Adjacent Metal Layers Research Articles

The influence of exchange-bias on the resonance frequencies and damping in IrMn3/[Co/Pt] multilayers

In order to realise single on-chip three axis magnetic field sensing technology without the need for convoluted die stacking, perpendicular media must be exploited. This poses additional challenges in both static-bias and the dynamics of the stack. Presented here are ferromagnetic resonance measurements (FMR) on exchange-biased multilayers of IrMn3/[Co/Pt]n. We chart the evolution of the different anisotropies caused by both magnetic field annealing and increasing repetition number n. The damping of these stacks does not obey the usual symmetry seen in single and bilayer samples with in-plane anisotropy, but instead follows a sin2(θ) dependence. This, we propose, is entirely dominated by spin diffusion from the Co layers into the adjacent heavy metal layers. This is modelled using a simple effective circuit model, providing a guide for the optimisation of complex multilayers.

Asymmetric magnetization switching and programmable complete Boolean logic enabled by long-range intralayer Dzyaloshinskii-Moriya interaction

After decades of efforts, some fundamental physics for electrical switching of magnetization is still missing. Here, we report the discovery of the long-range intralayer Dzyaloshinskii-Moriya interaction (DMI) effect, which is the chiral coupling of orthogonal magnetic domains within the same magnetic layer via the mediation of an adjacent heavy metal layer. The effective magnetic field of the long-range intralayer DMI on the perpendicular magnetization is out-of-plane and varies with the interfacial DMI constant, the applied in-plane magnetic fields, and the magnetic anisotropy distribution. Striking consequences of the effect include asymmetric current/field switching of perpendicular magnetization, hysteresis loop shift of perpendicular magnetization in the absence of in-plane direct current, and sharp in-plane magnetic field switching of perpendicular magnetization. Utilizing the intralayer DMI, we demonstrate programable, complete Boolean logic operations within a single spin-orbit torque device. These results will stimulate investigation of the long-range intralayer DMI effect in a variety of spintronic devices.

Highly Efficient Room-Temperature Spin-Orbit-Torque Switching in a Van der Waals Heterostructure of Topological Insulator and Ferromagnet.

All-Van der Waals (vdW)-material-based heterostructures with atomically sharp interfaces offer a versatile platform for high-performing spintronic functionalities at room temperature. One of the key components is vdW topological insulators (TIs), which can produce a strong spin-orbit-torque (SOT) through the spin-momentum locking of their topological surface state (TSS). However, the relatively low conductance of the TSS introduces a current leakage problem through the bulk states of the TI or the adjacent ferromagnetic metal layers, reducing the interfacial charge-to-spin conversion efficiency (qICS). Here, a vdW heterostructure is used consisting of atomically-thin layers of a bulk-insulating TI Sn-doped Bi1.1Sb0.9Te2S1 and a room-temperature ferromagnet Fe3GaTe2, to enhance the relative current ratio on the TSS up to ≈20%. The resulting qICS reaches ≈1.65 nm-1 and the critical current density Jc ≈0.9×106Acm-2 at 300 K, surpassing the performance of TI-based and heavy-metal-based SOT devices. These findings demonstrate that an all-vdW heterostructure with thickness optimization offers a promising platform for efficient current-controlled magnetization switching at room temperature.

The role of magnetic anisotropy in the magnetoresistance of Cr2O3/Al2O3 thin film antiferromagnets

