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The interfacial Dzyaloshinskii-Moriya interaction (DMI) holds promises for design and control of chiral spin textures in low-dimensional magnets with efficient current-driven dynamics. Recently, an interlayer DMI has been found to exist across magnetic multilayers with a heavy-metal spacer between magnetic layers. This opens the possibility of chirality in these three-dimensional magnetic structures. Here we show the existence of the interlayer DMI in a synthetic antiferromagnetic multilayer with both inversion and in-plane asymmetry. We analyse the interlayer DMI's effects on the magnetization and the current-induced spin-orbit torque (SOT) switching of magnetization through a combination of experimental and numerical studies. The chiral nature of the interlayer DMI leads to an asymmetric SOT switching of magnetization under an in-plane magnetic field. Our work paves the way for further explorations on controlling chiral magnetizations across magnetic multilayers through SOTs, which can provide a new path in the design of SOT devices. Exchange interactions between spins in a magnetic system can be engineered using magnetic multilayer systems in order to investigate a rich variety of magnetic phenomenon. Here the authors investigate the nature and control of magnetization of a synthetic antiferromagnetic stack with built in planar asymmetry and find evidence of an asymmetric current-driven switching in the chiral magnetization across the magnetic multilayers. [ABSTRACT FROM AUTHOR]

Utilizing a novel nitronyl nitroxide biradical bisNITPhPyrim involving a pyrimidine group ([5-(5-pyrimidyl)-1,3-bis(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl)]benzene), three heterometallic Ln–Cu complexes with formulas [Ln(hfac)3Cu(hfac)2(bisNITPhPyrim)] (LnIII = Gd 1, Tb 2, and Dy 3; hfac = hexafluoroacetylacetonate) have been achieved. In these complexes, the CuII ions are linked by N atoms of pyrimidine rings of bisNITPhPyrim radicals to form a one-dimensional chain structure, whereas each LnIII ion is chelated with two neighboring NO groups of two NIT moieties of the radical. Magnetic studies reveal the presence of ferromagnetic interactions between the GdIII ion and coordinated NO groups, and between the pyrimidine-bridged copper(II) spins, which are quantified by a magnetic model, giving J1 = 4.20 cm−1 and J3 = 0.50 cm−1 (J1 and J3 are magnetic exchanges for GdIII–ON and CuII–CuII, respectively). Interestingly, ac magnetic measurements show that complex 3 exhibits slow relaxation of the magnetization. [ABSTRACT FROM AUTHOR]

We propose a concept of magnetic logic circuits engineering, which takes an advantage of magnetization as a computational state variable and exploits spin waves for information transmission. The circuits consist of magneto-electric cells connected via spin wave buses. We present the result of numerical modeling showing the magneto-electric cell switching as a function of the amplitude as well as the phase of the spin wave. The phase-dependent switching makes it possible to engineer logic gates by exploiting spin wave buses as passive logic elements providing a certain phase-shift to the propagating spin waves. We present a library of logic gates consisting of magneto-electric cells and spin wave buses providing 0 or π phase shifts. The utilization of phases in addition to amplitudes is a powerful tool which let us construct logic circuits with a fewer number of elements than required for CMOS technology. As an example, we present the design of the magnonic Full Adder circuit comprising only 5 magneto-electric cells. The proposed concept may provide a route to more functional wave-based logic circuitry with capabilities far beyond the limits of the traditional transistor-based approach. [ABSTRACT FROM AUTHOR]

This article focuses on computational studies evaluating the influence of crystallinity, residual stresses, and out-of-plane (OOP) deterministic switching on Terfenol-D nano/microstructures. The computational models use both coupled and uncoupled Landau–Liftshitz–Gilbert equations with elastodynamics to study strain-induced magnetization reorientation. A Voronoi tessellation approach models the crystal distribution in the microstructures subjected to residual stresses with good agreement to experimental data including large changes in coercivity values, i.e., from 100 to 3000 Oe. Parametric studies show how the coercivity is manipulated with residual stresses, including a magnetoelastically induced perpendicular-magnetic-anisotropy (PMA), important for memory applications. Additional parametric studies focus on epitaxially deposited micro-disks, revealing that residual stresses can create magnetoelastically dominant easy axes along the ⟨ 110 ⟩ directions, which are energetically favorable relative to the intrinsic ⟨ 111 ⟩ magnetocrystalline easy axes. Modification of the global easy axis is used to design a strain-mediated multiferroic composite consisting of a 20 nm epitaxially deposited Terfenol-D memory bit with PMA grown on a PZT substrate. The multiferroic disk achieves OOP deterministic clocking with an applied voltage. [ABSTRACT FROM AUTHOR]

