Driven Magnetization Switching Research Articles

Thermal effect on microwave pulse-driven magnetization switching of Stoner particle

We investigate the cosine-chirped microwave pulse (cosine CMP)-driven magnetization switching of a nanoparticle or stoner particle at a finite temperature in the framework of the stochastic Landau–Lifshitz-Gilbert equation. Numerical results reveal that the ultrafast and efficient magnetization switching is robust even at room temperature, and hence we estimate the maximal temperature at which the magnetization switching is still valid. The maximal temperature increases with the enlargement (by increasing cross-sectional area) of the nanoparticle/stoner particle volume to a certain value, and afterward, the maximal temperature decreases with the further increment of the nanoparticle size. Initially, the shape anisotropy (approximated by the easy-plane) coefficient does not become dominant although the stoner particle volume increases, which plays a role in increasing thermal stability (maximal temperature), and later the shape anisotropy field becomes dominant, which opposes the uniaxial anisotropy, i.e., reduces the energy barrier, which reduces the maximal temperature. For smaller volumes, the parameters of cosine CMP show a decreasing trend with temperature. The initial frequency requirement significantly decreases with shape anisotropy. Therefore, these findings might be useful to realize cosine CMP-driven fast and energy-efficient magnetization switching in device applications.

Probability of spin-orbit torque driven magnetization switching assisted by spin-transfer torque

Probability of spin-orbit torque driven magnetization switching assisted by spin-transfer torque

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.

Room temperature energy-efficient spin-orbit torque switching in two-dimensional van der Waals Fe3GeTe2 induced by topological insulators

Two-dimensional (2D) ferromagnetic materials with unique magnetic properties have great potential for next-generation spintronic devices with high flexibility, easy controllability, and high heretointegrability. However, realizing magnetic switching with low power consumption at room temperature is challenging. Here, we demonstrate the room-temperature spin-orbit torque (SOT) driven magnetization switching in an all-van der Waals (vdW) heterostructure using an optimized epitaxial growth approach. The topological insulator Bi2Te3 not only raises the Curie temperature of Fe3GeTe2 (FGT) through interfacial exchange coupling but also works as a spin current source allowing the FGT to switch at a low current density of ~2.2×106 A/cm2. The SOT efficiency is ~2.69, measured at room temperature. The temperature and thickness-dependent SOT efficiency prove that the larger SOT in our system mainly originates from the nontrivial topological origin of the heterostructure. Our experiments enable an all-vdW SOT structure and provides a solid foundation for the implementation of room-temperature all-vdW spintronic devices in the future.

Deterministic Magnetization Switching via Tunable Noncollinear Spin Configurations in Canted Magnets.

Spin obit torque (SOT) driven magnetization switching has been used widely for encoding consumption-efficient memory and logic. However, symmetry breaking under a magnetic field is required to realize the deterministic switching in synthetic antiferromagnets with perpendicular magnetic anisotropy (PMA), which limits their potential applications. Herein, we report all electric-controlled magnetization switching in the antiferromagnetic Co/Ir/Co trilayers with vertical magnetic imbalance. Besides, the switching polarity could be reversed by optimizing the Ir thickness. By using the polarized neutron reflection (PNR) measurements, the canted noncollinear spin configuration was observed in Co/Ir/Co trilayers, which results from the competition of magnetic inhomogeneity. In addition, the asymmetric domain walls demonstrated by micromagnetic simulations result from introducing imbalance magnetism, leading to the deterministic magnetization switching in Co/Ir/Co trilayers. Our findings highlight a promising route to electric-controlled magnetism via tunable spin configuration, improve our understanding of physical mechanisms, and significantly promote industrial applications in spintronic devices.

Unusual spin–orbit torque switching in perpendicular synthetic antiferromagnets with strong interlayer exchange coupling

Synthetic antiferromagnet (SAF) is an outstanding system for controlling magnetic coupling via tuning the layer thickness and material composition. Here, we control the interlayer exchange coupling (IEC) in a perpendicularly magnetized SAF Pt/Co/Ir/CoFeB/MgO multilayer, which is tuned by varying the nonmagnetic layer Ir thickness and the magnetic layer Co thickness. And we study the spin–orbit torque (SOT) driven magnetization switching of the SAF. In the SAF with a weak IEC, the SOT-driven switching behavior is similar to that of a single ferromagnet system, which is dominated by the external magnetic field. In contrast, in the SAF with an ultra-strong IEC, the saturation magnetic field is large than 50 kOe, and the SOT-driven switching behavior is decided by the effective magnetic field. The effective field is correlated to the external magnetic field, the IEC field, magnetic moments of CoFeB and Co, and magnetic anisotropy. These results may advance the understanding of SOT switching of perpendicular SAFs and promote the applications of SAFs with low stray fields and lower power in spintronic devices.

