Out Of Plane Direction Research Articles

Interfacial Magnetic Anisotropy Controlled Spin Pumping in Co60Fe20B20/Pt Stack

Controlled spin transport in magnetic stacks is required to realize pure spin current-driven logic and memory devices. The control over the generation and detection of the pure spin current is achieved by tuning the spin to charge conversion efficiency of the heavy metal interfacing with ferromagnets. Here, we demonstrate the direct tunability of spin angular momentum transfer and thereby spin pumping, in CoFeB/Pt stack, with interfacial magnetic anisotropy. The ultra-low thickness of the CoFeB thin film by tilting the magnetization from in-plane to out-of plane direction due to interfacial anisotropy from higher thickness of CoFeB thin film. The ferromagnetic resonance measurements are performed to investigate the magnetic anisotropy and spin pumping in CoFeB/Pt stacks. We clearly observe tunable spin pumping effect in the CoFeB/Pt stacks with varying CoFeB thicknesses. The spin current density, with varying ferromagnetic layer thickness, is found to increase from 1.10[Formula: see text]MA/m2 to 2.40[Formula: see text]MA/m2, with increasing in-plane anisotropy field. Such interfacial anisotropy-controlled generation of pure spin current can potentially lead to next-generation anisotropic spin current-controlled spintronic devices.

Microstructural evolution during the crystallization process of sol-gel derived PbZrO3 nanocomposite thin films

For the application of dielectric materials in energy storage, nanocomposition is one of the effective methods to improve their electric breakdown field strength. In this study, PbZrO3-Al2O3 nanocomposite films were prepared by combined thermal evaporation deposition and a sol–gel method. By changing the annealing time, the crystallization process of PbZrO3 matrix and the formation mechanism of Al2O3 nanoparticles were studied, and the microstructure evolution process of composite films was elucidated. The results indicate that before the final annealing at 700 ℃, Al atoms have diffused into the amorphous PbZrO3 film, and some fine grains of the perovskite phase have been generated at the bottom of the film. As the annealing time increases, the perovskite grains grow along the out of plane direction of the thin film to form columnar grains, and Al atoms diffuse into the perovskite phase lattice; As the annealing time further increases, Al2O3 nanoparticles began to precipitate at the interlayer interfaces of PbZrO3 coating layers, forming a layered distribution. The changes in electric properties with annealing time also demonstrate the microstructural evolution process of the composite film during annealing. Therefore, controlling annealing time is an effective means to control the microstructure and electric properties of composite films prepared by the new method for the application of energy storage.

Comparative Study of the Orientation and Order Effects on the Thermoelectric Performance of 2D and 3D Perovskites.

Calcium titanium oxide has emerged as a highly promising material for optoelectronic devices, with recent studies suggesting its potential for favorable thermoelectric properties. However, current experimental observations indicate a low thermoelectric performance, with a significant gap between these observations and theoretical predictions. Therefore, this study employs a combined approach of experiments and simulations to thoroughly investigate the impact of structural and directional differences on the thermoelectric properties of two-dimensional (2D) and three-dimensional (3D) metal halide perovskites. Two-dimensional (2D) and three-dimensional (3D) metal halide perovskites constitute the focus of examination in this study, where an in-depth exploration of their thermoelectric properties is conducted via a comprehensive methodology incorporating simulations and experimental analyses. The non-equilibrium molecular dynamics simulation (NEMD) was utilized to calculate the thermal conductivity of the perovskite material. Thermal conductivities along both in-plane and out-plane directions of 2D perovskite were computed. The NEMD simulation results show that the thermal conductivity of the 3D perovskite is approximately 0.443 W/mK, while the thermal conductivities of the parallel and vertical oriented 2D perovskites increase with n and range from 0.158 W/mK to 0.215 W/mK and 0.289 W/mK to 0.309 W/mK, respectively. Hence, the thermal conductivity of the 2D perovskites is noticeably lower than the 3D ones. Furthermore, the parallel oriented 2D perovskites exhibit more effective blocking of heat transfer behavior than the perpendicular oriented ones. The experimental results reveal that the Seebeck coefficient of the 2D perovskites reaches 3.79 × 102 µV/K. However, the electrical conductivity of the 2D perovskites is only 4.55 × 10-5 S/cm, which is one order of magnitude lower than that of the 3D perovskites. Consequently, the calculated thermoelectric figure of merit for the 2D perovskites is approximately 1.41 × 10-7, slightly lower than that of the 3D perovskites.