Spin–orbit torques (SOTs) provide an efficient way to electrically manipulate the magnetic order in spintronic devices. Compared with conventional ferromagnetic materials, ferrimagnetic materials have the advantages of antiferromagnetically coupled sublattices and induced ultrafast spin dynamics. In this paper, we study the current-induced magnetization switching in the ferrimagnetic Ta/GdFeCo/MgO system. Robust SOT-induced magnetization switching can be achieved at the magnetic compensation temperature point of around 70 K, where the magnetization is nearly zero and the coercivity can reach almost 3 T. The temperature dependence of the SOT efficiency is quantified by the second harmonic method, and the enhanced SOT efficiency near the magnetic compensation temperature is attributed to the negative exchange coupling between the two sublattices of CoFe and Gd. This work demonstrates the SOT switching of the nearly compensated ferrimagnet, with great potential for future magnetic interaction-free and ultrafast ferrimagnetic applications. [ABSTRACT FROM AUTHOR]

The switching of perpendicularly magnetized ferromagnets via current-induced spin–orbit torques is of great interest because of its potential applications in memory and logic devices. However, the in-plane electric current itself is not enough to switch the magnetization. In addition to the electric current, an in-plane external magnetic field is required for magnetization switching. This limits the usage of such devices in spintronic applications. Here, we work on the current-driven perpendicular magnetization switching in the Pt/Ta(wedge)/CoFeB/MgO multilayer. The structural symmetry is broken in both z-axis and in-plane due to the wedge Ta layer, which results in a field-like spin–orbit torque. The β z value extracted from the slope of the offset field vs current density increases with Ta layer thickness (<1.0 nm) and then decreases up to <1.3 nm. Thanks to both in-plane and z-axis asymmetries that enable the current-driven magnetization switching without the need for a magnetic field. We showed switching of the magnetization with a perpendicular magnetic anisotropy, switching in a wide range of Ta layer in Pt/Ta(wedge)/CoFeB/MgO multilayer. [ABSTRACT FROM AUTHOR]

This paper presents numerical and experimental data for dipole-dipole coupled Ni nanodots on a piezoelectric [Pb(Mg1/3Nb2/3)O3]0.68[PbTiO3]0.32 substrate. Simulation results show that the dipole coupling produces artificial ferromagnetic (parallel magnetization alignment in the nanodot arrays) behavior that can be modified to artificial antiferromagnetic behavior with an applied voltage. Experimental results show the trends in Mr and Hc predicted by the model, but discrepancies arise due to geometric defects present in the fabricated samples. Geometric defects are introduced into the Ni nanodot models, thus dramatically improving the correlation between experiments and analysis. This work shows, through numerical simulations, that artificial multiferroic nanostructures can be designed to produce switching from parallel (artificial ferromagnetic) to antiparallel (artificial antiferromagnetic) magnetization ordering by leveraging dipole coupling with voltage induced changes in magnetic anisotropy. [ABSTRACT FROM AUTHOR]

We report the temperature dependence of the spin–orbit torque (SOT) in the in situ grown Bi2Te3/MnTe heterostructures by molecular beam epitaxy. By appropriately designing the film stack, robust ferromagnetic order with high Curie temperature and strong perpendicular magnetic anisotropy is established in the MnTe layer. Meanwhile, the sharp hetero-interface warrants highly efficient spin current injection from the conductive topological insulator (TI) channel. Accordingly, SOT-driven magnetization switching is observed up to 90 K with the critical current density within the 106 A⋅cm−2 range. More importantly, the temperature-dependent harmonic measurement data can be divided into two categories, namely, the spin Hall effect of the TI bulk states gives rise to a relatively small spin Hall angle in the high-temperature region, whereas the spin-momentum locking nature of the interfacial Dirac fermions leads to the enhancement of the SOT strength once the topological surface states become the dominant conduction channel at deep cryogenic temperatures. Our results offer direct evidence of the underlying mechanism that determines the SOT efficiency and may set up a suitable platform to realize TI-based spin–orbit applications toward room temperature. [ABSTRACT FROM AUTHOR]

