activity. We explore various strategies for modulating spin states, review state-of-the-art techniques for spin state characterization, and elucidate the mechanisms by which spin effects enhance catalytic efficiency. Additionally, we discuss future research directions, emphasizing the potential of spin regulation to drive innovation in electrocatalyst design and application. This review aims to provide a foundational understanding of spin effects in electrocatalysis, guiding future efforts in the rational design of high-performance catalysts.

Tailoring of structural, morphological, electrical, and magnetic properties of LaMn1-x Fe x O3 ceramics

This study undertakes a comparative analysis of the structural, morphological, electrical, and magnetic characteristics of Fe-doped LaMnO3 ceramics. The solid-state reaction method was used to prepare Fe-doped LaMnO3 at different concentrations (0.00 ≤ x ≤ 1.00) and has been characterized using X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS), and vibrating sample magnetometry (VSM). The structural transformation from rhombohedral to orthorhombic with Fe-doping is demonstrated by Rietveld's refined XRD patterns. The positive slope in Williamsons-Hall's (W-H) plots confirms the presence of tensile strain with increasing average crystallite size. Quasi-spherical morphology of all the compositions with similar uniformity was confirmed by FESEM images. The chemical distribution of all the elements has been identified by EDS mapping images. Normal dielectric dispersion behaviour of all the samples with NTCR response is confirmed by dielectric and impedance analysis respectively. Increasing lattice volume with Fe-concentration results is increasing E a. The presence of antiferromagnetic ordering, in addition to weak ferromagnetic ordering, is indicated by the unsaturated magnetization even up to a high external field. The decrease in M S and increase in H C values due to Fe-doping reflect the influence of particle size on various magnetic parameters.

Investigating Fe-doped Ba0.67Ni0.33Mn1-xFexO3 (x = 0, 0.2) ceramics: insights into electrical and dielectric behaviors

This study investigates the characteristics of the Ba0.67Ni0.33Mn1-xFexO3 perovskite compound, focusing on its structural and electrical aspects under varying Fe doping levels at the Mn-site (x = 0, 0.2). X-ray diffraction patterns confirm the material's consistent structure, with Fe3+ ions substituting Mn3+ ions while maintaining their identical ionic radius. Nano-crystallinity studies reveal single-phase crystallization in the orthorhombic structure with space group Imma. Samples are prepared through conventional solid-state sintering. The Williamson-Hall method calculates crystallite sizes, averaging 37 nm for x = 0 and 33 nm for x = 0.2. Electrical properties are examined using complex impedance spectroscopy at different temperatures and frequencies. Techniques such as energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM) assess chemical composition. Activation energy values increase from 0.138 eV for x = 0 to 0.171 eV for x = 0.2, leading to reduced dc conductivity across the investigated temperature range. Dielectric permittivity enhances proportionally with increasing Fe doping. Variations in impedance profiles reveal a relaxation phenomenon. A circuit model, Rg + (Rgb//CPEgb), elucidates impedance data. This study illuminates the interplay between Fe doping, activation energy, and electrical conductivity in Ba0.67Ni0.33Mn1-xFexO3 perovskite, offering insights applicable to electronic and energy-related devices. Perovskite-based nanomaterials have diverse environmental applications, including solar cells, light-emitting devices, transistors, sensors, and energy storage.

Materials and Schemes of Multimodal Reconfigurable Micro/Nanomachines and Robots: Review and Perspective

Mechanically programmable, reconfigurable micro/nanoscale materials that can dynamically change their mechanical properties or behaviors, or morph into distinct assemblies or swarms in response to stimuli have greatly piqued the interest of the science community due to their unprecedented potentials in both fundamental research and technological applications. To date, a variety of designs of hard and soft materials, as well as actuation schemes based on mechanisms including chemical reactions and magnetic, acoustic, optical, and electric stimuli, have been reported. Herein, state-of-the-art micro/nanostructures and operation schemes for multimodal reconfigurable micro/nanomachines and swarms, as well as potential new materials and working principles, challenges, and future perspectives are discussed.

