Crystal Symmetry Research Articles

Crystal orientation dependent spin pumping in a Bi0.1Y2.9Fe5O12/Pt interface

Ferromagnetic resonance (FMR) based spin pumping is a versatile tool to quantify the spin-mixing conductance and spin-to-charge conversion (S2CC) efficiency of ferromagnet–normal metal (FM/NM) heterostructures. The spin-mixing conductance at the FM–NM interface can also be tuned by the crystal orientation symmetry of epitaxial FM. In this work, we study the S2CC in epitaxial bismuth-substituted yttrium iron garnet (Bi0.1Y2.9Fe5O12) thin-film Bi–YIG (100 nm) interfaced with heavy metal platinum (Pt, 8 nm) deposited by pulsed laser deposition on different crystal orientations of Gd3Ga5O12 substrates, i.e. [100] and [111]. The crystal structure and surface roughness characterized by x-ray diffraction and atomic force microscopy measurements establish epitaxial Bi–YIG [100] and Bi–YIG [111] orientations, and atomically flat surfaces, respectively. The S2CC quantification was realized using two complementary techniques, namely (i) FMR-based spin pumping and the inverse spin Hall effect (ISHE) at GHz frequencies and (ii) temperature-dependent spin Seebeck measurements. The FMR-ISHE results demonstrate that the [111]-oriented Bi–YIG/Pt sample shows significantly higher values of spin mixing conductance ((2.31 ± 0.23) × 1018 m−2) and spin Hall angle (0.01 ± 0.001) as compared to the [100]-oriented Bi–YIG/Pt. Longitudinal spin Seebeck measurements reveal that the [111]-oriented sample has a higher spin Seebeck coefficient (106.40 ± 10 nV mm−1 K−1). The anisotropic nature of the spin-mixing conductance and spin Seebeck coefficient in the [111] and [100] orientations are discussed using the magnetic environment elongation along the surface normal or parallel to the growth direction. Our results aid in understanding the role of crystal orientation symmetry in S2CC-based spintronics devices.

Probing the Multiexcitonic Dynamics in CsPbI3 Nanocrystals across the Temperature‐Induced Reversible Phase Transitions

AbstractCsPbI3 nanocrystals (CPI NCs) have become a trending research topic due to their impressive potential in functional optoelectronic devices and optical gain applications. Their optical responses are governed by carrier dynamics, which is greatly influenced by temperature and corresponding phase structure due to the effects of inherently electron‐phonon coupling. Notably, CPI NCs have been identified to adopt an unexpectedly stable cubic phase from room temperature to liquid helium temperature. Here, using in situ cryogenic electron diffraction measurements, it is unambiguously demonstrated that CPI NCs undergo consecutive cubic‐tetragonal‐orthorhombic phase transitions from 298 to 100 K. The corresponding temperature‐dependent multiexcitonic dynamics are investigated in each phase by combining time‐resolved photoluminescence and transient absorption spectroscopy. In addition to the temperature dependency, the lifetime of both excitons and biexcitons evidently depends on the phase structures of the CPI NCs, highlighting the crucial effect of crystal structure on the carrier dynamics. Moreover, the biexciton binding energy increases with higher crystal symmetry due to the decrease of the dielectric constant. The findings shed light on the structural phase transition and its relationship to the carrier dynamics in all‐inorganic perovskite NCs, which provides critical insight into the structure‐performance relationship in CPI NCs for promising applications in optoelectronic devices.

Atomic scale mechanism of β to γ phase transformation in gallium oxide

We report the detailed mechanism behind the β to γ phase transformation in Sn-doped and Si-implanted Ga2O3 that we determined based on the direct observation of the atomic scale structure using scanning transmission electron microscopy (STEM). Quantitative analysis of the STEM images revealed that the high concentration of impurity atoms favored the formation of interstitial–divacancy complexes, which then leads to the secondary relaxation that creates additional interstitial atoms and cation vacancies, resulting in a local structure that closely resembles γ-Ga2O3. We explain the mechanism of how the impurity atoms facilitate the transformation, as well as the detailed sequence of the local γ phase transformation. The findings here offer an insight on how the lattice respond to the external stimuli, such as doping and strain, and transform into different structures, which is important for advancing Ga2O3 but also a variety of low symmetry crystals and oxides with multiple polymorphs.

