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Current-induced spin–orbit torque (SOT) has attracted much attention due to its potential applications in energy-efficient logic, memory, and artificial neuron devices. In this work, we report an enhanced SOT efficiency in perpendicularly magnetized Pt/Sm/Co/Ta heterostructures by inserting a light rare-earth Sm layer with large spin–orbit coupling. A series of Ta/Pt/Sm/Co/Ta samples with the Sm layer thickness (tSm) of 0, 0.6, 1.2, and 1.6 nm were prepared using direct-current magnetron sputtering. Perpendicular magnetic anisotropy, SOT efficiency, and current-driven magnetization reversal were characterized using electrical transport methods based on the anomalous Hall effect. The experimental results indicated that the switching field and magnetic anisotropic field decreased monotonically with an increase in tSm, while the damping-like effective field and effective spin Hall angle ( θ S H eff ) gradually increased. It demonstrates that interface modification with a Sm layer can improve the SOT efficiency and reduce the pinning potential barrier. Owing to the enhanced SOT and reduced pinning field, the critical switching current density (Jc) exhibits a steady decline when increasing tSm. In particular, the lowest Jc of approximately 7.83 × 106 A/cm2 was obtained when tSm was 1.6 nm. X-ray photoelectron spectroscopy revealed that electron transfer occurred between the Co, Pt, and Sm layers, which may be primarily responsible for the enhanced SOT by interface alloying to effectively strengthen the spin Hall effect of Sm and/or Pt. Our results provide a strategy for improving SOT efficiency and reducing Jc by interface alloying in SOT-based spintronic devices. [ABSTRACT FROM AUTHOR]

Magnetization reversal in a synthetic antiferromagnetically coupled composite of perpendicularly magnetized nanomagnets is theoretically explored based on the macrospin model. The analytical expressions of magnetization reversal are derived. The analytical results are confirmed by the results of the Landau–Lifshitz–Gilbert simulation. Furthermore, we find that a critical antiferromagnetic coupling constant exists at which the dynamics of magnetization reversal changes, and we obtain its analytical expression. This report provides a fundamental analysis insight into antiferromagnetic spintronic phenomena suitable for applications in ultra-high speed devices and nonvolatile memory technologies, for example, state-of-the-art voltage-controlled magnetoresistive random access memory. [ABSTRACT FROM AUTHOR]

This study reports the growth and investigation of (001)-oriented MnN/Fe thin films on the W buffer layer, focusing on detailed exchange bias (EB) studies, including thermal evolution (300–10 K) and the training effect. At room temperature, the magnetically annealed α -W/MnN/Fe/Ta stack exhibits an EB field ( H E B ) of 118 Oe. With decreasing temperature, particularly below 100 K, both H E B and coercive field ( H C ) show substantial increases, with H E B displaying a more pronounced enhancement. Analysis of the temperature-dependent H E B and H C data reveals an exponential trend, indicative of a spin-glass-like interface in the MnN/Fe system. At 10 K, the pronounced EB is accompanied by an asymmetric "kinked" magnetization reversal, suggesting a transition from uniaxial to biaxial anisotropy below 50 K due to spin-glass-like magnetic frustration at the interdiffused MnN/Fe interface. Training effect measurements further support the spin-glass-like MnN/Fe interface, with two distinct training mechanisms observed at 10 K: "athermal" and "thermal." Finally, the spin-glass model demonstrates an excellent fit for the training effect data, validating the presence of spin-glass-like disorder at the MnN/Fe interface. [ABSTRACT FROM AUTHOR]

We report the growth, structural characterization, and transport properties of the quantum anomalous Hall insulator Vy(BixSb1−x)2−yTe3 (VBST) grown on a GaAs buffer layer by molecular beam epitaxy on a GaAs(111)A substrate. X-ray diffraction and transmission electron microscopy show that the implementation of a GaAs buffer layer improves the crystal and interface quality compared to the control sample grown directly on an InP substrate. Both samples exhibit the quantum anomalous Hall effect (QAHE), but, with similar thermal stability despite their different structural properties. Notably, the QAHE in the sample grown on a GaAs buffer layer displays a significantly larger (almost double) coercive field with a much smaller resistivity peak at magnetization reversal. Possible effects of the interface quality on the magnetic properties of VBST and the QAHE are discussed. [ABSTRACT FROM AUTHOR]

We report the growth, structural characterization, and transport properties of the quantum anomalous Hall insulator Vy(BixSb1−x)2−yTe3 (VBST) grown on a GaAs buffer layer by molecular beam epitaxy on a GaAs(111)A substrate. X-ray diffraction and transmission electron microscopy show that the implementation of a GaAs buffer layer improves the crystal and interface quality compared to the control sample grown directly on an InP substrate. Both samples exhibit the quantum anomalous Hall effect (QAHE), but, with similar thermal stability despite their different structural properties. Notably, the QAHE in the sample grown on a GaAs buffer layer displays a significantly larger (almost double) coercive field with a much smaller resistivity peak at magnetization reversal. Possible effects of the interface quality on the magnetic properties of VBST and the QAHE are discussed. [ABSTRACT FROM AUTHOR]

In this study, we investigate the pseudo-static magnetic properties of Permalloy conical frustum nanowires using micromagnetic simulations. We thoroughly examine how both the major and minor radii influence the magnetic reversal mechanism when an external magnetic field is applied parallel to the nanowire axis. The obtained results show that under specific geometrical conditions, magnetization reverts though a Bloch point-type domain wall. In these cases, hysteresis curves exhibit two Barkhausen jumps during magnetization reversal, forming a plateau field range in which a Bloch point domain wall nucleates and propagates until its annihilation after the second Barkhausen jump. The nucleation of a Bloch point domain wall in a frustum conical nanowire geometry is reported. These findings highlight the significance of this geometry in nucleating these attractive topological defects for promising applications. [ABSTRACT FROM AUTHOR]