Effect of Fe Doping on the Structural, Electrical and Magnetic Properties of Perovskite La_0.7Ca_0.3Mn_1-<i>_x</i>Fe<i>_x</i>O ₃ (<i>X</i> = 0, 0.01, 0.03 and 0.05)

The effect of Fe-substitution at the Mn-site in La0.7Ca0.3Mn1-xFexO3 (x = 0, 0.01, 0.03 and 0.05) on its structure, electrical and magnetic properties has been studied. These properties were investigated via X-ray diffraction (XRD) analysis, temperature-dependent resistance measurements and temperature-dependent AC magnetic susceptibility measurements. XRD analysis showed all samples are single phase materials. Temperature dependent resistance measurements between 30–300 K showed all samples to undergo insulator-metal transition as temperature decreases. Increase in Fe doping for x = 0, 0.01, 0.03 and 0.05 caused the transition temperature TIM to decrease from 257 K, 244 K, 205 K and 162 K respectively. The magnetic susceptibility measurements showed the samples to exhibit paramagnetic to ferromagnetic transition as temperature decreased. Increase in Fe substitution x at the Mn-site progressively decreased the Curie temperature TC from 250 K at x = 0 to 170 K at x = 0.05.

Physical properties of epitaxial SrMnO2.5-δ F γ oxyfluoride films

Recently, topotactic fluorination has become an alternative way of doping epitaxial perovskite oxides through anion substitution to engineer their electronic properties instead of the more commonly used cation substitution. In this work, epitaxial oxyfluoride SrMnO_2.5-δ F _γ films were synthesized via topotactic fluorination of SrMnO_2.5 films using polytetrafluoroethylene as the fluorine source. Oxidized SrMnO₃ films were also prepared for comparison with the fluorinated samples. The F content, probed by x-ray photoemission spectroscopy, was systematically controlled by adjusting fluorination conditions. Electronic transport measurements reveal that increased F content (up to γ  =  0.14) systematically increases the electrical resistivity, despite the nominal electron-doping induced by F substitution for O in these films. In contrast, oxidized SrMnO₃ exhibits a decreased resistivity and conduction activation energy. A blue-shift of optical absorption features occurs with increasing F content. Density functional theory calculations indicate that F acts as a scattering center for electronic transport, controls the observed weak ferromagnetic behavior of the films, and reduces the inter-band optical transitions in the manganite films. These results stand in contrast to bulk electron-doped La_1-x Ce _x MnO₃, illustrating how aliovalent anionic substitutions can yield physical behavior distinct from A-site substituted perovskites with the same nominal B-site oxidation states.

Magnetoresistance and robust resistivity plateau in MoAs2

We have grown the MoAs2 single crystal which crystallizes in a monoclinic structure with C2/m space group. Transport measurements show that MoAs2 displays a metallic behavior at zero field and undergoes a metal-to-semiconductor crossover at low temperatures when the applied magnetic field is over 5 T. A robust resistivity plateau appears below 18 K and persists for the field up to 9 T. A large positive magnetoresistance (MR), reaching about 2600% at 2 K and 9 T, is observed when the field is perpendicular to the current. The MR becomes negative below 40 K when the field is rotated to be parallel to the current. The Hall resistivity shows the non-linear field-dependence below 70 K. The analysis using two-band model indicates a compensated electron-hole carrier density at low temperatures. A combination of the breakdown of Kohler's rule, the abnormal drop and the cross point in Hall data implies that a possible Lifshitz transition has occurred between 30 K and 60 K, likely driving the compensated electron-hole density, the large MR as well as the metal-semiconductor transition in MoAs2. Our results indicate that the family of centrosymmetric transition-metal dipnictides has rich transport behavior which can in general exhibit variable metallic and topological features.

