In-plane Anisotropy Research Articles

Giant ab-Plane Birefringence in Quasi-1D Fibrous Red Phosphorus.

Quasi-one-dimensional (quasi-1D) van der Waals crystal fibrous red phosphorus (RP) exhibits pronounced in-plane optical anisotropy, positioning it as a potential candidate for polarization-related micro-nano devices. Unfortunately, a comprehensive investigation into the complex refractive index of fibrous RP and the structure-activity relationship connecting the distinctive quasi-1D structure with optical anisotropy is currently deficient. Herein, we have collectively determined the complex refractive index of the fibrous RP flakes within the ab-plane through Kramers-Kronig (KK) analysis and theoretical calculation. Notably, the maximum birefringence of fibrous RP reaches 0.642@475 nm with an absolute extinction coefficient of only 0.08, superior to the reported traditional optical crystals and the emerging low-dimensional materials as well. The remarkable birefringence can be attributed to the synergistic influence of the large electronic dipole polarizability, anisotropic electron density distribution and the distortion of stereochemically active lone pair (SCALP). This work demonstrates the potential of fibrous RP for polarization-sensitive devices, illuminating possibilities to exploit novel giant birefringent crystals based on the structure-activity relationship.

Magnetization reversal phenomena in thin films presenting stripe domains

We present a study of the properties related to the magnetization reversal process in two thin-film samples with magnetic stripe domains: Fe0.82Ga0.18 (Fe–Ga) and Ni0.81Fe0.19 (permalloy). In Fe–Ga thin films, we focus on magnetization reversal driven by thermal activation by considering the magnetic viscosity behavior. The results suggest that the reversal process occurs gradually, where the magnetization switches direction via ∼10 nm-long jumps of the magnetic domain walls. On the other hand, vectorial hysteresis loops were performed in permalloy thin films with the aim to study the behavior of the transverse magnetization component (perpendicular to the applied field) during the magnetization reversal process. We show that the measurement of the transversal magnetization component shows a much higher sensitivity for the determination of the in-plane magnetic anisotropy than the usual hysteresis loops where the magnetization is parallel to the applied field. Moreover, this allows to highlight the competition between the intrinsic and rotatable anisotropies in thin films that present stripe domains.

A comparison between tensile and hole expansion properties in 800 MPa tensile strength grade hot-rolled steels

Sheared edge formability can play a critical role in cold forming of high-strength hot-rolled steels due to susceptibility to edge cracking. Standardized ISO 16630 hole expansion test is currently the most widely used method to estimate sheared edge formability of steel sheets, however, there has been increasing interest in the industry to reduce the amount of required testing. The aim of this paper was to compare hole expansion performance of hot-rolled strip steels to various uniaxial tensile test results. The five investigated steels were selected to have 3 mm thickness and similar (838±10 MPa) longitudinal tensile strength level while consisting of different microstructures. Tensile properties were measured in 0°, 45°, and 90° angle relative to the rolling direction to investigate anisotropy. Plastic strain ratios were determined by digital image correlation measurement. Local ductility was evaluated with thickness strain measurements (εp_amin) on fracture surfaces of the tensile specimens. To investigate stretch-flangeability, ISO 16630 conforming hole expansion tests were performed. Test holes were produced by punching and by wire electrical discharge machining (W-EDM) to evaluate edge damage tolerance of the materials. The hole expansion ratios (HER) were not observed to correlate with majority of the investigated tensile test results, such as uniform elongation and yield strength. However, a good correlation between HER and planar anisotropy was observed. Planar anisotropy is seen to affect strain localization tendency around the hole. The HER values of neither punched nor W-EDM specimens correlated clearly with εp_amin measurement results. The results show that at a similar strength level, anisotropy is highly influencing the hole expansion performance of hot-rolled steels, and that the HER is not reliably predicted by a single local formability parameter.

