United States

Magnetic skyrmions [1] are magnetic quasi-particles with interesting properties for possible future applications in efficient low-power neuromorphic computing concepts. Thermally excited skyrmions in confined geometries, as necessary for device applications, have been shown to arrange based on commensurability effects [2]. Here, we investigate the enhanced dynamics and altered equilibrium state of a system in which the intrinsic skyrmion-skyrmion and skyrmion-boundary interaction compete with spin-orbit torques (SOTs) due applied currents [3]. In particular, we employ particle-based simulations to study four skyrmions in a triangular confinement, while injecting spin-polarized currents between two corners of the structure [4]. To analyze the observed positions of the skyrmion ensemble, we coarse-grain the skyrmion states in the system. In the context of neuromorphic computing, such coarse-graining may be key to identify the most suitable positions for potential readouts as well as to understand the collective skyrmion dynamics in systems with competing interactions at different scales. &lt;br&gt;
**References** &lt;br&gt;
[1] K. Everschor-Sitte et al., Journal of Applied Physics 124, 240901 (2018)&lt;br&gt;
[2] C. Song et al., Adv. Funct. Mater. 31, 2010739 (2021)&lt;br&gt;
[3] K. Raab et al., arxiv:2204.14720 (2022)&lt;br&gt;
[4] T. Winkler et al., in preparation (2022)&lt;br&gt;


MMM 2022

Analyzing collective thermal Skyrmion Dynamics by coarse graining

Magnetic skyrmions [1] are magnetic quasi-particles with interesting properties for possible future applications in efficient low-power neuromorphic computing concepts. Thermally excited skyrmions in confined geometries, as necessary for device applications, have been shown to arrange based on commensurability effects [2]. Here, we investigate the enhanced dynamics and altered equilibrium state of a system in which the intrinsic skyrmion-skyrmion and skyrmion-boundary interaction compete with spin-orbit torques (SOTs) due applied currents [3]. In particular, we employ particle-based simulations to study four skyrmions in a triangular confinement, while injecting spin-polarized currents between two corners of the structure [4]. To analyze the observed positions of the skyrmion ensemble, we coarse-grain the skyrmion states in the system. In the context of neuromorphic computing, such coarse-graining may be key to identify the most suitable positions for potential readouts as well as to understand the collective skyrmion dynamics in systems with competing interactions at different scales. 
**References** 
[1] K. Everschor-Sitte et al., Journal of Applied Physics 124, 240901 (2018) 
[2] C. Song et al., Adv. Funct. Mater. 31, 2010739 (2021) 
[3] K. Raab et al., arxiv:2204.14720 (2022) 
[4] T. Winkler et al., in preparation (2022)

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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Two-phase self-assembled epitaxial multiferroics are formed by co-deposition of BiFeO3(BFO) and CoFe2O3(CFO) on a SrTiO3(STO) substrate,in which the ferroelectric and ferrimagnetic phases are coupled elastically via their vertical interfaces yielding a magnetoelectric response. By templating the self-assembly,the locations of the BFO and CFO can be controlled, increasing the utility of the nanocomposite and simplifies modeling.Here,we make use of ion-matter interaction as a nucleation site to control the growth of two phases,enabling complex geometries including nano-fins and nano-dots, and extending the templating process beyond the use of 001-STO substrates.In order to counter the charging of insulating substrates (STO) during FIB patterning, a Au layer is deposited on the substrate (step2).After FIB patterning,due to ion implantation,the patterned area is expanded locally (step3,red bump) then the substrate is immersed in Au etchant and HCl, leaving patterned nanoscale trenches or dots on the surface (step4). Post annealing at 850C for 10min is used to recover the atomic flatness of the substrate surface (step5).Then a seed layer of CFO is grown on the patterned substrate(step5),followed by BFO and CFO co-deposition (step6) by pulsed laser deposition.At 700C growth temperature,the maximum diffusion length of CFO is around 200 nm defining the upper range of pattern period.The final morphology is controlled by the processing and growth parameters,including the shape, depth and width of the patterned features and the relative ratio of BFO to CFO.A conductive oxide underlayer of SRO or LSMO is used to enable mapping of the ferroelectric response.This approach was used to form fins of alternating CFO and BFO. Figure2 (top) shows the SEM morphology of the BFO/CFO composite (step 6), in which the BFO and CFO are well separated, achieving ferroelectric/ferrimagnetic nano fins with dimensions: width &lt;100nm; length &gt;5um. A cross-section STEM HADDF image of the nano-fins is presented in Figure 2 (bottom): the two phases are clearly defined and exhibit different heights (BFO~30 nm;CFO~15 nm). The magnetic and ferroelectric domain patterns mapped by magnetic force microscopy and piezoresponse force microscopy will be described.

