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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 Fe&lt;sub&gt;3&lt;/sub&gt;GeTe&lt;sub&gt;2 &lt;/sub&gt;(FGT)/Ir&lt;sub&gt;22&lt;/sub&gt;Mn&lt;sub&gt;78 &lt;/sub&gt;(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 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.

![](https://assets.underline.io/uploads/markdown_image/1/image/acc94c8690514d4c33c542dacf41d203.jpg)

Magnetic properties and SOT-driven perpendicular magnetization switching in the FGT/Pt bilayer device. (a) Hall resistance as a function of the out-of-plane field at different temperatures. (b) Arrott plots of the Hall resistance for the FGT/Pt device. The extracted Tc is about 208 K. (c) RAHE as a function of in-plane (IP) and out-of-plane (OOP) magnetic field at 100 K. (d) Current-driven perpendicular magnetization switching for in-plane magnetic fields of +2000 Oe and −2000 Oe at 100 K with clockwise and anticlockwise switching polarity, respectively. The dashed lines mark the RAHE at saturated magnetization states.



2022 Joint MMM-INTERMAG

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

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INTERMAG 2021

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 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.

![](https://assets.underline.io/uploads/markdown_image/1/image/acc94c8690514d4c33c542dacf41d203.jpg)

Magnetic properties and SOT-driven perpendicular magnetization switching in the FGT/Pt bilayer device. (a) Hall resistance as a function of the out-of-plane field at different temperatures. (b) Arrott plots of the Hall resistance for the FGT/Pt device. The extracted Tc is about 208 K. (c) RAHE as a function of in-plane (IP) and out-of-plane (OOP) magnetic field at 100 K. (d) Current-driven perpendicular magnetization switching for in-plane magnetic fields of +2000 Oe and −2000 Oe at 100 K with clockwise and anticlockwise switching polarity, respectively. The dashed lines mark the RAHE at saturated magnetization states.

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The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

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In recent years, various methods have been reported to boost the magneto-optical (MO) response. Several works have reported the enhancements of the MO response relying on the plasmonic effects attributed to the strongly confined electromagnetic field in the structures1-3. However, the nonnegligible disadvantage of this approach is the optical losses due to the high absorption coefficient of the metal materials1. Therefore, combining the all-dielectric metasurfaces which have high-refractive-index and low intrinsic loss with planar photonic structures offers an alternative route to these problems4,5 .But most of the observations so far are focused on enhancement of existing magneto-optical effects in planar MO thin films. A high index contrast, all dielectric magneto-optical metasurface featuring strong Mie resonance modes have not been fabricated. Here, we report observation of circular displacement current induced novel magneto-optical effects in a high index contrast Si/Ce:YIG/YIG/SiO2 all dielectric metasurface. We observe giant transverse magneto-optical Kerr effect (TMOKE) up to 7 % under s-polarized incidence, which is non-existent in planar magneto-optical thin films. This phenomenon is essentially originated from the unique circular displacement current when exciting the magnetic resonance modes, which changes the incident electric field direction locally. These results indicate promising potential of controlling light propagation by utilizing the complex Mie resonance modes in magneto-optical all dielectric metasurfaces. Our work may inspire the development of novel magneto-nanophotonic devices such as vectoral magnetic field sensing, free space non-reciprocal photonic devices and magneto-optical imaging.

![](https://assets.underline.io/uploads/markdown_image/1/image/d3d7bd3c840418fd37285dae4d310845.jpg)

Figure 1. (a) Schematic diagram of the metasurface. (b) Scanning electron microscope image of a fabricated device.

![](https://assets.underline.io/uploads/markdown_image/1/image/22950e3df3d860eae0c79b53767f7e8a.jpg)

Figure 2. (a) Schematic diagram of s-polarized TMOKE characterization set-up. (b)Measured s-polarized TMOKE and reflection spectra of the metasurface compared with bare Ce:YIG/YIG thin films. (c) Measured TMOKE hysteresis for the metasurface and the bare MO films at 1230 nm wavelength. (d) Simulated reflection spectra and TMOKE responses of the metasurface for s-polarized light.