The magnetic states of antiferromagnetic insulating thin films are a promising medium for information storage, but characterization of these states has proven to be challenging. One approach is via magnetotransport measurements in an adjacent heavy metal layer. To this end, we synthesized and characterized a series of Cr2O3 films and bilayers on Al2O3 substrates with three different orientations: m-plane, a-plane, and c-plane. X-ray diffraction results demonstrated orientation control of the Cr2O3 thin film, with m-plane films displaying a higher degree of mosaic spread than the a- and c-plane films. Reciprocal space maps showed that the films are mostly relaxed, although there was a small and different degree of strain in each orientation. The m-plane films were under 2% compressive strain, the a-plane film was under 0.5% compressive strain, and the c-plane film was completely relaxed to bulk values. To probe the magnetic state of the films, we measured the angular dependent magnetoresistance of Cr2O3/Pt bilayers for each orientation. We found a nontrivial temperature dependence of the sign of the magnetoresistance, pointing to the complex interplay between the exchange and anisotropy energies that vary with orientation. We propose that strain and mosaic spread may contribute to a difference in magnetic anisotropies among the samples and the resulting temperature dependence of the magnetoresistance. This work demonstrates the importance of considering the competition between antiferromagnetic exchange and magnetic anisotropy when storing information in the spin state of an antiferromagnetic insulator.

Issues of laser welding technology of the ends of heat exchange pipes in pipe gratings.

The paper shows that the reliability and service life of shipboard heat exchangers largely depends on the quality of fixing heat exchange pipes in pipe grids. The methods of fixing pipes in a pipe grid depends on many factors: the type of heat exchanger, the material from which the pipes and pipe grids are made, the thickness of pipes and pipe grids, technological capabilities taking into account the chosen design, etc. One of the most effective ways of fixing pipes in the tube grids of heat exchangers is welding. Welds are characterized by strength, manufacturability, and provide a high service life of the joint.
 In the article, it is proposed to use laser welding to perform welded joints. Laser welding provides a high focused energy density concentrated on a very small area with relatively low energy input and heating of adjacent metal layers. In laser welding, there is no strong ionizing radiation, the magnetization of the workpieces does not affect the laser beam, which is relevant when welding magnetic materials. The effect of laser radiation is highly local, carried out in the air, including in the environment of protective gases. Thanks to this, laser welding can be used without problems to connect large-sized metal structures.
 The laser beam is easily transported with the help of mirror optical systems or through a light guide and is directed to hard-to-reach places. At the same time, reliable and operational control of the laser welding process with adjustable energy characteristics is provided. The article describes the technological equipment that can be used for welding heat exchange pipes and pipe gratings.

Field‐Free Switching and Enhanced Electrical Detection of Ferrimagnetic Insulators Through an Intermediate Ultrathin Ferromagnetic Metal Layer

AbstractPerpendicularly magnetized ferrimagnetic insulators offer great potential for the development of fast and energy‐efficient spintronic devices. However, a major challenge for these devices is the requirement of an auxiliary magnetic field to achieve spin‐orbit torque (SOT)‐driven magnetization switching, along with the extremely small electric read‐out signal from the adjacent heavy metal layer. In this work, an approach by introducing an ultrathin Co layer primarily with in‐plane magnetization at the interface of the Tm3Fe5O12/Pt bilayers, which enables field‐free deterministic switching of the perpendicular Tm3Fe5O12 layer is demonstrated. Meanwhile, it is observed that a large anomalous Hall resistance readout signal from the coupling‐induced perpendicular component of the interfacial Co, which is nearly two orders of magnitude larger than that observed in Tm3Fe5O12/Pt bilayers. The crucial role played by the Co layer in modifying the SOT is elucidated. This research represents a significant step toward the practical implementation of ferrimagnetic insulator devices.

Highly integrated, breathable, metalized phase change fibrous membranes based on hierarchical coaxial fiber structure for multimodal personal thermal management

