Antiparallel Alignment Research Articles

Existence of structural, electronic and magnetic correlations in Sm$ _{2} $NiMnO$ _{6} $ double perovskite.

Coupling between different interactions allows the control of physical aspects in multifunctional materials by perturbing any degrees of freedom. Here, we aim to probe the correlation among structural, electronic, and magnetic observables in Sm$ _{2} $NiMnO$ _{6} $ (SNMO) ferromagnetic insulator double perovskite. Our employed methodology includes thermal evolution of X-ray diffraction, X-ray absorption spectroscopy, and bulk magnetometry. The magnetic ordering in SNMO adopts two transitions, at T$ _{C} $=160 K due to the ferromagnetic arrangement of Ni-Mn sublattice and at T$ _{d} $=34 K because of anti-parallel alignment of polarized Sm paramagnetic moments with respect to Ni-Mn network. Signature of Ni/Mn anti-site disorders are evidenced from short-range structure and magnetization analysis. The long-range as well as short-range crystal structure of SNMO undergo changes across T$ _{C} $ and T$ _{d} $, observed through temperature dependent variation in Ni/Mn-O bonding characters. Hybridization between Ni, Mn 3\textit{d}, O 2\textit{p} electronic states show changes in the vicinity of magnetic transition. The change in crystal environments governs the magnetic response by imposing alteration in metal - ligand orbital overlap. On the other hand, it is observed that application of electric bias causes monotonic reduction in the saturation magnetic moment. By using these experimental methods, we demonstrate how the structural, electronic, and magnetic properties are correlated in SNMO, which makes it a potential platform for technological usage.

Tuning the magnetic properties by partial substitution of Cr in D022-Mn3Ga: A potential material for spin transfer torque applications

This report presents the effect of partial substitution of the Cr atom at the itinerant octahedral site (Y2b site) of D022-type Mn3Ga. The Cr introduces a reduction of magnetization due to the antiparallel alignment of Cr atoms at the itinerant site to Mn atoms at the localized site (X4d) with variation in mixed valence states (Mn4+ and Mn3+) from that of the pristine as revealed from the deconvolution of the Mn2p peak. The alloy possesses irreversible magneto-structural phase transformation during heating and cooling modes of temperature-dependent magnetization study. During heating, the magnetic interaction between Mn and Cr atoms possesses an abrupt change in magnetization over temperature, leading to Hopkinson’s like effect with magneto-structural transition temperature (Tc) ∼ 780 K, notably higher than the parent alloy. The thermal variation of uniaxial magnetocrystalline anisotropy ≈1.20-0.2 Merg/cc in addition to high coercivity (∼1.2–2.85 kOe) can be utilized as potential material for spin transfer torque-based memory applications.

Complexes of d‐ and f‐metal Ions with Redox‐Active and Highly Symmetric Truxenone Ligand: Effect of Cations and Coordination on Distortions of Radical Anions and Singlet–Triplet Transition in Dianions

Truxenone (Tr) with high C3h symmetry forms crystalline radical anion and dianion salts. The {Bu3MeP+}(Tr·−)(1) and {Cp*2Co+)}(Tr·‐).2C6H4Cl2(2) show intense low‐energy absorption up to 2000nm. Calculations predict Jahn–Teller distortions for Tr·‐, which are enhanced by the asymmetric approach of cations to Tr·‐, leading to C=O bond length alternation and EPR signal asymmetry in 2. Two cesium ions form short contacts of 3.07–3.35Å with oxygen atoms of Tr2‐ in {Cryptand[2.2.2](Cs+)}2(Tr2‐)(3), linking the dianions into a 1D polymer. Calculations suggest a triplet state for the dianions, but the unsymmetric approach of Cs+ to the oxygen atoms of Tr2‐ stabilizes the singlet ground state. The triplet state is populated above 100K. An estimated singlet–triplet energy gap is 344±7K. Radical anions of Tr·‐ coordinate with one d‐ or f‐metal, forming {Cp*2Co+}{TbIII(TMHD)3×Tr}‐.1.5C7H8(4) and {Cp*2Co+}{MnII(acac)2×Tr}‐.2.4C6H4Cl2(5). Strong antiferromagnetic TbIII–Tr·‐ coupling (J =−7.6cm−1) aligns spins of TbIII and Tr·‐ antiparallel in 4. The χMT value of 3.32 emu×K/mol at 300K for 5 with high‐spin MnII is lower‐than‐expected. That indicates a spin state of S=2 owing to the antiparallel alignment of MnII and Tr·‐ spins. Strong MnII–Tr·‐ coupling arising from the spin density localization on the oxygen coordinated to MnII. Complexes with metals demonstrate low‐energy absorption with maxima at 1504–1740nm.