Voltage control of magnetization offers substantial advantages in energy efficiency for the development of spintronics technology. However, achieving a complete 180° magnetization switching remains as a challenging task since the electric field cannot provide torques to turn the magnetic moment in the ferromagnetic material. To address this challenge, we explore the utilization of synthetic antiferromagnetic (sAFM) structure coupled by Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction in the two ferromagnetic (FM) Co layers separated by a suitable thickness Ru spacer layer. One of the FM layers was prepared to be in contact with the GdOx layer, where ionic motion of oxygen can be manipulated via an application of electric field. Depending on the oxidation state at the interface with GdOx, the RKKY coupling can be adjusted and achieves reversible transitions between antiferromagnetic (AFM) and FM orders of FM layers at room temperature. The transition is mediated by the migration and redistribution of oxygen ions, transforming the Co/Gd interface into Co/GdOx and vice versa. This method suggests a stable and electrical route for magnetization reversals without an external magnetic field. [ABSTRACT FROM AUTHOR]

The precipitation-hardening Sm-Co magnets not only have irreplaceable applications under extreme conditions such as high temperatures, but are also the most typical magnets with pinning-controlled magnetization reversal mechanism. However, there have always been two views on this type of pinning, attractive or repulsive. In this article, the modification of the parallel interface to the titled interface, led to occurrence of quasi-repulsive and quasi-attractive pinning modes, by employing micromagnetic simulation methods. The corresponding domain wall energy relationship between the pinning phase and main phase was analyzed for different pinning modes, according to the morphology of domain wall from the simulation results. The analysis results indicated that relatively small difference in domain wall energy between the two phases led to quasi-repetitive and quasi-attractive pinning modes. Our findings can provide a reference for further understanding of the magnetization reversal mechanism of precipitation-hardening Sm-Co magnets. The emphasis on the influence of 1:5/2:17 interface orientation on pinning also provided a perspective on the magnetization reversal mechanism of other nanostructured permanent magnet materials. [ABSTRACT FROM AUTHOR]

The spin current can be generated by passing an electric current through a heavy metal. The spin current generation depends on the spin Hall angle (θsh) of the material. To manipulate the effective θsh, a thin layer of Au has been introduced at the bottom Pt/Co and the top Co/Pt interfaces in Ta/Pt/Co/Pt based perpendicularly magnetic anisotropy systems, and current-induced magnetization reversal of Co has been studied to estimate Jc. The introduction of the Au layer at the top Co/Pt interface (Ta/Pt/Co/Au/Pt) did not produce any significant reduction in the Jc. However, a significant reduction of Jc (∼ 34 %) has been observed, while the Au layer has been deposited at the bottom Pt/Co interface (Ta/Pt/Au/Co/Pt), indicating an enhancement in the value of θsh. We also performed a micromagnetic simulation to understand the qualitative change of the θsh. Micromagnetic simulation suggested that the θsh becomes 0.07 in Ta/Pt/Au/Co/Pt multilayer compared to θ s h = 0.05 of the Ta/Pt/Co/Pt system. Pt/Co/Au/Co/Au exhibits a reduction in Jc up to ∼ 30 % and corresponds to θ s h = 0.09. A Ta capping layer has been introduced to inject more spin current into the Co layer since Pt and Ta have opposite spin Hall angles. The Jc lowers up to ∼ 58 % in Ta/Pt/Au/Co/Pt/Ta multilayer, corresponding to θ s h = 0.23. We also achieved field-free switching at J c = 1.55 × 10 11 by depositing an in-plane magnetized layer of Co in Ta/Pt/Au/Co/Pt/Ta/Co/Pt multilayer. [ABSTRACT FROM AUTHOR]

With the advent of nanotechnologies, it has been possible to extend the number of stimuli that can be used to control the state of a magnetic nanostructure. Among those stimuli, single laser pulse excitation allows, under certain conditions, to obtain energy-efficient ultrafast magnetization reversal. With this respect, two different types of single pulse switching mechanisms have been reported. The first one consists in a sub-picosecond ultrafast toggle switching, which was observed mainly in Gd based alloys. The second type relies on sub-nanosecond precessional switching occurring in rare earth–transition metal alloys/multilayers. Here, we demonstrate that single pulse all optical switching is achieved in Co68Tb32/Co100−xGdx/Co68Tb32 trilayers in which the behavior can be tuned from toggle to precessional by changing the composition of the Co100−xGdx alloy. [ABSTRACT FROM AUTHOR]

Rare-earth ferromagnetic (RE–FM) heterostructures have attracted significant attention due to their intricate spin structures and physical phenomena. The antiferromagnetic coupled (AFC) interface formed by the distinctive interaction between the FM and RE elements has critical contributions to the magnetization reversal process. In this work, we investigate the enhancement of current-induced magnetization switching with the AFC interface at the Co/Ho heterostructure. The results shows that an increased spin–orbit torque (SOT) efficiency of up to 250% was achieved at a Ho thickness of 7 nm, with a critical switching current density of 2.7 × 1010 A/m2. When a Cu interlayer was introduced between the Co/Ho interface, a decreased SOT efficiency was observed, indicating that the SOT enhancement is primarily attributed to the AFC interfacial effect. At the AFC interface, the interaction between Co and Ho atoms generates an additional torque, enhancing the effective SOT efficiency. [ABSTRACT FROM AUTHOR]

Pure electric field-controlled 180° magnetization switching plays a vital role in low-power magnetoelectric memory devices. Using micromagnetic simulation, we engineered a square-shaped epitaxial Fe3Si nanomagnet on a PMN-PT piezoelectric substrate to make the magnetic easy axis slightly deviate 18° from the piezostrain axis, aiming to break the symmetry of the magnetization distribution and achieve deterministic magnetization reversal paths. Under the coaction of a magnetic field and an electric field, the simulated magnetic hysteresis loops and magnetic domain patterns reveal a fourfold to twofold magnetic anisotropy transition and magnetization reversal paths. Stimulated by pure electric field-induced piezoelectric strain, deterministic 180° magnetization reversals are accomplished by the two successive clockwise 90° switching process. The results help to comprehend electrically regulated deterministic magnetization reversal and pave an avenue for designing multistate spintronics devices. [ABSTRACT FROM AUTHOR]