We report strain-induced coercive field changes in patterned 300 × 100 × 35 nm3 Ni nanostructures deposited on Si/SiO2 substrate using the magnetoelastic effect. The coercive field values change as a function of the applied anisotropy strain (∼1000 ppm) between 390 and 500 Oe, demonstrating that it is possible to gradually change the coercive field elastically. While the measured changes in coercive field cannot be accurately predicted with simple analytical predictions, fairly good agreement is obtained by using a micromagnetic simulation taking into account the influence of nonuniform strain distribution in the Ni nanostructures. The micromagnetic simulation includes a position dependant strain-induced magnetic anisotropy term that is computed from a finite element mechanical analysis. Therefore, this study experimentally corroborates the requirement to incorporate mechanical analysis into micromagnetic simulation for accurately predicting magnetoelastic effects in patterned ferromagnetic nanostructures. [ABSTRACT FROM AUTHOR]

Although spin transfer torque (STT)-based magnetic tunneling junction (MTJ) owns advantages of nonvolatility, nonlimited endurance, and fast write/read, its demand for high current density significantly casts a shadow over its future prospects. Recently, a novel three-terminal MTJ cell that combines voltage-controlled magnetic anisotropy (VCMA) effect and negative capacitance (NC) effect is proposed. Drawing support from the NC amplified VCMA effect and the three-step operation scenario, this novel MTJ cell can dramatically lower the energy consumption to fJ as well as keep high operation speed within nanoseconds. The feasibility of the proposed NC enhanced VCMA spintronics device for memory and logic application is proved by extensive physical simulation in our previous work. However, a SPICE compatible compact model of the proposed NC enhanced VCMA spintronics device is still demanded for circuit and system level evaluation. In this paper, we provide an accurate and fast compact model of NC enhanced VCMA device for both memory and logic applications. [ABSTRACT FROM AUTHOR]

Stateful in-memory logic (IML) is a promising paradigm to realize the unity of data storage and processing in the same die, exhibiting great feasibility to break the bottleneck of the conventional von Neumann architecture. On the roadmap toward developing such a logic platform, a critical step is the effective and efficient realization of a complete set of logic functions within a memory. In this paper, we report a realization of stateful reconfigurable logic functions via a single three-terminal magnetic tunnel junction (MTJ) device within a spintronic memory by exploiting the novel voltage-gated spin Hall-effect driven magnetization switching mechanism. This proposed reconfigurable IML methodology can be implemented within either a typical memory array or a cross-point array architecture. The feasibility of the proposed approach is successfully demonstrated with hybrid MTJ/CMOS circuit simulations. We believe our work may promote the research and development of the revolutionary IML for future non-von Neumann architectures. [ABSTRACT FROM PUBLISHER]

Majorana fermion is a hypothetical particle that is its own antiparticle.We report transport measurements that suggest the existence of one-dimensional chiral Majorana fermion modes in the hybrid system of a quantum anomalous Hall insulator thin film coupled with a superconductor. As the external magnetic field is swept, half-integer quantized conductance plateaus are observed at the locations of magnetization reversals, giving a distinct signature of the Majorana fermion modes. This transport signature is reproducible over many magnetic field sweeps and appears at different temperatures. This finding may open up an avenue to control Majorana fermions for implementing robust topological quantum computing. [ABSTRACT FROM AUTHOR]

