Polycrystalline Samples Research Articles

Substrate Charge Transfer Induced Ferromagnetism in MnSe/SrTiO3 Ultrathin Films.

The observation of superconductivity in MnSe at 12 GPa motivated us to investigate whether superconductivity could be induced in MnSe at ambient conditions. A strain-induced structural change in the ultrathin film could be one route to the emergence of superconductivity. In this report, we present the physical property of MnSe ultrathin films, which become tetragonal (stretched ab-plane and shortened c-axis) on a (001) SrTiO3 (STO) substrate, prepared by the pulsed laser deposition (PLD) method. The physical properties of the tetragonal MnSe ultrathin films exhibit very different characteristics from those of the thick films and polycrystalline samples. The tetragonal MnSe films show substantial conductivity enhancement, which could be associated with the presence of superparamagnetism. The optical absorption data indicate that the electron transition through the indirect bandgap to the conduction band is significantly enhanced in tetragonal MnSe. Furthermore, the X-ray Mn L-edge absorption results also reveal an increase in unoccupied state valance bands. This theoretical study suggests that charge transfer from the substrate plays an important role in conductivity enhancement and the emergence of a ferromagnetic order that leads to superparamagnetism.

Metal-Free Perovskite Ferroelectrics with the Most Equivalent Polarization Axes.

Ferroelectricity in metal-free perovskites (MFPs) has emerged as an academic hotspot for their lightweight, eco-friendly processability, flexibility, and degradability, with considerable progress including large spontaneous polarization, high Curie temperature, large piezoelectric response, and tailoring coercive field. However, their equivalent polarization axes as a key indicator are far from enough, although multiaxial ferroelectrics are highly preferred for performance output and application flexibility that profit from as many equivalent polarization directions as possible with easier reorientation. Here, by implementing the synergistic overlap of regulating anionic geometries (from spherical I- to octahedral [PF6]- and to tetrahedral [ClO4]- or [BF4]-) and cationic asymmetric modification, we successfully designed multiaxial MFP ferroelectrics CMDABCO-NH4-X3 (CMDABCO = N-chloromethyl-N'-diazabicyclo[2.2.2]octonium; X = [ClO4]- or [BF4]-) with the lowest P1 symmetry. More impressively, systemic characterizations indicate that they possess 24 equivalent polarization axes (Aizu notations of 432F1 and m3̅mF1, respectively)─the maximum number achievable for ferroelectrics. Benefiting from the multiaxial feature, CMDABCO-NH4-[ClO4]3 has been demonstrated to have excellent piezoelectric sensing performance in its polycrystalline sample and prepared composite device. Our study provides a feasible strategy for designing multiaxial MFP ferroelectrics and highlights their great promise for use in microelectromechanical, sensing, and body-compatible devices.

Near-room-temperature magnetic properties and magnetocaloric effect of polycrystalline and nano-scale manganites Pr(0.65-x)NdxSr0.35MnO3 (x ≤ 0.35)

Here we report investigations of structural, electrical and magnetic properties of bulk and nano-sized Pr0.65-xNdxSr0.35MnO3 compounds (x ≤ 0.35). Polycrystalline compounds were produced by solid – state reaction and nanocrystalline samples were obtained by sol–gel method. Analysis of x-ray diffraction patterns revealed a change in lattice structure from ‘Pbnm’ to ‘R3c’ symmetry, with diminishing cell volume upon increasing Nd ions substitution for all samples. Optical microscopy was used for bulk surface morphology and transmission electron microscopy was implemented for nano-sized samples. Iodometric titration showed oxygen deficiency for bulk compounds and oxygen excess for nano-sized particles. Measurements of resistivity of bulk samples revealed a single peak at temperatures associated with grain boundary conditions and with ferromagnetic/paramagnetic transition and negative magnetoresistivity. Critical magnetic behavior analysis disclosed that the polycrystalline samples are governed by a tricritical mean field and by 3D Heisenberg models while nanocrystalline samples are governed by a mean field model. Curie temperature Tc values remain in near room temperature range for all bulk compounds; they lower with increasing Nd ions substitution from 295 K for the parent bulk compound to 268 K for x = 0.35. Tc is lowered from 255 K for the parent nano-sized compound in small temperature intervals. All compounds exhibit second-order magnetic phase transitions and relatively high magnetic entropy change, with the highest value of 5.74 J/kgK for x = 0.25 bulk sample in μ˳∆H = 4 T. Strong magnetocaloric effect, stability and the possibility of fine-tuning Tc by Nd ions substitution make the investigated bulk polycrystalline compounds promising for application in magnetic refrigeration. Nano-sized samples possess lower magnetic entropy changes of maximum 2.4 J/kgK in μ˳∆H = 4 T for x = 0.15, but wider effective entropy change temperature (δTfwhm) and relative cooling power on par with other manganites, bringing them into the conversation as a viable option in cooling materials.