The development of personal thermal management textile is of great significance to satisfy the individual thermal comfort in an energy saving manner. However, major challenges remain, such as the sacrificed permeability, and limited mechanical durability, hindering long-term wearing comfort and reliability. Herein, a breathable, integrated thermoregulating fibrous membrane combining photo/electrothermal conversion and energy storage/release performance was fabricated for all-weather, on-demand, personal thermal management. We have delicately constructed a hierarchically ordered coaxial fiber structure that assembled functional components together for a versatile platform, through facile coaxial electrospinning followed by polydopamine (PDA) assisted metal deposition techniques. Interestingly, the intermediate PDA layer not only favors homogeneous loading of Ag nanoparticles (AgNPs), but also facilitates the interfacial bonding of the adjacent metal layer and the phase change fiber substrate for a seamlessly integrated system with improved structural stability and robust electrical performance. As a result, benefiting from the hierarchical coaxial structure of individual fibers and the overall well-preserved porous structure, we have fabricated an highly integrated, breathable, metalized phase change fibrous membrane with admirable heat enthalpy of 101.1 J/g, decent solar heating capability (up to 63.2 °C at 100 mW/cm2), and low voltage-driven Joule heating performance (up to 76.8 °C at 3.5 V), which exhibited a broad application prospect in next-generation wearable personal thermal management.

Emission of coherent THz magnons in an antiferromagnetic insulator triggered by ultrafast spin–phonon interactions

Antiferromagnetic materials have been proposed as new types of narrowband THz spintronic devices owing to their ultrafast spin dynamics. Manipulating coherently their spin dynamics, however, remains a key challenge that is envisioned to be accomplished by spin-orbit torques or direct optical excitations. Here, we demonstrate the combined generation of broadband THz (incoherent) magnons and narrowband (coherent) magnons at 1 THz in low damping thin films of NiO/Pt. We evidence, experimentally and through modeling, two excitation processes of spin dynamics in NiO: an off-resonant instantaneous optical spin torque in (111) oriented films and a strain-wave-induced THz torque induced by ultrafast Pt excitation in (001) oriented films. Both phenomena lead to the emission of a THz signal through the inverse spin Hall effect in the adjacent heavy metal layer. We unravel the characteristic timescales of the two excitation processes found to be < 50 fs and > 300 fs, respectively, and thus open new routes towards the development of fast opto-spintronic devices based on antiferromagnetic materials.

Ultrafast electron dynamics in Au/Fe/MgO(001) analyzed by Au- and Fe-selective pumping in time-resolved two-photon photoemission spectroscopy: Separation of excitations in adjacent metallic layers

The transport of optically excited, hot electrons in heterostructures is analyzed by femtosecond, time-resolved two-photon photoelectron emission spectroscopy (2PPE) for epitaxial Au/Fe/MgO(001). We compare the temporal evolution of the 2PPE intensity upon optically pumping Fe or Au, while the probing occurs on the Au surface. In the case of Fe-side pumping, assuming independent relaxation in the Fe and Au layers, we determine the hot electron relaxation times in these individual layers by an analysis of the Au layer thickness dependence of the observed, effective electron lifetimes in the heterostructure. We show in addition that such a systematic analysis fails for the case of Au-side pumping due to the spatially distributed optical excitation density, which varies with the Au layer thickness. This work extends a previous study [Beyazit et al., Phys. Rev. Lett. 125, 076803 (2020)] by new data leading to reduced error bars in the determined lifetimes and by a non-linear term in the Au-thickness dependent data analysis which contributes for similar Fe and Au film thicknesses.

Improving the stability of P2-type NaMn2/3Ni1/3O2 via phasic intergrowth induced by Li-ion substitution

Layered transition metal oxides are attractive cathode materials for sodium-ion batteries but are largely hindered by the low capacity and poor cycling stability. Herein, Na is substituted by Li to enhance the capacity and stability of Na1-xLixMn2/3Ni1/3O2. It is found that Li substitution can provide robust structure benefiting from contracted adjacent transition metal layers owing to strong bonding property of O–Li–O and incremental inactive Mn4+. So it follows that noxious Mn3+ Jahn-Teller distortion and slabs slipping are mitigated. Also, the presence of “Li pillar” disturbs the Na+/vacancies and transition metal ordering during Na extraction, preventing phase transformation during deep desodiation process. Consequently, the Na1-xLixMn2/3Ni1/3O2 demonstrates high capacity, remarkable rate capability, and long-term cycling life. Among them, Na0.8Li0.2Mn2/3Ni1/3O2 cathode delivers a discharge capacity of 115.3 mA h/g, with a capacity retention of 86.0% after 100 cycles. This simple strategy to stabilize the layered structure oxides is inspiring to design high-performance cathode materials for sodium-ion batteries.