Long wavelength interdomain phonons and instability of dislocations in small-angle twisted bilayers

Abstract We develop a theory for long wavelength phonons originating at dislocations separating domains in small-angle twisted homobilayers of 2D materials such as graphene and MX2 transition metal dichalcogenides (M=Mo,W; X=S,Se). We find that both partial and perfect dislocations, forming due to lattice relaxation in the twisted bilayers with parallel and anti-parallel alignment of unit cells of the constituent layers, respectively, support several one-dimensional subbands of the interdomain phonons. We show that spectrum of the lowest gapless subband is characterized by imaginary frequencies, for wave-numbers below a critical value, dependent on the dislocation orientation, which indicates an instability for long enough straight partial and perfect dislocations. We argue that pinning potential and/or small deformations of the dislocations could stabilize the gapless phonon spectra. The other subbands are gapped, with subband bottoms lying below the frequency of interlayer shear mode in domains, which facilitates their detection with the help of optical and magnetotransport techniques.

Magnon signatures of multidimensional reconfigurations in multilayer square artificial spin ices

We present an all-electrical, broadband spin-wave spectroscopy study of three-dimensional square artificial spin ices composed of dipolarly coupled ferromagnetic layers of varying thicknesses separated by a non-magnetic spacer. Our experiments, in the saturated regime, reveal that the spin-wave spectra exhibit a strong dependence on both the angle of the applied magnetic field and the geometrical aspect ratio of the ferromagnetic layers. Micromagnetic simulations and analytical calculations, utilizing the Smit–Beljers formalism, demonstrate good agreement with our experimental findings. In the magnetic switching regime, the spin-wave spectra indicate an antiparallel alignment between the two ferromagnetic layers. This configuration is highly sensitive to the field angle, suggesting the presence of multidimensional reconfigurations within the multilayer artificial spin ice. Furthermore, employing a minor loop field protocol, we show that the spin-wave modes associated with the antiparallel alignment remain reproducible, even after 100 minor loop cycles, providing intriguing possibilities for magnonic engineering.

Rapidly Generated, Ultra-Stable, and Switchable Photoinduced Radicals: A Solid-State Photochromic Paradigm for Reusable Paper Light-Writing.

Although photochromic molecules have attracted widespread interest in various fields, solid-state photochromism remains a formidable challenge, owing to the substantial conformational constraints that hinder traditional molecular photoisomerization processes. Benefiting from the significant color change upon radical generation, chemical systems enabling a photoinduced radical (PIR) behavior through photoinduced electron transfer (PET) could be ideal candidates for solid-state photochromism within minimized need of conformational freedom. However, the transient nature of radicals causes a dilemma in this Scheme. Herein, we present a general crystal engineering strategy for rapidly generated (7-s irradiation to saturation) and ultra-stable (lasting 12 weeks) PIRs in the solid state, based on the anti-parallel alignment of para-hydroxyphenyl groups of persulfurated arenes to form a strong non-covalent network for efficient PET and radical stabilization. Using this strategy, a PIR platform was constructed, with a superior photochromic behavior remaining in different solid forms (even in the fully-ground sample) due to their transcendent crystallization ability. On this basis, our compounds can be further processed into reusable papers for light-writing, accompanied by water fumigation for modulating the reversible process. This work provides new insights into addressing solid-state photochromism and can inspire a wide range of optical material design from the switchable radical perspective.