Molecular Design of a Metal-Nitrosyl Ferroelectric with Reversible Photoisomerization.

The development of photo-responsive ferroelectrics whose polarization may be remotely controlled by optical means is of fundamental importance for basic research and technological applications. Herein, we report the design and synthesis of a new metal-nitrosyl ferroelectric crystal (DMA)(PIP)[Fe(CN)5(NO)] (1) (DMA = dimethylammonium, PIP = piperidinium) with potential phototunable polarization via a dual-organic-cation molecular design strategy. Compared to the parent non-ferroelectric (MA)2[Fe(CN)5(NO)] (MA = methylammonium) material with a phase transition at 207 K, the introduction of larger dual organic cations both lowers the crystal symmetry affording robust ferroelectricity and increases the energy barrier of molecular motions, endowing 1 with a large polarization of up to 7.6 μC cm-2 and a high Curie temperature (Tc) of 316 K. Infrared spectroscopy shows that the reversible photoisomerization of the nitrosyl ligand is accomplished by light irradiation. Specifically, the ground state with the N-bound nitrosyl ligand conformation can be reversibly switched to both the metastable state I (MSI) with isonitrosyl conformation and the metastable state II (MSII) with side-on nitrosyl conformation. Quantum chemistry calculations suggest that the photoisomerization significantly changes the dipole moment of the [Fe(CN)5(NO)]2- anion, thus leading to three ferroelectric states with different values of macroscopic polarization. Such optical accessibility and controllability of different ferroelectric states via photoinduced nitrosyl linkage isomerization open up a new and attractive route to optically controllable macroscopic polarization.

Anisotropic elastic, opto-electronic and photocatalytic properties of BaTi2O5: First-principles calculations

In this work, the structural, elastic, electronic, photocatalytic and optical properties of BaTi2O5 have been explored using density functional theory (DFT). A comprehensive study of elastic properties revealed that BaTi2O5 is relatively hard, ductile, strongly anisotropic, and exhibits moderate machinability and toughness. The electronic structure analysis revealed indirect transition with bandgap value of 1.91 eV (GGA) and 3.69 eV (HSE03). The redox potential suggested that this compound is suitable for water splitting and agent of pollutant killers. The directional variation is confirmed from the optical properties and bandgap values. Additionally, the TiO bond distortion and the lowering of the crystal symmetry are endorsed as the causes of the considerable optical anisotropy along various polarization directions. The transmittance data confirmed that BaTi2O5 is highly transparent suitable for window materials. We anticipate that our findings will help in the development of high-performance optoelectronic devices as well as experimental investigations.

Leucopterin, the white pigment in butterfly wings: structural analysis by PDF fit, FIDEL fit, Rietveld refinement, solid-state NMR and DFT-D.

