United States

The prospect of controlling topologically protected spin textures such as skyrmions lattices in high-density race-track memories offers an alternative to conventional domain wall based spintronic devices (1, 2). A variety of skyrmion spin structures have been observed in non-centrosymmetric compounds and understanding the phase field stability and size of the magnetic texture is of fundamental importance to control the desired functionality in the materials.
The lacunar spinel family with the net formula AB4X8 (A = Al, Ga, Ge; B = V, Mo; X = S, Se) has gained much attention in this respect as several compounds crystallize in the non-centrosymmetric polar rhombohedral structure (R3m, C3v) at low temperature and are magnetically ordered, with skyrmion lattice observed in GaV4S8 (3), GaV4Se8 (4) and GaMo4S8 (5). So far only polycrystalline samples of GaMo4Se8 have been studied (6).
We have performed extensive structural and magnetic characterisation on both single and poly-crystals of GaMo4Se8. Using high resolution powder neutron diffraction we confirms the phase separation below the phase transition from cubic to mixture of rhombohedral and orthorhombic phases and a significant magneto-structural coupling. Among lacunar spinels, the phenomenon of phase separation is unique to GaMo4Se8 and likely to result from the high compressive strain relaxation through the formation of the minority phase (Fig. 1a). Our small angle neutron scattering study on single crystals reveals a cycloid spin structure with a period of 15.4 nm (Fig. 1b) and upon the application of a magnetic field along the polar axis, pattern compatible with a skyrmion lattice is observed (Fig. 1c). The temperature-magnetic field phase field is established and shows that the spin texture is preserved down to the lowest temperature and under a large magnetic field of 1 T.&lt;br&gt;

**References:**&lt;br&gt;
(1) S. S. P. Parkin, M. Hayashi, L. Thomas, Science, 2008, 320, 190.&lt;br&gt;
(2) A. Fert, V. Cros, J. Sampaio, Nature Nanotechnology, 2013, 8, 152.&lt;br&gt;
(3) I. Kezsmarki et al., Nature Materials, 2015, 14, 1116.&lt;br&gt;
(4) S. Bordacs et al., Scientific Reports, 2017, 7, 7584&lt;br&gt;
(5) A. Butykai et al., npj Quantum Materials, 2022, 7, 26&lt;br&gt;
(6) E. C. Schueller et al., Phys. Rev. Materials, 2020, 4, 064402&lt;br&gt;

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MMM 2022

Magneto structural coupling and skyrmions lattice phase field in the lacunar spinel GaMo4Se8

The prospect of controlling topologically protected spin textures such as skyrmions lattices in high-density race-track memories offers an alternative to conventional domain wall based spintronic devices (1, 2). A variety of skyrmion spin structures have been observed in non-centrosymmetric compounds and understanding the phase field stability and size of the magnetic texture is of fundamental importance to control the desired functionality in the materials.
The lacunar spinel family with the net formula AB4X8 (A = Al, Ga, Ge; B = V, Mo; X = S, Se) has gained much attention in this respect as several compounds crystallize in the non-centrosymmetric polar rhombohedral structure (R3m, C3v) at low temperature and are magnetically ordered, with skyrmion lattice observed in GaV4S8 (3), GaV4Se8 (4) and GaMo4S8 (5). So far only polycrystalline samples of GaMo4Se8 have been studied (6).
We have performed extensive structural and magnetic characterisation on both single and poly-crystals of GaMo4Se8. Using high resolution powder neutron diffraction we confirms the phase separation below the phase transition from cubic to mixture of rhombohedral and orthorhombic phases and a significant magneto-structural coupling. Among lacunar spinels, the phenomenon of phase separation is unique to GaMo4Se8 and likely to result from the high compressive strain relaxation through the formation of the minority phase (Fig. 1a). Our small angle neutron scattering study on single crystals reveals a cycloid spin structure with a period of 15.4 nm (Fig. 1b) and upon the application of a magnetic field along the polar axis, pattern compatible with a skyrmion lattice is observed (Fig. 1c). The temperature-magnetic field phase field is established and shows that the spin texture is preserved down to the lowest temperature and under a large magnetic field of 1 T. 