Evolution of magnetic anisotropy in La0.67Sr0.33MnO3 thin films due to the appearance of out-of-plane magnetization at low temperature

We have observed quadrupolar angle-dependent anisotropic magnetoresistance (AMR) at low temperature in La0.67Sr0.33MnO3 (LSMO) films grown on SrTiO3 substrate, where the magnetic field was applied while rotating the direction of the applied magnetic field from out-of-plane (OP) to in-plane. At room temperature, the easy axis is in-plane and has a two-fold magnetic anisotropy. As the temperature decreases, it changes to a quadrupolar anisotropy. Along with the AMR, we have measured the magnetoresistance (MR) in the OP direction at various temperatures. Like the AMR, we found the appearance of a new magnetic configuration in the OP direction at low temperatures. We suggest that one of the important origins of the new OP magnetism, which appears at temperature much lower than the Curie temperature (Tc), is the d3z2−r2 orbital at the interface between the LSMO films and SrTiO3 substrate. It has been reported that despite the tensile strain imposed by the SrTiO3 substrate, the d3z2−r2 orbital exists at the interface and causes the OP magnetism. We demonstrate by a polarized x-ray resonant scattering that there is a higher density of d3z2−r2 orbitals at the interface than in the region away from the interface. As other references have proposed, we suggest the orbital reconstructions and the orbital reconstruction-driven magnetic reorientation at the interface as the origin of the appearance of the OP magnetism present in the AMR and MR results.

Rotational stress-induced shish-kebab governs the balance of enhanced thermal conductivity and mechanical performance of high-density polyethylene (HDPE) / boron nitride (BN) composites via axial hot compression

Polymer-based composites with high BN sheets loadings have potential to improve thermal conductivity without compromising mechanical performance. In this work, a balanced enhancement in both thermal conductivity and tensile strength were achieved using rotational shear followed by axial hot compression. For neat HDPE matrix, the highly oriented shish-kebab structures induced by shear field improved tensile strength from 20.4 MPa to 80.9 MPa, compared with unsheared specimens. The in-plane thermal conductivity of sheared HDPE/BN composite was 25.0% higher than the unsheared one. Axial hot compression resulted in denser crystal and oriented fillers, leading to a 63% increase in tensile strength while simultaneously increasing thermal conductivity in both in-plane and out-plane directions. This work has utilized rotation shear and axial hot compression to manufacture HDPE/BN composites with effective two-way thermal conductivity and higher tensile strength. The excellent thermo-mechanical properties mean a longer service time and less replaced frequency of material under extreme operating conditions. The two-step methods provide a key information for the preparation of composites with balanced mechanical properties and thermal conductivity.

A Novel Hydrophobic Polyimide Film with Sag Structure Derived from Multi-Hybrid Strategy.

Polyimide (PI) film with hydrophilic greatly limits their application in the field of microelectronic device packaging. A novel hydrophobic PI film with sag structure and improved mechanical properties is prepared relying on the reaction between anhydride-terminated isocyanate-based polyimide (PIY) containing a seven-membered ring structure and the amino-terminated polyamide acid (PAA) via multi-hybrid strategy, this work named it as hybrid PI film and marked it as PI-PIY-X. PI-PIY-30 showed excellent hydrophobic properties, and the water contact angle could reach to 102°, which is 20% and 55% higher than simply PI film and PIY film, respectively. The water absorption is only 1.02%, with a decrease of 49% and 53% compared with PI and PIY. Due to that the degradation of seven-membered ring and generation of carbon dioxide led to the formation of sag structure, the size of sag structures is ≈16.84 and 534.55nm for in-plane and out-plane direction, which are observed on surface of PI-PIY-30. Meanwhile, PI-PIY-30 possessed improved mechanical properties, and the tensile strength is 109.08MPa, with 5% and more than 56% higher than that of pure PI and PIY film, showing greatly application prospects in the field of integrated circuit.