Leucopterin (C6H5N5O3) is the white pigment in the wings of Pieris brassicae butterflies, and other butterflies; it can also be found in wasps and other insects. Its crystal structure and its tautomeric form in the solid state were hitherto unknown. Leucopterin turned out to be a variable hydrate, with 0.5 to about 0.1 molecules of water per leucopterin molecule. Under ambient conditions, the preferred state is the hemihydrate. Initially, all attempts to grow single crystals suitable for X-ray diffraction were to no avail. Attempts to determine the crystal structure by powder diffraction using the direct-space method failed, because the trials did not include the correct, but rare, space group P2/c. Attempts were made to solve the crystal structure by a global fit to the pair distribution function (PDF-Global-Fit), as described by Prill and co-workers [Schlesinger et al. (2021). J. Appl. Cryst. 54, 776-786]. The approach worked well, but the correct structure was not found, because again the correct space group was not included. Finally, tiny single crystals of the hemihydrate could be obtained, which allowed at least the determination of the crystal symmetry and the positions of the C, N and O atoms. The tautomeric state of the hemihydrate was assessed by multinuclear solid-state NMR spectroscopy. 15N CPMAS spectra showed the presence of one NH2 and three NH groups, and one unprotonated N atom, which agreed with the 1H MAS and 13C CPMAS spectra. Independently, the tautomeric state was investigated by lattice-energy minimizations with dispersion-corrected density functional theory (DFT-D) on 17 different possible tautomers, which also included the prediction of the corresponding 1H, 13C and 15N chemical shifts in the solid. All methods showed the presence of the 2-amino-3,5,8-H tautomer. The DFT-D calculations also confirmed the crystal structure. Heating of the hemihydrate results in a slow release of water between 130 and 250 °C, as shown by differential thermal analysis and thermogravimetry (DTA-TG). Temperature-dependent powder X-ray diffraction (PXRD) showed an irreversible continuous shift of the reflections upon heating, which reveals that leucopterin is a variable hydrate. This observation was also confirmed by PXRD of samples obtained under various synthetic and drying conditions. The crystal structure of a sample with about 0.2 molecules of water per leucopterin was solved by a fit with deviating lattice parameters (FIDEL), as described by Habermehl et al. [Acta Cryst. (2022), B78, 195-213]. A local fit, starting from the structure of the hemihydrate, as well as a global fit, starting from random structures, were performed, followed by Rietveld refinements. Despite dehydration, the space group remains P2/c. In both structures (hemihydrate and variable hydrate), the leucopterin molecules are connected by 2-4 hydrogen bonds into chains, which are connected by further hydrogen bonds to neighbouring chains. The molecular packing is very efficient. The density of leucopterin hemihydrate is as high as 1.909 kg dm-3, which is one of the highest densities for organic compounds consisting of C, H, N and O only. The high density might explain the good light-scattering and opacity properties of the wings of Pieris brassicae and other butterflies.

Resolving the sintering conundrum of high-rhenium tungsten alloys

Tungsten-rhenium (W-Re) alloys with high-Re contents are the preferred refractory metal materials in many applications because of the improved ductility and processability over pure W and low-Re tungsten alloys. However, the sintering concurrently becomes increasingly more difficult with increasing Re contents. Here we proposed that the sintering conundrum is caused by the lowered crystal symmetry and the wider dihedral angle distribution when body-center-cubic (BCC) W is alloyed with more hexagonal-close-packed (HCP) Re, which results in inefficient pore removal in the final stage sintering. We showed that the conundrum can be resolved by pressureless two-step sintering (TSS) which suppresses accelerating final-stage grain growth, and our proposal is supported by the data of the critical density ρc that is required to start the second step for successful TSS at different W-Re compositions. Dense ultrafine-grained W-Re alloys with ∼300 nm average grain size and up to 25 wt% Re were successfully produced. Our work demonstrates the unique opportunities offered by two-step sintering to advance the scientific understanding and technological practices in powder metallurgy and related fields.

Long-Range Orbital Torque by Momentum-Space Hotspots.

While it is often assumed that the orbital response is suppressed and short ranged due to strong crystal field potential and orbital quenching, we show that the orbital response can be remarkably long ranged in ferromagnets. In a bilayer consisting of a nonmagnet and a ferromagnet, spin injection from the interface results in spin accumulation and torque in the ferromagnet, which rapidly oscillate and decay by spin dephasing. In contrast, even when an external electric field is applied only on the nonmagnet, we find substantially long-ranged induced orbital angular momentum in the ferromagnet, which can go far beyond the spin dephasing length. This unusual feature is attributed to nearly degenerate orbital characters imposed by the crystal symmetry, which form hotspots for the intrinsic orbital response. Because only the states near the hotspots contribute dominantly, the induced orbital angular momentum does not exhibit destructive interference among states with different momentum as in the case of the spin dephasing. This gives rise to a distinct type of orbital torque on the magnetization, increasing with the thickness of the ferromagnet. Such behavior may serve as critical long-sought evidence of orbital transport to be directly tested in experiments. Our findings open the possibility of using long-range orbital response in orbitronic device applications.