We studied the impact of different insertion layers (Ta, Pt, and Mg) at the CoFeB∣MgO interface on voltage-controlled magnetic anisotropy (VCMA) effect and other magnetic properties. Inserting a very thin Mg layer of 0.1-0.3 nm yielded a VCMA coefficient of 100 fJ/V-m, more than 3 times higher than the average values of around 30 fJ/V-m reported in Ta∣CoFeB∣MgO-based structures. Ta and Pt insertion layers also showed a small improvement, yielding VCMA coefficients around 40 fJ/V-m. Electrical, magnetic, and X-ray diffraction results reveal that a Mg insertion layer of around 1.2 nm gives rise to the highest perpendicular magnetic anisotropy, saturation magnetization, as well as the best CoFe and MgO crystallinity. Other Mg insertion thicknesses give rise to either under- or over-oxidation of the CoFe∣MgO interface; a strong over-oxidation of the CoFe layer leads to the maximum VCMA effect. These results show that precise control over the Mg insertion thickness and CoFe oxidation level at the CoFeB∣MgO interface is crucial for the development of electric-field-controlled perpendicular magnetic tunnel junctions with low write voltage. [ABSTRACT FROM AUTHOR]

We study the heavy metal layer thickness dependence of the current-induced spin-orbit torque (SOT) in perpendicularly magnetized Hf∣CoFeB∣MgO multilayer structures. The damping-like (DL) current-induced SOT is determined by vector anomalous Hall effect measurements. A nonmonotonic behavior in the DL-SOT is found as a function of the thickness of the heavy-metal layer. The sign of the DL-SOT changes with increasing the thickness of the Hf layer in the trilayer structure. As a result, in the current-driven magnetization switching, the preferred direction of switching for a given current direction changes when the Hf thickness is increased above ∼7 nm. Although there might be a couple of reasons for this unexpected behavior in DL-SOT, such as the roughness in the interfaces and/or impurity based electric potential in the heavy metal, one can deduce a roughness dependence sign reversal in DL-SOT in our trilayer structure. [ABSTRACT FROM AUTHOR]

We study the effect of the oxide layer on the current-induced spin-orbit torques (SOTs) in perpendicularly magnetized Hf|CoFeB|MgO (MgO-capped) or Hf|CoFeB|TaOx (TaOx-capped) structures. The effective fields corresponding to both the field-like and damping-like current-induced SOTs are characterized using electric transport measurements. Both torques are found to be significantly stronger in MgO-capped structures than those in TaOx-capped structures. The difference in fieldlike and damping-like SOTs in the different structures may be attributed to the different Rashbalike Hamiltonian, arising from the difference in the electric potential profiles across the oxide| ferromagnet interfaces in the two cases, as well as possible structural and oxidation differences in the underlying CoFeB and Hf layers. Our results show that the oxide layer in heavymetal |ferromagnet|oxide trilayer structures has a very significant effect on the generated SOTs for manipulation of ferromagnetic layers. These findings could potentially be used to engineer SOT devices with enhanced current-induced switching efficiency. [ABSTRACT FROM AUTHOR]

We study the current-driven perpendicular magnetization switching in Ta/CoFeB(wedge)/[TaOx or MgO/TaOx] devices with a lateral structural asymmetry introduced by a varying CoFeB thickness. In these devices, an in-plane current can generate a field-like torque and its corresponding effective magnetic field (HzFL) is out-of-plane, which can deterministically switch perpendicular magnetiza-tion at zero magnetic field. Experimental results indicate that the method used for breaking lateral structural symmetry greatly affects the resulting field-like torque, and that the gradient of perpen-dicular anisotropy, resulting from the CoFeB thickness variation, is not by itself sufficient to give rise to the current-induced HzFL. Analysis of the oxidation gradient at the CoFeB/TaOx interface indicates that the oxidation gradient may play a more important role than the gradient of magnetic anisotropy for the generation of HzFL. For practical applications, the demonstration of perpendicular magnetization switching in Ta/CoFeB(wedge)/MgO/TaOx devices potentially allows for using MgO-based magnetic tunnel junctions for readout in three-terminal memory devices without the need for external magnetic fields [ABSTRACT FROM AUTHOR]