Phase Change Nanoelectromechanical Relay for Nonvolatile Low Leakage Switching

AbstractThe design, modeling, and experimental validation of a highly scalable phase change electromechanical relay are present. The Phase Change NEMS Relay (PCNR) is a nonvolatile mechanical relay actuated by the volumetric expansion of phase change material. GeTe is used as the active phase change material, and nonvolatile relay states are changed by converting it between amorphous and crystalline phases, which differ in volume by 10%. Phase conversion is induced by Joule heating an adjacent metal layer. Finite element analysis (FEA) models are developed to predict actuator temperature distributions and quench times for varied actuation pulses. Additional models are developed to simulate actuator deflection including reflow of molten phase change material during an actuation pulse. The smallest fabricated device has a heater footprint of 3 µm × 1 µm, with a 20 nm air‐gap. The FEA model, which calculates the actuation voltage, energy, and ON–OFF current ratio for this device to be 1.1 V, 42 nJ, and 108, respectively, are experimentally verified. A PCNR scaled down to a 15 nm × 5 nm heater footprint with a 2 nm air‐gap is predicted to actuate at 400 mV and 1.7 pJ.

Antiferromagnetic spin Seebeck effect across the spin-flop transition: A stochastic Ginzburg-Landau simulation

We investigate the antiferromagnetic spin Seebeck effect across the spin-flop transition in a numerical simulation based on the time-dependent Ginzburg-Landau equation for a bilayer of a uniaxial insulating antiferromagnet and an adjacent metal. By directly simulating the rate of change of the conduction-electron spin density $\mathbit{s}$ in the adjacent metal layer, we demonstrate that a sign reversal of the antiferromagnetic spin Seebeck effect across the spin-flop transition occurs when the interfacial coupling of $\mathbit{s}$ to the staggered magnetization $\mathbit{n}$ of the antiferromagnet dominates, whereas no sign reversal appears when the interfacial coupling of $\mathbit{s}$ to the magnetization $\mathbit{m}$ dominates. Moreover, we show that the sign reversal is influenced by the degree of spin dephasing in the metal layer. Our result indicates that the sign reversal is not a generic property of a simple uniaxial antiferromagnet, but controlled by microscopic details of the exchange coupling at the interface and the spin dephasing in the metal layer.

Unusual Site-Selective Doping in Layered Cathode Strengthens Electrostatic Cohesion of Alkali-Metal Layer for Practicable Sodium-Ion Full Cell.

P2-type Na0.67 Ni0.33 Mn0.67 O2 is a dominant cathode material for sodium-ion batteries due to its high theoretical capacity and energy density. However, charging P2-type Na0.67 Ni0.33 Mn0.67 O2 to voltages higher than 4.2 V (vs. Na+ /Na) can induce detrimental structural transformation and severe capacity fading. Herein, stable cycling and moisture resistancy of Na0.67 Ni0.33 Mn0.67 O2 at 4.35 V (vs. Na+ /Na) are achieved through dual-site doping with Cu ion at transition metal site (2a) and unusual Zn ion at Na site (2d) for the first time. The Cu ion doping in 2a site stabilizes the metal layer, while more importantly, the unusual alkali-metal site doping by Zn ion serves as O2- Zn2+ O2- "pillar" for enhancing electrostatic cohesion between two adjacent transition metal layers, preventing the crack of active material along the a-b-plane and restraining the generation of O2 phase upon deep desodiation. This unique dual-site-doped [Na0.67 Zn0.05 ]Ni0.18 Cu0.1 Mn0.67 O2 cathode exhibits a prominent cyclability with 80.6% capacity retention over 2000 cycles at an ultrahigh rate of 10C, demonstrating its great potential for practical applications. Impressively, the full cell devices with [Na0.67 Zn0.05 ]Ni0.18 Cu0.1 Mn0.67 O2 and commercial hard carbon as cathode and anode, respectively, can deliver a high energy density of 217.9Wh kg-1 and excellent cycle life over 1000 cycles.

