Magnetization Switching Process Research Articles

Gate‐tunable Berry curvature in van der Waals itinerant ferromagnetic Cr7Te8

AbstractThe anomalous Hall effect (AHE) that associated with the Berry curvature of occupied electronic states in momentum‐space is one of the intriguing aspects in condensed matter physics, and provides an alternative for potential applications in topological electronics. Previous experiments reported the tunable Berry curvature and the resulting magnetization switching process in the AHE based on strain engineering or chemical doping. However, the AHE modulation by these strategies are usually irreversible, making it difficult to realize switchable control of the AHE and the resultant spintronic applications. Here, we demonstrated the switchable control of the Berry‐curvature‐related AHE by electrical gating in itinerant ferromagnetic Cr7Te8 with excellent ambient stability. The gate‐tunable sign reversal of the AHE can be attributed to the redistribution of the Berry curvature in the band structure of Cr7Te8 due to the intercalation‐induced change in the Fermi level. Our work facilitates the applications of magnetic switchable devices based on gate‐tunable Berry curvature.image

Asymmetric tunneling of holes through a semiconductor junction in an arbitrary magnetization configuration

In this paper, we investigate the asymmetry of holes tunneling through GaMnAs/GaAs/GaMnAs heterostructures in the cases general, where the magnetization of the two electrodes are not colinear and their magnitude are not equal. The six-bands $\textbf{k.p}$ Hamiltonian is employed to describe the holes in the GaAs and GaMnAs layers, taking into account both spin-orbit and exchange interactions. The multi-band transfer-matrix formalism is applied for numerically solving the Schrodinger equation to derive the hole wave transmission. We then calculate the transmission asymmetry and discuss its dependence on the right electrode magnetization magnitude, as well as the angles determining relatively the orientation of two magnetization vectors. The study may provide the insights into dynamic of Anomalous Tunneling Hall current during magnetization switching process which are important in spintronics technology for device design and measurement.

A feasible path for the use of ferromagnetic josephson junctions in quantum circuits: The ferro-transmon

We discuss the capabilities of ferromagnetic (F) Josephson junctions (JJs) in a variety of layouts and configurations. The main goal is to demonstrate the potential of these hybrid JJs to disclose new physics and the possibility to integrate them in superconducting classical and quantum electronics for various applications. The feasible path towards the use of ferromagnetic Josephson junctions in quantum circuits starts from experiments demonstrating macroscopic quantum tunneling in NbN/GdN/NbN junctions with ferro-insulator barriers and with triplet components of the supercurrent, supported by a self-consistent electrodynamic characterization as a function of the barrier thickness. This has inspired further studies on tunnel ferromagnetic junctions with a different layout and promoted the first generation of ferromagnetic Al-based JJs, specifically Al/AlOx/Al/Py/Al. This layout takes advantage of the capability to integrate the ferromagnetic layer in the junction without affecting the quality of the superconducting electrodes and of the tunnel barrier. The high quality of the devices paves the way for the possible implementation of Al tunnel-ferromagnetic JJs in superconducting quantum circuits. These achievements have promoted the notion of a novel type of qubit incorporating ferromagnetic JJs. This qubit is based on a transmon design featuring a tunnel JJ in parallel with a ferromagnetic JJ inside a SQUID loop capacitively coupled to a superconducting readout resonator. The effect of an external RF field on the magnetic switching processes of ferromagnetic JJs has been also investigated.

Strain-tunable Berry curvature in quasi-two-dimensional chromium telluride

Magnetic transition metal chalcogenides form an emerging platform for exploring spin-orbit driven Berry phase phenomena owing to the nontrivial interplay between topology and magnetism. Here we show that the anomalous Hall effect in pristine Cr2Te3 thin films manifests a unique temperature-dependent sign reversal at nonzero magnetization, resulting from the momentum-space Berry curvature as established by first-principles simulations. The sign change is strain tunable, enabled by the sharp and well-defined substrate/film interface in the quasi-two-dimensional Cr2Te3 epitaxial films, revealed by scanning transmission electron microscopy and depth-sensitive polarized neutron reflectometry. This Berry phase effect further introduces hump-shaped Hall peaks in pristine Cr2Te3 near the coercive field during the magnetization switching process, owing to the presence of strain-modulated magnetic layers/domains. The versatile interface tunability of Berry curvature in Cr2Te3 thin films offers new opportunities for topological electronics.