Organic spintronics is an emerging research field that offers numerous fundamental physics and has shown potential in future spintronic applications. The spin-polarized hybridized interface formed at the ferromagnet (FM)/organic molecule (OM) interface is called the "spinterface." It has been found that the spinterface helps to reduce the well-known impedance mismatch issue in spin valves, enhances spin-polarization of the effective FM electrode, and aligns the molecular levels for easy spin transport. High magnetoresistance (MR) of ∼ 400% has been observed at low temperatures (∼10 K) for OM-based spin valves. However, the MR value at room temperature for such OM-based spin valves is low (∼10%) due to the complex nature of the FM/OM interface. During the last decade, much attention has been devoted to understand the nature of FM/OM interface for tailoring spintronic device functionalities. In this context, the role of spinterface on the global magnetization reversal, magnetic domains, and magnetic anisotropy in FM/OM systems becomes very important. Furthermore, it is also essential to understand the impact of crystallinity and thickness of FM on the induced moment in the non-magnetic OM in such heterostructures. Here, in this brief review, we give our Perspective on the progress and future challenges of the role of spinterface on various magnetic properties in FM/OM systems. Furthermore, we also discuss the recent observation of spin pumping in FM/OM systems where the OMs exhibit reasonable spin–orbit coupling. This shows the potential of OMs for spin–orbit torque-based physics and applications. [ABSTRACT FROM AUTHOR]

Seeking the magnetic heterostructures with large current-induced torque efficiency is currently one of the core hotspots in spintronics. In this work, we report the large and composition-dependent damping-like (DL) torque in the structure consisting of light metal Cr and Ti layers and a ferrimagnetic Tb–Co layer. The DL torque efficiency in the structures reaches a maximum (around −0.55) as the Tb content in the Tb–Co layer is in the range of 0.15–0.18. This composition-dependent behavior is different from that observed in the usual heavy-metal/ferrimagnetic structures. We also demonstrated the efficient current-induced magnetization reversal in these structures with a low threshold current density down to 8 × 10 10 A / m 2 . In comparison, only very low efficiency values of −0.06 and −0.086 are obtained in the Ti/Co/Cr and Ti/Tb–Co/SiN control samples, respectively, suggesting that the large DL torque in the Ti/Tb–Co/Cr structures may originate from the orbital Hall effect in the Cr metal. By fitting the Cr layer thickness dependence of the torque efficiency with a simple orbital current diffusion model, we obtained an effective orbital Hall angle of − 0.57 ± 0.02 for the Ti/Tb0.85Co0.15/Cr samples. This work demonstrated the possibility to enhance the orbital torque effect by using the magnetic layer containing the element with strong spin–orbit coupling. [ABSTRACT FROM AUTHOR]

The saturated magnetization (mtot) and the Gilbert damping constant (α) are the two key factors that determine the critical current density of the magnetization reversal in the spin-transfer-torque magnetic memory devices. Here, this study demonstrates the efficient modulation of these two parameters by tunning the composition of the Heusler Co3–xFexAl thin films, utilizing the x-ray magnetic circular dichroism technique and ferromagnetic resonance measurements. With the increase in Fe concentration, the mtot shows a downward trend mainly resulting from the decrease in Fe local magnetic moment instead of Co. On the other hand, the ultralow α decreases from 0.004 to 0.0012. This has been attributed to the reduction in the spin–orbit coupling, which is corroborated by the decrease in the orbit-to-spin moment ratio. Our findings add a building block for the Heusler compounds with tunable Gilbert damping and appropriate magnetization and show great potential in spintronic applications. [ABSTRACT FROM AUTHOR]

Bilayers of an amorphous CoFeB ferromagnet coupled to an epitaxially grown IrMn antiferromagnet, whose anisotropy is fourfold symmetric, are modeled to study the angular (φ) dependence of magnetization reversal mechanism and exchange bias behavior, based on a modified Monte Carlo method. It is found that positive and negative exchange-bias field (HE) maximum values appear in the antiferromagnetic easy-axis directions, and the HE zero-value transition/return points exist in the antiferromagnetic hard-axis directions. Furthermore, the value of HE(φ) is well fitted by considering cos3φ/sin3φ terms with larger or comparable coefficients as compared to the first-order terms in the Fourier expansion. Finally, the microscopic spin configuration results evidence these phenomena originating from the tailoring of antiferromagnetic spins by simply rotating the field-cooling direction between antiferromagnetic easy- and hard-axis directions. We open an exchange-bias mode governed by antiferromagnetic fourfold anisotropy and propose a method to precisely detect antiferromagnetic higher-order anisotropies on an exchange-bias support. [ABSTRACT FROM AUTHOR]

The anomalous Hall effect measurements are used to probe the magnetization reversal of terbium iron garnet (TbIG) thin films at different temperatures. The compensation temperature (Tcomp) of TbIG thin films is revealed, and the film thickness effect on the Tcomp is studied. The results indicate a rise of Tcomp along with decreasing film thickness. We postulate two possible origins for the observed behavior, namely interfacial element diffusion and strain effects between TbIG films and Gd3Ga5O12 substrates. The results have implications for the study of spintronic devices based on ultrathin rare-earth iron garnet thin films. [ABSTRACT FROM AUTHOR]

