Interlayer Ordering Research Articles

Ground state magnetic structure and magnetic field effects in the layered honeycomb antiferromagnet YbOCl

YbOCl is a representative member of the van der Waals layered honeycomb rare-earth chalcohalide RChX (R = rare earth; Ch = O, S, Se, and Te; and X = F, Cl, Br, and I) family reported recently. Its spin ground state remains to be explored experimentally. We grew high-quality single crystals of YbOCl and conducted comprehensive thermodynamic, elastic, and inelastic neutron scattering experiments down to 50 mK. The experiments reveal an antiferromagnetic phase below 1.3 K which is identified as a spin ground state with an intralayer ferromagnetic and interlayer antiferromagnetic ordering. By applying sophisticated numerical techniques to a honeycomb (nearest-neighbor)–triangle (next-nearest-neighbor) model Hamiltonian which accurately describes the highly anisotropic spin system, we are able to simulate the experiments well and determine the diagonal and off-diagonal spin-exchange interactions. The simulations give an antiferromagnetic Kitaev term comparable to the Heisenberg one. The experiments under magnetic fields allow us to establish a magnetic field–temperature phase diagram around the spin ground state. Most interestingly, a relatively small magnetic field (∼0.3 to 3 T) can significantly suppress the antiferromagnetic order, suggesting an intriguing interplay of the Kitaev interaction and magnetic fields in the spin system. The present study provides fundamental insights into the highly anisotropic spin systems and opens a window to look into Kitaev spin physics in a rare-earth-based system. Published by the American Physical Society 2024

Influence of Interlayer Cation Ordering on Na Transport in P2-Type Na0.67-xLiy Ni0.33-zMn0.67+zO2 for Sodium-Ion Batteries.

P2-type Na2/3Ni1/3Mn2/3O2 (PNNMO) has been extensively studied because of its desirable electrochemical properties as a positive electrode for sodium-ion batteries. PNNMO exhibits intralayer transition-metal ordering of Ni and Mn and intralayer Na+/vacancy ordering. The Na+/vacancy ordering is often considered a major impediment to fast Na+ transport and can be affected by transition-metal ordering. We show by neutron/X-ray diffraction and density functional theory (DFT) calculations that Li doping (Na2/3Li0.05Ni1/3Mn2/3O2, LFN5) promotes ABC-type interplanar Ni/Mn ordering without disrupting the Na+/vacancy ordering and creates low-energy Li-Mn-coordinated diffusion pathways. A structure model is developed to quantitatively identify both the intralayer cation mixing and interlayer cationic stacking fault densities. Quasielastic neutron scattering reveals that the Na+ diffusivity in LFN5 is enhanced by an order of magnitude over PNNMO, increasing its capacity at a high current. Na2/3Ni1/4Mn3/4O2 (NM13) lacks Na+/vacancy ordering but has diffusivity comparable to that of LFN5. However, NM13 has the smallest capacity at a high current. The high site energy of Mn-Mn-coordinated Na compared to that of Ni-Mn and higher density of Mn-Mn-coordinated Na+ sites in NM13 disrupts the connectivity of low-energy Ni-Mn-coordinated diffusion pathways. These results suggest that the interlayer ordering can be tuned through the control of composition, which has an equal or greater impact on Na+ diffusion than the Na+/vacancy ordering.

General Synthesis of 2D Magnetic Transition Metal Dihalides via Trihalide Reduction.