**References:** 
(1) S. S. P. Parkin, M. Hayashi, L. Thomas, Science, 2008, 320, 190. 
(2) A. Fert, V. Cros, J. Sampaio, Nature Nanotechnology, 2013, 8, 152. 
(3) I. Kezsmarki et al., Nature Materials, 2015, 14, 1116. 
(4) S. Bordacs et al., Scientific Reports, 2017, 7, 7584 
(5) A. Butykai et al., npj Quantum Materials, 2022, 7, 26 
(6) E. C. Schueller et al., Phys. Rev. Materials, 2020, 4, 064402 

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technical paper

#### Welcome to the 67th Annual Conference on Magnetism and Magnetic Materials, MMM 2022!

The Conference was held from October 31 to November 4 and offers both in-person and on-demand content.

MMM 2022 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 tutorial, and several special sessions. 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 the present work, the microstructure of a zero-field-annealed off-stoichiometric Ni50Mn45In5 Heusler alloy is investigated by magnetic small-angle neutron scattering (SANS) (1). Thanks to its unique mesoscopic length scale sensitivity, magnetic SANS appears to be a powerful technique to disclose the structural and magnetic microstructure of magnetic materials (2) such as nanocrystalline materials (3,4). The neutron data analysis reveals a significant spin-misalignment scattering, which is mainly related to the formation of annealing-induced ferromagnetic nanoprecipitates in an antiferromagnetic matrix. These particles represent a source of perturbation, which, due to dipolar stray fields, give rise to canted spin moments in the surroundings of the particle-matrix interface. The presence of anticorrelations in the computed magnetic correlation function reflects the spatial perturbation of the magnetization vector around the nanoprecipitates. The magnetic field dependence of the zero-crossing and the minima of the magnetic correlation function are qualitatively explained using the law of approach to ferromagnetic saturation for inhomogeneous spin states. More specifically, at remanence, the nanoprecipitates act magnetically as one superdefect with a correlation length that lies outside of the experimental q-range, whereas near saturation the magnetization distribution follows each individual nanoprecipitate. Analysis of the neutron data yields an estimated size of 30 nm for the spin-canted region and a value of about 75 nm for the magnetic core of the individual nanoprecipitates. The presented neutron data analysis (in Fourier and real-space) is particularly useful to study the nanoscale magnetic inhomogeneities of bulk materials at the mesoscopic length scale. Finally, it demonstrates that unpolarized magnetic SANS might be a practicable alternative to time-consuming and low intensity polarized neutron measurements. 

This research was partly funded by the National Research Fund of Luxembourg (PRIDE MASSENA Grant No. 10935404 and CORE SANS4NCC Grant). 

**References:** 
(1) M. Bersweiler, P. Bender, I. Peral, E. Pratami Sinaga, D. Honecker, D. Alba Venero, I. Titov, and A. Michels, J. Appl. Cryst. 55, in press (2022) 
(2) A. Michels, Magnetic Small-Angle Neutron Scattering: A Probe for Mesoscale Magnetism Analysis (Oxford University Press, Oxford, 2021). 
(3) M. Bersweiler, E. P. Sinaga, I. Peral, N. Adachi, P. Bender, N. J. Steinke, E. P. Gilbert, Y. Todaka, A. Michels, and Y. Oba, Phys. Rev. Mat. 5, 044409 (2021). 
(4) M. Bersweiler, M. P. Adams, I. Peral, J. Kohlbrecher, K. Suzuki, and A. Michels, IUCrJ 9, 65 (2022).