Tunable in-plane anisotropy of quasiparticles in twisted MoS2/CrOCl heterostructures

Twisted isotropic-anisotropic van der Waals heterostructures provide a platform for controlling the electronic and phononic properties of 2D materials and inducing in-plane anisotropy in some isotropic materials. Herein, angle-resolved polarized Raman spectroscopy and photoluminescence spectroscopy are used to investigate the induced in-plane anisotropy of the quasiparticles in the twisted MoS2/CrOCl heterostructures. Both the phonons (Eg2 MoS2 and Ag1 MoS2 modes) and excitons (A and B excitons) in MoS2 represent a strong in-plane orientation dependence, and the maximum intensities are along the [100]CrOCl. The induced anisotropy ratios of phonons vary continuously in the range from 1.22 to 1.13 for the Eg2 MoS2 mode and 1.15 to 1.09 for the Ag1 MoS2 mode with changing twisted angles, which originate from the anisotropic carrier mobility induced by the localized charge distribution from the anisotropic CrOCl substrates, and are further tuned by the uniaxial local limit of charge carriers caused by 1D moiré pattern. Our findings provide a way to controllably regulate the induced in-plane optical anisotropy in heterostructures.

Stoichiometry‐Induced Ferromagnetism in Altermagnetic Candidate MnTe

AbstractThe field of spintronics has seen a surge of interest in altermagnetism due to novel predictions and many possible applications. MnTe is a leading altermagnetic candidate that is of significant interest across spintronics due to its layered antiferromagnetic structure, high Neel temperature (TN ≈ 310 K) and semiconducting properties. The results on molecular beam epitaxy (MBE) grown MnTe/InP(111) films are presented. Here, it is found that the electronic and magnetic properties are driven by the natural stoichiometry of MnTe. Electronic transport and in situ angle‐resolved photoemission spectroscopy show the films are natively metallic with the Fermi level in the valence band and the band structure is in good agreement with first‐principles calculations for altermagnetic spin‐splitting. Neutron diffraction confirms that the film is antiferromagnetic with planar anisotropy and polarized neutron reflectometry indicates weak ferromagnetism, which is linked to a slight Mn‐richness that is intrinsic to the MBE‐grown samples. When combined with the anomalous Hall effect, this work shows that the electronic response is strongly affected by the ferromagnetic moment. Altogether, this highlights potential mechanisms for controlling altermagnetic ordering for diverse spintronic applications.

Exploiting in-plane anisotropy in Ta2NiSe5 spanning near to mid-infrared photodetection

Miniaturized and stabilized polarization-sensitive mid-Infrared photodetectors at room temperature are indispensable in fields ranging from medical diagnostics to military surveillance in the next-generation on-chip polarimeters. Emerging two-dimensional materials offer a promising avenue to fulfill these requirements, facilitated by their ease of integration onto complex structures, inherent in-plane anisotropic crystal structures that enhance polarization sensitivity, and robust quantum confinement effects that enable superior photodetection performance at room temperature. Here, we report the systematic investigation of polarization-dependent infrared photoresponse based on Ta2NiSe5, revealing significant anisotropy photocurrent with excellent stability at room temperature. Significantly, a large anisotropic ratio of Ta2NiSe5 ensures the polarization sensitivity achieves a ratio of 1.23 at 1550 nm. Moreover, at 4.6 μm, the device exhibits a peak photocurrent response of 1.16 A/W along the armchair orientation, with an anisotropy ratio of approximately 3.3. These findings not only enhance our understanding of the photophysical mechanisms in two-dimensional materials but also guide the optimization of photodetector design for enhanced performance.

Assessment of the Influence of Fabric Structure on Their Electro-Conductive Properties.