The robustness of spin–orbit torque (SOT) induced magnetization switching and ease of deposition make type-X devices, where the in-plane easy axis lies perpendicular to the spin polarization, attractive in the field of spintronics. However, universally applicable and straightforward detection of type-X magnetization reversal is still elusive, unlike type-Z switching, which employs DC-based anomalous Hall effect measurement. Here, we demonstrated that the odd planar Hall voltage (O-PHV) signal exhibits an odd symmetry with the application of an external magnetic field which motivates us to develop a reading mechanism for detecting magnetization switching of in-plane magnetized type-X devices. We verified our DC-based reading mechanism in the Pt/Co/NiFe/Pt stack where a thin Co layer is inserted to create dissimilar interfaces about the NiFe layer. Remarkably, the current-induced in-plane fields are found to be significantly large in Pt/Co/NiFe/Pt stack. Furthermore, we employed the O-PHV method to detect the current-induced magnetization switching. The pure DC nature of the writing and reading mechanism of our proposed type-X detection technique through O-PHV makes it the easiest in-plane magnetization detection technique. Moreover, the high repeatability and easy detection of our proposed method will open avenues toward in-plane SOT switching based memory devices and sensors. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate that V0.027Bi0.973TeI, a material with both giant bulk Rashba effect and ferromagnetism, can reverse its magnetization by self-generated spin–orbit torque. Through first-principles calculation, it is found that the giant bulk Rashba effect arises from both bulk space inversion asymmetry and strong spin–orbital coupling, while the ferromagnetism originates from the itinerant d-electrons of doped element vanadium. More importantly, its field-like spin–orbit torque efficiency is determined to be as high as 4.53 × 10−4 mT/(A cm−2), which is more than two orders of magnitude higher than that typically observed in magnetic heterostructures. It is further shown that by using such magnetic bulk Rashba material to form a homogenous spintronic device, the power consumption for magnetization switching can be significantly reduced. [ABSTRACT FROM AUTHOR]

Single-pulse magnetization switching by femtosecond laser pulses is the fastest way to manipulate magnetization. To date, among rare-earth transition metal alloys, single-pulse switching is limited to Gd-based structures. Here, we demonstrate ultrafast single-pulse switching of Tb-dominant CoTb alloys within several tens of picoseconds. Our further analysis shows that the ultrafast magnetization reversal is linked to ultrafast heating of laser pulses and an external field. [ABSTRACT FROM AUTHOR]

Pulsed current-induced magnetization reversal is investigated in the layer of (Ga,Mn)(Bi,As) dilute ferromagnetic semiconductor (DFS) epitaxially grown under tensile misfit strain causing perpendicular magnetic anisotropy in the layer. The magnetization reversal, recorded through measurements of the anomalous Hall effect, appearing under assistance of a static magnetic field parallel to the current, is interpreted in terms of the spin–orbit torque mechanism. Our results demonstrate that an addition of a small fraction of heavy Bi atoms, substituting As atoms in the prototype DFS (Ga,Mn)As and increasing the strength of spin–orbit coupling in the DFS valence band, significantly enhances the efficiency of current-induced magnetization reversal, thus reducing considerably the threshold current density necessary for the reversal. Our findings are of technological importance for applications to spin–orbit torque-driven nonvolatile memory and logic elements. [ABSTRACT FROM AUTHOR]

Methods to fabricate and characterize monodisperse magnetic nanoplatelets for fluid/bio-based applications based on spintronic thin-film principles are a challenge. This is due to the required top-down approach where the transfer of optimized blanket films to free particles in a fluid while preserving the magnetic properties is an uncharted field. Here, we explore the use of substrate conformal imprint lithography (SCIL) as a fast and cost-effective fabrication route. We analyze the size distribution of nominal 1.8 μm and 120 nm diameter platelets and show the effect of the fabrication steps on the magnetic properties which we explain through changes in the dominant magnetization reversal mechanism as the size decreases. We show that SCIL allows for efficient large-scale platelet fabrication and discuss how application-specific requirements can be solved via process and material engineering. [ABSTRACT FROM AUTHOR]

Switching of magnetization by spin–orbit torque in the (Ga,Mn)(As,P) film was studied with currents along ⟨100⟩ crystal directions and an in-plane magnetic field bias. This geometry allowed us to identify the presence of two independent spin–orbit-induced magnetic fields: the Rashba field and the Dresselhaus field. Specifically, we observe that when the in-plane bias field is along the current (I ∥ Hbias), switching is dominated by the Rashba field, while the Dresselhaus field dominates magnetization reversal when the bias field is perpendicular to the current (I ⊥ Hbias). In our experiments, the magnitudes of the Rashba and Dresselhaus fields were determined to be 2.0 and 7.5 Oe, respectively, at a current density of 8.0 × 105 A/cm2. [ABSTRACT FROM AUTHOR]

The control of perpendicular magnetic anisotropy (PMA) in thin films by strain has considerable potential for energy-efficient information storage and data processing. Here, we report on the control of PMA in Pt/Co/Ir thin films by the strain produced by standing surface acoustic waves (SAWs). A significant (∼21%) coercivity reduction (from 4.80 ± 0.03 to 3.80 ± 0.02 mT) can be obtained by applying a standing SAW with a center frequency of 93.35 MHz. Furthermore, the standing SAWs induce a greater-than 11-fold increase in magnetization reversal speed (from 168 ± 3 to up to 2100 ± 80 μm2/s) at 3.2 mT for a total applied RF power of 22.5 dBm. During application of SAWs, wide-field Kerr microscopy reveals the formation of domains in stripes with a periodicity of half of the SAW wavelength. Micromagnetic simulations indicate that the anti-nodes of the standing SAW locally lower the anisotropy due to the magneto-elastic coupling effect, decreasing domain nucleation field while promoting magnetization reversal. Our study suggests the possibility of remote and energy-efficient control of magnetization switching using SAWs. [ABSTRACT FROM AUTHOR]

