United States

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, &quot;Room-temperature intrinsic ferromagnetism in epitaxial CrTe2 ultrathin films&quot;, Nature Communications 12:2492 (2021) &lt;br&gt;

(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, &quot;Giant Topological Hall Effect in van der Waals Heterostructures of CrTe2/Bi2Te3,&quot; ACS Nano 15, 15710 (2021)&lt;br&gt;

(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, &quot;Self-Intercalation Tunable Interlayer Exchange Coupling in a Synthetic Van der Waals Antiferromagnet,&quot; Advanced Functional Materials, 202202977 (2022)&lt;br&gt;

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MMM 2022

Emergent phenomena and device applications of 2D magnetic heterostructures

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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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

Magnetoelectric materials present a unique opportunity for electric field-controlled magnetism. Even though strain-mediated multiferroic heterostructures have shown unprecedented increase in magnetoelectric coupling compared to single-phase materials, further improvements must be made before ultra-low power memory, logic, magnetic sensors, and wide spectrum antennas can be realized. Previously, we demonstrated strain control and converse magnetoelectric coupling in Fe0.5Co0.5/Ag multilayers on (011) Pb(In1/2Nb1/2)O3â€“Pb(Mg1/3Nb2/3)O3â€“PbTiO3 piezoelectric crystals [1]. In this presentation, we will reveal how magnetoelectric coupling can be enhanced by simultaneously exploiting multiple strain engineering approaches by both applying strain during measurement, as well as growing the films with the substrates under compressive stress [2]. When both grown and measured under strain, these heterostructures exhibit an effective converse magnetoelectric coefficient in the order of 10â€“5 s mâ€“1: the highest directly measured, non-resonant value to-date. This response occurred at room temperature and at low electric fields (&lt;2 kV cmâ€“1). This large effect is enabled by magnetization reorientation caused by changing the magnetic anisotropy with strain from the substrate and the use of multilayered magnetic materials to minimize the internal stress from deposition. Additionally, the coercive field dependence of the magnetoelectric response under strain suggests contributions from domain-mediated magnetization switching modified by voltage-induced magnetoelastic anisotropy. This work will highlight how multicomponent strain engineering enables enhanced magnetoelectric coupling in heterostructures and provides an approach to realize energy-efficient magnetoelectric applications.

Large Converse Magnetoelectric Effect in Strain Engineered Multiferroic Heterostructures

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. 

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Figure 1 Schematic circuit of measurement and optical micrograph of system. 

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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

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

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

â€œTheranosticsâ€ by magnetic nanofluid hyperthermia (MNFH) combined with T2-weighted MR contrast imaging (MRI) using superparamagnetic nanoparticles (SPNPs) has been drawn a huge attraction in nanomedicine [1,2]. However, insufficient AC heating power at the biologically safe range of AC magnetic field (HAC) (Happl &lt; 190 Oe, fappl &lt; 120 kHz) and unsatisfactorily low r2-relaxivity keep SPNPs challenging for cancer theranostics agent applications [3,4]. In this work, innovatively designed and developed AC and DC magnetic softness enhanced dual-doped (Ni0.6Zn0.4)-Î³Fe2O3 (MSEÎ³-IO) SPNPs with significantly enhanced both intrinsic loss power (ILP, ~ 4.0 nH m2 kg-1) at the HapplÃ—fappl =1.23Ã—109 A m-1 s-1 and r2-relaxivity (r2 = 660.4 mM-1 s-1) are reported. The significantly enhanced ILP, and r2-relaxivity of dual-doped MSEÎ³-IO SPNPs were primarily attributed to the distinctly enhanced AC magnetic softness directly related to the HAC absorption and fappl resonance efficiency, and the DC magnetic softness dominantly controlled by the occupation and spatial distribution of Ni2+ in Oh vacancies sites, and Zn2+ cations in Td sites of Î³-Fe2O3, respectively. The biocompatibility and bioavailability experimentally evaluated by in-vitro and in-vivo studies demonstrated that the dual-doped MSEÎ³-IO SPNPs can be a promising candidate for highly efficient cancer theranostics agent for future nanomedicine.