Electric wind induced texturing for enhanced thermoelectric performance of p-type Mg3Sb2-based materials

High-intensity electric pulse treatment (EPT) can induce electric wind effect in materials, which facilitates the grain rearrangement and reorientation in polycrystalline samples. For the first time, this study employed the EPT technique to construct texture in Mg3.04Ag0.02Sb2 bulk compounds, and a highly conductive channel was produced to promote the charge carrier transport. This leads to a 53 % improvement in carrier mobility of the EPT sample (4#20) over the pristine one at room temperature. Additionally, EPT does not affect the carrier concentration of the material, making the EPT samples possess significantly improved electrical conductivities and untouched Seebeck coefficients. Consequently, a 36 % improvement in zT value is achieved for the EPT sample (4#20) at 723 K, compared to the pristine one. This work demonstrates that EPT technique is an effective approach for constructing textured Mg3Sb2-based materials, offering a valuable avenue for high thermoelectric performance in other potential materials via manipulating properties-related texture.

A novel mixed metal orthoborate Ba2ZnTb2(BO3)4: Crystal structure and multicolor emitting properties introduced by Eu3+ doping

Novel mixed metal orthoborate Ba2ZnTb2(BO3)4 was obtained through the high-temperature solid-state reaction at 950 °C. Its crystal structure was determined by single-crystal X-ray diffraction for the first time. The compound crystallizes in the orthorhombic system, Pbca space group, with cell parameters a = 13.4360(1), b = 6.4539(1), c = 25.3262(2) Å, V = 2196.15(4) Å3 and Z = 8. It represents a novel structure type in which ZnO4 tetrahedra and TbO8 polyhedra are interconnected via corner-, edge-, and face-sharing to form 1D [Zn2Tb4O24]n32n− chains. Some B atoms reside in triangular voids of the chains to strengthen the structure, while the others ‘stitch’ the chains together via B–O bonds to create a 3D [Zn2Tb4(BO3)8]n8n− network, with the open channels hosting Ba2+ ions. In addition, polycrystalline samples of Ba2ZnTb2-2xEu2x(BO3)4 (0 ≤ x ≤ 1) were synthesized via solid-state reaction at 780 °C and systematically characterized by powder XRD combined with Rietveld refinements, SEM, IR/Raman, XPS and photoluminescence spectroscopy. As it was revealed, due to the Tb3+ → Eu3+ energy transfer, the emission color of the obtained phosphors can be continuously tuned from green (0.2947, 0.5876) to orange (0.5766, 0.3994) and eventually to red (0.6419, 0.3536) upon the near-UV excitation at 377 nm through changing the Eu3+/Tb3+ ratio. The representative Ba2ZnTb1.998Eu0.002(BO3)4 sample shows a QY of ∼14.84 % (λex = 377 nm), and its emission intensity at 423 K still maintains ∼66 % of that at 303 K. All these observations indicate that, by properly doping activators and selecting the excitation wavelength, this borate phosphor displays multicolor tunable emission that may have potential applications in multicolor lighting and color display.