Control of magnetization states in full-Heusler [formula omitted] alloy-based MTJ with four-fold anisotropy using VCMA-assisted STT

The magnetization switching process in four-fold anisotropy materials is characterized by an intermediate state (IS) due to the interplay between magnetic anisotropy and spin-transfer torque (STT). Practically, the presence of an IS can impede the switching process in a single-step, causing switching errors during data storage. Here, we investigate the STT-induced magnetization switching in the MTJ device based on half-metallic full-Heusler Co2FeAl0.5Si0.5 (CFAS) alloy with four-fold anisotropy in the presence of voltage-controlled magnetic anisotropy (VCMA) using micromagnetic simulation. Our results demonstrate that VCMA-assisted STT can effectively tune the magnetic states during the switching by adjusting the VCMA effect at appropriate intervals and strengths. As a result, the magnetization can overcome the limitations posed by the IS in the CFAS alloy, leading to single-step switching modes for low spin current density. Additionally, we revealed that pulsed voltage-assisted STT results in shorter switching times compared to conventional switching in four-fold anisotropy materials.

Magnetization switching process by dual spin–orbit torque in interlayer exchange-coupled systems

We report current-induced magnetization switching in Pt/Co/Ir/Co/Pt multilayers with different Ir layer thicknesses (tIr), where the perpendicularly magnetized Co layers are coupled ferromagnetically or antiferromagnetically through an interlayer exchange coupling and are sandwiched by the Pt spin Hall layers. The domain structures formed during switching vary depending on the magnetization alignment, i.e., a ferromagnetically coupled or antiferromagnetically coupled configuration. These results clarify the macroscopic picture of switching process for interlayer exchange-coupled systems. The local picture of the switching process is also examined by a numerical calculation based on a macrospin model, which reveals the switching dynamics triggered by dual spin–orbit torques for both antiferromagnetically and ferromagnetically coupled cases. The numerical calculation shows that the dual spin–orbit torques from the two Pt layers effectively act on the two Co layers not only for the antiferromagnetically coupled case but also for the ferromagnetically coupled one. Our findings deepen the understanding of the switching mechanism in a magnetic multilayer and provide an avenue to design spintronic devices with more efficient spin–orbit torque switching.

Fourfold magnetic anisotropy induced in CoFeB/IrMn bilayers by interfacial exchange coupling

Exchange bias (EB) occurring in ferromagnetic (FM)/antiferromagnetic (AFM) bilayers conventionally can lead to a unidirectional magnetic anisotropy () as well as an accompanied uniaxial magnetic anisotropy (). We observed an additional fourfold magnetic anisotropy () induced by interfacial exchange coupling in amorphous CoFeB/epitaxial IrMn bilayers with an EB. Because of the combined effect of the three kinds of magnetic anisotropies, one- and two-step magnetic switching processes were observed at different magnetic field orientations, which usually appear in single-crystal FM layer with an intrinsic magnetocrystalline anisotropy but not in amorphous FM layer. The angular dependent magnetic switching fields can be nicely fitted by a phenomenological model based on domain wall nucleation and propagation with the in-plane along <100>. The ferromagnetic resonance measurements indicate that the specific strength of for EB along [100] is larger than that for EB along [110]. The induced can be understood by considering two types of AFM domains caused by both monatomic steps and defects and their induced net uncompensated spins along the in-plane <100> axes. The different dependence of on the EB direction are because of the different effects of growth magnetic field on the presence of AFM domains.