Field-free approaches for deterministic spin–orbit torque switching of the perpendicular magnet

Abstract All-electrical driven magnetization switching attracts much attention in next-generation spintronic memory and logic devices, particularly in magnetic random-access memory (MRAM) based on the spin–orbit torque (SOT), i.e. SOT-MRAM, due to its advantages of low power consumption, fast write/read speed, and improved endurance, etc. For conventional SOT-driven switching of the magnet with perpendicular magnetic anisotropy, an external assisted magnetic field is necessary to break the inversion symmetry of the magnet, which not only induces the additional power consumption but also makes the circuit more complicated. Over the last decade, significant effort has been devoted to field-free magnetization manipulation by using SOT. In this review, we introduce the basic concepts of SOT. After that, we mainly focus on several approaches to realize the field-free deterministic SOT switching of the perpendicular magnet. The mechanisms mainly include mirror symmetry breaking, chiral symmetry breaking, exchange bias, and interlayer exchange coupling. Furthermore, we show the recent progress in the study of SOT with unconventional origin and symmetry. The final section is devoted to the industrial-level approach for potential applications of field-free SOT switching in SOT-MRAM technology.

Spin\u2013orbit torque driven magnetization switching in W/CoFeB/MgO-based type-Y three terminal magnetic tunnel junctions

We have studied current induced magnetization switching in W/CoFeB/MgO based three terminal magnetic tunnel junctions. The switching driven by spin—orbit torque (SOT) is evaluated in the so-called type-Y structure, in which the magnetic easy-axis of the CoFeB layer lies in the film plane and is orthogonal to the current flow. The effective spin Hall angle estimated from the bias field dependence of critical current (Ic) is ~ 0.07. The field and current dependence of the switching probability are studied. The field and DC current induced switching can be described using a model based on thermally assisted magnetization switching. In contrast, the 50 ns long pulse current dependence of the switching probability shows significant deviation from the model, even if contribution from the field-like torque is included. The deviation is particularly evident when the threshold switching current is larger. These results show that conventional thermally assisted magnetization switching model cannot be used to describe SOT induced switching using short current pulses.

Exchange bias and spin–orbit torque in the Fe3GeTe2-based heterostructures prepared by vacuum exfoliation approach

Magnetic two-dimensional (2D) van der Waals (vdWs) materials are receiving increased attention due to their exceptional properties and potential applications in spintronic devices. Because exchange bias and spin–orbit torque (SOT)-driven magnetization switching are basic ingredients for spintronic devices, it is of pivotal importance to demonstrate these effects in the 2D vdWs material-based magnetic heterostructures. In this work, we employ a vacuum exfoliation approach to fabricate Fe3GeTe2 (FGT)/Ir22Mn78 (IrMn) and FGT/Pt bilayers, which have high-quality interfaces. An out-of-plane exchange bias of up to 895 Oe is obtained in the former bilayer, which is larger than that of the previously studied bilayers. In the latter bilayer, the SOT switching of the perpendicularly magnetized FGT is realized, which exhibits higher SOT-driven switching performance compared to the previously studied FGT/Pt bilayer devices with interfacial oxidation. The minimum of SOT efficiency is further determined to be 0.18 ± 0.04, comparable to the previously reported values for the Pt/Co and Pt/CoFeB bilayers. This work highlights the importance of the high-quality interface for the exchange bias and SOT effect and may pave the way for implementing 2D vdWs in spintronic devices.

Quantum theory of spin-torque driven magnetization switching

Magnetization dynamics driven by the current-induced spin torque is conventionally determined by the classical Landau-Lifshitz-Gilbert-Slonczewski equation in which the spin (magnetization) fluctuation at finite temperature is modeled by a white-noise random field. We propose a quantum approach for current driven magnetization switching that explicitly includes the spin fluctuation by the quantum statistics of magnon excitations. We find that the spin fluctuation substantially reduces the critical spin torque at high temperatures. Since the spin fluctuations are fundamentally stronger in lower-dimensional systems, this reduction is stronger in two-dimensional (2D) than in three-dimensional magnets. The result implies that the 2D magnets may have an advantage in terms of electrically manipulating magnetization states for spintronic applications.