Effect of Mg/Ag co–doping on crystal structure, optical, and transport properties of SnO2 compound

The attempt to search for novel materials for optoelectronics material has become a highly debated and intensively investigated field of study. Within the scope of this investigation, Sn0.94Ag0.06-xMgxO2 (0 ≤ x ≤ 0.06) polycrystalline samples were produced using the traditional solid–state reaction method, and their crystalline structure, micro–structure, Raman spectroscopy, optical, and transport characteristics were investigated. Confirmation of a single rutile phase with a tetragonal crystal structure through XRD (X–ray diffraction) analysis is revealed. The morphology study by scanning electron microscopy indicated the formation of nanometric grains. All elements are evenly distributed throughout the structure, as seen by the elemental color mapping. The successful incorporation of Mg/Ag to the SnO2 lattice is evidenced by two prominent peaks in the Raman spectra of these compounds, with wavenumbers of 634 and 775 cm−1, which correspond to the A1g and B2g Raman modes, respectively. The UV–Vis spectrophotometer facilitated the acquisition of absorbance and transmittance data, which revealed that the optical band gap exhibited an expansion when the quantity of Mg/Ag co–doping increased in the SnO2 material. The transmittance value was also shown to increase from 80 % to 90 % with increased Mg co–doping concentration. The Maxwell–Weigner model has been employed to fully understand how the dielectric constant (εr), loss tangent (tan δ), complex impedance, and ac conductivity of Mg/Ag co–doped SnO2 compounds behave depending on frequency. The current–voltage (I–V) characteristics of the sample were measured using a Keithley 6517b electrometer in two–probe mode with a Tin metal pressure contact. The properties of I–V exhibited an Ohmic behavior. A study on the room temperature resistivity reveled that the materials are highly resistive in the nature.

Investigation of the structural and microstructural properties of copper and tantalum substituted BiMeVOx compounds with enhanced oxygen ion conductivity: Bi4V2-xCux/2Tax/2O11-3x/4 (0.1≤ x ≤ 0.5)

In this study, the objective was to improve the performance of bismuth vanadium oxide Bi4V2O11 by synthesizing double substituted compounds using copper ions Cu2+ and tantalum ions Ta5+. Bi4V2-xCux/2Tax/2O11-3x/4 (0.1 ≤ x ≤ 0.5) polycrystalline samples of were prepared via the solid-state route. XRD patterns measured at room temperature revealed the stabilization of the monoclinic α-Bi4V2O11 type structure for x = 0.1 and the tetragonal γ or γ' -Bi4V2O11 for x > 0.2. This result has been confirmed by thermogravimetric analysis (DTA), FT-IR spectroscopy and Raman scattering measurements. The influence of the composition on the microstructure and grain size of the prepared samples was explored through dilatometric study, density measurements, and scanning electron microscopy (SEM). Thermal Raman spectra evolution was also investigated. The temperature-dependent Raman spectroscopy analysis of the compound α-BiCuTaVOx (x = 0.1) demonstrated variations in the position, intensity, and width of the Raman mode around 850 cm−1, indicating temperature-assisted structural modifications. One defining feature of the tetragonal-dominated phase of the BiMeVOx systems is the increasing merging of the weak band at 930 cm−1 with the dominating band at 850 cm−1. This behavior was also observed for our samples. The V–O bond lengths were calculated using an empirical relation based on the diatomic approximation. Electrochemical impedance spectroscopy (EIS) was used to investigate the changes in electrical conductivity with the substitution rate across the temperature range of 300–720 °C. The sample with x = 0.3 exhibited the highest electrical conductivity at both high and low temperatures. However, the optimal substitution rate to achieve the best conductivity in this series of copper and tantalum-substituted BiCuTaVOx was found to be x = 0.3 (σ = 4 × 10−3 S cm−1 at 600 °C).

Apparatus for the room temperature measurement of low field Nernst and magneto-Seebeck coefficients.