AC and DC Magnetic Softness Enhanced Dual doped γ

Skyrmionsâ€”topologically protected vortex-like spin structuresâ€”have been proposed as the new information carriers in racetrack memory devices [1]. In order to realise such devices a small size, high speed of propagation, and minimal deflection angle are required. Modelling has shown that synthetic antiferromagnets (SAFs) present the ideal materials system to realise these aims [2]. However, their magnetic compensation makes observation of skyrmions difficult and indeed this was only recently achieved [3]. There is thus significantly more to understand about the behaviour of synthetic antiferromagnets and the skyrmions therein. Here we present a comprehensive magnetic force microscopy (MFM) and XMCD-PEEM study of a SAF multilayer composed of 20 magnetic layers alternating between CoB and CoFeB each coupled antiferromagnetically with a Ru spacer layer to the one above and below. PEEM results show that in the SAF phase the sample is spontaneously single-domain, and when exposed to a complicated field protocol, large defect-pinned domains can be stabilized. As shown in the hysteresis loop presented in Fig. 1 the SAF undergoes a phase transition between the compensated antiferromagnetic state and its field-polarised ferromagnetic state as a field is applied. MFM shows that in our samples this is as a result of defect-driven bubble nucleation where FM ordered regions nucleate and then expand to cover the entire film. Once the FM regions exceed a critical size they collapse into a skyrmion/stripe domain pattern and so retain a net zero magnetisation. At a narrow range of fields, e.g. as shown in Fig. 2 we observe a phase coexistence between the compensated AF state and the net-zero magnetisation FM state. As the magnetic field is increased we go on to observe isolated skyrmions at fields below saturation as expected in a FM system. These results give perspective on the ferromagnetic nature of skyrmions observed in systems at fields just below saturation and can help to inform the observation of true antiferromagnetic skyrmions.

Phase Coexistence and Transitions between Anti and Ferromagnetic States in a Synthetic Antiferromagnet

Research interest in rare-earth lean SmFe12-based compounds has been revived due to their excellent intrinsic hard magnetic properties making them potential for new permanent magnet materials that are not dependent on scarce elements such as Dy [1,2]. In order to realize these materials for practical applications, the main challenge is development of anisotropic SmFe12-based sintered magnet with a large coercivity and high remanent magnetization. 
We carried out machine-learning on a dataset extracted from literature on Sm(Fe,X)12-based alloys to understand the most influential parameters for coercivity. It was found addition of V to the alloy composition is the most influential to coercivity [3]. The prediction from machine learning was experimentally validated by developing SmFe11Ti and SmFe10TiV melt-spun ribbons where coercivity increased from 0.5 T to 1.1 T upon addition of V. Detailed microstructure characterizations revealed enhanced coercivity is originated from formation of Sm-rich intergranular phase enveloping SmFe12-based grains. The formation of Sm-rich intergranular phase acts as pinning cites against magnetic domain wall propagation resulting in an enhanced coercivity in the V-containing magnet. Motivated by this study, we have developed anisotropic Sm(Fe,Ti,V)12-based sintered magnet via conventional powder processing including the development of jet-milled powders, preparation of green compact, and liquid sintering process [4,5]. The sintered magnets showed coercivity of μ0Hc=0.6-1.0 T and remanent magnetization of μ0Mr = 0.6-0.8 T depending on Ti content (Fig. 1). Detailed multi-scale microstructure characterizations showed the origin of realizing a coercivity of above 0.6 T is the formation of Sm-rich intergranular phase [4,5]. However, {101} twins were also observed in the microstructure of the magnets as shown in Fig. 2 (a). The origin of the twins is induced stress in the powders during the jet-milling process. MOKE observations showed that the magnetization reversal can start from twinned grains which can be detrimental for coercivity (Fig. 2). However, micromagnetic simulations showed that the existence of intergranular phase isolating individual grains can overcome the detrimental effect of twins to coercivity by preventing the propagation of reversed domains to the neighboring grains and hence resulting in a large coercivity. Based on our detailed microstructure investigations and micromagnetic simulations, we will discuss how an optimum microstructure can be realized in the anisotropic SmFe12-based magnets which results in a large μ0Hc and μ0Mr. 
**References:** [1] K. Ohashi, Y. Tawara, R. Osugi, M. Shimao, J. Appl. Phys. 64 (1988) 5714-5716. 
[2] P. Tozman, H. Sepehri-Amin, Y.K. Takahashi, S. Hirosawa, K. Hono, Acta Mater. 153 (2018) 354. 
[3] Xin Tang, J Li, AK Srinithi, H Sepehri-Amin, T Ohkubo, K Hono, Scripta Mater. 200 (2021) 113925. 
[4] J.S. Zhang, Xin Tang, H. Sepehri-Amin, A.K. Srinithi, T. Ohkubo, K. Hono, Acta Mater. 217 (2021) 117161. 
[5] J.S. Zhang, Xin Tang, A. Bolyachkin, A.K. Srinithi, T. Ohkubo, H. Sepehri-Amin, K. Hono, Submitted. 

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Development of rare earth lean SmFe12

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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