Detecting a three-dimensional (3D) magnetic field by a compact and simple structure or device has always been a challenging work. The recent discovery of 3D magnetic field sensing through the single spin–orbit torque device consisting of the Ta/CoFeB/MgO heterostructure, based on the domain wall motion, offers a revolutionary way to tackle this problem. Here, we demonstrate a 3D magnetic field sensor based on the W/CoFeB/MgO heterostructure via domain nucleation dominated magnetization reversal. In such a heterostructure, the in-plane (IP) and out-of-plane (OOP) magnetic field components drive the grains reversal with different manners, enabling the distinguishment of the contributions from IP and OOP components. The linear modulations of anomalous Hall resistance by x, y, and z components of magnetic fields have been obtained, respectively, with the same linear range of −20 to +20 Oe for each component. Typically, a higher linearity is realized in this work compared with the previous domain wall motion based sensor, which is a critical characteristic for the magnetic field sensor. [ABSTRACT FROM AUTHOR]

Grain boundary diffusion (GBD) is an effective approach for improving the coercivity of Nd-Fe-B magnets with less heavy rare earth consumption. However, it generally only works well for thin magnets since the infiltration depth of diffusion source is limited. Here, a GBD approach that mainly diffuses the source from the edge and corner areas of the magnet, named selected area GBD (SAGBD), is proposed for treating thick magnets. After diffusing Pr-Tb-Al-Cu alloy by SAGBD, the coercivity of a 12-mm thick magnet was increased from 1070 to 1675 kA/m. By this approach, the coercivity enhancement with 1 wt. % Tb was 465 kA·m−1, 1.6 times as much as that by diffusion from two easy magnetization planes. For achieving a coercivity enhancement of ∼600 kA/m, the thickness of treated magnet was increased by 4 mm. Although the diffusion from six planes can further increase the coercivity, SAGBD leads to high efficient use of Tb and less reduction of remanence. The microstructure characterizations and micromagnetic simulation demonstrated that the edges and corners are magnetic "weak" areas of the magnet, and SAGBD can effectively hinder the nucleation of reversed domains in these places and the rapid reversal propagation in whole magnet. The present approach is important for the high-efficient use of the diffusion source and the fabrication of large-size Nd-Fe-B products with high stability. [ABSTRACT FROM AUTHOR]

Phenomenology similar to the non-reciprocal charge transport violating Onsager's reciprocity relations can develop in directionally inhomogeneous conducting films with non-uniform Hall coefficient along the current trajectory. The effect is demonstrated in ferromagnetic CoPd films and analyzed in comparison with the unidirectional magnetoresistance phenomena. We suggest to use an engineered inhomogeneity for spintronics applications and present the concept of mixed symmetry Hall devices in which transverse to current Hall signal is measured in a longitudinal contacts arrangement. Magnetization reversal and memory detection are demonstrated in the three-terminal and the partitioned normal metal–ferromagnet (NM-FM) device designs. Multi-bit memory is realized in the partitioned FM-NM-FM structure. The relative amplitude of the antisymmetric signal in the engineered ferromagnetic devices is few percent, which is 10–103 times higher than in their unidirectional magnetoresistance analogues. [ABSTRACT FROM AUTHOR]

Co-substituted bismuth ferrite, BiFe0.9Co0.1O3, thin film is a promising candidate material for low-power-consumption nonvolatile magnetic memory devices because magnetization reversal by an electric field has been directly observed at room temperature. However, this phenomenon takes place in a limited region where the ferroelectric domain is composed of two polarization variants forming stripe patterns. We demonstrate the extension of the stripe domain structure to the entire electrically poled region by utilizing an effective in-plane electric field called a trailing field. A one-to-one correlation between ferroelectric and ferromagnetic domains was also demonstrated. [ABSTRACT FROM AUTHOR]

118, 172403 (2021).10.1063/5.0045855 32 S. Finizio, S. Wintz, S. Mayr, A. J. Huxtable, M. Langer, J. Bailey, G. Burnell, C. H. Marrows, and J. Raabe, " Time-resolved visualization of the magnetization canting induced by field-like spin-orbit torques", Appl. Phys. This might be achieved, for instance, by means of radio frequency filters based on mesoscopic spin-wave cavities[43] or circulators enabled by chiral spin-wave routing across two stacked ferromagnetic layers without interlayer exchange coupling.[44] Magnetization dynamics in synthetic antiferromagnets, i.e., acoustic and optical magnons in layers with interlayer-exchange coupling, are considered theoretically by Dai and Ma[45] and Jeffrey I et al. i [46] Aiming at magnonic platforms for devices exploiting hybridized quantum excitations, they predict strong magnon-magnon coupling in tilted fields and a suppressed exceptional point, respectively. 118, 242403 (2021).10.1063/5.0050872 26 M. Schöbitz, S. Finizio, A. D. Riz, J. Hurst, C. Thirion, D. Gusakova, J.-C. Toussaint, J. Bachmann, J. Raabe, and O. Fruchart, " Time-resolved imaging of Œrsted field induced magnetization dynamics in cylindrical magnetic nanowires", Appl. Phys. In addition, non-linear magnetization dynamics through the effect of magnetic fields, spin currents, voltages, or optical pulses in confined magnetic dots transforms information by switching, tilting, deforming, or exciting the magnetization locally. [Extracted from the article]

We present experimental and numerical results on the magnetization reversal induced by spin–orbit torques of micronic disks of a ferromagnetic multilayer with perpendicular magnetic anisotropy on top of a Pt track: Pt (6 nm)/[Co(0.2 nm)/Ni(0.6 nm)] × 5/Al(5 nm). The current induced magnetization switching process is probed by anomalous Hall effect measurements and Kerr microscopy. The electrical characterization reveals the critical current for the complete reversal to be about 3 × 10 11 A/m2, and Kerr microscopy uncovers a deterministic nucleation that depends on current and field polarity. Through the use of experimental switching phase diagrams coupled to micromagnetic simulations, we evaluated the field-like to damping-like torque ratio to be 0.73 ± 0.05, which is in good agreement with experimental values observed by second harmonic measurements. These measurements emphasize an unexpectedly large field-like contribution in this relatively thick Co/Ni multilayer (4 nm). In light of these experiments and simulations, we discuss the key parameters needed to understand the magnetization reversal, namely, the field and damping-like torques and the Dzyaloshinskii–Moriya interaction. [ABSTRACT FROM AUTHOR]