Effect of interfacial spin configuration on y-type spin–orbit torque switching in an antiferromagnetic heavy alloy/ferromagnet bilayer

This work applied an anisotropic magneto-resistance effect for studying the spin–orbit torque (SOT)-driven magnetization switching in an antiferromagnetic heavy alloy/ferromagnet, PtMn/Co bilayer, under y-type SOT geometry. The tailorable magneto-structural ordering of PtMn provides an additional dimension to study the interplay among SOT efficiency, the interfacial spin configuration, and the y-type SOT switching. The results reveal that the SOT efficiency of PtMn, effective field generated by current, can be enhanced via forming the L10 (antiferromagnetic) phase after annealing; however, the efficiency appears to be less sensitive to the interfacial spin configuration. On the other hand, the critical current for the y-type SOT switching is even strongly associated with the PtMn/Co interfacial spin configuration. The lowest (highest) critical current is yielded when Co is antiferromagnetically (ferromagnetically) coupled to PtMn through the exchange bias. Engineering the interfacial spin configuration may provide an effective strategy to promote the critical current for the SOT device.

Spin Torque Gate Magnetic Field Sensor

Spin-orbit torque provides an efficient pathway to manipulate the magnetic state and magnetization dynamics of magnetic materials, which is crucial for energy-efficient operation of a variety of spintronic devices, such as magnetic memory, logic, oscillator, and neuromorphic computing. Here, we describe and experimentally demonstrate a strategy for the realization of a spin torque gate magnetic sensor with an extremely simple structure by exploiting the longitudinal field dependence of the spin torque driven magnetization switching. Unlike most magnetoresistance sensors, which require a delicate magnetic bias to achieve a linear response to the external field, the spin torque gate sensor can achieve the same without any magnetic bias, which greatly simplifies the sensor structure. Furthermore, by driving the sensor using an ac current, the dc offset is automatically suppressed, which eliminates the need for a bridge or compensation circuit. We verify the concept using the ${\mathrm{W}\mathrm{Te}}_{2}/\mathrm{Ti}/(\mathrm{Co},\mathrm{Fe})\mathrm{B}$ trilayer and demonstrate that the sensor can work linearly in the range of \ifmmode\pm\else\textpm\fi{}3--10 Oe with negligible dc offset.

Spin–orbit torque-induced magnetization switching in Pt/Co–Tb/Ta structures

Although transition metal (TM)-rare earth (RE) alloy film has potential application as an information storage medium in spintronic devices, study of the physical mechanism and microscopic process for the current-induced magnetization switching by spin–orbit torque (SOT) in TM-RE is still inadequate. In this work, we investigated the SOT effect and its driven magnetization switching in Pt/Co–Tb/Ta structures with various Co–Tb compositions. The results show that the current-induced SOT effective fields follow 1/Ms law near the compensation composition in this structure. Because of the large SOT effective field and the low coercivity for the Co–Tb layer near the compensation composition, the current-induced magnetization switching with a threshold current density as low as 1010 A/m2 was achieved in the system. The direct Kerr imaging on the switching process verifies two different current-induced switching mechanisms in the Pt/Co–Tb/Ta system.

Spin‐Orbit Torque Driven Magnetization Switching and Precession by Manipulating Thickness of CoFeB/W Heterostructures

AbstractThe switching of magnetization via spin‐orbit torque has attracted much attention because of its fast switching and low power consumption. Numerous studies have focused on increasing the conversion efficiency from charge to spin current and out‐of‐plane magnetization cases. Recently, there have been reports on the fast and deterministic switching of in‐plane magnetization devices. It is reported that an in‐plane spin‐orbit torque (SOT) device can archive the oscillation, precession, and direct switching by a combination of torques—controlling the thickness of the ferromagnet and normal metal. With proper layer thicknesses, the device can show the three dynamics listed above at each current density in a macro spin simulation. Based on an understanding of the role of torque‐driving magnetization dynamics, a dynamic map of an in‐plane SOT device depending on torque efficiency and current density is shown.

Magnetization switching using topological surface states.

Topological surface states (TSSs) in a topological insulator are expected to be able to produce a spin-orbit torque that can switch a neighboring ferromagnet. This effect may be absent if the ferromagnet is conductive because it can completely suppress the TSSs, but it should be present if the ferromagnet is insulating. This study reports TSS-induced switching in a bilayer consisting of a topological insulator Bi2Se3 and an insulating ferromagnet BaFe12O19. A charge current in Bi2Se3 can switch the magnetization in BaFe12O19 up and down. When the magnetization is switched by a field, a current in Bi2Se3 can reduce the switching field by ~4000 Oe. The switching efficiency at 3 K is 300 times higher than at room temperature; it is ~30 times higher than in Pt/BaFe12O19. These strong effects originate from the presence of more pronounced TSSs at low temperatures due to enhanced surface conductivity and reduced bulk conductivity.