Magnetic nanoprecipitates and interfacial spin disorder in zero field

There is a growing interest in materials exhibiting large spin-orbit torques (SOT) to achieve significant improvements in magnetoresistive random access memory (MRAM) technology [1]. It is well-recognized that materials with SOT ratios much greater than unity are needed to bring energy efficiency in SOT MRAM; however, only a handful of such materials have been identified using conventional theoretical and experimental methodologies. Thus, understanding the physics and materials for large SOT is a topic of ongoing research [1-2].

In this talk, I will discuss a new approach using machine intelligence to quantitatively predict new materials with large SOT ratios. I'll show that a machine can learn special concepts in materials sciences, physics, and engineering by reading the literature. Such a "well-trained" machine can identify patterns hidden within a large body of literature and quantitatively relate materials to the phenomenon of "spin-orbit torque."

We use a word embedding model [3] to train a neural network with a collection of unlabeled abstract text from various scientific journals relevant to our work. The word embedding model represents words in the text corpus into high-dimensional vectors, and the relationship among these vectors exhibits knowledge in magnetism and spintronics. A correlation pattern among various vectors representing materials names and the word "spin-orbit torque" quantitatively project spin Hall conductivity and SOT factor for corresponding materials. The projected numbers for known materials agree with known experimental reports. Such quantitative agreement is non-trivial as the machine does not learn numerical values reported in the literature, but the patterns are obtained based on the context in which the words appeared in the text corpus.

Surprisingly, our machine intelligence-based approach predicted 32 new materials to exhibit SOT, which have not been discussed yet in the context of SOT to our knowledge. Interestingly, 9 of these predicted materials are expected to show a SOT factor much greater than unity, with the largest expected value of 36.4. One of them quantitatively matched our independent experiment on a silicide. 
**References** [1] IEEE Trans. Magnetics 57(7), 1-39 (2021).
[2] Phys. Rev. Applied 15, 054004 (2021).
[3] Nature 571, 95-98 (2019).
 
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Machine intelligence in new materials identification for efficient spin orbit torque (SOT) MRAM.

Spin transfer torque magnetic random access memory (STT-MRAM) shows great advantages for computing-in-memory (CIM) [1][2]. Time-domain (TD) in-MRAM computing can be implemented with unlimited signal accumulation and low power consumption characteristics thanks to its low precision [3]. In this paper, we propose a novel TD-CIM topology that converts bit-line (BL) voltage to time delay.
Fig.1 (a) shows the structure of proposed STT-MRAM for TD-CIM. Fig.1 (b) illustrates the proposed AND/OR/Full-Adder (FA) Boolean logic circuit, with one transistor-one magnetic tunnel junction (1T-1MTJ) bit-cell. RP/RAP (parallel and anti-parallel magneto-resistance) is with data ‘0’/‘1’. During computation mode, word-line (WL) activates two bit-cell within one row. The calculation-line (CL) generates differential VBL according to the state of bit-cell. Current starved inverters (CSI) circuit is used to convert the voltage of BL to time delay [4]. The inverter chains (REF0/REF1) generate delay to represent data ‘0’/1’ for FA logic, which is controlled by signal Cin. Time-to-Digital converter (TDC) converts CSI outputs from time domain to digital domain. The inverter chains generate reference delay for AND/OR/FA logic. CSI outputs sample the reference delay by D-flip-flop (one flip-flop for AND/OR, three flip-flops and one Multiplexer for FA).
The performance is analyzed with a 28-nm CMOS process and a MTJ compact model [5]. Fig.2 (a) demonstrates the simulated 500 runs Monte-Carlo analysis of CSI outputs under different cases. Results show the successfully distinguished CSI accumulation. The power consumption of AND/OR and FA is 7.89-μW and 14.1-μW at nominal 0.9V supply (see Fig. 2(b)). Fig.2 (c) shows the computation accuracy of AND/OR/FA logic in varied tunnel magnetoresistance ratio (TMR) with different data cases. When TMR=200%, 94.2% to 100% computation accuracy can be obtained, whereas the accuracy is deteriorated when TMR equals to 125%. 
**References** [1] M. Wang et al., Nature Communications, vol. 9, p. 671 (2018).
[2] X. Fong et al., IEEE Trans. on Very Large Scale Integration (VLSI) Systems, vol. 22, pp. 384–395 (2014).
[3] P. -C. Wu et al., IEEE International Solid- State Circuits Conference (ISSCC), pp. 1-3 (2022).
[4] Q. -K. Trinh et al., IEEE Trans. on Circuits and Systems I: Regular Papers, vol. 65, no. 10, pp. 3338-3348 (2018).
[5] Y. Wang et al., IEEE Trans. on Electron Devices, vol. 63, pp. 1762-1767 (2016). 