Spin–orbit torque (SOT) enables the efficient manipulation of magnetization with charge current injection. Electronic measurement techniques have been widely used as common experimental tools for SOT analysis (e.g., anomalous Hall measurement, spin-transfer ferromagnetic resonance, and planar Hall effect). However, electronics-based techniques usually observe the final static states of the magnetization motion of the ferromagnetic layer, and it is difficult to observe detailed kinetics during ultrafast operation. Here, we introduce a time-resolved measurement technique for a pulsed SOT. We investigate the precessional motion of the magnetization vector, driven by a pulsed SOT, employing the time-resolved magneto-optical Kerr effect. A fabricated photoswitch can convert an optical pulse into a charge current pulse that results in a pulsed SOT. We believe that this time- and vector-resolved measurement would be useful for studying the underlying mechanisms of SOT. [ABSTRACT FROM AUTHOR]

The magnetic radial vortex is a nanoscale magnetization configuration that is typically stabilized by the interfacial Dzyaloshinskii–Moriya interaction (i-DMI). The existing control methods for the radial vortex core polarity rely on the use of current flow or magnetic fields, which may cause long consumption times or limit device miniaturization. Here, we investigate a repeated reversal of a radial vortex that can be driven by strain from a piezoelectric substrate using micromagnetic simulations. A phase diagram for the representative regions against perpendicular anisotropy, i-DMI, and the applied strain was obtained. The derived phase diagram was used to associate the mechanism of the core reversal with edge magnetization rotation during core magnetization switching, which exhibits a relationship by transforming a quasi-Bloch wall into a Néel wall. The existence of the i-DMI effect causes the core polarity and radial chirality of the radial vortex to be reversed simultaneously without resulting in larger core movements. These results offer an alternative and efficient way to achieve core reversal, which is expected to stimulate the radial vortex application in magnetoresistive memory devices. [ABSTRACT FROM AUTHOR]

We demonstrate that the spin-Seebeck effect can be used to estimate the volume of edge domains formed in a giant magnetoresistive (GMR) device. The thermal gradient induced by Joule heating can be harnessed by the addition of a ferromagnetically insulating channel of Fe2O3 on the sides of the GMR pillar. This generates a spin wave in Fe2O3, which couples with the free-layer edge magnetization and controls the reversal of the ferromagnetic layers in one direction only, increasing the current density from (1.1 ± 0.1) × 107 A/cm2 to (7.0 ± 0.5) × 10 7 A/cm2. By simple assumption, we estimate the effect of the edge domain on magnetization reversal to be 10%–15% by spin-transfer torque. [ABSTRACT FROM AUTHOR]

Geometric curvature in magnetic systems can induce several unique magnetic interactions, the most notable of which are the curvature induced magnetic anisotropy and the curvature introduced Dzyaloshinski–Moria (DM) like interaction. Of the two, the DM-like interaction is particularly interesting as it provides a unique way to control domain wall motion, which is particularly relevant to the field of spintronics. In this work, we study the effect of geometric curvature on magnetization reversal in Permalloy strips patterned into Archimedean spirals with varying widths. We simulated the magnetization reversal of Permalloy strips for several widths ranging from microscale to nanoscale to determine a lengthscale at which the curvature effects are strong. Simulations showed that in the microscale spirals, magnetization reversal primarily occurs through the appearance of magnetization ripple in which domains with reversed magnetization nucleate. On the other hand, the nanoscale spirals showed that reversal primarily proceeded through the motion of domain walls into the arms of the spiral. Our experimental in situ Lorentz transmission electron microscopy data of the microscale spirals, however, showed that magnetization reversal occurred with both mechanisms. At the nanoscale, the effect of local variation of curvature leads to hysteresis loops with stepped behavior. This behavior is characteristic of the curvature induced DM-like interaction affecting domain wall motion in the arms of the nanoscale spirals. [ABSTRACT FROM AUTHOR]

We present a field-free spin–orbit torque magnetic random access memory (SOT-MRAM) element using an in-plane ferromagnet (FL1)/coupling layer/perpendicular ferromagnet (FL2) as a composite free layer. By using micromagnetic simulations, we investigate the magnetic switching of the composite free layer in different conditions. Leveraging on interlayer exchange coupling, a field-free and efficient spin–orbit torque-induced reversal of perpendicular magnetization is realized, which can reduce the switching current density of SOT-MRAM. When the current density is increased to a certain value, the oscillations of magnetization are observed. Furthermore, by adjusting the magnetic anisotropy of FL1 and FL2, multilevel magnetization states can be achieved by varying the amplitude of the writing current. This work paves the way toward practical spin–orbit torque-based memory, oscillating, and logic devices. [ABSTRACT FROM AUTHOR]

A shape-anisotropy magnetic tunnel junction (MTJ) holds promise for its scaling into single-digit nanometers while possessing high data-retention capability. Understanding magnetization reversal mode is crucial to quantify the thermal stability factor Δ for data retention with high accuracy. Here, we study magnetization reversal mode in the shape-anisotropy MTJ with a 15-nm-thick CoFeB layer by evaluating Δ from two different methods: switching probability and retention time measurements. We find that magnetization reversal coherently proceeds in the 15-nm-thick and X/1X-nm-diameter cylindrical nanomagnet in the shape-anisotropy MTJs, in contrast to the conventional interfacial-anisotropy MTJs with a smaller thickness and larger diameter. The coherent magnetization reversal of the shape-anisotropy MTJ is also confirmed by astroid curve measurements. This study provides insight into the development of ultrasmall and high-reliability MTJ devices. [ABSTRACT FROM AUTHOR]