Intermixing induced anisotropy variations in CoB-based chiral multilayer films

We examine the atomic intermixing phenomenon in three distinct amorphous CoB-based multilayer thin film platforms — Pt/CoB/Ir, Ir/CoB/Pt and Pt/CoB/MgO — which are shown to stabilise room-temperature chiral magnetic textures. Intermixing occurs predominantly between adjacent metallic layers. Notably, it is stack-order dependent, and particularly extensive when Ir sits atop CoB. Intermixing induced variations in magnetic properties are ascribed to the formation of magnetic dead layer arising from CoIr alloying in the metallic stacks. It also produces systematic variations in saturation magnetization, by as much as 30%, across stacks. Crucially, the resulting crossover CoB thickness for the transition from perpendicular to in-plane magnetic anisotropy differs by more than 2 across the stacks. Finally, with thermal annealing treatment over moderate temperatures of 150–300 °C, the magnetic anisotropy increases monotonically across all stacks, coupled with discernibly larger H c for the metallic stacks. These are attributed to thermally induced CoPt alloying and MgO crystallization in the metallic and oxide stacks, respectively. Remarkably, the CoB in the Pt/CoB/MgO stacks retains its amorphous nature after annealing. Our results set the stage for harnessing the collective attributes of amorphous CoB-based material platforms and associated annealing processes for modulating magnetic interactions, enabling the tuning of chiral magnetic texture properties in ambient conditions.

Heisenberg Exchange and Dzyaloshinskii–Moriya Interaction in Ultrathin Pt(W)/CoFeB Single and Multilayers

We present results of the analysis of Brillouin light-scattering (BLS) measurements of spin waves performed on ultrathin single and multirepeat CoFeB layers with adjacent heavy metal layers. From a detailed study of the spin-wave dispersion relation, we independently extract the Heisenberg exchange interaction (also referred to as symmetric exchange interaction), the Dzyaloshinskii–Moriya interaction (DMI, also referred to as antisymmetric exchange interaction), and the anisotropy field. We find a large DMI in CoFeB thin films adjacent to a Pt layer and nearly vanishing DMI for CoFeB films adjacent to a W layer. Furthermore, the influence of the dipolar interaction on the dispersion relation and on the evaluation of the Heisenberg exchange parameter is demonstrated. Eventually, an experimental analysis of the impact of the DMI on the spin-wave lifetime is presented.

Temperature-Dependent Spin Transport and Current-Induced Torques in Superconductor-Ferromagnet Heterostructures.

We investigate the injection of quasiparticle spin currents into a superconductor via spin pumping from an adjacent ferromagnetic metal layer. To this end, we use NbN-Ni_{80}Fe_{20}(Py) heterostructures with a Pt spin sink layer and excite ferromagnetic resonance in the Permalloy layer by placing the samples onto a coplanar waveguide. A phase sensitive detection of the microwave transmission signal is used to quantitatively extract the inductive coupling strength between the sample and the coplanar waveguide, interpreted in terms of inverse current-induced torques, in our heterostructures as a function of temperature. Below the superconducting transition temperature T_{c}, we observe a suppression of the dampinglike torque generated in the Pt layer by the inverse spin Hall effect, which can be understood by the changes in spin current transport in the superconducting NbN layer. Moreover, below T_{c} we find a large fieldlike current-induced torque.