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Time domain Computing for Boolean Logic using STT

Cr1/3NbS2, the first known magnetic soliton system, has abundant magnetic phases like chiral helimagnetic order (HM), chiral conical phase, chiral soliton lattice (CSL), tilted chiral soliton lattice and forced ferromagnetic (FM) due to the competition between Dzyaloshinskii–Moriya exchange, Heisenberg interaction, magnetocrystalline anisotropy and Zeeman energy (1, 2). These rich magnetic textures display attractive properties, such as magnetocaloric effect (3), topological Hall effect and planar Hall effect (4), etc. Especially, magnetic soliton, a real-space topological magnetic structure like skyrmion, owns topological protection properties and quasi-particle nature which makes Cr1/3NbS2 a promising platform for the spintronic devices (5, 6).
Recently, we have studied the transition of various magnetic structures by magnetoresistance (MR) (7), a.c. magnetic susceptibility (7), and Lorentz transmission electron microscopy (L-TEM). As shown in Fig. 1(a), when a magnetic field was applied along the c-axis (H ‖ c - axis) at low temperatures, we found signatures of weak antilocalization which may originate from the strong spin–orbit coupling of Cr1/3NbS2. When the magnetic field was applied along the ab-plane (H ‖ ab - plane), the transition from HM to CSL and FM can be detected by a.c. magnetic susceptibility (Fig. 1(b)). To better understand CSL, we adopted L-TEM measurement. As shown in Fig. 1(c) and (d), a helical period longer than theoretical calculations (~48 nm) and showing opposite chirality due to grain boundary modulation were observed in some regions on the sample. The reason for the difference in period can be the uneven content of Cr intercalation. This may provide an effective way to regulate the helical period, thus facilitating its practical application. 

**References:** 
(1) T. Miyadai, K. Kikuchi, H. Kondo, et al., J. Phys. Soc. Jpn. 52 (4), 1394-1401 (1983). 
(2) Y. Togawa, T. Koyama, K. Takayanagi, et al., Phys. Rev. Lett. 108 (10), 107202 (2012). 
(3) N. J. Ghimire, M. A. McGuire, D. S. Parker, et al., Phys. Rev. B 87 (10), 104403 (2013). 
(4) D. A. Mayoh, J. Bouaziz, A. E. Hall, et al., Phys. Rev. Research 4 (1), 013134 (2022). 
(5) Y. Togawa, T. Koyama, Y. Nishimori, et al., Phys. Rev. B 92 (22), 220412 (2015). 
(6) L. Wang, N. Chepiga, D. K. Ki, et al., Phys. Rev. Lett. 118 (25), 257203 (2017). 
(7) X. Li, Z. Li, H. Li, et al., Appl. Phys. Lett. 120 (11), 112408 (2022). 