Effects of Fe doping on the thermal hysteresis of the La0.5Ca0.5MnO3 system

A series of polycrystalline La_0.5Ca_0.5Mn_1−xFe_xO₃ (x = 0.010, 0.025, 0.050, 0.075, 0.100, 0.125, 0.150, 0.175 and 0.200) was synthesized using solid state reaction.

Structural, magnetic and magnetocaloric effects in epitaxial La0.67Ba0.33Ti0.02Mn0.98O3 ferromagnetic thin films grown on 001-oriented SrTiO3 substrates

Epitaxial La_0.67Ba_0.33Ti_0.02Mn_0.98O₃ (denoted as LBTMO hereafter) thin films of approximately 95 nm thickness were deposited by a pulsed laser deposition technique onto SrTiO₃ (STO) (001) substrates.

Effects of Interface Layers and Domain Walls on the Ferroelectric-Resistive Switching Behavior of Au/BiFeO3/La0.6Sr0.4MnO3 Heterostructures

The electric field effects on the electric and magnetic properties in multiferroic heterostructures are important for not only understanding the mechanisms of certain novel physical phenomena occurring at heterointerfaces but also offering a route for promising spintronic applications. Using the Au/BiFeO3/La0.6Sr0.4MnO3 (Au/BFO/LSMO) multiferroic heterostructure as a model system, we investigated the ferroelectric-resistive switching (RS) behaviors of the heterostructure. Via the manipulation of the BFO ferroelectric polarizations, the nonvolatile tristate of RS is observed, which is closely related to the Au/BFO and BFO/LSMO interface layers and the highly conducting BFO domain walls (DWs). More interestingly, according to the magnetic field dependence of the RS behavior, the negative magnetoresistance effect of the third resistance state, corresponding to the abnormal current peak in current-pulse voltage hysteresis near the electric coercive field, is also observed at room temperature, which mainly arises from the possible oxygen vacancy accumulation and Fe ion valence variation in the DWs.

Suppression of itinerant ferromagnetism and a spin-glass-like state in Zn substituted La0.67Ca0.33MnO3

We examine the magneto-transport, static and dynamic magnetic responses of the single phase glassy insulating compound La(0.67)Ca(0.33)Mn(1-x)Zn(x)O(3) (x = 0.10). This compound undergoes a field induced metal-insulator transition and exhibits colossal magnetoresistance for H ≥ 2 T. Many experimental features, such as a frequency dependent cusp in the in-phase component of linear ac susceptibility at a temperature T'(f), a broad maximum (at T(a)) in the ZFC cooled thermo-magnetization close to T'(f), large thermo-magnetic irreversibility below T(a), non-saturation of magnetization at 5 K even under 12 T with a characteristic S shape in the virgin curve, monotonic increase of the coercivity at low fields under ZFC condition as one approaches the T'(f), logarithmic relaxation of thermo-magnetization and ageing effects below T(a) and a characteristic maximum in the magnetic viscosity below the spin-glass transition temperature (T(g)) indicate a spin-glass-like state at low temperatures. This is further substantiated by the absence of second order non-linear ac susceptibility, a characteristic negative maximum at T(g) in third order non-linear ac susceptibility (χ'(3)), the critical divergence of χ'(3) as a function of temperature and ac probe field and an unusually large linear term in the low temperature specific heat.