Two-dimensional (2D) transition metal dihalides (TMDHs) have been receiving extensive attention due to their diversified magnetic properties and promising applications in spintronics. However, controlled growth of 2D TMDHs remains challenging owing to their extreme sensitivity to atmospheric moisture. Herein, using a home-built nitrogen-filled interconnected glovebox system, a universal chemical vapor deposition synthesis route of high-quality 2D TMDH flakes (1T-FeCl2, FeBr2, VCl2, and VBr2) by reduction of their trihalide counterparts is developed. Representatively, ultrathin (∼8.6 nm) FeCl2 flakes are synthesized on SiO2/Si, while on graphene/Cu foil the thickness can be down to monolayer (1L). Reflective magnetic circular dichroism spectroscopy shows an interlayer antiferromagnetic ordering of FeCl2 with a Neel temperature at ∼17 K. Scanning tunneling microscopy and spectroscopy further identify the atomic-scale structures and band features of 1L and bilayer FeCl2 on graphene/Cu foil.

Effect of the Interlayer Ordering on the Fermi Surface of Kagome Superconductor CsV_{3}Sb_{5} Revealed by Quantum Oscillations.

The connection between unconventional superconductivity and charge density waves (CDWs) has intrigued the condensed matter community and found much interest in the recently discovered superconducting Kagome family of AV_{3}Sb_{5} (A=K, Cs, Rb). X-ray diffraction and Raman spectroscopy measurements established that the CDW order in CsV_{3}Sb_{5} comprises of a 2×2×4 structure with stacking of layers in a star-of-David (SD) and inverse-star-of-David (ISD) pattern along the c-axis direction. Such interlayer ordering will induce a vast normalization of the electronic ground state; however, it has not been observed in Fermi surface measurements. Here we report quantum oscillations of CsV_{3}Sb_{5} using tunnel diode oscillator frequency measurements. We observed a large number of frequencies, many of which were not reported. The number of frequencies cannot be explained by DFT calculations when only SD or ISD distortion is considered. Instead, our results are consistent with calculations when interlayer ordering is taken into account, providing strong evidence that the CDW phase of CsV_{3}Sb_{5} has complicated structure distortion which in turn has dramatic effects on the Fermi surface properties.

Pressure-driven electronic and structural phase transition in intrinsic magnetic topological insulator MnSb2Te4

Intrinsic magnetic topological insulators provide an ideal platform to achieve various exciting physical phenomena. However, this kind of materials and related research are still very rare. In this work, we reported the electronic and structural phase transitions in the intrinsic magnetic topological insulator $\mathrm{Mn}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{4}$ driven by hydrostatic pressure. Electric transport results revealed that temperature dependent resistance showed a minimum value near short-range antiferromagnetic (AFM) ordering temperature ${{T}_{N}}^{\ensuremath{'}}$, which declines with pressure. The short-range AFM ordering was sensitive to pressure and fully suppressed above 11.5 GPa. The intensity of three Raman vibration modes in $\mathrm{Mn}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{4}$ declined quickly starting from 7.5 GPa and these modes become undetectable above 9 GPa, suggesting possible insulator-metal transition, which is further confirmed by theoretical calculation. In situ x-ray diffraction demonstrated that an extra diffraction peak appears near 9.1 GPa and $\mathrm{Mn}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{4}$ started to enter an amorphouslike state above 16.6 GPa, suggesting the structural origin of suppressed AFM ordering and metallization. This work has demonstrated the correlation among interlayer interaction, magnetic ordering, and electric behavior, which could be benefit the understanding of the fundamental properties of this kind of materials and devices.

Сanted Magnetic Interlayer Ordering in a [Fe(3.0 nm)/Cr(1.2 nm)]10 Structure Revealed by Synchrotron Mössbauer Reflectometry with Polarization Analysis

Mossbauer reflectivity spectra measured for the [Fe(3.0 nm)/Cr(1.2 nm)]10 structure in the half-order Bragg peak, which corresponds to the doubling of the period, have revealed the formation of a canted antiferromagnetic structure under the action of an external magnetic field of $${{B}^{{{\text{ext}}}}} = 0.06$$ Т applied perpendicular to the scattering plane. This result certainly follows from the appearance of the second and fifth lines in the Mossbauer sextet, which should be suppressed for any symmetric orientation of the magnetic hyperfine field in two 57Fe layers in one magnetic period. The experiment involves a polarization analysis of the reflected beam and shows that this new approach simplifies the form of angular dependences and reflectivity spectra, since it eliminates the interfering contribution of nonresonant scattering, and improves the reliability of the data interpretation.