Electro-conductive fabrics are key materials for designing and developing wearable smart textiles. The properties of textile materials depend on the production method, the technique which leads to high conductivity, and the structure. The aim of the research work was to determine the factors affecting the electrical conductivity of woven fabrics and elucidate the mechanism of electric current conduction through this complex, aperiodic textile material. The chemical composition of the material surface was identified using scanning electron microscopy energy dispersion X-ray spectroscopy. The van der Pauw method was employed for multidirectional resistance measurements. The coefficient was determined for the assessment of the electrical anisotropy of woven fabrics. X-ray micro-computed tomography was used for 3D woven structure geometry analysis. The anisotropy coefficient enabled the classification of electro-conductive fabrics in terms of isotropic or anisotropic materials. It was found that the increase in weft density results in an increase in sample anisotropy. The rise in thread width can lead to smaller electrical in-plane anisotropy. The threads are unevenly distributed in woven fabric, and their widths are not constant, which is reflected in the anisotropy coefficient values depending on the electrode arrangement. The smaller the fabric area covered by four electrodes, the fewer factors leading to structure aperiodicity.

Weakening the mechanical property anisotropy of additively manufactured medium entropy alloy by controlling the cellular structure

Cellular structure is a unique microstructure characteristic of the additively manufactured face-centered cubic phase metallic materials. It typically grows preferentially along the temperature gradient, leading to anisotropy in mechanical properties and restricting the practical application. Herein, we adopted a discontinuous laser scanning strategy for fabricating the face-centered cubic FeCrNi alloy. The scanning layer is divided into nine discontinuous equal-width regions along which the laser beam prints discontinuously. This strategy can increase the temperature gradient in the melt pool by weakening the thermal influence between the adjacent scanning regions, which helps to suppress cellular structure growth along the temperature gradient. Compared with the sample prepared by the conventional continuous laser scanning strategy, the sample printed using the discontinuous laser scanning strategy exhibits finer cellular structures with a significantly shorter length along the growth direction, and the anisotropy of mechanical properties is weakened. The in-plane anisotropy of ultimate tensile strength decreases from 21.6 to 6.4. This study presents a novel approach to optimize the mechanical properties of additively manufactured face-centered cubic phase metallic materials.

Influence of N2 plasma treatment on properties of black phosphorus devices in space electronic systems

In order to improve the country’s comprehensive national strength and seize space resources, the implementation of new space systems requires the use of advanced technology in key applications of microelectronics. To further improve device performance, black phosphorus (BP) is used to overcome feature size limitations for its atomic thickness. BP has excellent physical properties such as in-plane anisotropy, thickness-dependent direct band gap and high carrier mobility. However, the performance control of phosphene is a major challenge in practical applications. In order to tune the BP performance, various theoretical and experimental studies on the doping mechanism and strategies of BP have been proposed and reported. In this work, the performance of BP can be effectively tuned by N2 plasma treatment. By changing the power and processing time, the on-state current and mobility of the device can be effectively improved. This simple and efficient doping technique provides a valuable way to realize high performance BP thin film transistors.

Microstructural contribution to the magnetic anisotropy in Fe 1−x Ga x thin films: correlation between crystallographic texture and magnetic response

In this study, we present a systematic analysis of the relation between the structural properties and magnetic anisotropies of as-grown and heat-treated polycrystalline Fe 1−x Ga x (0.11 <x< 0.19) thin films deposited on glass and Si(100) substrates. The results show that the crystallographic texture of the films has a significant impact on the evolution of the magnetic anisotropies. The samples grown on glass do not exhibit a preferred texture while, for samples grown on Si(100), the appearance of a weak in-plane fourfold magnetic anisotropy is reported. Such anisotropy is enhanced and better defined in the heat treated samples. Via a phenomenological model we show that this anisotropy has a microstructural origin. These findings demonstrate the possibility of tuning magnetic anisotropies by growing on different substrates and/or performing thermal treatments, which in turn reinforces the possibility of developing smart magnetic switching materials for electronic applications.

Strongly Bound Excitons and Anisotropic Linear Absorption in Monolayer Graphullerene.