Structural Analysis and Processing Characterization of Chitins Extracted from Different Sources.

The characteristics of three different types of chitin extracted from commonly used seafood organisms; namely crabs, shrimps, and squids were investigated. X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) were employed to analyze these chitins' polymorphic structure and morphology. Bulk and tapped density measurements, along with Kawakita analysis, were used to assess the flowability and compression behaviour of the chitin powders. Chitin extracted from crabs and shrimp exhibited the α-polymorphic form, while chitin from squid showed the β-polymorphic form. SEM images of the two forms revealed distinct differences in chitin layer arrangement, with the α-form appearing more compact due to the anti-parallel alignment of its polymer chains. Both bulk and tapped density measurements and the calculated Hausner ratio (HR) and Carr Index (CI) indicated poor flowability for these chitins. However, Kawakita's analysis of compression and compaction properties demonstrated that both polymorphs are compressible, though they differ in their extent of compaction. Regardless of their source, chitin compacts exhibited high crushing strength. Based on the observed morphology, flowability, and compression characteristics, a blend of α- and β-polymorphic chitin could be an effective excipient for pharmaceutical solid dosage forms.

A Nanosized {NiII 18} Cluster with a 'Flying Saucer' Topology Exhibiting Slow Relaxation of Magnetisation Phenomena at Both 15 K and 1.3 K.

A high-nuclearity {Ni18} complex (1) with a unique 'flying saucer' motif has been prepared from the organic chelate, α-methyl-2-pyridine-methanol (mpmH), in conjunction with bridging azido (N3 -) and peroxido (O2 2-) ligands. Magnetic susceptibility measurements revealed the presence of both ferro- and antiferromagnetic exchange interactions between the metal centres in 1, and the stabilization of spin states with appreciable S values at two different temperature regimes. The end-on bridging azido and alkoxido groups are in all likelihood the ferromagnetic mediators, while the η3:η3:μ6-bridging peroxides most likely promote the antiparallel alignment of the metals' spin vectors, yielding an overall non-zero spin ground state for the centrosymmetric compound 1. Furthermore, the {Ni18} nanosized cluster behaves as a single-molecule magnet, exhibiting magnetic hysteresis at low temperatures and two relaxation processes at 15 K and 1.3 K, a very rare phenomenon in polynuclear magnetic 3d-metal clusters.

Ferrocene Appended Linear Chromophores for Aggregation‐Induced Emission (AIE) and Nonlinear Optics (NLO): Combined Experimental and Theoretical Studies

AbstractNew nonlinear optical (NLO)‐active chromophores, featuring phenyl and methoxy phenyl substitutions at the D‐π‐A motif [(Fc‐C(C6H4‐R) = CH‐CH = C(CN)‐C6H4‐Br)] [R = H (1), OCH3 (2)] are synthesized and structurally analyzed. Chromophore 2 crystallized in a triclinic system (P‐1), consistent with DFT‐optimized structures. Non‐covalent interactions in the crystal packing suppress antiparallel alignment, enhancing SHG efficiencies. Molecular electrostatic potential (MEP) maps reveal structure‐property relationship and electronic communication between donor–acceptor moieties. Both chromophores exhibit suppressed emission in solution due to twisted intramolecular charge transfer (TICT) facilitated by the cyano vinylene group. However, Upon aggregation‐induced emission in a THF/H2O mixture, fluorescence significantly increases, attributed to restricted intramolecular rotation (RIR). Second Harmonic Generation (SHG) efficiencies, measured using the Kurtz–Perry powder technique with potassium dihydrogen phosphate (KDP) as a reference, show chromophore 2 is 1.1 times higher efficiency than chromophore 1. Density functional theory (DFT) derived hyperpolarizability values follow this trend, with chromophore 2 (β0 = 40.39 × 10−30 esu in B3LYP functional) surpassing chromophore 1. DFT and time‐dependent density functional theory (TD‐DFT) calculations employing B3LYP, CAM‐B3LYP, and LC‐BLYP functionals determined second‐order nonlinear optical parameters, B3LYP and CAM‐B3LYP produced values with minimal differences and a close correlation with the experimental results.