Evidence for vortex state in Fe2CoGe thin films using FORC and magnetic imaging

We report on the evidence for the vortex state in the thin films of Fe2CoGe through first order reversal curves, magnetic force microscope, longitudinal magneto-optical Kerr effect and micro-magnetic simulations. Phase purity of the films confirmed through X-ray diffraction, which confirms the A2 type disorder Heusler alloy structure. Contour graph of first order reversal curves infers the formation of vortex state that is useful to understand magnetization reversal and switching process. We do observe the vortex state ∼1 μm with in – plane curling of the magnetization using magnetic force microscope phase analysis. We believe that realization of vortex state formation in Fe2CoGe thin films may cater applications in future magnetic data storage and microwave oscillators.

Enhancing all-optical switching of magnetization by He ion irradiation

All-optical switching (AOS) of magnetization by a single femtosecond laser pulse in Co/Gd based synthetic ferrimagnets is the fastest magnetization switching process. On the other hand, He ion irradiation has become a promising tool for interface engineering of spintronic material platforms, giving rise to significant modification of magnetic properties. In this paper, we explore the use of He ion irradiation to enhance single pulse AOS of Co/Gd bilayer-based synthetic ferrimagnets. The intermixing of the constituent magnetic layers by He ion irradiation was both numerically simulated and experimentally verified. We theoretically modeled the effects of intermixing on AOS using the layered microscopic 3-temperature model and found that AOS is enhanced significantly by breaking the pristine Co/Gd interface through intermixing. Following this notion, we studied the threshold fluence of AOS as a function of He ion irradiation fluence. We found that the AOS threshold fluence can be reduced by almost 30%. Our study reveals the control of AOS by He ion irradiation, which opens up an industrially compatible approach for local AOS engineering.

Energy exchange dependent transient ferromagnetic like state of ultrafast magnetization dynamics

The study of laser-induced ultrafast magnetization dynamics is crucial for the development of information recording technology. Due to the complex mechanism, there is still a lack of comprehensive understanding for ultrafast magnetization dynamics. As an essential stage of laser-induced ultrafast magnetization switching process, the transient ferromagnetic like state (TFLS), has attracted much attention. Different from other studies on TFLS through the difference of magnetization dynamics between rare-earth and transition-metal, our study mainly focuses on the influence of energy injection and relaxation on TFLS in the process of ultrafast magnetization dynamics. The influence of various parameters on the formation of energy exchange dependent TFLS is studied. The results of simulation well support our view. Understanding the mechanism behind the TFLS is of great significance to promote the application of laser-induced ultrafast magnetization switching.

Theoretical routes for current-free magnetization switching induced by joint effects of strain and Dzyaloshinskii–Moriya interaction

Voltage-induced strain is regarded as an energy-efficient choice of tuning spin-dynamics. However, studies on the strain-mediated switching of magnetization in a perpendicular-magnetic-anisotropy layer are few because of the uncertainties that arise from the magnetization oscillation at high strain. In this work, we demonstrate theoretically how to deterministically switch the perpendicular magnetization in an ultrathin magnetic nanodisk by combining biaxial in-plane strain with the Dzyaloshinskii–Moriya interaction (DMI). The magnetization-switching process is carefully investigated under different strains and DMI strengths. The underlying switching mechanism is attributed to the remnant magnetization component, which deviates away from the film plane during the strain-pulse-impulsion period and which is also highly dependent on the DMI. Based on simulation results, a theoretical route for obtaining deterministic switching regarding strain and DMI is established. In this route, the minimum duration of the strain pulse can be shortened to a critical time of 2.5 ns as the strain increases to 7000 ppm at a DMI value of 0.6 mJ/m2. Moreover, nonvolatile and reversible switching between the spin-up and spin-down states of perpendicular magnetization is realized using pulses of biaxial in-plane isotropic strain. This switching occurs via an intermediate skyrmion and shows potential in overcoming the edge-roughness-related pinning that occurs in spin–orbit-torque current-induced switching. This study provides a robust insight into strain-induced current-free magnetization switching, providing a guide for experimental research into the strain-mediated voltage control of memory applications.