We present an analytical model for calculating the energy barrier for the magnetic field-driven domain wall-mediated magnetization reversal of a magneto-resistive random access memory cell and apply it to study thermal stability factor Δ for various thicknesses of W layers inserted into the free layer (FL) as a function of the cell size and temperature. We find that, by increasing the W thickness, the effective perpendicular magnetic anisotropy (PMA) energy density of the FL film monotonically increases, but at the same time, Δ of the cell mainly decreases. Our analysis shows that, in addition to saturation magnetization Ms and exchange stiffness constant A ex of the FL film, the parameter that quantifies the Δ value of the cell is its coercive field Hc, rather than the net PMA field Hk of the FL film comprising the cell. [ABSTRACT FROM AUTHOR]

We investigated magnetization reversal of (Sm, Ce)2(Co, Fe, Cu, Zr)17 magnets as per x-ray magnetic circular dichroism microscopy. Magnetization reversal initially occurs at the ferromagnetic grain boundaries or in the vicinity of nonmagnetic Sm oxides. As the demagnetization field increases after magnetization reversal, the reversal region extends into the grain from these areas by the magnetic domain wall motion. Energy-dispersive x-ray analysis using an electron probe micro-analyzer shows that, at the grain boundaries, the Fe concentration is higher and the Cu concentration is lower compared to that inside of the grains; and concentrations of Sm, Co, Fe, and Cu vary in the vicinity of Sm oxides. By measuring the Co L3 absorption intensity, we verified that local coercivities in these areas are very low compared to those inside of the grain. These results imply that the magnetization reversal that occurs in these areas is induced by the variation in the composition. The results obtained in our research will be useful for improving the magnetic properties of Sm–Co magnets. [ABSTRACT FROM AUTHOR]

By employing temperature (T)-dependent soft x-ray magnetic circular dichroism (XMCD) in the Fe and Cr 2p absorption edges, the electronic structures of Li 0.5 FeCr 1.5 O4 spinel ferrite, which exhibits magnetization compensation, have been investigated. This work provides evidence that (i) both Fe and Cr ions are trivalent, (ii) most of Fe 3 + ions occupy the A (Td) sites, while Cr 3 + ions occupy the B (Oh) sites, (iii) the magnetic moments of Fe and Cr ions are coupled antiferromagnetically, and (iv) they are reversed at ∼ 255 K. The sum-rule analysis of Fe and Cr 2p XMCD spectra reveals that the orbital magnetic moments of Fe and Cr ions in Li 0.5 FeCr 1.5 O4 are much larger than those of metallic Fe and Cr, implying the large spin–orbit coupling and the non-fully occupied t 2 g orbitals of Fe 3 + and Cr 3 + ions. Based on these findings, we have provided a comprehensive model for the electronic and spin configurations of Fe and Cr ions in (Fe)A[ Li 0.5 Cr 1.5 ]BO4. [ABSTRACT FROM AUTHOR]

The anomalies in the transverse resistivity are usually thought to be Topological Hall Effects (THEs), which have been considered as the trait of topologically nontrivial spin textures, such as the skyrmion phase. However, the origin of the THE-like features is still under debate. Here, we present the observation of THE-like features in synthetic antiferromagnetic [Pd/Co]/Ru/[Co/Pd] and synthetic ferromagnetic [Pd/Co]/NiO/[Co/Pd] structures. The Pd-rich alloys, which are formed due to the heterogeneous component and the gradual intermixing at the Co/Pd interface, result in a negative anomalous Hall effect coefficient, causing the peak and dip features in transport measurements. By changing the external magnetic field from out-of-plane to in-plane, the magnitude and width of the bump feature in THE curves can be modified, which is caused by the different anisotropy energy of the components in the heterogeneous ferromagnets. The present work broadens the perception of THE-like features and may add a different dimension to understand the magnetization reversal in magnetic multilayers. [ABSTRACT FROM AUTHOR]

We report time-resolved measurements of magnetization switching by spin–orbit torques in the absence of an external magnetic field in perpendicularly magnetized magnetic tunnel junctions (MTJs). Field-free switching is enabled by the dipolar field of an in-plane magnetized layer integrated above the MTJ stack, the orientation of which determines the switching polarity. Real-time single-shot measurements provide direct evidence of magnetization reversal and switching distributions. Close to the critical switching voltage, we observe stochastic reversal events due to a finite incubation delay preceding the magnetization reversal. Upon increasing the pulse amplitude to twice the critical voltage, the reversal becomes quasi-deterministic, leading to reliable bipolar switching at sub-ns timescales in zero external field. We further investigate the switching probability as a function of dc bias of the MTJ and external magnetic field, providing insight into the parameters that determine the critical switching voltage. [ABSTRACT FROM AUTHOR]

We report on a theoretical study of thermal magnetization switching induced by nanosecond electric current pulse using Lagrangian formalism based on the Landau–Lifshitz–Gilbert equation. The parameters for modeling are obtained from the measurements of the anomalous Hall resistance at different probe currents. We obtain the switching diagrams, analyze how the switching rate depends on the pulse parameters and the applied magnetic field, and find the optimal set of values such as orientation of the field, electric pulse duration, and energy consumption. We find that the magnetization switching is particularly efficient near the compensation point, where a decrease in the magnetization of the rare-earth sublattices by 10% or less can lead to reversal of net magnetization. [ABSTRACT FROM AUTHOR]

The (011) Pb (Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT)/Ni heterostructure was prepared, and the influence of light on magnetization reversal behaviors of the Ni layer was investigated. We found that the ferroelectric domain of the PMN-PT substrate was tuned by a photostrictive effect, and it further changes the magnetization state of the adjacent Ni layer. Additionally, with electric field polarization, the PMN-PT/Ni heterostructure exhibits controllable magnetization switching behaviors under the application of a proper light intensity. It provides a reliable way to manipulate the magnetization switching process, which is promising for the design and implementation of low power memory and spintronic devices. [ABSTRACT FROM AUTHOR]