Microstructural and electrochemical properties of Ni-impregnated GDC10 and 8YSZ freeze tape cast scaffolds as fuel electrodes for solid oxide cells

Ni-impregnated Gd0.1Ce0.9O2 and Y0.08Zr0.92O2 fuel electrodes for solid oxide cells are manufactured by the combination of the freeze tape casting and infiltration techniques. Their morphological properties are investigated by scanning electron microscope and X-Ray microtomography while their electrochemical performance is evaluated in symmetrical Y0.08Zr0.92O2-supported button cells by electrochemical impedance spectroscopy. The microstructural analysis of the manufactured scaffolds highlights the characteristic anisotropy of porosity provided by the freeze tape casting method. The average tortuosity factor across the out of plane direction has been calculated equal to 1.38, being considerably lower than the average values of the other components, (τx = 10.2) and (τy = 6.87). The contribution provided by gas diffusion to the overall polarization resistance of the freeze tape cast electrodes has been estimated around 6·10−4 Ω cm2 in the 600–750 °C temperature range, thus lower than the best reported values for the state-of-the-art electrodes featuring sponge-like porosity. The measured impedance data highlighted the higher electrochemical performance of the Ni-impregnated Gd0.1Ce0.9O2 architecture, holding a polarization resistance of 0.823 Ω cm2 at 750 °C, which is regarded as a very promising result for a ∼600 μm thick electrode. The interpretation of the impedance data was supported by the distribution of relaxation times analysis and the complex non-linear least square fit. In particular, the electrochemical investigation highlighted the presence of two major resistive contributions which have been ascribed to the occurrence of a chemical capacitance within the GDC10 lattice (low frequency contribution) and to the multi-layered architecture of the tested symmetrical cells which increases the contact losses (high frequency contribution).

Significant regulation of stress on the contribution of optical phonons to thermal conductivity in layered Li2ZrCl6: First-principles calculations combined with the machine-learning potential approach

The layered solid electrolyte Li2ZrCl6 and Li metal electrodes have a very good contact stability, but the thermal transport properties of Li2ZrCl6 are still unclear. Here, we systematically study the intrinsic lattice thermal conductivity (κp) of Li2ZrCl6 using the machine-learning potential approach based on first-principles calculations combined with the Boltzmann transport theory. The results show that the κp of Li2ZrCl6 at room temperature is 3.94 W/mK along the in-plane (IP) direction and 1.05 W/mK along the out-plane (OP) direction, which means that the κp is significantly anisotropic. In addition, under the compressive stress in the OP direction, the κp evolution along the IP and OP directions exhibits completely different trends, because the stress has a significant regulatory effect on the contribution of optical phonons to κp. With the increase in stress, the κp in the IP direction monotonically decreases, while the κp in the OP direction increases by a factor of 2.2 under a compressive strain of 13%. This is because the contribution of low-frequency optical phonons to κp in the IP direction is as high as 58% when no stress is applied, and this contribution is significantly suppressed with increasing compressive strain. However, the contribution of optical phonons in the OP direction to the κp increases with the increase in stress. Our results reveal the thermal transport properties of Li2ZrCl6 and the effect of the compressive strain on the κp of Li2ZrCl6, thereby providing a reference for the use of Li2ZrCl6 in Li-metal batteries.

Anisotropic degradation mechanism on low-velocity impact of 3D braided composites after thermo-oxidative ageing

Anisotropic mechanical behaviors are the most prominent feature of 3D braided composites compared with homogeneous materials. This study reports anisotropic low-velocity impact behaviors of 3D braided carbon fiber/epoxy composites along in-plane (IP) and out-of-plane (OP) directions after thermo-oxidative ageing. The stress–strain responses, local strain and damage evolution were obtained. The stress distribution of each yarn and the interface damage propagation were analyzed with numerical analysis method. The retention rate of peak stress of 94.4% and elastic modulus of 91.45% along OP direction are greater than those along IP direction, which are 76.21% and 71.27% respectively. It reveals that the OP direction loading has a better performance on resistance ageing degradation than that in IP loading, and the stiffness degradation is more sensitive. There are X-shape shear damages along OP direction, and interior damages in surrounding area and yarn path along IP direction. Furthermore, the tight braided structure contributed to resisting degradation of mechanical properties along IP direction.