Magnetic interlayer coupling between ferromagnetic SrRuO3 layers through a SrIrO3 spacer

A key element to tailor the properties of magnetic multilayers is the coupling between the individual magnetic layers. In the case of skyrmion hosting multilayers, coupling of skyrmions across the magnetic layers is highly desirable. Here, the magnetic interlayer coupling was studied in epitaxial all-oxide heterostructures of ferromagnetic perovskite SrRuO3 layers separated by spacers of the strong spin–orbit coupling oxide SrIrO3. This combination of oxide layers is being discussed as a potential candidate system to host Néel skyrmions. First order reversal curve (FORC) measurements were performed in order to distinguish between magnetic switching processes of the individual layers and to disentangle the signal of soft magnetic impurities from the sample signal. Additionally, FORC investigations enabled us to determine whether the coupling between the magnetic layers is ferromagnetic or antiferromagnetic. The observed interlayer coupling strength was very weak for the heterostructure with a two monolayer (ML) thick SrIrO3 spacer, and no coupling was observed for spacers of 6 and 12 ML thickness. The decoupling of the magnetic SrRuO3 layers due to the SrIrO3 spacer is a disadvantage for the study of skyrmions in such multilayers and indicates that other oxides have to be identified for realizing strong magnetic coupling.

Magnetic anisotropy and reversal in epitaxial FeGa/IrMn bilayers with different orientations of exchange bias

Epitaxial FeGa/IrMn bilayers with exchange biases along the FeGa[100] and [110] directions are prepared on MgO(001) single crystal substrates by magnetron sputtering through controlling the orientation of the external field &lt;i&gt;in situ&lt;/i&gt; applied during growth. The effect of the exchange bias orientation on the magnetic switching process and the magnetic switching field are studied. The X-ray &lt;i&gt;φ&lt;/i&gt;-scan indicates that the FeGa layer is epitaxially grown with a 45° in-plane rotation on the MgO(001) substrate along the FeGa(001)[110] direction and the MgO(001)[100] direction. The measurements of the angular dependence of the ferromagnetic resonance field and the corresponding fitting to the Kittel equation show that the samples have a superposition of fourfold symmetric magnetocrystalline anisotropy &lt;inline-formula&gt;&lt;tex-math id="M4"&gt;\begin{document}$ {K}_{1} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M4.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M4.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, unidirectional magnetic exchange bias anisotropy &lt;inline-formula&gt;&lt;tex-math id="M5"&gt;\begin{document}$ {K}_{\mathrm{e}\mathrm{b}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M5.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M5.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, and uniaxial magnetic anisotropy &lt;inline-formula&gt;&lt;tex-math id="M6"&gt;\begin{document}$ {K}_{\mathrm{u}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M6.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M6.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; with configuration of &lt;inline-formula&gt;&lt;tex-math id="M7"&gt;\begin{document}$ {K}_{\mathrm{e}\mathrm{b}}//\left[100\right] $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M7.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M7.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; or &lt;inline-formula&gt;&lt;tex-math id="M8"&gt;\begin{document}$ {K}_{\mathrm{e}\mathrm{b}}//\left[110\right] $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M8.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M8.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;. The combined longitudinal and transverse magneto-optical Kerr effect measurements show that sample with &lt;inline-formula&gt;&lt;tex-math id="M9"&gt;\begin{document}$ {K}_{\mathrm{e}\mathrm{b}}//\left[100\right] $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M9.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M9.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; exhibits square loops, asymmetrically shaped loops, and one-sided two-step loops in different external magnetic field directions. In contrast, the sample with &lt;inline-formula&gt;&lt;tex-math id="M10"&gt;\begin{document}$ {K}_{\mathrm{e}\mathrm{b}}//\left[110\right] $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M10.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M10.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; exhibits one-sided two-step and two-sided two-step loops as the magnetic field orientation changes. Because the &lt;inline-formula&gt;&lt;tex-math id="M11"&gt;\begin{document}$ {K}_{1} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M11.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M11.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; is superimposed by &lt;inline-formula&gt;&lt;tex-math id="M12"&gt;\begin{document}$ {K}_{\mathrm{u}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M12.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M12.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and &lt;inline-formula&gt;&lt;tex-math id="M13"&gt;\begin{document}$ {K}_{\mathrm{e}\mathrm{b}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M13.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M13.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, the in-plane fourfold symmetry of the magnetic anisotropy energy is broken. The local minima are no longer strictly along the in-plane &lt;inline-formula&gt;&lt;tex-math id="M14"&gt;\begin{document}$ \left\langle{100}\right\rangle $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M14.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M14.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; directions, but make a deviation angle which depends on the relative orientation and strength of magnetic anisotropy. A model based on the domain wall nucleation and propagation is proposed with considering the different orientations of &lt;inline-formula&gt;&lt;tex-math id="M15"&gt;\begin{document}$ {K}_{\mathrm{e}\mathrm{b}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M15.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M15.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, which can nicely explain the change of the magnetic switching route with the magnetic field orientation and fit the angular dependence of the magnetic switching fields, indicating a significant change of domain wall nucleation energy as the orientation of &lt;inline-formula&gt;&lt;tex-math id="M16"&gt;\begin{document}$ {K}_{\mathrm{e}\mathrm{b}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M16.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M16.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; changes.