Magnetic chiral skyrmion bubbles and achiral bubbles are two independent magnetic domain structures, in which the former with an equivalent winding number to skyrmions offer great promise as information carriers for further spintronic devices. Here, in this work, we experimentally investigate the generation and annihilation of magnetic chiral skyrmion bubbles and achiral bubbles in the Mn–Ni–Ga thin plate by using Lorentz transmission electron microscopy (L-TEM). The two independent magnetic domain structures can be directly controlled after field cooling manipulation by varying the titled angles of external magnetic fields. By imaging the magnetization reversal with increasing temperature, we found an extraordinary annihilation mode of magnetic chiral skyrmion bubbles and a non-linear frequency for the winding number reversal. The quantitative analysis of such dynamics was performed by using L-TEM to directly determine the barrier energy for the magnetization reversal of magnetic chiral skyrmion bubbles. [ABSTRACT FROM AUTHOR]

Magnetic insulators (MIs) have attracted great attention because of their low Gilbert damping, long spin transmission length, and no Ohmic loss. In this study, the high quality TbIG films with perpendicular magnetic anisotropy were epitaxially grown on GGG (111) substrates. In TbIG/Pt bilayers, the angular dependence of coercivity is found to obey the Kondorsky model, suggesting the magnetization reversal mechanism of magnetic domain nucleation and expansion. The transverse component of spin Hall magnetoresistance (SMR), which is analogous to the planar Hall resistance in a ferromagnetic metal, is found to be about seven times larger than the SMR-induced anomalous Hall resistance (analogous to the anomalous Hall resistance in a ferromagnetic metal). Moreover, the phase diagrams of the current-induced magnetization switching with different angles and magnitudes of the assisting magnetic field were drawn for the TbIG/Pt bilayers. The current-induced damping-like effective field (HDL) characterized by the harmonic measurements was evaluated to be about 164 Oe/ 10 8 A cm − 2 . By providing a comprehensive investigation of magnetization switching behaviors in MIs, our results will promote the application of ultralow-dissipation MI based spintronic devices. [ABSTRACT FROM AUTHOR]

We demonstrate a simple method to tailor the magnetization reversal mechanisms of Co/Pt multilayers by depositing them onto large area nanoporous anodized alumina (AAO) with various aspect ratios, A = pore depth/diameter. Magnetization reversal of composite (Co/Pt)/AAO films with large A is governed by strong domain-wall pinning which gradually transforms into a rotation-dominated reversal for samples with smaller A, as investigated by a first-order reversal curve method in conjunction with analysis of the angular dependent switching fields. The change of the magnetization reversal mode is attributed to topographical changes induced by the aspect ratio of the AAO templates.

Magnetic configurations in heterostructures are often difficult to probe when the magnetic entities are buried inside. In this study we have captured magnetic and magnetoresistance "fingerprints" of Co nanodiscs embedded in Co/Cu multilayered nanowires using a first-order reversal curve method. In 200nm diameter nanowires, the magnetic configurations can be tuned by adjusting the Co nanodisc aspect ratio. Nanowires with the thinnest Co nanodiscs exhibit single domain behavior, while those with thicker Co reverse via vortex states. A superposition of giant and anisotropic magnetoresistance is observed, which corresponds to the different magnetic configurations of the Co nanodiscs.

The interface between the organic semiconductor (OSC)/ferromagnetic (FM) material can exhibit ferromagnetism due to their orbital hybridization. Charge/spin transfer may occur from the FM to OSC layer leading to the formation of "spinterface," i.e., the interface exhibiting a finite magnetic moment. In this work, the magnetic properties of the Co / C 60 bilayer thin film have been studied to probe the interface between the Co and C60 layer. Polarized neutron reflectivity (PNR) measurement indicates that the thickness and moment of the spinterface are ∼2 ± 0.18 nm and 0.8 ± 0.2 μB/cage, respectively. The comparison of the magnetization reversal between the Co / C 60 bilayer and the parent single layer Co thin film reveals that spinterface modifies the domain microstructure. Further, the anisotropy of the bilayer system shows a significant enhancement (∼two times) in comparison to its single layer counterpart which is probably due to an additional interfacial anisotropy arising from the orbital hybridization at the Co / C 60 interface. [ABSTRACT FROM AUTHOR]

L 1 0 -ordered magnetic alloys such as FePt, FePd, CoPt, and FeNi are well known for their large magnetocrystalline anisotropy. Among these, the L 1 0 -FeNi alloy is an economically viable material for magnetic recording media because it does not contain rare earth and noble elements. In this work, L 1 0 -FeNi films with three different strengths of anisotropy were fabricated by varying the deposition process in a molecular beam epitaxy system. We have investigated magnetization reversal along with domain imaging via a magneto-optic Kerr effect based microscope. It is found that in all three samples, the magnetization reversal happens via domain wall motion. Furthermore, ferromagnetic resonance spectroscopy was performed to evaluate the damping constant (α) and magnetic anisotropy. It was observed that the FeNi sample with a moderate strength of anisotropy exhibits a low value of α ∼ 4.9 × 10 − 3 . In addition to this, it was found that the films possess a mixture of cubic and uniaxial anisotropies. [ABSTRACT FROM AUTHOR]

A perpendicularly magnetized synthetic antiferromagnetic structure is a promising alternative to a single ferromagnetic layer in spintronic applications because of its low net magnetization and high thermal stability. In general, the reversal sequences of the two ferromagnetic layers in the structure are fixed for a specific sample since they have different magnetic anisotropy. Here, we investigate the anomalous Hall effect of the [Pd/Co]/Ru/[Co/Pd] synthetic antiferromagnetic structure. By rotating the external field from out-of-plane to in-plane, three different types of anomalous Hall effect curves can be observed, which shows obvious magnetic field direction dependent magnetization reversal behavior. The mechanism can be explained with the help of the Stoner-Wohlfarth model calculation, and the result indicates that the competition among Zeeman, anisotropy, and exchange coupling energies in the system is sensitive to the magnetic field direction, which changes the switching sequences. Besides the fundamental significance, our finding provides a different dimension to manipulate the performance of spintronics. [ABSTRACT FROM AUTHOR]