Suppressing Energy Migration via Antiparallel Spin Alignment in One‐Dimensional Mn2+ Halide Magnets with High Luminescence Efficiency

AbstractPhotoexcited energy migration is prone to causing luminescence quenching in Mn2+ luminescent materials, presenting a formidable challenge for optoelectronic applications. Although various strategies and mechanisms have been proposed to mitigate this issue, the role of spin alignment between adjacent Mn2+ ions has remained largely unexamined. In this study, we have elucidated the influence of spin alignment on energy migration within the one‐dimensional Mn2+‐metal halide compound (CH3)4NMnCl3 (TMMC) through variable‐temperature photoluminescence (PL) and magnetic‐optical spectroscopy. This investigation was conducted with reference to (CH6N3)2MnCl4 (GUA) with isolated [Mn3Cl12]6− trimers and Cd2+‐doped TMMC. The spin order in TMMC below approximately 55 K is demonstrated by the disorder‐order transition observed in the temperature‐dependent magnetic susceptibility. This finding is further corroborated by the negligible shift in the temperature‐ and field‐dependent emission peaks, a consequence of magnetic saturation. Our results indicate that the antiparallel spin alignment along the Mn2+ chain in TMMC effectively suppresses energy migration and multiphonon relaxation, thereby reducing nonradiative transitions and enhancing the photoluminescence quantum yield (PLQY). This research casts new light on the potential for developing high‐performance Mn2+‐doped phosphors for optoelectronic and spin‐photonic applications, offering insights into the manipulation of spin and energy dynamics in these materials.

Suppressing Energy Migration via Antiparallel Spin Alignment in One-Dimensional Mn2+ Halide Magnets with High Luminescence Efficiency.

Photoexcited energy migration is prone to causing luminescence quenching in Mn2+ luminescent materials, presenting a formidable challenge for optoelectronic applications. Although various strategies and mechanisms have been proposed to mitigate this issue, the role of spin alignment between adjacent Mn2+ ions has remained largely unexamined. In this study, we have elucidated the influence of spin alignment on energy migration within the one-dimensional Mn2+-metal halide compound (CH3)4NMnCl3 (TMMC) through variable-temperature photoluminescence (PL) and magnetic-optical spectroscopy. This investigation was conducted with reference to (CH6N3)2MnCl4 (GUA) with isolated [Mn3Cl12]6- trimers and Cd2+-doped TMMC. The spin order in TMMC below approximately 55 K is demonstrated by the disorder-order transition observed in the temperature-dependent magnetic susceptibility. This finding is further corroborated by the negligible shift in the temperature- and field-dependent emission peaks, a consequence of magnetic saturation. Our results indicate that the antiparallel spin alignment along the Mn2+ chain in TMMC effectively suppresses energy migration and multiphonon relaxation, thereby reducing nonradiative transitions and enhancing the photoluminescence quantum yield (PLQY). This research casts new light on the potential for developing high-performance Mn2+-doped phosphors for optoelectronic and spin-photonic applications, offering insights into the manipulation of spin and energy dynamics in these materials.

A comprehensive molecular dynamics simulation of plastic and liquid succinonitrile: Structural, dynamic, and dielectric properties.