Vapor Deposition of Magnetic Van der Waals NiI2 Crystals.

The recent discovery of van der Waals magnetic materials has attracted great attention in materials science and spintronics. The preparation of ultrathin magnetic layers down to atomic thickness is challenging and is mostly by mechanical exfoliation. Here, we report vapor deposition of magnetic van der Waals NiI2 crystals. Two-dimensional (2D) NiI2 flakes are grown on SiO2/Si substrates with a thickness of 5-40 nm and on hexagonal boron nitride (h-BN) down to monolayer thickness. Temperature-dependent Raman spectroscopy reveals robust magnetic phase transitions in the as-grown 2D NiI2 crystals down to trilayer. Electrical measurements show a semiconducting transport behavior with a high on/off ratio of 106 for the NiI2 flakes. Lastly, density functional theory calculation shows an intralayer ferromagnetic and interlayer antiferromagnetic ordering in 2D NiI2. This work provides a feasible approach to epitaxy 2D magnetic transition metal halides and also offers atomically thin materials for spintronic devices.

Iodine orbital moment and chromium anisotropy contributions to CrI3 magnetism

The recent discovery of two-dimensional (2D) magnets, with a number of interesting magnetic properties, has drawn much interest due to their potential for future 2D spintronic device applications. CrI3, a van der Waals magnet, exhibits two-dimensional ferromagnetism even in monolayer form, stabilized by strong magnetic anisotropy. Its interlayer magnetic ordering is coupled to structural layer stacking, implying that the charge density distribution mediating van der Waals interactions plays a key role in the magnetic interaction between the layers. Using polarization-dependent x-ray spectroscopy, we investigated the response of the electronic environment around Cr and I sites to structural changes of layer stacking order. The highly anisotropic nature of the Cr local environment is significantly enhanced and is accompanied by changes in the valence band, in the rhombohedral phase. Magnetic spectroscopy measurements reveal a sizable iodine orbital moment, indicating the iodine contribution to magnetic anisotropy. Our results uncover an important role for the extended nature of anisotropic Cr orbital states in dictating interlayer magnetic interactions and the iodine contribution to magnetic anisotropy.

Helical structures in layered magnetic superconductors due to indirect exchange interactions mediated by interlayer tunneling

Motivated by the recent discovery of helical magnetic structure in RbEuFe$_{4}$As$_{4}$, we investigate interlayer ordering of magnetic moments in materials composed of spatially-separated superconducting and ferromagnetically-aligned layers. We consider the interplay between the normal and superconducting indirect exchange interaction mediated by tunneling between the conducting layers. We elaborate a recipe to evaluate the normal interlayer interaction via two-dimensional density of states of an isolated layer and demonstrate that for bands with small fillings, such interaction is typically ferromagnetic and short-range. The nearest-layer interaction is proportional to the ratio of the interlayer hopping and in-plane band width squared. On the other hand, the superconducting contribution always gives antiferromagnetic interaction and may extend over several layers when the interlayer hopping energy exceeds the superconducting gap. The frustration caused by the interplay between the normal and superconducting parts may lead to spiral ground-state magnetic configuration. The four-fold in-plane anisotropy may lock the rotation angle between the moments in the neighboring layers to $90^\circ$, as it was observed in RbEuFe$_{4}$As$_{4}$

Confinement of atomically defined metal halide sheets in a metal-organic framework.