Variable-range hopping conductivity of La(1 - x)Sr(x)Mn(1 - y)Fe(y)O₃

The temperature dependence of the resistivity, ρ, of ceramic La(1 - x)Sr(x)Mn(1 - y)Fe(y)O(3) (LSMFO) samples with x = 0.3 and y = 0.03, 0.15, 0.20 and 0.25 (or simply #03, #15, #20 and #25, respectively) is investigated between temperatures T ∼ 5 and 310 K in magnetic fields B up to 8 T. Metallic conductivity in #03 is changed eventually to activated in #25. In #15 and #20 the behavior of ρ(T) is more complicated, comprising of two extremes, divided by an interval of metallic behavior in #15, and two inflections of ρ(T) in #20 within similar intervals ΔT below approximately 100 K. Mott variable-range hopping (VRH) conductivity is observed in #15 above the ferromagnetic Curie temperature, T(C). In #20 the Mott VRH conductivity takes place in three different temperature intervals at T > T(C), T close to T(C) and T < T(C). In #25, the Mott VRH conductivity is observed in two different intervals, above and below T(C), divided by an intermediate interval of the Shklovskii-Efros VRH conduction regime. Analysis of the VRH conductivity yielded the values of the localization radius, α, and the dependence of α and of the density of the localized states, g, near the Fermi level, on B. Above T(C) the localization radius in all samples at B = 0 has similar values, α approximately 1.0-1.2 Å, which is enhanced to α approximately 3.3 Å (#20) and 2.0 Å (#25) below T(C). The sensitivity of α and g to B depend on y and T. The complicated behavior of the mechanisms of the hopping charge transfer, as well as of the microscopic parameters α and g, is attributable to different electronic and magnetic phases of LSMFO varying with temperature and Fe doping.

Ferromagnetic insulating and spin glass behavior in Cr substituted La(0.85)Ag(0.15)MnO(3) compounds

Single phase samples of polycrystalline La(0.85)Ag(0.15)Mn(1-y)Cr(y)O(3) (y = 0, 0.05, 0.10, 0.15, 0.20) were prepared by the solid-state route. These samples were studied by recording x-ray diffraction patterns to investigate their crystal structure, by measuring temperature and frequency variations of ac susceptibility and high temperature magnetization to investigate their magnetic properties and by measuring magneto-resistivity. X-ray diffraction patterns could be refined by using the [Formula: see text] space group. The lattice parameters and Mn-O bond lengths were found to decrease with Cr doping. Paramagnetic to ferromagnetic transitions followed by low temperature spin glass like behavior have been observed from ac susceptibility results. The above transitions could be understood on the basis of double exchange ferromagnetic interaction in Mn(3+)-O(2-)-Mn(4+), super-exchange ferromagnetic interaction in Cr(3+)-O(2-)-Mn(3+) and super-exchange antiferromagnetic interaction in Mn(4+)-O(2-)-Mn(4+) networks. Even though a strong ferromagnetic signal was observed in all the Cr doped samples, no metal-insulator transition has been observed. Thus Cr doping gives rise to a ferromagnetic insulating state and the Cr might take part in super-exchange ferromagnetic interactions. Colossal magneto-resistivity has been observed up to 20% of Cr doping in a wide temperature range down to low temperatures.

Lattice distortions, magnetoresistance and hopping conductivity in LaMnO(3+δ)

Structural and transport properties of ceramic LaMnO(3+δ) are investigated for δ = 0-0.154. According to x-ray diffraction measurements at room temperature the crystal structure of this compound varies from orthorhombic (Pbnm) for δ = 0 to rhombohedrally distorted cubic (Pm3m) for δ = 0.065-0.112 and to rhombohedral ([Formula: see text]) crystal symmetry for δ = 0.125-0.154. These structural modifications are confirmed by the Raman micro-spectroscopy measurements. The resistivity displays in the range δ = 0-0.154 an activated behaviour both above and below the paramagnetic (PM) to ferromagnetic transition temperature, T(C). In the field of 8 T the relative magnetoresistance, Δρ(B)/ρ(0), reaches at δ = 0.154 the values of -88% near T(C) and -98% at [Formula: see text] K. The resistivity of the PM phase of LaMnO(3+δ) with δ = 0.100-0.154 satisfies the Shklovskii-Efros-like variable-range hopping (VRH) conductivity law between [Formula: see text] K and the VRH onset temperature [Formula: see text] K. The resistivity is governed by a complex energy dependence of the density of the localized states near the Fermi level, comprising a soft Coulomb gap [Formula: see text] eV and a rigid gap [Formula: see text] eV, the latter being connected to formation of small polarons.