Molecular dynamics simulations at constant temperature and pressure were carried out to investigate the structural, dynamical, and dielectric properties of succinonitrile in its plastic and liquid phases at several thermodynamic states. A six-site united atom model was employed with a force field incorporating an intramolecular torsional term that accurately describes gauche and trans conformers. Analysis of the radial distribution function showed that succinonitrile adopts a body-centered cubic arrangement below its melting point, transitioning to a less ordered state in the liquid phase. In addition, examination of alignments between methylene bonds and the diagonals of the simulating cubic box revealed pronounced directional preferences in the plastic phase. The study of conformational states suggested that succinonitrile molecules predominantly adopt gauche conformations, which exhibit longer lifetimes than trans conformers. Spectral density analysis highlighted distinct peaks for different molecular sites, revealing significant differences between gauche and trans conformers. The correlation functions of bending and torsional angles, as well as vectors joining different atoms, illustrated a sensitivity to internal motions, which were notably faster for trans conformers. Differences in decay rates between trans and gauche conformers underscored the influence of gauche-trans transitions. The static dielectric constant, which has been derived from the total dipole moment, was primarily influenced by the contribution of the gauche conformers. In addition, the distance-dependent Kirkwood factor was computed, revealing antiparallel alignment at short distances. Finally, the dielectric relaxation time and the static dielectric constant values were compared with experimental data.

Visible-Photo-Assisted Phase Switching of Antiferroelectric-to-Ferroelectric Orders in an I3 --Intercalated 2D Perovskite.

Antiferroelectric (AFE) has emerged as a promising branch of electroactive materials, due to intriguing physical attributes stemming from the electric field-induced antipolar-to-polar phase transformation. However, the requirement of extremely high electric field strength to switch adjacent sublattice polarization poses great challenges for exploiting new molecular AFE system. Although photoirradiation is striking as a noncontact and nondestructive manipulation tool to optimize physical properties, optical control of antiferroelectricity still remains unexplored. Here, by adopting light-sensitive I3 - anion into 2D perovskite family, we design a new I3 --intercalated molecular AFE of (t-ACH)2EA2Pb3I10(I3)0.5 ⋅ ((H3O)(H2O))0.5 (1, t-ACH=trans-4-aminomethyl-1-cyclohexanecarboxylate, EA=ethylammonium). The I3 --intercalating gives an ultra-narrow band gap of 1.65 eV with strong absorption. In term of AFE structure, the anti-parallel alignment of electric dipoles results in a large spontaneous polarization of 4.3 μC/cm2. Strikingly, 1 merely shows AFE behaviour in the dark even under ultrahigh voltage, while the field-induced ferroelectric state can be facilely obtained upon visible illumination. Such unprecedented visible-photo-assisted phase switching ascribes to the incorporation of photoactive I3 - anions that reduces AFE-to-ferroelectric switching barrier. This pioneering work on the photo-assisting transformation of ferroic orders paves a way to develop future photoactive materials with potential applications.

Control Patterning of Cyanobiphenyl Liquid Crystals for Electricity Applications.

Controlling molecular self-assembly from organic solution evaporation is an important strategy for developing many functional materials and systems. In this work, it is demonstrated that 4-octyloxy-4'-cyanobiphenyl (8OCB) liquid crystals can be patterned into well-oriented stripes with very high micrometer-scale precision using a sandwich system through a dewetting method. The preparation temperature, concentration, and surface energy are combined to control the morphology and orientation of 8OCB microstripe arrays assisted by silicon micropillars. Microstripes prepared below the isotropic temperature were uniform, well-ordered, and showed high electricity. In addition, 8OCB molecules have a strong tendency toward antiparallel alignment, nearly standing up on the substrate with long axes parallel to the microstripe. Also, we point out the mechanism for the self-assembly process of 8OCB on the air-liquid and liquid-solid surface.