Nernst coefficient measurements are a classic approach to investigate charge carrier scattering in both metals and semiconductors. However, such measurements are not commonly performed, despite the potential to inform material design strategies in applications such as thermoelectricity. As dedicated instruments are extremely scarce, we present here a room temperature apparatus to measure the low field Nernst coefficient (and magneto-Seebeck coefficient) in bulk polycrystalline samples. This apparatus is specifically designed to promote accurate and facile use, with the expectation that such an instrument will make Nernst measurements de rigueur. In this apparatus, sample loading and electrical contacts are all pressure-based and alignment is automatic. Extremely stable thermal control (10 mK of fluctuation when ΔT = 1K) is achieved from actively cooled thermoelectric modules that operate as heaters or Peltier coolers. Magneto-Seebeck measurements are integrated into the system to correct for residual probe offsets. Data from the apparatus are provided on bulk polycrystalline samples of bismuth, InSb, and SnTe, including raw data to illustrate the process of calculating the Nernst coefficient. Finally, we review how Nernst measurements, in concert with Seebeck, Hall, and electrical resistivity, can be analyzed via the Boltzmann equation in the relaxation time approximation to self-consistently predict the Fermi level, effective mass, and energy-dependent relaxation time.

Influence of Al doping on crystal structure, magnetic and optical properties of TiO2 compound

Recently, an attempt to search for the novel material which can be applicable for spintronics devices, has become a highly debated and intensively investigated field of study. Within the scope of this investigation, Ti1−xAlxO2 (0≤x≤0.12) polycrystalline samples were produced using the traditional solid-state reaction method, and their crystal structure, magnetic, and optical characteristics were investigated. Single rutile phase with tetragonal crystal structure of titanium oxide is seen from the X-ray diffraction patterns study. The variation in the lattice parameter elucidate that Al3+ ions successfully substitute the Ti4+ ions. The analyses of the optical characteristics reveals that the incorporation of Al into the TiO2 matrix leads to a reduction in the optical band gap. Investigation on magnetic characteristics showed that all Ti1−xAlxO2 compounds displayed room temperature ferromagnetic nature with 81Oe≤Hc≤930Oe. Hall effect measurements show that all doped samples display p-type conductivity while un-doped TiO2 exhibits n-type conductivity and with increasing Al-doping concentration, the hole carrier density rises.

Mechanochemical synthesis of (Mg1−x Fe x )2SiO4 olivine phases relevant to Martian regolith: structural and spectroscopic characterizations

Abstract To fabricate metals from the base materials for future Mars exploration, synthesis of representative olivine phases and their structural and spectroscopic characterizations are of crucial importance. Using mechanochemical technique that mimics the mechanical weathering, a complete solid solution of (Mg1−x Fe x )2SiO4 has been synthesized to investigate the associated crystal chemical properties. X-ray powder diffraction data Rietveld analysis confirms that each polycrystalline sample crystallizes in space group Pbnm. The average crystallite size ranges between 80(1) nm and 223(4) nm. Each lattice parameter increases with increasing Fe-content due to the larger Fe2+ radius than that of Mg2+, following Vegard’s rule. For a given nominal chemical composition, substitution of Mg with Fe at the M1-site (4a: 0,0,0) is preferred to the M2-site (4c: x,y,¼). As a consequence, the average Fe-content lies slightly below the equivalence line for x = 0.2–0.8, indicating that the Fe/Mg ratio in the amorphous scattering content is most likely greater than unity. Characteristic Raman spectral features of the olivines have been explained in terms of the chemical composition (x). Simple regression models are demonstrated based on both X-ray diffraction and Raman spectroscopic data for the calculation of Mg/Fe in olivines. Diffuse reflectance UV/Vis spectra RATD analysis shows each olivine phase possesses direct band-gap between 3.38(3) eV and 4.90(3) eV. This study could keep valuable information to relevant databases for future human missions on Mars, in particular, for precise estimation of the representative olivines from the remote X-ray diffraction and spectroscopic data.