Interface birefringence in asymmetric CdTe/CdZnTe quantum wells

Photoluminescence and polarized reflection spectra of quantum well structures with symmetric ${\mathrm{Cd}}_{0.9}{\mathrm{Zn}}_{0.1}\mathrm{Te}/\mathrm{CdTe}/{\mathrm{Cd}}_{0.9}{\mathrm{Zn}}_{0.1}\mathrm{Te}$ and asymmetric ${\mathrm{Cd}}_{0.9}{\mathrm{Zn}}_{0.1}\mathrm{Te}/\mathrm{CdTe}/{\mathrm{Cd}}_{0.4}{\mathrm{Mg}}_{0.6}\mathrm{Te}$ barriers were studied. The Stokes parameters of the reflected light from these structures were measured. In structures with asymmetric barriers, in the region of exciton resonances, the phenomenon of light birefringence was detected, caused by a lower symmetry of the interfaces compared with the symmetry of bulk crystals. A discussion of this phenomenon is given.

Boosting piezocatalytic activity of graphitic carbon nitride for degrading antibiotics through morphologic regulation and chlorine doping

Graphitic carbon nitride (GCN) has been demonstrated to be a potential piezocatalyst in environmental remediation. The common piezoelectric materials synthesized by GCN are often designed to have a larger specific surface area to increase the adsorption and degradation performance of environmental pollutants. However, these process will also decrease the particle size of two-dimensional GCN, which thus affect the in-plane polarization intensity and inhibit the piezoelectric catalytic performance. Herein, we proposed an NH4Cl assistant synthesis to obtain ultrathin Cl-doped GCN (Cl-GCN) with large surface area and developed porosity. The introduced Cl with strong electronegativity can better change the electron cloud density distribution in GCN. From the experiment measurements and the theoretical calculation, Cl dopant in GCN skeleton resulted in partially destroyed crystal symmetry, and increased the structural polarity. As a result, the Cl-GCN simultaneously possessing large surface area and high piezoelectric polarization contributed enhanced piezocatalytic activity for degradation of antibiotics compared to the pristine GCN. Within 30 min, the degradation efficiency of tetracycline hydrochloride (TC-HCl) reached to ca. 94%. Besides, the effects of antibiotic concentration as well as the piezocatalytic durability for eliminating different antibiotics were investigated. Finally, based on determinations of mainly active species and the intermediate products during the piezocatalytic process, a plausible piezocatalytic degradation mechanism was proposed. This study implies that enhancing the piezoelectric polarization of piezocatalyst by heteroatomic doping and meanwhile improving its surface area are promising strategies to promoting piezocatalytic performance both for environmental application and for clean energy production.

Theory of the low- and high-field superconducting phases of UTe2

Recent nuclear magnetic resonance and calorimetric experiments have observed that ${\mathrm{UTe}}_{2}$ exhibits a transition between two distinct superconducting phases as a function of magnetic field strength for a field applied along the crystalline $b$ axis. To determine the nature of these phases, we employ a microscopic two-band minimal Hamiltonian with the essential crystal symmetries and structural details. We also adopt anisotropic ferromagnetic exchange terms. We study the resulting pairing symmetries and properties of these low- and high-field phases in mean-field theory.