Tunable goniopolarity of graphenelike boron layers in metal diborides

The orientation-dependent conduction polarity, e.g., $p$-type conduction along one direction and $n$-type conduction along another direction, namely ``goniopolarity,'' observed in highly anisotropic materials brought us an alternative concept for novel electronic devices. But goniopolarity has hardly been utilized due to the rarity of goniopolar materials. Here, we associate goniopolarity with the saddle points in electronic band structure and the hyperbolic Fermi surface of materials and highlight the potential of layered metal diboride ($M{\mathrm{B}}_{2}$) materials in achieving this interesting phenomenon using first-principles calculations. We demonstrate that the electron-doped ${\mathrm{MgB}}_{2}$, ${\mathrm{CaB}}_{2}$, and ${\mathrm{SrB}}_{2}$ can exhibit remarkable orientation-dependent conduction polarity with opposite Seebeck coefficients which are detectable in verifying goniopolarity. We attribute the goniopolarity with the ${p}_{x,y}$ orbitals of the boron layers of these materials which constitute anisotropic electronic states along in-plane and out of plane directions. Moreover, their anisotropic Seebeck coefficients can be efficiently enhanced by applying tensile strain. This work offers a promising strategy for design of goniopolar materials and regulation of goniopolarity.

Edge-Driven Phase Transitions in 2D Ice

2D water, confined by atomically flat layered materials, may transit into various crystalline phases even at room temperature. However, to gain full control over the crystalline state, we should not only confine water in the out of plane direction but also restrict its in plane motion, forming 2D water clusters or ribbons. One way to do this is by using an electric field, in particular the intrinsic electric field of an adjacent polar material. We have found that the crystalline phases of 2D water clusters placed between two hexagonal boron nitride hBN nanoribbons are crucially determined by the nanoribbons edges, the resulting polarity of the nanoribbons, and their interlayer distance. We make use of density functional theory with further assistance of molecular dynamics simulations to establish the comprehensive phase diagrams demonstrating transitions between liquid and solid phases and between the states of different crystalline orders. We also show that the crystalline orders are maintained when water flows between hBN channels under external pressure. Our results open a promising pathway towards the control of water structure and its flow by the use of the microscopic electric field of polar materials.

Halide Remixing under Device Operation Imparts Stability on Mixed‐Cation Mixed‐Halide Perovskite Solar Cells

Mixed-halide mixed-cation hybrid perovskites are among the most promising perovskite compositions for application in a variety of optoelectronic devices due to their high performance, low cost, and bandgap-tuning capabilities. Instability pathways such as those driven by ionic migration, however, continue to hinder their further progress. Here, an operando variable-pitch synchrotron grazing-incidence wide-angle X-ray scattering technique is used to track the surface and bulk structural changes in mixed-halide mixed-cation perovskite solar cells under continuous load and illumination. By monitoring the evolution of the material structure, it is demonstrated that halide remixing along the electric field and illumination direction during operation hinders phase segregation and limits device instability. Correlating the evolution with directionality- and depth-dependent analyses, it is proposed that this halide remixing is induced by an electrostrictive effect acting along the substrate out-of-plane direction. However, this stabilizing effect is overwhelmed by competing halide demixing processes in devices exposed to humid air or with poorer starting performance. The findings shed new light on understanding halide de- and re-mixing competitions and their impact on device longevity. These operando techniques allow real-time tracking of the structural evolution in full optoelectronic devices and unveil otherwise inaccessible insights into rapid structural evolution under external stressconditions.

Anomalous magnetoresistance and Hall effect in amorphous Pt/TbFeCo thin films

Among the magnetic materials in technological usage, amorphous rare-earth transition metal (RE–TM) alloys are of great interest due to their adjustable magnetic properties and favorable perpendicular magnetic anisotropic (PMA) advantages. In this study, the properties of Tb25Fe61Co14 system with 2, 5, and 10 nm Pt underlayers have been systematically explored by X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature and magnetic field dependence of Hall resistivity, magnetoresistivity, and magneto-optic Kerr Effect (MOKE) measurements. According to the results, whole thin films are amorphous in nature and display an out-of-plane magnetic anisotropy without annealing. Increasing the Pt underlayer thickness helps the TbFeCo layer to reach significantly enhanced perpendicular magnetic anisotropic values and visualize the appearance of anomalous magnetoresistance in the Hall effect measurements. The thin films with 5 and 10 nm Pt underlayer has a ratio of remanence magnetization/saturation magnetization (MR/MS) of around 1, which is the out of plane direction of MOKE signal. Besides, the present study also includes some pieces of evidence that might be related to the Berry phase trend.