The size-dependent and shape-dependent characteristics that distinguish nanoscale materials from bulk solids arise from constraining the dimensionality of an inorganic structure1-3. As a consequence, many studies have focused on rationally shaping these materials to influence and enhance their optical, electronic, magnetic and catalytic properties4-6. Although a select number of stable clusters can typically be synthesized within the nanoscale regime for a specific composition, isolating clusters of a predetermined size and shape remains a challenge, especially for those derived from two-dimensional materials. Here we realize a multidentate coordination environment in a metal-organic framework to stabilize discrete inorganic clusters within a porous crystalline support. We show confined growth of atomically defined nickel(II) bromide, nickel(II) chloride, cobalt(II) chloride and iron(II) chloride sheets through the peripheral coordination of six chelating bipyridine linkers. Notably, confinement within the framework defines the structure and composition of these sheets and facilitates their precise characterization by crystallography. Each metal(II) halide sheet represents a fragment excised from a single layer of the bulk solid structure, and structures obtained at different precursor loadings enable observation of successive stages of sheet assembly. Finally, the isolated sheets exhibit magnetic behaviours distinct from those of the bulk metal halides, including the isolation of ferromagnetically coupled large-spin ground states through the elimination of long-range, interlayer magnetic ordering. Overall, these results demonstrate that the pore environment of a metal-organic framework can be designed to afford precise control over the size, structure and spatial arrangement of inorganic clusters.

Neutron Spectroscopic and Thermochemical Characterization of Lithium–Aluminum-Layered Double Hydroxide Chloride: Implications for Lithium Recovery

Lithium–aluminum-layered double hydroxide chloride (LDH) has been recently demonstrated to be a promising sorbent material for selective lithium extraction and recovery from geothermal brine. In this research, LDH samples synthesized from two different starting materials (alumina and gibbsite) and with two post-drying conditions (ambient-dried and oven-dried) as well as and Fe-doped LDH are studied using neutron vibrational spectroscopy. The results reveal differences in the ordering of interlayer water molecules. Thermochemical measurements of LDHs show that a higher interlayer ordering of water is directly related to the stability of gibbsite- and alumina-derived LDH. This corroborates with the previous work on increasing the stabilization of LDH via partial substitution of aluminum with iron. These findings on the properties of LDH have implications on their lithium extraction abilities and subsequent recovery.

Probing magnetism in 2D materials at the nanoscale with single-spin microscopy.

The discovery of ferromagnetism in two-dimensional (2D) van der Waals (vdW) crystals has generated widespread interest. Making further progress in this area requires quantitative knowledge of the magnetic properties of vdW magnets at the nanoscale. We used scanning single-spin magnetometry based on diamond nitrogen-vacancy centers to image the magnetization, localized defects, and magnetic domains of atomically thin crystals of the vdW magnet chromium(III) iodide (CrI3). We determined the magnetization of CrI3 monolayers to be ≈16 Bohr magnetons per square nanometer, with comparable values in samples with odd numbers of layers; however, the magnetization vanishes when the number of layers is even. We also found that structural modifications can induce switching between ferromagnetic and antiferromagnetic interlayer ordering. These results demonstrate the benefit of using single-spin scanning magnetometry to study the magnetism of 2D vdW magnets.

Polarization Analysis in Mössbauer Reflectometry with Synchrotron Mössbauer Source

Polarization selection of the reflected radiation has been employed in Mössbauer reflectivity measurements with a synchrotron Mössbauer source (SMS). The polarization of resonantly scattered radiation differs from the polarization of an incident wave so the Mössbauer reflectivity contains a scattering component with 90° rotated polarization relative to the π-polarization of the SMS for some hyperfine transitions. We have shown that the selection of this rotated π→σ component from total reflectivity gives an unusual angular dependence of reflectivity characterized by a peak near the critical angle of the total external reflection. In the case of collinear antiferromagnetic interlayer ordering, the “magnetic” maxima on the reflectivity angular curve are formed practically only by radiation with this rotated polarization. The first experiment on Mössbauer reflectivity with a selection of the rotated polarization discovers the predicted peak near the critical angle. The measurement of the rotated π→σ polarization component in Mössbauer reflectivity spectra excludes the interference with non-resonant electronic scattering and simplifies the spectrum shape near the critical angle allowing for an improved data interpretation in the case of poorly resolved spectra. It is shown that the selected component of Mössbauer reflectivity with rotated polarization is characterized by enhanced surface sensitivity, determined by the “squared standing waves” depth dependence. Therefore, the new approach has interesting perspectives for investigations of surfaces, ultrathin layers and multilayers having complicated magnetic structures.