Study on crystal structure, electrical and magnetic properties of LaFe xCo1-xO3 prepared by sol-gel method

Lanthanum Ferri-cobaltates magnetic semiconducting materials are very interesting materials and they have a wide range of applications. Electrical and magnetic transport in such materials and their correlation with crystal structure have been investigated. All synthesized samples based on the sol-gel method are in the nanocrystalline range (27–38 nm) with the rhombohedral crystal system. The low electronic density was calculated from XRD patterns and the obtained results showed that a slight variation in electronic density is noted as a result of small cobalt substitution by iron in LaFe0.8Co0.2O3 and LaFe0.5Co0.5O3. A drastic increase in the electronic density was observed in LaFe0.2Co0.8O3 and again a decrease in the value of the electronic density in LaCoO3. IR spectra confirmed the formation of the proposed Perovskite crystal symmetry. Although the dc conductivity of all samples was small, we found a difference as a result of replacing iron with cobalt. The mechanism of electronic transfer in LaFexCo1-xO3 is mainly due to the electrons hopping between both Fe3+↔Fe2+ and Co3+↔Co2+ ions. Electrical measurements showed the semiconducting behavior of all samples. The optical properties studied by UV–Vis diffuse reflectance showed a large change in the optical energy gap with increasing Fe ions. All samples have a low energy band gap. The minimum Hci was 67G and the maximum was 715G as a result of doping. Magnetic hysteresis at room temperature showed antiferromagnetic order with weak ferromagnetism (canted antiferromagnetic order) enhanced with Fe content. The multi-domain grains appeared in La FexCo1-xO3 because the squareness ratio (Mr/Ms) in our case is in the range between 0.0 and 0.25.

Development of a novel triple perovskite barium bismuth molybdate material for thermistor-based applications

In this communication, development (synthesis and characterization) of a novel triple perovskite sample Ba3Bi2MoO9 (BBMO) is reported. The material has monoclinic crystal symmetry. A detailed study of microstructure and compositional analysis of the sample by using scanning electron microscopy (SEM) and EDX (energy dispersive X-rays) spectrum has provided the quality of the BBMO ceramic. The topological and surface roughness of the novel material has been analyzed to clarify the surface texture and compactness of the sample surface. The variation of conductivity under the alternating current of the material varies according to the Jonscher's universal power law. The high dielectric constant and low tangent loss are applicable for fabrication of various electrical instruments. The resistance decreases with an increase in temperature supports the NTCR (negative temperature coefficient of resistance) behavior, which is clarified by using TCR and β (thermistor constant) for NTC thermistor application.

Structure Evolution and Bonding Inhomogeneity toward High Thermoelectric Performance in Cu2CoSnS4-xSex Materials.

Lightweight diamond-like structure (DLS) materials are excellent candidates for thermoelectric (TE) applications due to their low costs, eco-friendly nature, and property stability. The main obstacles restricting the energy-conversion performance by the lightweight DLS materials are high lattice thermal conductivity and relatively low carrier mobility. By investigating the anion substitution effect on the structural, microstructural, electronic, and thermal properties of Cu2CoSnS4-xSex, we show that the simultaneous enhancement of the crystal symmetry and bonding inhomogeneity engineering are effective approaches to enhance the TE performance in lightweight DLS materials. Particularly, the increase of x in Cu2CoSnS4-xSex makes the DLS structure with the ideal tetrahedral bond angles of 109.5° favorable, leading to better crystal symmetry and higher carrier mobility in samples with higher selenium content. In turn, the phonon transport in the investigated DLS materials is strongly disturbed due to the bonding inhomogeneity between anions and three sorts of cations inducing large lattice anharmonicity. The increase of Se content in Cu2CoSnS4-xSex only intensified this effect resulting in a lower lattice component of the thermal conductivity (κL) for Se-rich samples. As a result of the enhanced power factor S2ρ-1 and the low κL, the dimensionless thermoelectric figure of merit ZT achieves a high value of 0.75 for Cu2CoSnSe4 DLS material. This work demonstrates that crystal symmetry and bonding inhomogeneity play an important role in the transport properties of DLS materials and provide a path for the development of new perspective materials for TE energy conversion.