Fin geometry Multiferroic BiFeO3/CoFe2O4 Nanocomposites formed by templated self

Artificial spiking neurons may form an element base for the next generation of neuromorphic computing devices. A promising design of an ultra-fast artificial neuron is based on antiferromagnetic (AFM) spin Hall oscillators driven by a sub-threshold spin current (1). These devices could produce ultra-short voltage spikes in response to a weak external stimulus (1). Fixed synapses can connect these AFM neurons in simple neuromorphic circuits (2). To create more complex neural networks, it is necessary to find learning algorithms that are compatible with AFM neurons.
Here, we study the problem of AFM neural network training for pattern recognition tasks. We use reservoir computing, such that only the weights connected to the output neuron are altered during training. A supervised machine learning algorithm based on the temporal position of the spikes, called spike pattern association neuron (SPAN) (3), is used during training. Synaptic weight adjustments are governed by the difference between spikes' desired and actual temporal position.
An AFM SPAN, trained to recognize a symbol made from a grid, will produce a spike at a target time when the symbol is supplied as input. SPANs, trained to recognize different symbols, are connected to the same inputs. An output layer is created to ensure that only the spike corresponding to the recognized symbol is sent to the output. This output layer consists of a clock neuron spiking at the target time and weakly fixed synapses (Fig. 1). To create an output spike, a SPAN must produce a spike at the target time along with the clock neuron (Fig. 2). Using the SPAN algorithm, we could develop a neural network with AFM artificial neurons capable of performing the pattern recognition tasks. 

**References:** 
(1) R. Khymyn et al. Sci. Rep. 8, 15727 (2018). 
(2) H. Bradley and V. Tyberkevych, Q3-01, MMM, 2020. 
(3) A. Mohemmed, et al., Neurocomputing, vol 107, pp 3-10, 2013. 

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Pattern Recognition Using Antiferromagnetic Artificial Spiking Neurons

The modulation of magnetization dynamics has attracted much attention for not only fundamental research but also application such as data processing and oscillators. It has been discovered that magnetization dynamics can be induced by spin transfer toque (STT) and spin-orbit-torque (SOT). The STT is exerted on the magnetization due to the spin angular momentum transfer, and the SOT occurs at the bilayer comprising a ferromagnetic metal (FM)/nonmagnetic heavy metal (HM).[1] In this study, using the rectifying planar Hall effect (PHE), we investigate the SOT-induced magnetization dynamics in the multilayer consisting of HM/FM/Antiferromagnetic layer (AFM)/FM.
Samples were pattered as the Hall bar device on a SiO2/Si substrate were fabricated via microfabrication technique based on the lift-off method using magnetron sputtering process and
electron beam lithography, as shown in Fig. 1. We fabricated the following system comprising 25-nm-thick N81Fe19/3-nm-thick NiO/5-nm-thick Ni81Fe19/Pt electrode on the substrate. An
external magnetic field was applied at an angle θ from the one axis of the cross-type electrode, which was fixed parallel along to rf + dc electric current, as shown in Fig. 1. To measure the
device, a ground-signal-ground (GSG)-type microwave probe was connected to the electrode. Using a home-made automatic rotating magnetic field application system, we evaluate the
simultaneous magnetoresistance and PHE properties as a function of θ.
Figures 2(a) shows a typical rectifying PHE voltage spectrum obtained at θ = 15°. The magnetic field angle dependences of these rectifying voltages are found to be in good agreement with
the analytical prediction curves of cos2θcosθ. [2] Figure 2(b) displays the resonance frequency as a function of dc current, Idc. The resonance frequency is linearly decreased with increasing Idc. Full width at Half Maximum (FWHM) is also linearly modulated by the application of Idc. These results indicate that the magnetization dynamics can be modulated by the spin current in the multilayer structure. 
**References** [1] X. Qiu, K. Narayanapillai, Y. Wu, P. Deorani, D. –H. Yang, W. –S. Noh, J. H. Park, K. –J. Lee, H. –W. Lee, and H. Yang, Nat. Nanotechnol. 10, 333 (2015).
[2] A. Yamaguchi, A. Hirohata, B. Stadler, Nanomagnetic Materials: Fabrication, Characterization and application, Elsevier, 2021. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/d9942331cf978ddaf832449a4943ee9a.png) 
Figure 1 Schematic circuit of measurement and optical micrograph of system. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/fc6da800f303bffabe95b64428bdd83a.png) 
Figure 2(a) Typical rectifying PHE spectrum obtained at θ=15°. (b) dc current dependence of resonance frequency.