Antisymmetric magnetoresistance in Fe3GeTe2 nanodevices of inhomogeneous thickness

With the emergence of the van der Waals two-dimensional (2D) ferromagnetic materials, ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$ (FGT) with a high Curie temperature (${T}_{\mathrm{C}}$) and the perpendicular magnetic anisotropy (PMA) provides a rich platform for the next generation spintronic devices. Up to now, in most 2D magnets-based devices, the easiest and the most convenient way to obtain thin flakes is still the mechanical exfoliation method. However, samples with thickness variation occur inevitably during this process, which are either ignored due to the thickness-inhomogeneity-induced complicated phenomena or far from been fully reached. Herein, unlike conventional symmetric magnetoresistance with respect to the magnetic field observed in thickness-uniform FGT flakes, we demonstrate a hitherto rarely observed antisymmetric magnetoresistance in thickness-inhomogeneous nanodevices. Since the ${T}_{\mathrm{C}}$ and coercive field (${H}_{\mathrm{C}}$) of FGT are thickness dependent, thickness variations in FGT flake lead to different regions with distinct ${H}_{\mathrm{C}}\mathrm{s}$. Together with the thickness variations-induced differences in ${H}_{\mathrm{C}}\mathrm{s}$ and the PMA, an eddy current generates in the proximity of the thickness boundary during the magnetic switching process. This eddy current perturbs the longitudinal resistance and results in the unexpected antisymmetry. Our work provides a new understanding and the device application in thickness-variation 2D ferromagnetic materials, which are more experimentally common but have been neglected thus far.

Magnetization switching and deterministic nucleation in Co/Ni multilayered disks induced by spin–orbit torques

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 3×1011 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.

Magnetization reversal in shape asymmetric permalloy nanocaps

Symmetric and asymmetric ferromagnetic permalloy nanocaps of 100 nm diameter are investigated using micromagnetic simulations to study the influence of geometrical asymmetry on the magnetization reversal as a function of thickness. Symmetric nanocaps are featured by having a maximum thickness exactly at the center, whereas, in asymmetric nanocaps, the maximum thickness is at an oblique direction, 20° off to the center of the caps. Magnetization reversal and switching processes in asymmetric nanocaps are found to be strongly dependent on the field direction as well as on the thickness of the nanocaps. In the symmetric nanocaps, magnetization reversal happens via coherent rotation of the magnetic moments. On the other hand, magnetization reversal in asymmetric nanocaps happens via the formation of a non-uniform C-state. An increase in the nucleation field of C-state with the thickness of nanocaps indicates that the stability of the C-state increases with the thickness of the nanocaps. Formation of a C-state due to the shape-induced asymmetry results in distinct M-H loops that depends on the orientation of the nanocaps to the external field direction.