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Angular dependent magnetoresistance and magnetic soliton lattice in Cr1/3NbS2

The anomalous Nernst effect (ANE) generates an electric field (EANE) orthogonal to both magnetization and temperature gradient in ferromagnetic materials. In order to realize high-performance ANE-based thermoelectric power generation devices, exploring a material with a large anomalous Nernst coefficient (SANE) is essential. Fe4N is a promising material with relatively large SANE of 2.2 μV/K [1]. In this study, Fe4-xNixN films were fabricated and their ANEs were characterized to reveal the Ni addition effect to Fe4N.
The Fe4-xNixN films were grown on MgAl2O4(MAO)(001) substrates at 450 °C. The structures of the samples were characterized by x-ray diffraction. The Ni/Fe ratio, x, in Fe4-xNixN films was changed in the range of 0 ≤ x ≤ 2.8. The samples were microfabricated into a Hall bar shape, and ANE, the Seebeck effect, and the anomalous Hall effect (AHE) were characterized [2]. The external magnetic field dependence of EANE was measured at different temperature gradient and SANE was estimated. The transverse conductivity (σxy) and the transverse thermoelectric conductivity (αxy) of Fe3NiN was calculated by the first-principles calculation [3].
The Fe4-xNixN films were epitaxially grown on the MAO(001) substrates, but the Fe4-xNixN phase started to decompose into FeNi at about x = 2.3. The relationship between SANE, Seebeck coefficient (SSE) and x in Fe4-xNixN is shown in Fig. 1. The SANE value decreased from 1.7 to 0.6 μV/K and the SSE value increased from -2.3 to 1.2 μV/K with the increase of x. By using the experimental data, αxy was calculated. The result showed that αxy decreased with the increase of x and the change of αxy dominated the change of SANE. In the presentation, the obtained σxy and αxy values will be compared with the calculation results.
This work was supported by the Grants-in-Aid for Scientific Research (S) (Grant No. JP18H05246) and (C) (Grant No. JP21K04859) from JSPS KAKENHI, Collaborative Research Center on Energy Materials, Institute for Materials Research, Tohoku University, and the Cooperative Research Project of the Research Institute of Electric Communication, Tohoku University. 
**References** [1] S. Isogami, K. Takanashi, and M. Mizuguchi, Appl. Phys. Express 10, 073005 (2017).
[2] J. Wang, Y.-C. Lau, W. Zhou, T. Seki, Y. Sakuraba, T. Kubota, K. Ito, and K. Takanashi, Adv. Electron. Mater. 8, 2101380 (2022).
[3] Y. Tsubowa, M. Tsujikawa, and M. Shirai, the 69th JSAP spring meeting 2022, 23a-E205-5 (2022).
 
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Anomalous Nernst effect in epitaxially grown Fe4 xNixN films

Nd-Fe-B based magnet is the more powerful than any other magnets at room temperature. It plays a dominant role in energy efficiency and renewable energy applications due to its high energy density. However, making Nd-Fe-B magnets, especially into small sizes, can be challenging and costly. The part failure rate can be high during machining due to its brittleness. The reproducibility can be poor due to the variance in composition and microstructure inherent to the currently available fabrication methods. And the manufacturing cost is high due to the limited productivity of the batch based processes. Moreover, Nd-Fe-B needs heavy rare earth elements to be functional at higher temperature. These HRE are critical materials. One approach to bypass this HRE criticality issue is to utilize the grain size effect on coercivity, e.g., nanograin size magnet can perform the same as the micron-grain size magnet with 4-6% of Dy. However, making nanograin magnet requires a two-steps process: hot-press for densification and hot-deformation for texture. It is an inherently expensive process. Here, we report a novel Nd-Fe-B fabrication method that is continuous and near-net-shape. The process starts with loading Nd-Fe-B powders into a metal tube, packing the powder to 60% dense, then hot-rolling the powders into full density. We showed that hot rolling at 800°C with 70% thickness reduction can result in nearly full density (93%) anisotropic magnet with high energy product (31.6 MGOe). This novel method allows cost-effective production of near-net-shape Nd-Fe-B magnetic with good and consistent magnetic properties. Moreover, the method allows the making of continuous strip magnet that can be curved to match motor radius, making it possible to maximize the magnetic flux density on rotor circumference, thereby increase motor powder density. 
**References:**