Study on magnetization dynamics modulated by spin orbit

Fe-Ga alloy is an advanced magnetostrictive material for actuators and sensors in terms of combining excellent mechanical and magnetostrictive properties. It is desirable to produce η(<100>//RD) textured Fe-Ga sheets due to the magnetostriction anisotropy with the largest coefficient along <100> direction and the serious eddy current loss in high-frequency use1,2. Current methods of promoting η texture in Fe-Ga alloy mainly include: (I) Micron-sized NbC particles were added to inhibit the normal grain growth, while the abnormal grain growth (AGG) of Goss ({110}<001>) texture was induced by surface energy effect from H2S atmosphere3-5. (II) Micron-sized NbC particles were precipitated, and AGG of Goss texture was induced by the surface energy effect under sulfur atmosphere6,7. (III) Nanometer-sized sulfides were dispersedly precipitated during rolling, and AGG of Goss texture was produced by the degrading pinning effect of inhibitor8-10. However, two-stage cold rolling and intermediate annealing processes are indispensable to regulating microstructure and texture in Fe-Ga alloy sheets. Distinct from the current methods in Fe-Ga alloy, a primary cold rolling method with a large reduction ratio was used in the grain-oriented silicon steel to produce sharp Goss texture with a lower deviation angle11,12. The nanometer-sized inhibitors are precipitated at hot rolling and normalization to induce secondary recrystallization of Goss grains. 
In this paper, sharp Goss texture is successfully produced in Fe-Ga alloy sheet by primary cold rolling with a reduction ratio of ~85%. The nanometer-sized composite inhibitor was precipitated during rolling and annealing to induce secondary recrystallization of Goss texture. Nanometer-sized sulfides and NbC are dispersedly precipitated during hot rolling and normalization as inhibitors for secondary recrystallization. Fine grains textured by strong {111}<112> distributed through sheet thickness in primarily annealed sheets, which can provide a favorable environment for secondary recrystallization. Centimeter-sized Goss grains and large magnetostriction coefficient are obtained in Fe-Ga alloy by conventional primary cold rolling and annealing methods without surface energy effect. 
**References:** 1S.-M. Na and A. B. Flatau, Scripta Mater. Vol. 66, p. 307-310 (2012). 
2J. H. Li, Q. L. Qi, C. Yuan, X. Q. Bao and X. X. Gao, Mater. Trans. Vol. 57, p. 2083-2088 (2016). 
3S. M. Na and A. B. Flatau, J. Mater. Sci. Vol. 49, p. 7697-7706 (2014). 
4S. M. Na, K. M. Atwater and A. B. Flatau, Scripta Mater. Vol. 100, p. 1-4 (2015). 
5S. M. Na and A. B. Flatau, AIP Adv. Vol. 7, p. 056406 (2017). 
6C. Yuan, J. H. Li, W. L. Zhang, X. G. Bao and X. X. Gao, J. Magn. Magn. Mater. Vol. 374, p. 459-462 (2015). 
7C. Yuan, J. H. Li, W. L. Zhang, X. Q. Bao and X. X. Gao, J. Magn. Magn. Mater. Vol. 391, p. 145-150 (2015). 
8Z. H. He, H. B. Hao, Y. H. Sha, W. L. Li, F. Zhang and L. Zuo, J. Magn. Magn. Mater. Vol. 478, p. 109-115 (2019). 
9F. Lei, Y. Sha, Z. He, F. Zhang and L. Zuo, Materials. Vol. 14, p. 3818 (2021). 
10Z. H. He, H. J. Du, Y. H. Sha, W. L. Li, S. H. Chen, X. F. Zhu, F. ZHang, L. J. Chen and L. Zuo, IEEE Trans. Magn. Vol., p. (2022). 
11Z. S. Xia, Y. L. Kang and Q. L. Wang, J. Magn. Magn. Mater. Vol. 320, p. 3229-3233 (2008). 
12S. Mishra and V. Kumar, Mater. Sci. Eng. B. Vol. 32, p. 177-184 (1995).