Investigating the effect of SiO2 thin films with sculptured topographies on the alignment properties of liquid crystals

Investigating the effect of SiO2 thin films with sculptured topographies on the alignment properties of liquid crystals

Effect of multi-donor and extended π-conjugation in ferrocene appended indanedione chromophores for aggregation induced emission enhancement (AIEE) and nonlinear optics†

Effect of multi-donor and extended π-conjugation in ferrocene appended indanedione chromophores for aggregation induced emission enhancement (AIEE) and nonlinear optics†

A complex magnetic study: evidence of spin-glass transition below long-range magnetic ordering and its correlation with renormalization of phonon modes

In this paper, we report a complex magnetic behavior arising due to the interplay of three active magnetic cations (Nd/Sm, Co and Ir), forming 3d-5d-4f magnetic sublattices. The B-site ordered double perovskites Nd2CoIrO6and Sm2CoIrO6were successfully prepared by conventional solid-state method. Detailed structural analysis revealed that both samples crystallized in monoclinic structure with P21/n (No.-14) space group. X-ray photoelectron spectroscopy analysis confirms the presence of multiple oxidation states of Ir (i.e. Ir4+and Ir5+). Both samples show a paramagnetic-ferrimagnetic (TFiM) transition around 100 K, additionally, a low temperature transition is observed at around 10 K in the SCIO sample. This FM-like behavior of the samples is attributed to the antiparallel alignment of the Co2+and Ir4+spins, resulting in FiM ordering. The ac susceptibility analysis confirms a spin glass type transition just below the long-range ordering temperature in NCIO sample, The obtained characteristic flipping time of a single spin from both the law (Power law and Vogel-Fulcher law) and nonzero Vogel-Fulcher temperature (T0≃ 89.1 K) further verified the existence of cluster spin-glass behavior below the ordering temperature. The temperature evolution of phonon modes (up to 4 K) suggests that the phonon mode above the magnetic ordering temperature is mainly governed by the lattice degrees of freedom; notable renormalization of the mode frequency below the ordering temperature is due to the coupling of lattice with the underlying magnetic degrees of freedom.

Twisted domains in ferroelectric nematic liquid crystals

Twisted domains in ferroelectric nematic liquid crystals

Dislocations in twistronic heterostructures

Long-period moiré superlattices at the twisted interface of van der Waals heterostructures relax into preferential stacking domains separated by dislocation networks. Here, we develop a mesoscale theory for dislocations in networks formed in twistronic bilayers with parallel (P) and antiparallel (AP) alignment of unit cells across the twisted interface. For P bilayers we find an exact analytical displacement field across partial dislocations and determine analytic dependences of energy per unit length and width on the orientation and microscopic model parameters. For AP bilayers we formulate a semi-analytical approximation for displacement fields across perfect dislocations, establishing parametric dependences for their widths and energies per unit length. In addition, we find regions in the parametric space of crystal thicknesses and Moiré periods for strong and weak relaxation of the Moiré pattern in multilayered twistronic heterostructures.

Ferromagnetic Insulating Ground-State Resolved in Mixed Protons and Oxygen Vacancies-Doped La0.67Sr0.33CoO3 Thin Films via Ionic Liquid Gating.

The realization of ferromagnetic insulating ground state is a critical prerequisite for spintronic applications. By applying electric field-controlled ionic liquid gating (ILG) to stoichiometry La0.67Sr0.33CoO3 thin films, the doping of protons (H+) has been achieved for the first time. Furthermore, a hitherto-unreported ferromagnetic insulating phase with a remarkably high Tc up to 180 K has been observed which can be attributed to the doping of H+ and the formation of oxygen vacancies (VO). The chemical formula of the dual-ion migrated film has been identified as La2/3Sr1/3CoO8/3H2/3 based on combined Co L23-edge absorption spectra and configuration interaction cluster calculations, from which we are able to explain the ferromagnetic ground state in terms of the distinct magnetic moment contributions from Co ions with octahedral (Oh) and tetrahedral (Td) symmetries following antiparallel spin alignments. Further density functional theory calculations have been performed to verify the functionality of H+ as the transfer ion and the origin of the novel ferromagnetic insulating ground state. Our results provide a fundamental understanding of the ILG regulation mechanism and shed light on the manipulating of more functionalities in other correlated compounds through dual-ion manipulation.