Source-configured symmetry-broken hyperbolic polaritons

Polaritons are quasi-particles that combine light with matter, enabling precise control of light at deep subwavelength scales. The excitation and propagation of polaritons are closely linked to the structural symmetries of the host materials, resulting in symmetrical polariton propagation in high-symmetry materials. However, in low-symmetry crystals, symmetry-broken polaritons exist, exhibiting enhanced directionality of polariton propagation for nanoscale light manipulation and steering. Here, we theoretically propose and experimentally demonstrate the existence of symmetry-broken polaritons, with hyperbolic dispersion, in a high-symmetry crystal. We show that an optical disk-antenna positioned on the crystal surface can act as an in-plane polarized excitation source, enabling dynamic tailoring of the asymmetry of hyperbolic polariton propagation in the high-symmetry crystal over a broad frequency range. Additionally, we provide an intuitive analysis model that predicts the condition under which the asymmetric polaritonic behavior is maximized, which is corroborated by our simulations and experiments. Our results demonstrate that the directionality of polariton propagation can be conveniently configured, independent of the structure symmetry of crystals, providing a tuning knob for the polaritonic response and in-plane anisotropy in nanophotonic applications.

Symmetry indicators in commensurate magnetic flux

We derive a framework to apply topological quantum chemistry in systems subject to magnetic flux. We start by deriving the action of spatial symmetry operators in a uniform magnetic field, which extends Zak's magnetic translation groups to all crystal symmetry groups. Ultimately, the magnetic symmetries form a projective representation of the crystal symmetry group. As a consequence, band representations acquire an extra gauge invariant phase compared to the non-magnetic theory. Thus, the theory of symmetry indicators is distinct from the non-magnetic case. We give examples of new symmetry indicators that appear at $\pi$ flux. Finally, we apply our results to an obstructed atomic insulator with corner states in a magnetic field. The symmetry indicators reveal a topological-to-trivial phase transition at finite flux, which is confirmed by a Hofstadter butterfly calculation. The bulk phase transition provides a new probe of higher order topology in certain obstructed atomic insulators.

High-performance photodetectors based on two-dimensional perovskite crystals with alternating interlayer cations

Organic-inorganic halide perovskite, as a low-cost, solution-processable material with remarkable optoelectronic properties, is ideal candidate to fabricate high-performance photodetectors and is expected to significantly reduce device costs. Compared to the common Dion-Jacobson and Ruddlesden-Popper two-dimensional (2D) layered hybrid perovskite compounds, the perovskites with alternating cations in the interlayer (ACI) phase show higher crystal symmetry and narrower optical bandgaps, which exhibit great potential for excellent photodetection performance. Herein, we report a high-performance photodetector based on the 2D bilayered hybrid lead halide perovskite single crystal with the ACI phase (GAMA2Pb2I7; GA = C(NH2)3 and MA = CH3NH3). The single-crystal photodetector exhibits high photoresponsivity of 1.56, 2.54, and 2.60 A/W for incident light wavelengths of 405, 532, and 635 nm under 9.82 nW, respectively, together with the correspondingly high detectivity values of 1.86 × 1012, 3.04 × 1012, and 3.11 × 1012 Jones under the same operating conditions. Meanwhile, a high-resolution imaging sensor is built based on the GAMA2Pb2I7 single-crystal photodetector, confirming the high stability and photosensitivity of the imaging system. These results show that the 2D hybrid lead halide perovskites with alternating interlayer cations are promising for high-performance visible light photodetectors and imaging systems.

Multi-state data storage in a two-dimensional stripy antiferromagnet implemented by magnetoelectric effect

A promising approach to the next generation of low-power, functional, and energy-efficient electronics relies on novel materials with coupled magnetic and electric degrees of freedom. In particular, stripy antiferromagnets often exhibit broken crystal and magnetic symmetries, which may bring about the magnetoelectric (ME) effect and enable the manipulation of intriguing properties and functionalities by electrical means. The demand for expanding the boundaries of data storage and processing technologies has led to the development of spintronics toward two-dimensional (2D) platforms. This work reports the ME effect in the 2D stripy antiferromagnetic insulator CrOCl down to a single layer. By measuring the tunneling resistance of CrOCl on the parameter space of temperature, magnetic field, and applied voltage, we verified the ME coupling down to the 2D limit and probed its mechanism. Utilizing the multi-stable states and ME coupling at magnetic phase transitions, we realize multi-state data storage in the tunneling devices. Our work not only advances the fundamental understanding of spin-charge coupling, but also demonstrates the great potential of 2D antiferromagnetic materials to deliver devices and circuits beyond the traditional binary operations.