Spin orbit torque driven magnetization switching with sputtered Bi2Se3 spin current source

Current induced spin orbit torques (SOTs) offer an efficient pathway to manipulate the magnetization of a ferromagnet for future magnetic memories and logic devices. Among the various non-magnets utilized, the topological insulators, such as Bi2Se3, have proven to be one of most efficient spin current generators for SOTs. So far, the preferred growth technique for such materials is the molecular beam epitaxy technique which is not compatible with the magnetic memory industry. In this study, we utilize a sputter deposited Bi2Se3 to demonstrate highly efficient SOT generation and subsequently magnetization switching.

Electrically controlled switching of the magnetization state in multiferroic BaTiO3/CoFe submicrometer structures

The development of reliable and highly energy efficient multiferroic nanosystems, which can function at room temperature, is key for the design of ultralow-power magnetoelectric devices. Here, we report electrically controlled magnetic domain wall motion and magnetization switching in $\mathrm{BaTi}{\mathrm{O}}_{3}\text{/}\mathrm{C}{\mathrm{o}}_{50}\mathrm{F}{\mathrm{e}}_{50}$ microstructures, at room temperature. The perfect one-to-one connection between the ferroelectric domain pattern of the $\mathrm{BaTi}{\mathrm{O}}_{3}$ crystal and the ferromagnetic state of the CoFe microstructures, which relies on a strain-induced magnetic anisotropy modification, is the cause of the observed magnetoelectric effect. As a result, the observed electrically driven magnetization switching is highly reliable, independent of the shape and size of the microstructures. This is a key factor that makes the studied multiferroic system very promising for integration in real-world magnetoelectric devices.

Analytic modeling of dipolar field requirements for robust coupling in a non-identical biaxial two-magnet system

Magnetic bodies interact with each other through magnetic dipolar fields that depend on the instantaneous magnetization vectors of the coupled magnetic bodies in a system. Previous studies have shown that reliable, deterministic coupling can be achieved in identical two-magnet systems and is a function of the longitudinal and perpendicular components of the dipolar field. In this work, we extend previous work significantly by developing analytic models that map the regions of dipolar field driven magnetization reversal of a non-identical two-magnet system. Models are obtained for mono-domain magnetic bodies with biaxial magnetic anisotropy. The analytic models presented map the necessary requirements for a deterministically coupled two-magnet system. In these deterministic, stable reversals, the two-magnet system stabilizes in an anti-parallel configuration along the natural free-axis of the system, regardless of thermal effects. However, non-deterministic reversals can also occur in certain non-identical systems. These pseudo-reversals occur because only one of the nanomagnets meets the critical field requirements. In this case, the system reversal is a result of thermal drift and therefore complex function system parameters and observation time. We also note that multi-magnet systems may find steady-state orientations away from the free-axis if the perpendicular components of the dipolar field are too large. We present models which accurately map the field magnitudes which result in these meta-stable reversals. Lastly, models to interpret the impact of dipolar coupling on the critical current requirement for spin-transfer-torque driven magnetization switching are also presented in this manuscript. This work greatly expands our understanding of the complex-field interaction in multi-magnet systems and is crucial when evaluating complex magnetic devices.

Stateful Reconfigurable Logic via a Single-Voltage-Gated Spin Hall-Effect Driven Magnetic Tunnel Junction in a Spintronic Memory

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.

Field-free spin Hall effect driven magnetization switching in Pd/Co/IrMn exchange coupling system

All electrical manipulation of magnetization is crucial and of great important for spintronics devices for the sake of high speed, reliable operation, and low power consumption. Recently, widespread interests have been aroused to manipulate perpendicular magnetization of a ferromagnetic layer using spin-orbit torque (SOT) without field. We report that a commonly used antiferromagnetic material IrMn can be a promising candidate as a functional layer to realize field-free magnetization switching driven by SOT in which IrMn is employed to act as both the source of effective exchange bias field and SOT source. The critical switching current density within our study is Jc = 2.2 × 107 A/cm2, which is the same magnitude as similar materials such as PtMn. A series of measurements based on anomalous Hall effect was systematically implemented to determine the magnetization switching mechanism. This study offers a possible route for IrMn application in similar structures.