Graphullerene is a novel two-dimensional carbon allotrope with unique optoelectronic properties. Despite significant experimental characterization and prior density functional theory calculations, unanswered questions remain as to the nature, energy, and intensity of the electronic and optical excitations. Here, we present first-principles calculations of the quasiparticle band structure, neutral excitations, and absorption spectra of monolayer graphullerene and bulk graphullerite, employing the GW-Bethe-Salpeter equation (GW-BSE) approach. We show that strongly bound excitons dominate the absorption spectrum of monolayer graphullerene with binding energies up to 0.8 eV, while graphullerite exhibits less pronounced excitonic effects. Our calculations also reveal a strong linear polarization anisotropy, reflecting the in-plane structural anisotropy from intermolecular coupling between neighboring C60 units. We further show that the presence of Mg atoms, crucial to the synthesis process, induces structural modifications and polarizability effects, resulting in a ∼1 eV quasiparticle gap renormalization and a reduction in the exciton binding energy to ∼0.6 eV.

Anisotropic charge transport at the metallic edge contact of ReS2 field effect transistors

The in-plane anisotropy of electrical conductance in two-dimensional materials has garnered significant attention due to its potential in emerging device applications, offering an additional dimension to control carrier transport in 2D devices. However, previous research has primarily focused on the anisotropy within electrical channel, neglecting the significant impact of anisotropic electrical contacts of 2D materials. Here, we investigate anisotropic charge transport at the metal contacts of hBN-encapsulated ReS2 using edge-contacted Field Effect Transistors. We observed the marked difference in contact resistance between the cross-b and b directions, suggesting that charge transport from the metal to ReS2 is more efficient along the b direction. This difference in efficiency results in a substantial contact anisotropy, reaching ~70 at 77 K. Our findings indicate that the measured Schottky Barrier Height along the b direction is ~35 meV, which is smaller than along the cross-b direction. Moreover, the tunneling probability along the b direction is two times larger than along the cross-b direction. Our results indicate that both Schottky Barrier Height and tunneling amplitude are the primary contributors to the high contact anisotropy of ReS2. This work provides a valuable guideline for understanding how in-plane orientation influences charge transport at metallic contacts in 2D devices.

Precise Crystal Orientation Identification and Twist-Induced Giant Modulation of Optical Anisotropy in 1T'-ReS2.

The ability to precisely identify crystal orientation as well as to nondestructively modulate optical anisotropy in atomically thin rhenium dichalcogenides is critical for the future development of polarization programmable optoelectronic devices, which remains challenging. Here, we report a modified polarized optical imaging (POI) method capable of simultaneously identifying in-plane (Re chain) and out-of-plane (c-axis) crystal orientations of the monolayer to few-layer ReS2, meanwhile, propose a nondestructive approach to modulate the optical anisotropy in ReS2 via twist stacking. The results show that parallel and near-cross POI are effective to independently identify the in-plane and out-of-plane crystal orientations, respectively, while regulating the twist angle allows for giant modulation of in-plane optical anisotropy from highly intrinsic anisotropy to complete optical isotropy in the stacked ReS2 bilayer (with either the same or opposite c-axes), as well modeled by linear electromagnetic theory. Overall, this study not only develops a simple optical method for precise crystal orientation identification but also offers an efficient light polarization control strategy, which is a big step toward the practical application of anisotropic van der Waals materials in the design of nanophotonic and optoelectronic devices.

Temperature dependent interfacial-coupling and magnetization reversal of La2/3Sr1/3MnO3 film with inverted hysteresis features

Temperature-dependent magnetic anisotropy and interfacial coupling of La2/3Sr1/3MnO3 (LSMO) epitaxial films with inverted hysteresis (IHLs) features are investigated using a broadband ferromagnetic resonance (FMR) spectrometer. Through the dispersion relation obtained along [100], [110] and [010] axes, a simplified method is proposed to investigation in-plane magnetic anisotropy by broadband FMR in a cryostat. According to this method, the perpendicular uniaxial anisotropy, magneto-crystalline anisotropy, and interfacial coupling between the LSMO film and hard-magnetic interface layer are investigated as a whole. The measured value of interfacial coupling is −17.6 Oe at 300 K, close to the bias field found in minor loop, i.e., −18.4 Oe. The interfacial coupling is enhanced with the dropping of temperatures, and the value of interfacial coupling changed to −112 Oe at 10 K. A Stoner-Wohlfarth-like model is employed to calculate the hysteresis loops of the films based on the measured values of in-plane magnetic anisotropy and interfacial-coupling. The calculation reveals the mechanism of magnetization reversal and the origin of IHLs found in LSMO films.