Sharp Goss Texture and Magnetostriction in Primary Cold Rolled Fe Ga Thin Sheets by Composite Precipitates

Control of the electromagnetic properties of synthetic magnetic structures at gigahertz frequencies is advantageous for the simulation and design of components for high-frequency applications, such as shielding materials in magnetic recording. In such applications, it is desirable to have a high saturation magnetization, low coercivity, high permeability, and near-zero magnetostriction. A typical material is NixFe100-x, where x ~ 80 provides near-zero magnetostriction but relatively low magnetization. Multilayer structures such as Ni80Fe20/Ni20Fe80 may benefit some static properties such as magnetization while retaining low magnetostriction [1] and therefore will extend the parameter space. We present a systematic study of the ferromagnetic resonance (FMR) of sputter-deposited thin-film NiFe bilayers of the form NixFe100-x/NiyFe100-y using VNA-FMR [2], vibrating sample magnetometry and x-ray diffraction, with the purpose of investigating the relation between dynamic magnetic and microstructure properties of such structures. Of particular interest are layer combinations involving both fcc and bcc crystal structures since studies on single films of NixFe100-x have shown dramatically increased damping of the FMR when Ni content is reduced across the transition from fcc to bcc near x ~ 40, figure 1. A result that was not to be expected from the single-layer studies was that the FMR response of certain bilayers was strong even when the bcc NiFe layer was the dominant layer in the structure, figure 2. The possibility of incorporating the best properties of both layers in this way has significance for achieving an optimized material design. 
**References:** [1] C.B. Hill. “Manipulation and Magnetostriction of NiFe Films for Advanced Reader Shielding Application”, PhD Thesis, Queen’s University Belfast (2013) 
[2] Y. Ding, T. J. Klemmer and T. M. Crawford, J. Appl. Phys. Vol. 96, p.2969 (2004) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/b5852ff51f9bfd694f13268e2842e1e2.png) 
Fig. 1: FMR spectra of 100nm NixFe100-x single layer thin films with x varying from 10 to 50 across the fcc/bcc phase transition boundary. Note that all measurements were performed at an applied field H=253Oe. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/b76d6eeb3f1aa18965a3c31b5d4041ce.png) 
Fig. 2: FMR spectra of Ni80Fe20(60-t nm) / Ni20Fe80(t nm) thin films with varying bcc layer thickness, t. Note that all measurements were performed at an applied field of 253Oe. Magnetization trend and structure schematic is inset.