Circular Displacement Current induced Novel Magneto-Optical Effects in All-dielectric Metasurfaces

Recently, the range of applications of magnetic emulsions has significantly expanded due to the development of microfluidics [1] and biomedical technologies [2]. Using magnetically sensitive emulsions, methods have been proposed for measuring the viscosity and surface tension of liquids [3] and even for determining the content of methyl alcohol [4]. In this work, we present the results of a study of the effect of diffraction scattering of light in magnetic emulsions with low interfacial tension, synthesized based on AMG-10 hydraulic oil. Magnetic emulsions were produced by mixing kerosene-based magnetic fluid in AMG-10 hydraulic oil. The size of microdroplets could vary from 1000 to 7000 nm. To study the effect of diffraction scattering of light, an optical setup was used, which consisted of a helium-neon laser with a radiation wavelength of 633 nm, a cylindrical cuvette, and a screen. The image of the diffraction pattern was recorded by the CMOS matrix of a camera. Image processing was performed using specialized software ImageJ. The sample cuvette was a glass cylinder, fixed on a fluoroplastic tube driven by a DC motor with a belt drive. The range of rotation frequencies was 9–200 rpm. The diffraction pattern is oriented in the direction perpendicular to the long axes of the elongated microdroplets. When the cell is rotated, the droplet axes deviate from the direction of the magnetic field along the direction of rotation, which leads to a rotation of the diffraction band relative to the initial direction. The deflection angle depends on the cell rotation speed and the magnetic field strength (Fig. 1 and Fig. 2). The interpretation of the effect of diffraction scattering in magnetic emulsions is based on considering the diffraction of light by an irregular structure of elongated microdroplets of various sizes, located randomly. Calculations give a result that is in complete agreement with the experiment. This work was financially supported by the Ministry of Science and Higher Education of Russia (project no. 0795-2020-007).

![](https://assets.underline.io/uploads/markdown_image/1/image/e6e5e813cc0937954adfe430afa77353.jpg)

Photographs of the diffraction pattern at the various magnetic fields and rotation speeds

![](https://assets.underline.io/uploads/markdown_image/1/image/d097e27fe9c0f03ed59cd09cccf39265.jpg)

Dependence of the angle of rotation on the rotation speed (magnetic field is H=2 kA/m)

Light diffraction in rotating magnetic emulsions in a magnetic field

Iron-based garnet films that have large magneto-optical (MO) effect are a promising material for MO device applications. In particular, terbium iron garnet (TbIG) can crystallize directly on a Si substrate without garnet seed layers [1-4] and, therefore, recent investigations show quite practical optical isolators taking advantage of TbIG [1,2]. However, crystallization for TbIG requires high temperatures and it is desirable to limit the heating to those regions of the chip where devices are formed. In this study, we compare the structure, magnetic and MO properties of TbIG and Bi doped TbIG (Bi-TbIG) films processed by rapid thermal annealing (RTA) to those annealed locally using an embedded resistor with 40-μm-square area. TbIG (Tb2.77Fe5O12) and Bi-TbIG (Bi0.02Tb2.82Fe5O12) films are made by pulsed laser deposition at room temperature, which allows for liftoff patterning using a photoresist mask. The crystal structure for the films is characterized by micro-Raman spectroscopy and X-ray diffraction (XRD) and the magnetic properties by vibrating sample magnetometry. XRD shows single phase garnet after RTA 1073 – 1273 K. Raman spectra for Bi-TbIG film before/after 1173 K annealing and for the Si substrate are shown in Fig. 1. The Raman spectrum for the as deposited film is almost the same as that of the Si substrate while a Raman peak corresponding to the strongest peak of TbIG (Eg) is observed around 261 cm-1 in the annealed film. Raman spectroscopy enables detection of local crystallization in Bi-TbIG on embedded resistors. Figure 2 shows room temperature in-plane M-H loops of the annealed TbIG and Bi-TbIG films. The TbIG film is not saturated at 1 T while the Bi-TbIG is saturated at 0.7 T. Coercivity in TbIG rapidly increases in the vicinity of the compensation temperature (Tcomp) [3] which is ~250 K for bulk TbIG, and slightly lower for thin film TbIG with Tb deficiency [4]. Bi doping lowers (Tcomp) further [4] explaining the easier saturation of the Bi-TbIG film. The high figure of merit of Bi-TbIG and its higher remanence make this material attractive for integrated photonic devices.