Spin Hall magnetoresistance in Pt/Cr2O3/YIG structure

Temperature dependence of the spin Hall magnetoresistance (SMR) has been investigated herein Pt/Cr2O3/Y3Fe5O12 structure. Well below the Néel temperature of Cr2O3, the SMR is not observed at the noise level of 1.2 ppm. In vicinity of the Néel temperature, only a positive SMR tracks the YIG magnetic switching process, supporting that the SMR of normal metal/antiferromagnetic insulator/ferromagnetic insulator trilayer is controlled by the Néel vector of the antiferromagnetic insulator. A high field magnetoresistance is observed up to an external magnetic field of 20000 Oe which has a field angle dependence symmetry consistent with the SMR. We attribute this high field magnetoresistance to be induced by the Hanle magnetoresistance in Pt.

Interface-driven magnetic anisotropy of epitaxial [formula omitted] thin films

The effect of film-substrate interface on the magnetic anisotropy (MA) of epitaxial Fe4N thin films grown on single crystalline MgO (100) and MgO (111) substrates has been studied in this work. Both samples were grown simultaneously using a reactive dc magnetron sputtering process at a substrate temperature of 250°C. Single phase Fe4N samples were found to grow epitaxially on (100) and (111) oriented MgO substrates as confirmed from out-of-plane x-ray diffraction and in-plane ϕ-scan measurements. The MA of (100) and (111) oriented Fe4N samples was measured using longitudinal magneto-optical Kerr effect (MOKE). In spite of being grown simultaneously, the MA of both these samples was found to be different. Secondary ion mass spectroscopy and x-ray reflectivity measurements revealed the formation of a dense layer at the film-substrate interface. The MA of this dense layer along with the MA of Fe4N has a dramatic effect on magnetic reversal depending on the orientation of the substrate. Further, from the MOKE measurements, the difference in the magnetization switching processes was found to depend on the microstructure and orientation of Fe4N thin films.

The diameter effect on the magnetization switching time of sphere-shaped ferromagnets using micromagnetic approach

In this work, the magnetization switching time has been studied as the diameter variation of sphere-shaped ferromagnets by means of micromagnetic simulation. Some ferromagnetic elements such as cobalt, iron, nickel, and permalloy were numerically simulated with diameter size variation from 50 nm to 100 nm. The micromagnetic simulation was performed by public software Object Oriented Micromagnetic Framework (OOMMF) based on the Landau-Lifshitz-Gilbert (LLG) equation. The ferromagnetic nano-sphere was induced by the quasi-static magnetic field to observe its magnetization response. Generally, it is observed that the switching time increases as the diameter size increases on the ferromagnetic elements. However, the switching time are relatively insensitive as the diameter increases in the Cobalt element for the diameter range from 60 nm to 90 nm. This behavior is contributed to the distribution of magnetization easy axis on the ferromagnetic elements. The understanding of domain structures during magnetization switching process is important in the development of nano-patterned magnetic memory storage.

Enhancement of zero-field skyrmion density in [Pt/Co/Fe/Ir]2 multilayers at room temperature by the first-order reversal curve

Magnetic skyrmions are novel topological spin textures on the nanoscale, and significant efforts have been taken to improve their zero-field density at room temperature (RT). In this work, we reported an approach of improving zero-field skyrmion density in [Pt/Co/Fe/Ir]2 multilayers at RT by using the first-order reversal curve (FORC) technique to obtain information on the irreversible or reversible behaviors in the magnetization switching process. It was found from the FORC diagram that the magnetization reversal mechanism can be characterized into three stages: (1) reversible labyrinth stripe domains expanding or shrinking stage; (2) irreversible stripe domains fracturing stage; and (3) irreversible skyrmion annihilation stage. Furthermore, the zero-field skyrmion density can be highly improved by choosing reversal fields from the irreversible stripe domains fracturing stage. The highest skyrmion density was approached according to the maximum FORC distribution ρ. Our results have established the FORC measurement as a valuable tool for investigating magnetic multilayers of high skyrmion densities.