Anisotropic magnetostructural transition in epitaxial Mn–Ni–Co–Ti Heusler alloy thin film

Heusler alloys are distinctive functional materials related to the phase transitions due to the strong magnetic and structural coupling. By the epitaxial strain from the rigid substrates, anisotropic magnetostructural transition (MST) might be observed in different crystalline orientations, leading to novel properties and functions. In this work, 62 nm thick (001)-oriented Mn49.1Ni34.0Co9.6Ti7.3 films are epitaxially grown on (001) MgO substrates. Clear MST is observed accompanied by a broad transition hysteresis from the thermomagnetic (M–T) curves with an out-of-plane (OP) magnetic field, while the transition hysteresis is absent under an in-plane (IP) magnetic field. It is related to the main lattice distortion occurring in OP orientation during the martensitic transformation because of the kinetic arrest of the IP structure by the MgO substrate. The spin glass (SG) phase is observed in IP orientation, which is lacking in OP orientation and the bulk. Clear exchange bias (EB) is observed in both the IP and OP directions. OP EB originates from exchange coupling between the ferromagnetic (FM) and antiferromagnetic phases, while IP EB is partially contributed by the exchange coupling between the SG and FM phases. It is ascribed to the establishment of metastable spin configuration in IP orientation with sufficient surrounding spins, but stable spin configuration in OP orientation due to the limited number of surrounding spins, which has been confirmed by Monte-Carlo simulation results. Our results provide a novel strategy for the modification of the physical properties of Heusler alloys and the design of novel magnetic devices.

Giant Photoresponse Enhancement in Mixed‐Dimensional Van der Waals Heterostructure through Dielectric Engineering

AbstractThe reduced dielectric screening in the out of plane direction, makes 2D materials sensitive to the surrounding environment, offering a unique platform with greatly tunable optoelectronic properties. Large exciton binding energy in 2D materials limits their photogeneration efficiency. The strong electric field generated at a p–n junction will help in separating these strongly bound electron hole pairs. Here, the present study demonstrates how engineering the surrounding dielectric environment would facilitate a mixed dimensional van der Waals p–n junction to improve the photoresponse to a great extent. A 3D silicon‐2D monolayer MoS2 heterostructure is fabricated as a model system. Nearly three orders of magnitude enhancement in photoresponse is observed by modulating the surrounding dielectric environment. This huge enhancement is attributed to the easy separation of photogenerated carriers due to the screening of Coulomb interaction. The dielectric also screens the impurity potential, reducing the charge carrier scattering. In addition, there is a change in the overall bandgap of the heterostructure producing a lower energy barrier for the charge carriers. The findings lay a general pathway for improving the efficiency of 2D material based photodetectors through dielectric engineering.

Parametric study on longitudinal and out-of-plane compressive properties, progressive damage and failure of 3D five-directional braided composites

The parametric finite element model (FEM) of three-dimensional five-directional (3D5d) braided composites was established by considering the yarn cross-section and the spatial contact between the yarns. The longitudinal and out-of-plane compressive mechanical properties and progressive damage of composites with various parameters were predicted and experimentally verified. As the fiber volume fraction increase, the mechanical performance improve, both in longitudinal and out-of plane direction. With the increase of braiding angle, the longitudinal mechanical properties decrease and the out-of-plane strength decreases while the modulus increases. The stress–strain curves show brittleness and toughness in longitudinal and out-of-plane, respectively. Due to the influence of stress transfer and component contact, damage is more likely to occur at the connection parts of each component.

Slip and Crack Initiation Behavior of Carbon Steel Thin Films under Cyclic In-Plane Shear Loading

In the same materials, film and bulk materials show different mechanical properties. In fatigue testing of metallic thin film, several studies have been reported for axial and bending directions, however, there are few studies for shear direction. In addition, multiple parallel slips in the same grain are considered out-plane direction, a single linear slip in a grain is considered in-plane direction. Therefore, in this study we conducted fatigue tests under cyclic in-plane pure shear loading to S10C and S45C.We focused on the effect of pearlite volume fraction on slip generation and the relationship between cracks and slips. As a result, about 90% of the slip that occurred in S10C was out-plane direction. About 70% of the slip that occurred in S45C was in-plane slip. This is considered to be caused by the concentration of strain due to pearlite. In addition, more cracks were observed in S45C than in S10C, Consequently, cracks in the carbon steel film are considered to have grown from in-plane slip.