Near net shape fabrication of anisotropic Nd Fe

The synthetic antiferromagnetic (SAF) nanoplatelets (NPs) with perpendicular magnetic anisotropy (PMA) are of particular interest for torque-related applications due to their large anisotropy [1]. However, previous research indicates that the coercivity (Hc) increases significantly for small structures with PMA due to thermally activated-magnetization reversal [2]. As the size of NPs drops, larger field is required, and its distribution increases, to activate the NPs which is undesirable for applications. This raises a question of how the magnetization reversal characteristics of the SAF-PMA system scale with size. In this work, we study the magnetization reversal process of PMA-SAF systems of different sizes and materials (CoB/Pt and CoFeB/Pt). The basic thin-film stack is shown in the insert of Fig 1. PMA-SAF nanoplatelets with different sizes are fabricated through electron beam lithography (EBL) and measured using polar magneto-optic Kerr effect (MOKE) magnetometry. One example of the fabricated nanoplatelets is shown in Fig 1. An increase of Hc and its distribution (indicated by the error bar in Fig 2.) is observed with decreasing size as shown in Fig 2. An overall smaller Hc is observed in CoFeB/Pt system compared to CoB/Pt system which can be attributed to the decrease of anisotropy and the different defect-nucleation distribution of the materials. A model based on a local anisotropy distribution and thermal activation is established to simulate the data [3]. The model can accurately predict the Hc behavior, giving further insights into how the size, materials, and anisotropy affect the underlying reversal process. In this talk, we present the size-depended magnetization reversal process of SAF NPs, discuss the physics based on the simulation, and propose the methods to control the switching distribution. This will pave the way to tune the activating magnetic field of PMA-SAF NPs for applications.

Size dependent Magnetization Reversal Characteristics of Synthetic Antiferromagnetic Nanoplatelets

Fabrication of nanostructures can be categorized into top-down and bottom-up approaches. The top-down approach uses various kinds of lithography, which has
unprecedented accuracy and controllability, yet requires sophisticated equipment and expensive operating costs. On the other hand, the bottom-up approaches are cost-efficient and do not
rely on sophisticated facilities. However, it is determined by self-organization, which lacks strict repeatability and spatial homogeneity over a long distance. Here, we report an
unprecedented electrochemical growth of ordered metallic nanowire arrays from an ultrathin electrolyte layer, which is achieved by solidifying the electrolyte solution below the freezing
temperature. We apply the electric voltage pulses across two straight, parallel electrodes. The thickness of the electrodeposit is instantaneously tunable by the applied electric pulses,
leading to parallel ridges on webbed film without using any template. An array of metallic nanowires with desired separation and width determined by the applied pulses is formed on the
substrate with arbitrary surface patterns by etching away the webbed film thereafter. Unlike conventional nanowires growing along their longitudinal axial direction, here the whole
nanowire simultaneously develops in the direction perpendicular to the wire axis. Besides, the nanowires can be fabricated on a surface with any topography, including silicon grating with
a high–aspect ratio surface pattern. This work[1] demonstrates a previously unrecognized fabrication strategy that bridges the gap of top-down lithography and bottom-up self-organization
in making ordered metallic nanowire arrays over a large area with low cost. 