The role of Zn and Ru substitution on the structural, magnetic and dielectric properties of ferrite cuprospinels

A comprehensive study on the structural, magnetic and dielectric behavior of ferrite cuprospinels with site specific substitution of non-magnetic Zn and weakly magnetic Ru ions has been presented. Such substitution leads to two classes of stable crystal symmetries, (i) tetragonal (I41/amd): CuFe1.95Ru0.05O4 and Cu0.95Zn0.05Fe1.95Ru0.05O4 and (ii) cubic (Fd-3m):Cu0.60Zn0.40Fe1.95Ru0.05O4 and Cu0.05Zn0.95Fe1.95Ru0.05O4 bulk polycrystals. The former set of compounds undergo significant Jahn-Teller (JT) distortion due to high Cu content and such distortion gets lifted with the substitution of non-magnetic Zn ions. Ferrimagnetic (FiM) behavior is predominant in all these compounds except the highest Zn (95 at.%) content cubic system with diluted substitution of Ru (2.5 at.%) which exhibits antiferromagnetic ordering below the Néel temperature (T N ∼ 10.9 K). We employed Néel’s expression for FiM systems applicable for the two sublattice model to extract the dominant exchange interactions (J AA , J AB and J BB ) between the A-site and B-site cations. Subsequently the high temperature (300 K T 900 K) inverse paramagnetic susceptibility data has been fitted to the above expression which yields dominant ∼ 391 K with very high asymptotic Curie temperature for the tetragonally distorted dilute Zn substituted cuprospinel, while the Zn-rich cubic system exhibits ∼ 300 K. On the other hand, the tetragonally distorted spinel devoid of Zn exhibits dominant ∼ 229 K with negligible and moderate (65 K) signifying that the JT active ions cause the onset of magnetic frustration and enhanced ordering temperatures. All the investigated systems exhibit significant magneto-crystalline anisotropy with a maximum anisotropy field H K ∼ 6 kOe and maximum anisotropy constant (K 1 ∼ 10.88×105 erg cm−3). The broadband dielectric spectroscopy studies reveal significant enhancement of mid-frequency dielectric constant ε R (f, T) with plateau-like feature over a wide temperature and frequency window, together with low-loss as a result of the incorporation of Ru ions into the tetragonally distorted spinel lattice. The ac resistivity ρ(f, T) studies reveal that the mode of conduction follows Mott’s variable-range hopping (VRH) model with a linear logarithmic variation of ρ ac versus T −0.25. The temperature dependence of the VRH activation energy of charge carriers follows a linear behavior which indicates the presence of localized polaron in all the investigated systems.

A direct view on Ni substitution in Sc2Ir6-xNixB as probed by NMR

Intermetallic borides, such as the Sc2Ir6-xNixB (x = 0–6) series, exhibit technologically relevant physicochemical properties, that are all associated to boron ordering. X-ray diffraction has not yet fully investigated the effect of Ir substitution by Ni on the boron arrangement of these borides, primarily due to its weak scattering factor. Herein we employ 11B-NMR to probe the boron ordering of Sc2Ir6-xNixB series at atomic scale, overcoming limitations on low-Z materials. Across the Ni-substitution range, the spectral parameters and spin-lattice relaxation rates (T1−1) were responsive to changes in crystal symmetry and valence charges. The spectral analysis and T1−1 vs. x reveal that Ni substitution causes phase separation at the nanoscale between ordered and disordered borides. For x = 3, T1−1 is T-independent, indicating a relaxation mechanism caused by paramagnetic centers whereas x = 5 follows a T2-dependence that is consistent with band structure predictions of a reduction in the density of states, correlated with sharp features near the Fermi level.