Possible way to achieve anomalous valley Hall effect by piezoelectric effect in a GdCl2 monolayer

Ferrovalley materials can achieve manipulation of the valley degree of freedom with intrinsic spontaneous valley polarization introduced by their intrinsic ferromagnetism. A good ferrovalley material should possess perpendicular magnetic anisotropy (PMA), valence band maximum (VBM)/conduction band minimum (CBM) at valley points, strong ferromagnetic (FM) coupling and proper valley splitting. In this work, the monolayer $\mathrm{GdCl_2}$ is proposed as a potential candidate material for valleytronic applications by the first-principles calculations. It is proved that monolayer $\mathrm{GdCl_2}$ is a FM semiconductor with the easy axis along out of plane direction and strong FM coupling. A spontaneous valley polarization with a valley splitting of 42.3 meV is produced due to its intrinsic ferromagnetism and spin orbital coupling (SOC). Although the VBM of unstrained monolayer $\mathrm{GdCl_2}$ is away from valley points, a very small compressive strain (about 1\%) can make VBM move to valley points. We propose a possible way to realize anomalous valley Hall effect in monolayer $\mathrm{GdCl_2}$ by piezoelectric effect, not an external electric field, namely piezoelectric anomalous valley Hall effect (PAVHE). This phenomenon could be classified as piezo-valleytronics, being similar to piezotronics and piezophototronics. The only independent piezoelectric strain coefficient $d_{11}$ is -2.708 pm/V, which is comparable to one of classical bulk piezoelectric material $\alpha$-quartz ($d_{11}$=2.3 pm/V). The biaxial in-plane strain and electronic correlation effects are considered to confirm the reliability of our results. Finally, the monolayer $\mathrm{GdF_2}$ is predicted to be a ferrovalley material with dynamic and mechanical stabilities, PMA, VBM at valley points, strong FM coupling, valley splitting of 47.6 meV, and $d_{11}$ of 0.584 pm/V.

Shear-Induced Spin Polarization in Heavy-Ion Collisions.

We study the spin polarization generated by the hydrodynamic gradients. In addition to the widely studied thermal vorticity effects, we identify an undiscovered contribution from the fluid shear. This shear-induced polarization (SIP) can be viewed as the fluid analog of strain-induced polarization observed in elastic and nematic materials. We obtain the explicit expression for SIP using the quantum kinetic equation and linear response theory. Based on a realistic hydrodynamic model, we compute the differential spin polarization along both the beam direction z[over ^] and the out-plane direction y[over ^] in noncentral heavy-ion collisions at sqrt[s_{NN}]=200 GeV, including both SIP and thermal vorticity effects. We find that SIP contribution always shows the same azimuthal angle dependence as experimental data and competes with thermal vorticity effects. In the scenario that Λ inherits and memorizes the spin polarization of a strange quark, SIP wins the competition, and the resulting azimuthal angle dependent spin polarization P_{y} and P_{z} agree qualitatively with the experimental data.

Scaling theory of three-dimensional magnetic reconnection spreading

We develop a first-principles scaling theory of the spreading of three-dimensional (3D) magnetic reconnection of finite extent in the out of plane direction. This theory addresses systems with or without an out of plane (guide) magnetic field, and with or without Hall physics. The theory reproduces known spreading speeds and directions with and without guide fields, unifying previous knowledge in a single theory. New results include the following: (1) reconnection spreads in a particular direction if an x-line is induced at the interface between reconnecting and non-reconnecting regions, which is controlled by the out of plane gradient of the electric field in the outflow direction. (2) The spreading mechanism for anti-parallel collisionless reconnection is convection, as is known, but for guide field reconnection it is magnetic field bending. We confirm the theory using 3D two-fluid and resistive-magnetohydrodynamics simulations. (3) The theory explains why anti-parallel reconnection in resistive-magnetohydrodynamics does not spread. (4) The simulation domain aspect ratio, associated with the free magnetic energy, influences whether reconnection spreads or convects with a fixed x-line length. (5) We perform a simulation initiating anti-parallel collisionless reconnection with a pressure pulse instead of a magnetic perturbation, finding spreading is unchanged rather than spreading at the magnetosonic speed as previously suggested. The results provide a theoretical framework for understanding spreading beyond systems studied here and are important for applications including two-ribbon solar flares and reconnection in Earth's magnetosphere.