Influence of pre-stretching and annealing on microstructure and mechanical properties evolution of twin-roll cast Mg-2Al-1Zn-1Ca (wt.%) plates

Pre-stretching and annealing treatments were conducted on twin roll cast Mg-2Al-1Zn-1Ca (AZX211, in wt.%) plates with a rare earth-like texture. Varying amounts of deformation were applied along the rolling direction (RD) and transverse direction (TD) of AZX211 alloy in order to modify its mechanical properties at room temperature. The results demonstrate that pre-stretching treatment effectively enhances the yield strength (YS), especially along the RD. The strengthening mechanism is attributed to the production of a large number of dislocations and sub-grain boundaries, but the work-hardening ability of the plate will be greatly weakened. Additionally, annealing treatment substantially improves the plasticity and in-plane anisotropy and restores the work-hardening ability. The notable distinction in the pre-stretching process between different directions lies in the underlying deformation mechanism. In case of RD, deformation is predominantly governed by the slip mechanism of {0002} 〈11−20〉 basal slip and {10−10} 〈11−20〉 prismatic slip, while along the TD, deformation is primarily controlled by {0002} 〈11−20〉 basal slip without significant twinning deformation. When a 6 % pre-stretching is conducted, the initial rare earth-like texture of the sample transforms into a symmetrically distributed double-peak basal texture, accompanied by grain refinement. This texture transformation is chiefly due to the dominance of {0002} 〈11−20〉 basal slip-driven deformation. Moreover, the annealed sample maintains a strong basal texture, owing to strain-induced recrystallization.

Magneto-optical detection of non-collinear magnetization states in ferromagnetic multilayers

We have experimentally studied the relationship in between non-collinear magnetization states in ferromagnetic (FM) multilayers and their resulting magneto-optical (MO) properties. Hereby, we observe that the phase of the complex-valued MO parameters are especially sensitive towards non-collinear magnetization states and enable their unambiguous detection. For the purpose of our experimental study, we designed, fabricated and characterized a set of epitaxial FM/NM/FM multilayers with in-plane uniaxial anisotropy, in which the non-magnetic (NM) interlayer thickness t was varied, so that tunable FM interlayer exchange coupling strength in between the two FM layers could be achieved. Furthermore, the two FM layers were made from different alloys, so that they exhibit different levels of magnetocrystalline anisotropy, which enables a collinear to non-collinear magnetization state transition upon applying a magnetic field H away from the in-plane easy axis for samples with sufficiently large t . Utilizing generalized MO ellipsometry, we determined the full reflection matrix R as a function of H and we observed that the phases of the complex-valued MO coefficients in R change with H in multilayers that have sufficiently weak interlayer coupling strength, i.e. large t, which can only happen if non-collinear magnetization states of varying non-collinearity occur in those samples. For samples with small t, corresponding to strongly exchange coupled FM layers, this effect is absent, consistent with the existence of collinear magnetization states in those multilayers for all H values.

Tunable electronic properties of the ferromagnetic VS2/ZnPSe3 van der Waals heterostructure under external electric field

By using first-principles calculations, we demonstrate the coexistence of stable ferromagnetic ordering and tunable semiconductor characteristic in VS2/ZnPSe3 heterostructure under external electric field (E⊥). The in-plane magnetic anisotropy (IMA) in VS2 is almost unchanged by forming VS2/ZnPSe3, while the Curie temperature (TC) of VS2/ZnPSe3 (∼345 K) is slightly smaller than that of VS2 monolayer (∼360 K). Furthermore, a staggered type-II band alignment is spontaneously established at the interface between VS2 and ZnPSe3, and a direct band gap (∼0.47 eV) in the spin-up channel. A semiconductor-to-metal transition occurs when the positive E⊥ reaches 0.3 V/Å. The staggered type-II band alignment in the spin-up channel can be tuned to type-I once the negative E⊥ exceeds -0.3 V/Å. We systemically study the related mechanism, which can be attributed to charge transferring between VS2 and ZnPSe3 and the quasi-Fermi levels splitting of them under external electric field.