**References:** 

[1]. F. Chen, Z. Yang, J.-N. Li, F. Jia, F. Wang, D. Zhao, R.-W. Peng, M. Wang, Science Advances., Vol 8, p. eabk0180 (2022)

Formation of magnetic nanowire arrays by cooperative lateral growth

B2-ordered FeRh undergoes a thermally activated first-order phase transition between antiferromagnetic (AF) and ferromagnetic (FM) order upon heating, with a transition temperature between 350 - 380 K [1], making it an ideal candidate for use in a wide range of magnetic storage architectures [2]. The evolution of magnetic domains through the transition has been well-characterized [1-5]. However, behaviours such as the domain nucleation mechanism and subsequent evolution of the magnetic domains along the sample thickness through the phase transition remain unclear [1,3-5]. Here, we present three-dimensional (3D) reconstructions of the magnetic structure through the sample volume at various temperatures through the phase transition, achieved using magnetic laminography [6-7]. Imaging cross-sections through the sample thickness reveal that domains for both types of magnetic order nucleate at the surface and travel into the bulk of the sample with changing temperature. Creating a complex 3D magnetic structure, in which the evolution of the magnetic state along the sample thickness with temperature is non-uniform. We also observe quasi-uniform FM domains at 310 K when heating, in contrast to the expected flux-closed state [1], as well as AF regions where FM domain walls are expected. Both observations can be attributed to the exchange coupling between adjacent AF and FM regions, which plays a key role determining the FM configuration in this material. 

**References:** 

[1] T. P. Almeida et al., Phys. Rev. Materials 4, 034410 (2020). 
[2] R. C. Temple et al., Phys. Rev. Materials 2, 104406 (2018). 
[3] C. Gatel et al., Nat. Comms. 8, 15703 (2017). 
[4] V. Uhlir et al., Nat. Comms. 7, 13113 (2016). 
[5] M. A. de Vries et al., Appl. Phys. Lett. 104, 232407 (2014). 
[6] C. Donnelly et al., Nature Nanotech. 15, 356 (2020) 
[7] K. Witte et al., Nano Lett. 20, 1305 (2020). 

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Three Dimensional Nucleation Kinetics Through the First

The non-volatile spin-orbit torque (SOT)-MRAM is emerging as key enabling low-power technologies, which are expected to spread over large markets from embedded memories to the Internet of Things. Concurrently, the development and performances of devices based on two-dimensional (2D) heterostructures bring ultra-compact multilayers with unprecedented material-engineering capabilities. We first discuss an overview of the current developments and challenges in the field, and then outline the opportunities which can arise by implementing 2D materials into SOT-MRAM technologies (Fig. 1) [1]. We highlight the fundamental properties of atomically smooth interfaces, the reduced material intermixing, the crystal symmetries, and the proximity effects as the key drivers for possibly disruptive improvements for SOT-MRAM at advanced technology nodes.
Among various spin source materials, the 2D van der Waals topological materials such as topological insulators and Weyl semimetals, have attracted considerable attention because of their non-trivial band structures with strong spin-orbit coupling and expected giant SOT. Therefore, topological materials are regarded as promising candidates for future energy-efficient SOT device applications. However, some related physical, material, and device issues still need to be addressed. We review recent advances regarding the charge-to-spin conversion and SOT-driven magnetization switching based on the emerging 2D van der Waals materials, with an emphasis on topological insulators and Weyl semimetals, and present our perspective on practical SOT device applications using this emerging family of quantum van der Waals materials. Specifically, we show our SOT-related experimental advances that have been made in the topological material/ferromagnet heterostructures and devices, involving the giant SOT characterizations, interfacial Edelstein–Rashba effect, Dzyaloshinskii–Moriya interaction (DMI) and interfacial spin transmission. Furthermore, we highlight the highly efficient SOT-driven magnetization switching at room temperature based on 2D van der Waals heterostructures, along with the wafer-scale films prepared with industry-compatible techniques, such as molecular beam epitaxy, magnetron sputtering, and chemical vapor deposition. We anticipate that these studies will deepen the understanding of SOT on 2D van der Waals heterostructures and guide the design and applications of high-performance 2D material-based SOT devices. 

**References:** 

[1] H. Yang et al., “Two-dimensional Materials Prospects for Non-volatile Spintronic Memories” Nature 606, 663-673 (2022) 

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Magneto structural coupling and skyrmions lattice phase field in the lacunar spinel GaMo4Se8

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