Towards Optimised Tunable NiFe Multilayers for High Frequency Applications

Ultrathin asymmetrically sandwiched ferromagnetic films support fast moving chiral domain walls (DWs) and skyrmions [1,2]. This paves the way to the realization of prospective racetrack memory concept, the performance of which is determined by the static and dynamic micromagnetic parameters [3]. The necessity of having strong Dzyaloshinskii-Moriya interactions (DMI) and perpendicular magnetic anisotropy requires the utilization of ultrathin (~1 nm) layers, which compromize structural quality and substantially enhance the damping for non-collinear magnetic textures. 
Here, we present the experimental and theoretical analysis of ultrathin Co films with asymmetric interfaces //CrOx/Co/Pt and estimation of their micromagnetic parameters based on the analysis of the temperature dependence of magnetization as well as imaging of the DW morphology in stripes. We show that in the frame of magnon thermodynamics the best fit to the magnetometry data up to room temperature is obtained within a quasi-2D model, accounting for the lowest transversal magnons [4]. The developed approach provides access to the exchange constant in asymmetric stacks, which is found to be about 1 order of magnitude smaller compared to the bulk Co. The experimentally observed tilt of magnetic DWs in stripes in statics can be explained based on two models: (I) A unidirectional tilt could appear in equilibrium as a result of the competition between the DMI and additional in-plane easy-axis anisotropy, which breaks the symmetry of the magnetic texture and introduce tilts [5]. (II) A static DW tilt could appear due to the spatial variation of magnetic parameters, which introduce pinning centers for moving tilted DWs driven by magnetic field and can fix them at remanence [6]. We found that the second model is in line with the experimental observations and allows to determine self-consistently the DW damping parameter and DMI constant for the particular layer stack. The DW damping is found to be about 0.1 and explained by the enhanced longitudinal relaxation mechanism. The latter is shown to be much stronger than the standard transversal relaxation and can be even stronger than the spin pumping contribution for the case of ultrathin magnetic films [7]. 
**References:** [1] N. Nagaosa and Y. Tokura, “Topological properties and dynamics of magnetic skyrmions”, Nat. Nanotechnol. 8, 899 (2013). 
[2] A. Fert, N. Reyren, and V. Cros, “Magnetic skyrmions: advances in physics and potential applications”, Nat. Rev. Mater. 2, 17031 (2017). 
[3] C. Garg, S.-H. Yang, T. Phung, A. Pushp and S. S. P. Parkin, “Dramatic influence of curvature of nanowire on chiral domain wall velocity”, Sci. Adv. 3, e1602804 (2017). 
[4] I. A. Yastremsky, O. M. Volkov, M. Kopte, T. Kosub, S. Stienen, K. Lenz, J. Lindner, J. Fassbender, B. A. Ivanov and D. Makarov, “Thermodynamics and Exchange Stiffness of Asymmetrically Sandwiched Ultrathin Ferromagnetic Films with Perpendicular Anisotropy”, Phys. Rev. Appl. 12, 064038 (2019). 
[5] O. V. Pylypovskyi, V. P. Kravchuk, O. M. Volkov, J. Fassbender, D. D. Sheka and D. Makarov, “Unidirectional tilt of domain walls in equilibrium in biaxial stripes with Dzyaloshinskii–Moriya interaction”, J. Phys. D: Appl. Phys. 53, 395003 (2020). 
[6] O. M. Volkov, F. Kronast, C. Abert, E. Se. Oliveros Mata, T. Kosub, P. Makushko, D. Erb, O. V. Pylypovskyi, M.-A. Mawass, D. Sheka, S. Zhou, J. Fassbender and D. Makarov, “Domain-Wall Damping in Ultrathin Nanostripes with Dzyaloshinskii-Moriya Interaction”, Phys. Rev. Appl. 15, 034038 (2021). 
[7] I. A. Yastremsky, J. Fassbender, B. A. Ivanov, and D. Makarov, “Enhanced Longitudinal Relaxation of Magnetic Solitons in Ultrathin Films”, Phys. Rev. Appl. 17, L061002 (2022).