Interlayer coupling-driven magnetic ordering and magnetization processes in ultrathin Au/Co/Mo/Co/Au film

Abstract Interlayer magnetic coupling in an Au/Co/Mo/Co/Au system fabricated by molecular beam epitaxy was studied as a function of the thicknesses of the cobalt and molybdenum spacer layers (denoted as dCo and dMo, respectively). Magnetization processes and magnetic domain structures were investigated using magneto-optical techniques. In the investigated thickness ranges, various magnetization configurations of the Co layers were observed: (A) both perpendicular, (B) perpendicular and in-plane, and (C) both in-plane. The interlayer exchange coupling field HIEC was determined as a function of dMo. With increasing dMo, this coupling changed from antiferromagnetic with a huge coupling field of ≈0.27 T to ferromagnetic and again to antiferromagnetic. A coupling oscillation period of around 1.4 nm was deduced by comparing the experimental data with the Ruderman–Kittel–Kasuya–Yosida model. For configurations (B) and (C), oscillations of the saturation magnetic field HSAT(dMo) perpendicular to the sample plane were found. Simplified and precise analytical expressions for HSAT were proposed by considering HIEC as well as the uniaxial magnetic anisotropy of one and both magnetic layers, respectively. Magnetic ordering was numerically modeled taking into account the dependences of layer anisotropy and exchange coupling on dCo and dMo, respectively. This modeling well described the remanent magnetization map (dCo, dMo) determined using the polar Kerr effect. It is also shown that HIEC(dMo) induced magnetization reorientation from in-plane to out-of-plane or from out-of-plane to in-plane magnetization configurations and canted magnetization of the Co layers.

Raman spectroscopy of weathered shungites

Raman spectroscopy has proven to be a useful tool for the study of carbonaceous material (CM). This method is used to distinguish various types of CM and to study the evolution of Raman spectra characteristics of CM during metamorphic transformations. In the present study, we applied the Raman spectroscopy and electron diffraction methods to investigate the evolution of structural ordering of CM of shungite rocks, Karelia (Russia), during weathering. The studies of the CM structure evolution during weathering are rare and ambiguous. The Raman spectra of weathered shungites are characterized by increase of FWHM‐D1, that is accompanied by the decrease of intensity‐based ratio R1 = ID/IG and the change of the intensity of the bands in second‐order region. The Raman spectral data indicate that weathering results in the alteration of both intralayer and interlayer ordering of shungites, but there are some peculiarities for the shungites subjected to the various types of weathering. The present study establishes that the Raman spectra characteristics of weathered shungites can be used as the indicators of weathering for CM from various carbon‐bearing rocks. Copyright © 2017 John Wiley & Sons, Ltd.

Digital holographic microscopy of phase separation in multicomponent lipid membranes.

Lateral in-homogeneities in lipid compositions cause microdomains formation and change in the physical properties of biological membranes. With the presence of cholesterol and mixed species of lipids, phospholipid membranes segregate into lateral domains of liquid-ordered and liquid-disordered phases. Coupling of two-dimensional intralayer phase separations and interlayer liquid-crystalline ordering in multicomponent membranes has been previously demonstrated. By the use of digital holographic microscopy (DHMicroscopy), we quantitatively analyzed the volumetric dynamical behavior of such membranes. The specimens are lipid mixtures composed of sphingomyelin, cholesterol, and unsaturated phospholipid, 1,2-dioleoyl-sn-glycero-3-phosphocholine. DHMicroscopy in a transmission mode is an effective tool for quantitative visualization of phase objects. By deriving the associated phase changes, three-dimensional information on the morphology variation of lipid stacks at arbitrary time scales is obtained. Moreover, the thickness distribution of the object at demanded axial planes can be obtained by numerical focusing. Our results show that the volume evolution of lipid domains follows approximately the same universal growth law of previously reported area evolution. However, the thickness of the domains does not alter significantly by time; therefore, the volume evolution is mostly attributed to the changes in area dynamics. These results might be useful in the field of membrane-based functional materials.