Magnetic capacity in manganese sulfides with rare earth substitution Mn<sub>1–x</sub>Re<sub>x</sub>S

Polycrystalline samples Mn1–xGdxS and Mn1–xYbxS with a concentration x = 0.2, near the concentration of ion flow through the fcc lattice, are studied in order to determine fluctuations in the valence of the ytterbium ion on dielectric properties. Dielectric constant and dielectric losses were determined from measurements of capacitance and loss tangent in the frequency range 102–106 Hz at temperatures of 80–500 K without a magnetic field and in a magnetic field. The magnetic capacity and dielectric losses in the magnetic field of the sample were determined from the relative change in the real and imaginary parts of the dielectric constant of the sample in a magnetic field H = 12 kOe applied parallel to the capacitor plates. A temperature range with a sharp increase in dielectric constant and with a maximum dielectric loss has been discovered, which shifts with increasing frequency and magnetic field. An increase in dielectric constant and dielectric losses in a magnetic field above 170 K was found in Mn1-xYbxS. The increase in dielectric losses is explained by an increase in relaxation time, as a result of local deformations near ytterbium ions during valence fluctuations. The mechanism for reducing reactance in a magnetic field in Mn1–xYbxS at low frequencies due to capacitance, and at high frequencies due to inductance, has been determined. In the Mn0.8Gd0.2S compound, the imaginary part of the dielectric constant has two maxima. The low-temperature maximum shifts in a magnetic field towards high temperatures and is described in the model of localized electrons with freezing of dipole moments. Dielectric losses decrease in a magnetic field. The magnetic capacity decreases by an order of magnitude in Mn0.8Gd0.2S compared to Mn0.8Yb0.2S. The dielectric constant in both compounds is described in the Debye model with the activation dependence of the relaxation time on temperature, where the activation energies differ for ytterbium and gadolinium ions.

Texture tomography, a versatile framework to study crystalline texture in 3D.

Crystallographic texture is a key organization feature of many technical and biological materials. In these materials, especially hierarchically structured ones, the preferential alignment of the nano constituents heavily influences the macroscopic behavior of the material. To study local crystallographic texture with both high spatial and angular resolution, we developed Texture Tomography (TexTOM). This approach allows the user to model the diffraction data of polycrystalline materials using the full reciprocal space of the crystal ensemble and describe the texture in each voxel via an orientation distribution function, hence it provides 3D reconstructions of the local texture by measuring the probabilities of all crystal orientations. The TexTOM approach addresses limitations associated with existing models: it correlates the intensities from several Bragg reflections, thus reducing ambiguities resulting from symmetry. Further, it yields quantitative probability distributions of local real space crystal orientations without further assumptions about the sample structure. Finally, its efficient mathematical formulation enables reconstructions faster than the time scale of the experiment. This manuscript presents the mathematical model, the inversion strategy and its current experimental implementation. We show characterizations of simulated data as well as experimental data obtained from a synthetic, inorganic model sample: the silica-witherite biomorph. TexTOM provides a versatile framework to reconstruct 3D quantitative texture information for polycrystalline samples; it opens the door for unprecedented insights into the nanostructural makeup of natural and technical materials.

Enhanced magnon thermal transport in yttrium-doped spin ladder compounds Sr14−xYxCu24O41

Magnons are quasiparticles of spin waves, carrying both thermal energy and spin information. Controlling magnon transport processes is critical for developing innovative magnonic devices used in data processing and thermal management applications in microelectronics. The spin ladder compound Sr14Cu24O41 with large magnon thermal conductivity offers a valuable platform for investigating magnon transport. However, there are limited studies on enhancing its magnon thermal conductivity. Herein, we report the modification of magnon thermal transport through partial substitution of strontium with yttrium (Y) in both polycrystalline and single crystalline Sr14−xYxCu24O41. At room temperature, the lightly Y-doped polycrystalline sample exhibits 430% enhancement in thermal conductivity compared to the undoped sample. This large enhancement can be attributed to reduced magnon-hole scattering, as confirmed by the Seebeck coefficient measurement. Further increasing the doping level results in negligible change and eventually suppression of magnon thermal transport due to increased magnon-defect and magnon-hole scattering. By minimizing defect and boundary scattering, the single crystal sample with x = 2 demonstrates a further enhanced room-temperature magnon thermal conductivity of 19Wm−1K−1, which is more than ten times larger than that of the undoped polycrystalline material. This study reveals the interplay between magnon-hole scattering and magnon-defect scattering in modifying magnon thermal transport, providing valuable insights into the control of magnon transport properties in magnetic materials.