Recent demonstrations of magnetization switching induced by in-plane current in heavy metal/ferromagnetic heterostructures (HMFHs) have drawn great attention to spin torques arising from large spin-orbit coupling (SOC). Given the intrinsic strong SOC, topological insulators (TIs) are expected to be promising candidates for exploring spin-orbit torque (SOT)-related physics. Here we demonstrate experimentally the magnetization switching through giant SOT induced by an in-plane current in a chromium-doped TI bilayer heterostructure. The critical current density required for switching is below 8.9 × 104 A cm−2 at 1.9 K. Moreover, the SOT is calibrated by measuring the effective spin-orbit field using second-harmonic methods. The effective field to current ratio and the spin-Hall angle tangent are almost three orders of magnitude larger than those reported for HMFHs. The giant SOT and efficient current-induced magnetization switching exhibited by the bilayer heterostructure may lead to innovative spintronics applications such as ultralow power dissipation memory and logic devices. [ABSTRACT FROM AUTHOR]

Magnetization switching by current-induced spin-orbit torques is of great interest due to its potential applications in ultralow-power memory and logic devices. The switching of ferromagnets with perpendicular magnetization is of particular technological relevance. However, in such materials, the presence of an in-plane external magnetic field is typically required to assist spin-orbit torque-driven switching and this is an obstacle for practical applications. Here, we report the switching of out-of-plane magnetized Ta/Co20Fe60B20/TaOx structures by spin-orbit torques driven by in-plane currents, without the need for any external magnetic fields. This is achieved by introducing a lateral structural asymmetry into our devices, which gives rise to a new field-like spin-orbit torque when in-plane current flows in these structures. The direction of the current-induced effective field corresponding to this field-like spin-orbit torque is out-of-plane, facilitating the switching of perpendicular magnets. [ABSTRACT FROM AUTHOR]

In this work, we experimentally study the temperature dependence of the perpendicular magnetic anisotropy (PMA) and of the voltage-controlled magnetic anisotropy (VCMA) in nanoscale MgO|CoFeB|Ta-based magnetic tunnel junctions. We demonstrate that the temperature dependences of both the PMA and the VCMA coefficient follow power laws of the saturation magnetization, but with different exponents. We also find that the linear dependence of the PMA on electric field is maintained over a wide temperature range, although the VCMA strength decreases faster as a function of temperature as compared to the PMA. Possible mechanisms leading to the different exponents are discussed. [ABSTRACT FROM AUTHOR]

We theoretically study the equilibrium and dynamic properties of nanoscale magnetic tunnel junctions (MTJs) and magnetic wires, in which an electric field controls the magnetic anisotropy through spin-orbit coupling. By performing micromagnetic simulations, we construct a rich phase diagram and find that, in particular, the equilibrium magnetic textures can be tuned between Neel and Bloch domain walls in an elliptical MTJ. Furthermore, we develop a phenomenological model of a quasi-one-dimensional domain wall confined by a parabolic potential and show that, near the Neel-to-Bloch-wall transition, a pulsed electric field induces precessional domain-wall motion which can be used to reverse the chirality of a Neel wall and even depin it. This domain-wall motion controlled by electric fields, in lieu of applied current, may provide a model for ultralow-power domain-wall memory and logic devices. [ABSTRACT FROM AUTHOR]

Thermally induced domain wall motion in a magnetic insulator was observed using spatiotemporally resolved polar magneto-optical Kerr effect microscopy. The following results were found: (i) the domain wall moves towards hot regime; (ii) a threshold temperature gradient (5 K/mm), i.e., a minimal temperature gradient required to induce domain wall motion; (iii) a finite domain wall velocity outside of the region with a temperature gradient, slowly decreasing as a function of distance, which is interpreted to result from the penetration of a magnonic current into the constant temperature region; and (iv) a linear dependence of the average domain wall velocity on temperature gradient, beyond a threshold thermal bias. Our observations can be qualitatively explained using a magnonic spin transfer torque mechanism, which suggests the utility of magnonic spin transfer torque for controlling magnetization dynamics. [ABSTRACT FROM AUTHOR]

We have investigated the propagation of surface spin waves in a Permalloy thin film excited by an asymmetric coplanar antenna. A surprising oscillatory behavior superimposed on the exponential decay is observed in the spin wave intensity mapped with the micro-Brillouin light scattering technique. The oscillations can be modeled as the interference between a propagating spin wave and a background magnetization with spatially uniform phase. We use a simple closed-form equation that includes both contributions to fit our experimental results. From the fit results, we extract the spin wave propagation length and the spin wave vector in a frequency range limited by the antenna bandwidth. [ABSTRACT FROM AUTHOR]