![](https://assets.underline.io/uploads/markdown_image/1/image/db285f5491540908bdd48574e79691ed.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/ff4aa0a91ef334bb9894df68b9074960.jpg)

Crystallization of magneto-optical bismuth terbium iron garnet films

Graphene (Gr) is a particularly interesting material for spintronic and technological applications due to its low intrinsic spin orbit coupling and hyperfine interaction, which lead to high spin lifetimes and coherence lengths [1]. Furthermore, it is common in spintronic applications to introduce a structural isomorph to Gr, hexagonal Boron Nitride (hBN) to improve lattice matching in heterostructure engineering[2]. Specifically for spintronic and spin-caloritronic applications, a ferrimagnetic (FM) layer is often used as a magnon source. Therefore, it is important to understand the interfacial properties of FM/Gr(hBN) interfaces. Here, we explore the change in magnetic anisotropy in the FM insulator Nickel Ferrite (NFO) due to the inclusion of monolayer Gr and hBN. This was done by performing radio frequency transverse susceptibility measurements utilizing a tunnel diode oscillator technique, which is a sensitive probe of the system’s effective anisotropy[3]. Specifically, in-plane (IP) and out-of-plane (OOP) measurements were taken for bare NFO, NFO/Gr, NFO/hBN samples. We find that the inclusion of the Gr layer reduces the overall anisotropy for both IP and OOP drastically, by a factor of 2, in the entire temperature of 20 – 300 K. On the other hand, the inclusion of the hBN layer slightly reduces the in-plane anisotropy at low temperature (T &lt; 180 K) but increases it at high temperature (T &gt; 180 K). Since NFO is an insulator and Gr is a semimetal there is a large conductivity difference at the interface which likely leads to charge transfer reducing the overall anisotropy[4]. This is further supported by the less drastic change with the inclusion of monolayer hBN, a semiconductor. Relative to NFO, magnetometry measurements show an enhancement of the saturation magnetization in NFO/Gr and NFO/hBN, highlighting an additional role played by the magnetic proximity effect.

Proximity and Charge-Transfer Mediated Magnetism at Nickel Ferrite Interfaces with Graphene and Hexagonal Boron Nitride Monolayers

Over the past few years, the magnetic proximity effect (MPE) has gained intense attention of the magnetic community.[1] Despite the fact that the influence of MPE in bilayers of ferromagnetic (FM) and antiferromagnetic (AFM) materials has been extensively investigated, studies on MPE in bilayers of a FM and a non-collinear magnet are rather limited. Manganese Phosphide (MnP) is a well-known metallic magnet with helical spin configurations at low temperatures.[2-3] Our recent study on highly crystalline MnP thin films has shown the presence of strain-mediated magnetism with two magnetic transitions: a paramagnetic (PM) to FM transition at TC ~ 279 K and a FM to helimagnetic transition at TN ~ 110 K.[2] This finding has motivated us to investigate how the helimagnetic spin texture of the MnP film is influenced when another FM layer is placed in its close proximity. To address this, we sputtered a 5 nm Fe film on the 100 nm MnP film, with a 2 nm-thick capping layer of Ta, at room temperature. Magnetometry measurements show a large increase in TC and a large decrease in TN for the Fe/MnP bilayer (TC ~ 300 K and TN ~ 75 K) relative to the MnP sample (TC ~ 279 K and TN ~ 110 K), indicating the presence of strong MPE. The M-H data indicate that in the helimagnetic regime (T &lt; 75 K), the coercive field (HC) of the Fe/MnP sample (HCFe/MnP ~ 1367 Oe) has nearly doubled when compared to the average value of the individual HC of MnP and Fe reference samples (((HCFe + HCMnP)/2) = 780 Oe). Interestingly, the interfacial magnetic coupling strength, defined as ΔHC =|((HCFe + HCMnP)/2) - HCFe/MnP|, decreases significantly with decreasing temperature in the helimagnetic regime. Furthermore, the ratio of remanence magnetization (Mr) to saturation magnetization (Ms) of Fe/MnP is higher than the average value of individual Mr/Ms ratios of MnP and Fe. Overall, the observed shapes of the M-H loops of the Fe/MnP bilayer deviate remarkably from those of the reference samples. Since the exchange bias effect is negligible in the Fe/MnP system, these observations consistently validate the presence of the MPE.