Anelastic and Magnetic Properties of Polycrystalline La0.6Sr0.4Fe1−xCuxO3−δ

Perovskite La0.6Sr0.4Fe1−xCuxO3−δ (x = 0, 0.05, 0.1, and 0.2) polycrystalline samples have been synthesized in air and investigated by X‐Ray diffraction, scanning electron microscope, magnetization, and mechanical spectroscopy. An antiferromagnetic transition is observed around 300 K, while no corresponding anomaly is observed in the mechanical spectrum, indicating the absence of conventional magnetoelastic coupling. For La0.6Sr0.4FeO3, an internal friction peak (P1) presents around 140 K and shifts to lower temperatures with increasing Cu‐doping content. Meanwhile, a magnetic anomaly is also observed around P1 peak temperature. As explained, the P1 peak is related to the freezing of the ferroelastic domain walls, and the mechanical energy dissipation is induced by the lagging variation of the octahedral tilting under the alternating stress. This work suggests a peculiar magnetic property of the octahedra within ferroelastic domain walls.

Occupation distribution analysis of Co in La-Co substituted M-type hexaferrite and its significant effect on magnetic properties

In recent years, La-Co co-substituted M-type strontium hexaferrite (La-Co SrM) has gained significant attention due to its improved permanent magnet performance and elevated operating temperature. However, the occupation of Co ions within the lattice of La-Co SrM has sparked considerable debate over the past two decades. To address this, neutron powder diffraction and Raman spectroscopy were employed in this study to analyze Co occupancy in La-Co SrM single crystal and polycrystalline samples. Results consistently reveal a preference for most Co ions to occupy the spin-down tetrahedral 4f1 site, which enhances the net magnetic moment and uniaxial magnetic anisotropy. Differences in Co ion distribution between single crystals (octahedral 12k and 2a sites) and polycrystalline powders (bipyramidal 2b sites) are attributed to sample preparation conditions, often overlooked in previous discussions. Therefore, precise regulation of Co occupancy, particularly maximizing the occupation of the 4f1 site, proves pivotal in enhancing magnetic properties.

Studies of Structural, Optical, and Raman Analysis of Ni‐Substituted CoFe2O4

The polycrystalline ferrite samples of NixCo1−xFe2O4 (x = 0.1, 0.3, 0.5, 0.7, and 0.9) are synthesized through the well‐known sol–gel method. The X‐ray diffraction (XRD) pattern confirms the cubic single‐phase spinel structure. Rietveld refinement indicates the absence of any other impurity phases in the samples. Additionally, XRD analysis reveals variations in lattice parameters corresponding to the doping. The Debye Scherer formula has been used to calculate the crystallite size of the samples, the crystallite size of the samples existing in the nanoregime. The results from field emission scanning electron microscopy confirm the morphological structure of the prepared samples. Additionally, the energy‐dispersive X‐ray spectra confirm the elemental composition and purity of the synthesized samples, validating the appropriateness of doping in the polycrystalline samples. The Raman spectra give the information about the vibrational modes in the sample. The Fourier transform infrared rays spectrum shows that the samples have a broad range of chemical interactions. The photoluminescence spectroscopy (PL) suggests strong luminescence in the visible range. PL spectroscopy provides that PL intensity decreases with increasing excitation wavelength due to nanosize of the particle.