Ultrafast spin transfer torque (STT) switching in an in-plane MgO magnetic tunnel junction with 50 nm × 150 nm elliptical shape was demonstrated in this paper. Switching speeds as short as 165 ps and 190 ps at 50% and 98% switching probabilities, respectively, were observed without external field assistance in a thermally stable junction with a 101% tunnelling magnetoresistance ratio. The minimum writing energy of P-AP switching for 50% and 98% switching probability are 0.16 pJ and 0.21 pJ, respectively. The observed ultrafast switching is believed to occur because of partially cancelled out-of-plane demagnetizing field in the free layer from interface perpendicular anisotropy between the MgO layer and the Co20Fe60BV20 layer. High J/Jc0 ratio and magnetization nucleation at the edge of free layer, which result from the reduced perpendicular demagnetizing field, are possibly two major factors that contribute to the ultrafast STT switching. [ABSTRACT FROM AUTHOR]

We studied the spin transfer torque (STT) driven switching voltage distribution systematically by characterizing the switching probability density function (PDF) with large statistics (10^5 trials) across a wide time scale from 5 ns to 1 \mus. The skew normal distribution function is found to be a good one to fit the measured switching PDF down to low values, which would be used as a guideline to extrapolate read disturb rate (RDR) and write error rate (WER) in STT-RAM design. Moreover, the asymmetry of switching probability density function is observed to flip when the pulse width decreases. It is related to the fluctuation mechanism transition from the thermal agitation to the initial magnetization trajectory dispersion. [ABSTRACT FROM AUTHOR]

We report giant reversible and permanent magnetic anisotropy reorientation between two perpendicular easy axes in a magnetoelectric polycrystalline Ni thin film and (011) oriented [Pb(Mg1/3Nb2/3)O3](1-x)-[PbTiO3]x (PMN-PT) heterostructure. The PMN-PT is partially poled prior to Ni film deposition to provide a remanent strain bias. Following Ni deposition and full poling of the sample, two giant remanent strains of equal and opposite values are used to reversibly and permanently reorient the magnetization state of the Ni film. These experimental results are integrated into micromagnetic simulation to demonstrate the usefulness of this approach for magnetoelectric based magnetic random access memory. [ABSTRACT FROM AUTHOR]

We report giant reversible and permanent magnetic anisotropy reorientation in a magnetoelectric polycrystalline Ni thin film and (011)-oriented [Pb(Mg1/3Nb2/3)O3](1-x)-[PbTiO3]x heterostructure. The electric-field-induced magnetic anisotropy exhibits a 300 Oe anisotropy field and a 50% change in magnetic remanence. The important feature is that these changes in magnetization states are stable without the application of an electric field and can be reversibly switched by an electric field near a critical value (±Ecr). This giant reversible and permanent magnetization change is due to remanent strain originating from a non-180° ferroelectric polarization reorientation when operating the ferroelectric substrate in a specific non-linear regime below the electric coercive field. [ABSTRACT FROM AUTHOR]

A correction to the article "Electric Poling-Induced Magnetic Anisotropy and Electric-Field-Induced Magnetization Reorientation in Magnetoelectric Ni/(011) Pb(Mg1/3Nb2/3)O3](1-x)-[PbTiO3]x Heterostructure" is presented.

We theoretically study equilibrium and dynamic properties of nanosized magnetic skyrmions in thin magnetic films with broken inversion symmetry, where an electric field couples to magnetization via spin-orbit coupling. Based on a symmetry-based phenomenology and micromagnetic simulations we show that this electric-field coupling, via renormalizing the micromagnetic energy, modifies the equilibrium properties of the skyrmion. This change, in turn, results in a significant alteration of the current-induced skyrmion motion. Particularly, the speed and direction of the skyrmion can be manipulated by designing a desired energy landscape electrically, which we describe within Thiele's analytical model and demonstrate in micromagnetic simulations including electric-field-controlled magnetic anisotropy. We additionally use this electric-field control to construct gates for controlling skyrmion motion exhibiting a transistorlike and multiplexerlike function. The proposed electric-field effect can thus provide a low-energy electrical knob to extend the reach of information processing with skyrmions. [ABSTRACT FROM AUTHOR]