Magnetic proximity effect on the helimagnetic state of highly crystalline manganese phosphide films

Ultra-Short Pulsed Laser Ablation process performed on the surface of a Grain-Oriented Electrical Steel (GOES) has shown a significant decrease in the iron losses up to 20%. This is due to a modification of the domain structure that is re-organized using a total energy minimization. Therefore, this leads to a change in the permeability and in the magneto-mechanical behavior also known as the magnetostriction. These modifications are respectively due to the modification of the magnetostatic and the magnetoelastic energy contributions. In this study, the effect of the ablation on the magnetic and the magneto-mechanical properties is revealed and compared to classical irradiation and scribing processes in the static and the dynamic working conditions. Synchronous real time magnetic and mechanical measurements are performed using a dedicated test bench: the Single Sheet Tester with a mechanical adaptation using a fixed-free sample with a piezoelectric accelerometer. GOES samples are measured and compared before and after treatment for different optimal laser parameters. Results have shown that different performances can be simultaneously obtained: - Magnetostriction reduction up to 50% - Permeability increase at low induction up to 20% Physical origins of the change in both static and dynamic magneto-mechanical properties due a laser process will be discussed and proposed to orientate the optimization of laser process parameters towards the best compromise between iron loss reduction, permeability increase and magnetic induced vibrations.

![](https://assets.underline.io/uploads/markdown_image/1/image/f3a530642ac29649dfcf907edea86602.jpg)

Fig. 1: Peak-to-Peak Magnetostriction: Ref (Blue), ablation 1 (Red), ablation 2 (Black)

Ultra-short Pulsed Laser Ablation Process on a GO FeSi Electrical Single Sheet: Impact on the Static/Dynamic Magneto-mechanical Behavior and Optimization

Structural inversion asymmetry together with spin-orbit coupling can induce interfacial Dzyaloshinskii-Moriya Interaction (iDMI) in Heavy-Metal/Ferromagnet/Metal-Oxide heterostructuctures [1]. In such thin film systems with perpendicular magnetic anisotropy the iDMI combined with dipolar interactions can stabilize non-collinear chiral magnetic spin textures such as Néel Domain Walls (DWs), eventually forming magnetic skyrmion bubbles [2]. The iDMI amplitude and sign determine the spin texture of the DWs and their chirality [3]. Moreover, skyrmions can be moved by a current thanks to spin orbit torques, in a direction depending on their chirality. In this study we report on a deterministic control of their motion related to a chirality switch of magnetic skyrmion bubbles in Ta/FeCoB/TaOx trilayer, covered by a ZrO2 ionic conductor (Fig. 1a). Monitored under a polar-Magneto-Optical Kerr-Effect (p-MOKE) microscope we apply a gate voltage through a transparent Indium Tin Oxide (ITO) electrode and demonstrate by real space tracking the reversal of their current-induced motion (Fig. 1b). Micromagnetic simulations together with similar measurements on magnetic domain walls confirm the possibility to invert the chirality, eventually leading to versatile spintronic and logic devices. We have furthermore optimized the fabrication of skyrmion Hall-bar tracks (Fig. 2a), containing magnetic skyrmion bubbles (Fig. 2b), with deported ITO top electrodes. These skyrmion racetracks of different shapes and sizes allow to assess the effect of gate voltage and lateral confinement on the skyrmion motion. Eventually, the gate would play the role of a pinning potential and control the skyrmion velocity. In a similar Hall-bar geometry with multiple Hall-contacts we envision to demonstrate the electrical tracking of a moving skyrmion in replacement for the MOKE images that are limited in temporal and spatial resolution.

![](https://assets.underline.io/uploads/markdown_image/1/image/72f0bad1edbe95eec301d09cc8f44523.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/ce72f946d632a2abff10be5391d298b4.jpg)