First-order transition under a magnetic ordered state in SmPtSi2

We have synthesized polycrystalline and single-crystalline samples of SmPtSi2, and measured their resistivity, specific heat, magnetization, and Seebeck coefficient. The existence of two magnetic phase transitions has been confirmed, one at T H = 8.6 K and the other T L = 5.6 K. A hump-type anomaly in resistivity, a lambda-type anomaly in specific heat, a downward bend in magnetization, and a semiconductor-like increase in the Seebeck coefficient were observed at T H, indicating an antiferromagnetic transition accompanied by a gap opening on the Fermi surface. In contrast, a sharp drop in resistivity, a sharp spike in specific heat, and a drop in magnetization were observed at T L. The Seebeck coefficient showed metallic temperature dependence below T L. With increasing pressure, T H and T L shifted to higher temperatures. The transition at T L was no longer observed at pressures above 1.5 GPa. These findings suggest that the transition at T L is a transition from an antiferromagnetic ordered state with the gap on the Fermi surface to a different antiferromagnetic state.

Gadolinium spin dilution in the ferromagnetic solid solutions Gd2–x Y x Cu2Mg

Abstract Samples of the solid solution Gd2–x Y x Cu2Mg (in steps of x = 0.2) were synthesized from the elements in sealed tantalum ampoules in a high-frequency furnace. The polycrystalline samples were characterized by X-ray powder diffraction. The structure of Gd0.988(6)Y1.012(6)Cu2Mg was refined from single-crystal X-ray diffractometer data: Mo2B2Fe type, P4/mbm, a = 762.83(4), c = 375.48(2) pm, wR2 = 0.0277, 285 F 2 values and 13 variables. Single-crystal data gave no hint for Gd/Y ordering. All samples behave like Curie-Weiss paramagnets with stable trivalent gadolinium and ferromagnetic ordering at low temperature. Within the solid solution the Curie temperature drops almost linearly from T C = 113.5(1) K for Gd2Cu2Mg to 9.3(1) K for Gd0.2Y1.8Cu2Mg, allowing a precise adjustment of the magnetic ordering temperature through gadolinium spin dilution.

Effect of Ho3+ Doping on Structural and Magnetic Properties of Multiferroic YbMnO3

Using the traditional solid-state reaction approach, multiferroic ceramics with the compositional formula Yb1−xHoxMnO3, where x = 0 to 0.4 with 0.1 variation were synthesized. The structural and magnetic properties of the prepared poly-crystalline samples Yb1−xHoxMnO3 were investigated to show the effect of higher magnetic moment Ho3+ ion over the Yb ion. X-ray diffraction was used to analyze the compound’s crystal structure and confirm that they have a hexagonal single-phase structure with a P6 3 cm space group. The presence of functional groups and their shifting to lower frequency regions were revealed by Fourier-transform infrared spectroscopy. UV–vis absorbance spectra were used to calculate the energy gap values, and the resultant data shows a decrease in band gap values with an increase in Ho3+ doping. Crystal deformation with the doping of Ho3+ was observed using Raman spectra. Room-temperature magnetic studies were used to reveal the paramagnetic nature of the samples and the increase in magnetic parameters due to the doping of the higher magnetic moment Ho3+ ion.

Strong interlayer magnetic exchange coupling in La3Ni2O7−δ revealed by inelastic neutron scattering

After several decades of studies of high-temperature superconductivity, there is no compelling theory for the mechanism yet; however, the spin fluctuations have been widely believed to play a crucial role in forming the superconducting Cooper pairs. The recent discovery of high-temperature superconductivity near 80 K in the bilayer nickelate La3Ni2O7 under pressure provides a new platform to elucidate the origins of high-temperature superconductivity. We perform elastic and inelastic neutron scattering studies on a polycrystalline sample of La3Ni2O7−δ at ambient pressure. No magnetic order can be identified down to 10 K. The absence of long-range magnetic order in neutron diffraction measurements may be ascribed to the smallness of the magnetic moment. However, we observe a weak flat spin-fluctuation signal in the inelastic scattering spectra at ∼ 45 meV. The observed spin excitations could be interpreted as a result of strong interlayer and weak intralayer magnetic couplings for stripe-type antiferromagnetic orders. Our results provide crucial information on the spin dynamics and are thus important for understanding the superconductivity in La3Ni2O7.