Mechanical Properties and Microstructural Evolution of 6082 Aluminum Alloy with Different Heat Treatment Methods

The influence of solid solution treatment (SST), artificial aging treatment (AAT), and deep cryogenic-aging treatment (DCAT) on the mechanical properties and microstructure evolution of 6082 aluminum alloy was investigated. The tensile test was performed to obtain the true stress–strain curves through an electronic universal testing machine. The results show that the yield strengths of the SST specimens in all three directions are the lowest, of less than 200 MPa. In addition, the maximum elongation of the SST specimen is over 16% and the value of in-plane anisotropy (IPA) is 5.40%. For the AAT specimen, the yield strengths of the AAT alloy in three directions have distinct improvements, which are beyond 340 MPa. However, the maximum elongation and the IPA were evidently reduced. The yield strength and elongation of the DCAT alloy exhibit a slight enhancement compared with those in the AAT condition, and the corresponding IPA is 0.61%. The studied alloy specimens in all conditions exhibit ductile fracture. The DCAT alloy has the highest density of precipitates with the smallest size. Therefore, the dislocation pinning effect of the DCAT specimens are the strongest, which exhibit the highest yield strength accordingly. In addition, the uniformly distributed precipitates in the matrix with a large ratio of long and short axes can suppress the anisotropy caused by elongated grains.

Enhanced Spin–Orbit Torques in Graphene by Pt Adatoms Decoration

Abstract Graphene (Gr) with widely acclaimed characteristics, such as exceptionally long spin diffusion length at room temperature, provides an outstanding platform for spintronics. However, its inherent weak spin–orbit coupling (SOC) has limited its efficiency for generating the spin currents in order to control the magnetization switching process for applications in spintronics memories. Following the theoretical prediction on the enhancement of SOC in Gr by heavy atoms adsorption, here we experimentally observe a sizeable spin–orbit torques (SOTs) in Gr by the decoration of its surface with Pt adatoms in Gr/Pt(t Pt)/FeNi trilayers with the optimal damping-like SOT efficiency around 0.55 by 0.6-nm-thick Pt layer adsorption. The value is nearly four times larger than that of the Pt/FeNi sample without Gr and nearly twice the value of the Gr/FeNi sample without Pt adsorption. The efficiency of the enhanced SOT in Gr by Pt adatoms is also demonstrated by the field-free SOT magnetization switching process with a relatively low critical current density around 5.4 MA/cm2 in Gr/Pt/FeNi trilayers with the in-plane magnetic anisotropy. These findings pave the way for Gr spintronics applications, offering solutions for future low power consumption memories.

Anisotropic sensing based on single ReS2 flake for VOCs discrimination

Selective and sensitive detection of volatile organic compounds (VOCs) holds paramount importance in real-world applications. This study proposes an innovative approach utilizing a single ReS2 field-effect transistor (FET) characterized by distinct in-plane anisotropy, specifically tailored for VOC recognition. The unique responses of ReS2, endowed with robust in-plane anisotropic properties, demonstrate significant difference along the a-axis and b-axis directions when exposed to four kinds of VOCs: acetone, methanol, ethanol, and IPA. Remarkably, the responses of ReS2 were significantly magnified under ultraviolet (UV) illumination, particularly in the case of acetone, where the response amplified by 10–15 times and the detection limit decreasing from 70 to 4 ppm compared to the dark conditions. Exploiting the discernible variances in responses along the a-axis and b-axis under both UV and dark conditions, the data points of acetone, ethanol, methanol and IPA gases were clearly separated in the principal component space without any overlap through principal component analysis, indicating that the single ReS2 FET has a high ability to distinguish various gas species. The exploration of anisotropic sensing materials and light excitation strategies can be applied to a broad range of sensing platforms based on two-dimensional materials for practical applications.