Gate-Controlled Skyrmions in Magnetic Trilayer Tracks

Gate-Controlled Skyrmions in Magnetic Trilayer Tracks

Magnetic skyrmions are localized objects with a non-trivial topology. With their small sizes and stable magnetic properties, skyrmions are of great interest in particular due to their potential applications in future-generation magnetic storage devices. Multilayer ferromagnetic thin-film materials hosting room temperature (RT) skyrmions stabilized by interfacial Dzyaloshinskii-Moriya interactions in [1,2] allow a high tunability in terms of skyrmion size and density, making them very promising platforms for investigating functional skyrmions for future applications. However, several obstacles remain before implementing ferromagnetic skyrmions into applications. One of these problems is that the dipolar interactions in these materials makes it difficult to stabilize small skyrmions without an external field [3,4,5]. Another major difficulty concerns the skyrmion Hall effect which deflects the skyrmions to the device edges [6,7]. Both of these problems could potentially be solved by having skymions in antiferromagnetic (AF) materials, where the dipolar fields are minimized by having the two subsystems aligned antiparallel to each other, and the skyrmion Hall effect is compensated. This has been achieved by Legrand et al. in Ref. [5], where RT skyrmions at zero field were generated in a synthetic AF multilayer system and observed by magnetic force microscopy (MFM). Following the same general approach as in Ref. [5], we construct a system that can host high-density skyrmions at zero external field using interlayer exchange coupling and having Ir/Fe/Co/Pt multilayers as starting blocks. These skyrmion-generating layers are coupled with different bias layers that act as an external magnetic field. We will show magnetic characterization and high-resolution MFM imaging results of the impact of various bias layers and coupling strengths on the overall system properties.

Room Temperature Skyrmions at Zero Field in Ir/Fe/Co/Pt-based Systems with Antiferromagnetic Coupling

Room temperature magnetic skyrmions have the potential of enabling compact and energetically-efficient storage such as racetrack memories, albeit with two fundamental challenges: 1) Not being able to restrict their motion along straight paths, leading to skyrmions being lost at the device edge; one possible solution is the use of antiferromagnetically-coupled skyrmions [1]; and 2) Not having stable inter-skyrmion distances, leading to fluctuating distances among bits; a potential solution was revealed with the experimental observation of coexisting skyrmions and chiral bobbers [2], opening the possibility that a chain of binary data bits could be encoded by the two states. However, these observations were in B20-type crystalline materials and at low temperatures. In our previous work [3], we developed a ferro/ferri/ferromagnetic (FM/FI/FM) trilayer system that can host two distinct skyrmions at room temperature and can serve as a solution to the second challenge. The two phases represent a tubular skyrmion (running through the entire trilayer) and an incomplete skyrmion (existing in the FM layers only), as revealed from magnetic force microscopy (MFM) data and micromagnetic simulations. Such a two-skyrmion phase system exists for specific magnetic parameters of the individual sublayers. By exploring this parameter space, in this new study we reveal that the densities of the two skyrmions can be tuned via different routes: either by changing the magnetic properties of the FI or those of the FM. More specifically, we investigate the trilayer system when changing the thickness of the FM multilayers by using a combination of MFM, vibrating sample magnetometry and Brillouin light scattering experiments together with micromagnetic simulations. We show how the competition between different energies allows for the stabilization of either incomplete-only skyrmions, combination of both or mainly tubular skyrmions (Figure 1). Having a good understanding of the interplay between different magnetic properties can lead to better-tailored systems and possibly bring skyrmions a step closer to applications.

![](https://assets.underline.io/uploads/markdown_image/1/image/5ed95347749731b8a51d650ec9a59f11.jpg)

Fig. 1: Sample schematics and MFM images of three FM/FI/FM samples with varying Fe-layer thickness.

Tuning the Density of Incomplete and Tubular Skyrmions in Ferro/ferri/ferromagnetic Trilayers

The spin-momentum locking of surface states in topological quantum materials can produce a resistance that scales linearly with magnetic and electric fields and also depends on the current direction relative to the crystalline axes1,2. Such a bilinear magneto-electric resistance (BMER) effect offers a completely new approach for magnetic storage and magnetic field sensing applications. The effects demonstrated so far, however, are relatively weak or only for low temperatures1-3. In this presentation, we report a strong room-temperature BMER effect in topological Dirac semimetal α-Sn thin films4. The epitaxial α-Sn films were grown by magnetron sputtering on single-crystal silicon substrates at room temperature. They showed room-temperature BMER responses that are 106 times larger than previously reported at room temperature,2 and also larger than that previously reported at low temperatures.1,3 These results represent a major advance toward realistic BMER applications. Our experimental data also made possible the first characterization of the three-dimensional, Fermi-level spin texture of topological surface states in α-Sn thin films.

Next from 2022 Joint MMM-INTERMAG

Circular Displacement Current induced Novel Magneto-Optical Effects in All-dielectric Metasurfaces

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Exchange bias switching in an antiferromagnet/ferromagnet bilayer driven by spin–orbit torque

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