Quantification of Micromagnetic Parameters in Ultrathin Asymmetrically Sandwiched Magnetic Thin Films

The magnetic refrigeration, based on the magnetocaloric effect(MCE), is an efficient and environment-friendly solid-state cooling technology [1].Rare earth free nanoparticles and heterostructure systems can be used as an alternative to traditional bulk magnetocaloric materials(MCMs) due to control over the entropy change across the magnetic phase transition that can be maneuvered by varying particle size [2].The present study is focused on the MCE properties of Fe nanoparticles embedded in titanium nitride thin film grown on sapphire substrates using pulsed laser deposition.To study the effect of thermal hysteresis, M-T measurements were carried out in three different modes: zero-field cooled(ZFC),field cooled warming (FCW),and field cooled cooling (FCC).As seen in Fig.1, there is no separation between FCC and FCW curves, but there is a pronounced bifurcation between ZFC and FCW curves at 0.025T, 0.05T, and 0.1T.The absence of any separation between FCW and FCC curves suggests a negligible thermal hysteresis loss above blocking temperature. Quantitative information about the isothermal entropy change (Î”S) and the MCE in the Fe-TiN heterostructure system has been obtained by applying Maxwell relation to the magnetization versus temperature data at various fields.The Fe-TiN system shows a sizable isothermal entropy change (Î”S) over a broad range of temperatures (TB&lt;T&lt;300 K) as seen in Fig.2. With the dynamic magnetic hysteresis absent above the blocking temperature, the negative Î”S as high as 4.18Ã—103 J/Km3 is obtained for 3T at 300 K.The refrigeration capacity(RC) at various applied fields have also been evaluated with the realization of a maximum value of 7.4Ã—105 J/m3 at 3 T. With a combination of a broad range of usable Î”S and easy accessibility, the Fe-TiN material system can give us insight for the fabrication and design of novel MCMs with improved refrigeration efficiency needed for next-generation solid-state cooling.

Magnetic and Magnetocaloric Properties of Iron Nanoparticles Embedded Titanium Nitride Thin Film Matrix

Rare-earth (R) compounds of the form RCrTiO5, crystallizing in an orthorhombic structure with space group Pbam, belongs to the multiferroic family that are currently of interest as these can find applications in spintronic and memory devices. Recently, there were limited reports on the RCrTiO5 materials in their bulk form [1-4]. Das et al. [1] investigated the magnetic ground state of the DyCrTiO5 in a bulk sample through dc magnetization and showed the ferromagnetic nature of the material, as well as spin reorientation at low temperatures because of the interaction between Dy3+ and Cr3+. However, there are currently limited reports in the literature on DyCrTiO5 in its nano form, probing dimensionality effects [5]. Therefore, the present work highlights the magnetic transitions of the DyCrTiO5 nanoparticles and their magnetocaloric behavior. The nanoparticles were synthesized through a cost-effective sol-gel technique and subsequently calcined at 800 C. The orthorhombic structure of the material with lattice parameters, a, b, c of 7.3158(7), 8.6431(9), 5.8390(8) Ã…, respectively, is established from the x-ray diffraction (XRD) pattern. The particle size obtained from transmission electron microscopy (TEM) is 43 Â± 2 nm. The NÃ©el temperature has obtained from the magnetization as a function of temperature (M(T)) measurement, as TN = 146 Â± 1 K (Fig. 1). In addition, spin reorientation is observed at a temperature, TSR = 51 Â± 1 K (Fig. 1). A loop appeared in field-cool-cooling (FCC) and field-cool-warming (FCW) M(T) curves at low temperatures, not previously observed for the sample in bulk form, indicating a ferromagnetic-antiferromagnetic (FM-AFM) transition [5]. The FM nature, with exchange bias effect, is further confirmed for the sample from field-dependent magnetization measurements. Additionally, a change in isothermal magnetic entropy (-Î”Sm) of 6.6 Â± 0.3 J.kg-1.K-1 is found at a 6 T difference in the field. The observed magnetic behavior of DyCrTiO5 nanoparticles is discussed in terms of the competing interactions of Cr3+ and Dy3+, respectively.