Equilibrium states of pancake vortices in layered superconductors: coupling of inter-layer ordering and in-layer ordering

We numerically study the static configurations of pancake vortices in layered superconductors. We analyze how disordering induced by random pinning centers competes with inter-layer ordering and in-layer ordering. In general, for inter-layer ordering, 3D states composed of coupled vortex lines are formed for strong inter-layer coupling strength and weak pinning strength. In contrast, 2D states composed of decoupled individual pancake vortices are formed for weak inter-layer coupling strength and strong pinning strength. For in-layer ordering, with increasing pinning forces, the in-layer structure evolves from crystals to Bragg glasses (BGs), vortex glasses (VGs), and liquid-like structures. Changing the vortex density, an initially fast disordering, then slow ordering procedure is found for both in-layer and inter-layer ordering, which is a possible clue to second peak effect (SPE). The reason behind this non-monotonic behavior is discussed. Our results are summarized in a phase diagram in the plane of ‘inter-layer coupling strength sm versus pinning strength fp.

Transient phases during fast crystallization of organic thin films from solution

We report an in situ microbeam grazing incidence X-ray scattering study of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) organic semiconductor thin film deposition by hollow pen writing. Multiple transient phases are observed during the crystallization for substrate temperatures up to ≈93 °C. The layered smectic liquid-crystalline phase of C8-BTBT initially forms and preceedes inter-layer ordering, followed by a transient crystalline phase for temperature >60 °C, and ultimately the stable phase. Based on these results, we demonstrate a method to produce extremely large grain size and high carrier mobility during high-speed processing. For high writing speed (25 mm/s), mobility up to 3.0 cm2/V-s has been observed.

Coupling of magnetic order to planar Bi electrons in the anisotropic Dirac metalsAMnBi2 (A =Sr,Ca)

We report powder and single-crystal neutron diffraction measurements of the magnetic order in $A{\mathrm{MnBi}}_{2}$ ($A=\mathrm{Sr}$ and Ca), two layered manganese pnictides with anisotropic Dirac fermions on a Bi square net. Both materials are found to order at ${T}_{\mathrm{N}}\ensuremath{\approx}300$ K in $\mathbf{k}=0$ antiferromagnetic structures, with ordered Mn moments at $T=10$ K of approximately $3.8 {\ensuremath{\mu}}_{\mathrm{B}}$ aligned along the $c$ axis. The magnetic structures are N\'eel type within the Mn-Bi layers, but the interlayer ordering is different, being antiferromagnetic in ${\mathrm{SrMnBi}}_{2}$ and ferromagnetic in ${\mathrm{CaMnBi}}_{2}$. This allows a mean-field coupling of the magnetic order to Bi electrons in ${\mathrm{CaMnBi}}_{2}$ but not in ${\mathrm{SrMnBi}}_{2}$. We find clear evidence that magnetic order influences electrical transport. First-principles calculations explain the experimental observations and suggest that the mechanism for different interlayer ordering in the two compounds is the competition between the antiferromagnetic superexchange and ferromagnetic double exchange carried by itinerant Bi electrons.

ChemInform Abstract: The Interlayer Exchange Interaction in Multilayer Magnetic Systems Fe/Cr/Fe (Review Article)

AbstractReview: 50 refs.