A New Scalable Preparation of Metal Nanosheets: Potential Applications for Aqueous Zn‐Ion Batteries Anode

Abstract2D metal nanosheets are attractive for various applications stemming from the intriguing characteristics related with their dimensionality; however, their effective and scalable preparation remains a great challenge. Herein, a scalable preparation process of relatively active metal nanosheets (e.g., Zn, Al, and Cu) with the thickness down to several nanometers at low cost is demonstrated, which involves an initial self‐folding‐rolling step followed by the subsequent ultrasonication to exfoliate them without any etching step. The native oxide on the surface of the metals, which acts as a barrier between the adjacent metal layers, plays a special role in enabling the successful preparation of 2D metal nanosheets. As a demonstration for their practicability, a hierarchical Zn anode, which is constructed by the Zn microsheets coated with carbon (Zn MS@C) via in situ carbonization of carboxymethylcellulose (CMC) binder, is successfully implemented as anode for rechargeable aqueous Zn‐ion batteries. When applied in symmetrical battery, the Zn MS@C delivers a long lifespan of over 800 h at 0.2 mA cm−2 with a capacity of 0.1 mA h cm−2. Importantly, the full battery of MnO2 || Zn MS@C also performs a high discharge capacity of 217.4 mA h g−1 after 140 cycles at 300 mA g−1.

Differences in the magnon diffusion length for electrically and thermally driven magnon currents in Y3Fe5O12

Recent demonstration of efficient transport and manipulation of spin information by magnon currents have opened exciting prospects for processing information in devices. Magnon currents can be driven both electrically and thermally, even in magnetic insulators, by applying charge currents in an adjacent metal layer. Earlier reports in thin yttrium iron garnet (YIG) films suggested that the diffusion length of magnons is independent on the biasing method, but different values were obtained in thicker films. Here, we study the magnon diffusion length for electrically and thermally driven magnon currents in the linear regime in a 2-$\mu$m-thick YIG film as a function of temperature and magnetic field. Our results show a decrease of the magnon diffusion length with magnetic field for both biasing methods and at all temperatures from 5 to 300 K, indicating that sub-thermal magnons dominate the long-range transport. Moreover, we demonstrate that the value of the magnon diffusion length depends on the driving mechanism, suggesting that different non-equilibrium magnon distributions are biased for each method. Finally, we demonstrate that the magnon diffusion length for thermally driven magnon currents is independent of the YIG thickness and material growth conditions, confirming that this quantity is an intrinsic parameter of YIG.

Structural studies of magnetic C60/Cu multilayers

We report on x-ray and neutron scattering studies that reveal the structure of interfaces of C60 layers with adjacent transition metal layers, in this instance, Cu. Such interfaces produce room-temperature long-range spin order that is not described by conventional theories of metallic magnetism. We use a combination of hard x-ray reflectivity and neutron scattering to investigate the interfacial structure of two C60/Cu layered samples: a superlattice with multiple C60/Cu repeats and a simpler tri-layer structure. For both structures, we develop a consistent structural model for the two scattering techniques, which details the critical interfacial roughness between the layers. We find that while x-ray reflectivity provides a strong contrast between the C60 and Cu layers, the similar neutron scattering length density of the two materials severely reduces the neutron scattering contrast. Our results can be used to design material systems that permit studies of the magnetism of the C60/transition metal interfaces with spin-sensitive scattering probes such as polarized neutron reflectometry.

Current driven domain wall dynamics in ferrimagnetic strips explained by means of a two interacting sublattices model

The current-driven domain wall dynamics along ferrimagnetic elements are here theoretically analyzed as a function of temperature by means of micromagnetic simulations and a one dimensional model. Contrarily to conventional effective approaches, our model takes into account the two coupled ferromagnetic sublattices forming the ferrimagnetic element. Although the model is suitable for elements with asymmetric exchange interaction and spin-orbit coupling effects due to adjacent heavy metal layers, we here focus our attention on the case of single-layer ferrimagnetic strips where domain walls adopt achiral Bloch configurations at rest. Such domain walls can be driven by either out-of-plane fields or spin transfer torques upon bulk current injection. Our results indicate that the domain wall velocity is optimized at the angular compensation temperature for both field-driven and current-driven cases. Our advanced models allow us to infer that the precession of the internal domain wall moments is suppressed at such compensation temperature, and they will be useful to interpret state-of-the art experiments on these elements.