Magnetic phase transitions and magnetocaloric effect in DyCrTiO5 nanoparticles

In this talk, we will discuss the fabrication of ultra-thin vdWs magnet CrTe2 layers and prototypical spintronic devices, which can be tuned by the electrical field, the magnetic field as well as the substrate. We will review recent experimental progress on CrTe2 including (1) robust 2D ferromagnetism in CrTe2 ultrathin films; (2) topological Hall effects in CrTe2/Bi2Te3 heterostructures; and (3) giant magnetoresistance in chemically doped CrTe2 compound.
References (1) Xiaoqian Zhang, Qiangsheng Lu, Wenqing Liu, Wei Niu, Jiabao Sun, Jacob Cook, Mitchel Vaninger, Paul. F. Miceli, David J. Singh, Shang-Wei Lian, Tay-Rong Chang, Xiaoqing He, Jun Du, Liang He, Rong Zhang, Guang Bian, and Yongbing Xu, "Room-temperature intrinsic ferromagnetism in epitaxial CrTe2 ultrathin films", Nature Communications 12:2492 (2021) 

(2) Xiaoqian Zhang, Siddhesh C Ambhire, Qiangsheng Lu, Wei Niu, Jacob Cook, Jidong Samuel Jiang, Deshun Hong, Laith Alahmed, Liang He, Rong Zhang, Yongbing Xu, Steven S-L Zhang, Peng Li, and Guang Bian, "Giant Topological Hall Effect in van der Waals Heterostructures of CrTe2/Bi2Te3," ACS Nano 15, 15710 (2021) 

(3) Xiaoqian Zhang, Wenqing Liu, Wei Niu, Qiangsheng Lu, Wei Wang, Ali Sarikhani, Chunhui Zhu, Jiabao Sun, Mitchel Vaninger, Paul. F. Miceli, Jianqi Li, David J. Singh, Yew San Hor, Liang He, Rong Zhang, Guang Bian, Dapeng Yu, and Yongbing Xu, "Self-Intercalation Tunable Interlayer Exchange Coupling in a Synthetic Van der Waals Antiferromagnet," Advanced Functional Materials, 202202977 (2022) 

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Emergent phenomena and device applications of 2D magnetic heterostructures

Spin-transfer-torque switchable magnetic tunnel junction is an enabling device that brought the recent technology and product offerings of spin-transfer-torque magnetic random access memory. I’ll review some current understanding, with an emphasis on device and materials physics underpinning switching performance in memory technologies, and the likely requirements for future generations in related applications space[1-3]. Key considerations include switching current, speed, and data-retention trade-off, and the need to seek more efficient charge-to-spin conversion mechanisms. Finally, I will touch on some nascent applications ideas involving the magnetic tunnel junction as a compact and power-efficient CMOS backend-compatible entropy source for probabilistic computing, and the device physics related to sub-nanosecond stochastic bit-stream generation[4], with potential applications in computing schemes beyond von Neumann architecture. 
**References** 
1. Jonathan Z Sun, “Spin-transfer torque switched magnetic tunnel junction for memory technologies”, J. Magn. Magn. Mater. https://doi.org/10.1016/j.jmmm.2022.169479 (2022). 
2. Christopher Safranski, Jonathan Z. Sun, and Andrew D. Kent, “A perspective on electrical generation of spin current for magnetic random-access memories”, Appl. Phys. Lett. Perspectives, Appl. Phys. Lett. 120, 160502 (2022). 
3. G. Hu, G. Lauer, J. Z. Sun, P. Hashemi, C. Safranski, S. L. Brown, L. Buzi, E. R. J. Edwards, C. P. D’ Emic, E. Galligan, M. G. Gottwald, O. Gunawan, H. Jung, J. Kim, K. Latzko, J. J. Nowak, P. L. Trouilloud, S. Zare, and D. C. Worledge, “2X reduction of STT-MRAM switching current using double spin-torque magnetic tunnel junction”, 2021 IEEE Intl. Elect. Dev. Meeting (IEDM), 2.5.1, (2021). 
4. Christopher Safranski, Jan Kaiser, Philip Trouilloud, Pouya Hashemi, Guohan Hu, and Jonathan Z. Sun, “Demonstration of nanosecond operation in stochastic magnetic tunnel junctions”, Nano Letters 21, 2040 (2021).

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