In this talk, we first report the roadmap and development of advanced perpendicular magnetic tunnel junctions based on low-damping magnetic materials with crystalline anisotropy that can be scaled down to sub-3-nm diameter with 10 years’ retention time [1]. Then, we will present the perpendicular magnetic tunnel junctions (p-MTJs) switched utilizing bipolar electric fields. Traditional voltage-controlled magnetic anisotropy only linearly lowers the energy barrier of ferromagnetic layer via electric field effect and efficiently switches p-MTJs only with a unipolar behavior. Here we propose and demonstrate a bipolar electric field effect switching of 100-nm p-MTJs through voltage-controlled exchange coupling (VCEC) [2]. The switching current density, ~1.1×105 A/cm2, is one order of magnitude lower than that of the best-reported spin-transfer torque devices. Theoretical results suggest that electric field induces a ferromagnetic-antiferromagnetic exchange coupling transition and generates a field-like interlayer exchange coupling torque, which cause the bidirectional magnetization switching. We will further report our recent results to switch the p-MTJs using the interplay of SOT and VCEC, which lowers the VCEC switching current density to ~5×103 A/cm2[3]. These results could eliminate the major obstacle in the development of spin memory devices beyond their embedded applications. This technology can be used directly for the future spin-orbit-torque (SOT) MRAM [3] and spin logic devices [4]. 
**References** [1] D. Zhang, et al, Phys. Rev. Applied, (2018) vol. 9, 044028 
[2] D. Zhang, et al, Nano Letters (2022), doi.org/10.1021/acs.nanolett.1c03395 
[3] B. Zink, et al, Advanced Electronic Materials, (2022), DOI: 10.1002/aelm.202200382 
[4] M. Mankalale, et al, IEEE Journal on Exploratory Solid-State Computational Devices and Circuits, 3 (2017) 27-36; 10.1109/JXCDC.2017.2690629 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/92d7d6f805a33207236fcb11b73bca84.png)

Perpendicular Magnetic Tunnel Junctions with Crystalline Anisotropy and Energy efficient Switching of Synthetic Antiferromagnet pMTJs by voltage

The unidirectional spin Hall magnetoresistance (USMR) is initially discovered in ferromagnetic (FM) and normal metal (NM) structures[1] and magnetic semiconductor structures[2]. It is a phenomenon observed in bilayer structures and is related to interfacial spin generation and scattering processes at the interface. The similar unidirectional spin Hall and Rashba-Edelstein magnetoresistance (USRMR) is observed in FM-topological insulator (TI) bilayers being much larger than that in FM-NM bilayers in bilayer structures[3]. They are of particular interest due to its potential of 180-degree sensitive electrical readout of magnetization in bilayer structures for spin-orbit torque switching devices.
Here, we report large unidirectional spin Hall and Rashba−Edelstein magnetoresistance in a new material family - magnetic insulator (MI)/TI Y3Fe5O12 (YIG)/Bi2Se3 bilayers. Such heterostructures exhibit a USRMR that is about an order of magnitude larger than the highest values reported in all-metal Ta/Co bilayers[1]. The polarized neutron reflectometry (PNR) reveals a unique temperature-dependent magnetic intermediary layer at the MI-substrate interface and a proximity layer at the MI-TI interface. These PNR findings echo the magnetoresistance results in a comprehensive physics picture. Finally, we demonstrate a prototype memory device based on a MI/TI bilayer, using USRMR for electrical read out of current-induced magnetization switching aided by a small Oersted field[4].
 
**References** [1] C. O. Avci, K. Garello, A. Ghosh et al., Nat. Phys., vol. 11, no. 7, p. 570–575 (2015)
[2] K. Olejník, V. Novák, J. Wunderlich et al., Phys. Rev. B - Condens. Matter Mater. Phys., vol. 91, no. 18, p. 180402 (2015)
[3] Y. Lv et al., Nat. Commun., vol. 9, no. 1, p. 111 (2018)
[4] Y. Lv et al., Appl. Phys. Rev., vol. 9, no. 1, p. 011406, (2022) 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/1d133d85eb2273c2dd6a3ef286e8d822.png)

Large unidirectional spin Hall and Rashba−Edelstein magnetoresistance in topological insulator/magnetic insulator heterostructures

Magnetic random access memory (MRAM) is a promising candidate for beyond-CMOS memory and logic technologies and has been developed for commercial purposes in recent years (1). The key building block of commercial MRAM is magnetic tunnel junction (MTJ), which is operated through either spin transfer torque (STT) or spin-orbit torque (SOT). STT-based MRAM benefits from higher cell density but suffers from reliability and energy-efficiency due to the current flow through the MTJ whereas SOT-based MRAM has superior reliability, endurance, and faster switching times (2). For realizing the ultralow switching current density and ultrafast switching MRAM cell, two or more driving forces are normally employed to switch MTJs. One acts as the principal switching mechanism and the other serves to assist in switching. For example, ultrafast switching speed of ~ 0.27 ns has been reported in SOT switching of perpendicular MTJs (p-MTJs) assisted with STT and voltage-controlled magnetic anisotropy (VCMA), however, the key challenge is still large switching current densities (Jc) ~ 2.0×108 A/cm2 for SOT and ~ 2.3×106 A/cm2 for STT (3).
Voltage controlled exchange coupling (VCEC) occurs in perpendicular MTJs (p-MTJs) with synthetic antiferromagnetic (SAF) free layers and can realize bidirectional switching at switching current densities as low as 1 x 105 A/cm2 (4). In this work, we designed and fabricated the p-MTJ stacks with SAF free layers on bi-layered spin Hall channels (Ta/Pd). The p-MTJ stacks were patterned into 150-nm pillars, and MTJ devices are switched through combination of SOT and VCEC effects, as illustrated in Fig. 1(a). Bidirectional switching of p-MTJs were obtained with current densities as low as 3×103 A/cm2 for VCEC and 6.8×107 A/cm2 for SOT, as shown in Fig. 1(b), where the VCEC switching current density is two orders of magnitude lower than the reported value for VCEC-only switching [4]. Furthermore, by studying the contribution of SOT and VCEC for MTJ switching, it is found that SOT plays a crucial role for ultralow-energy VCEC bidirectional magnetization switching. 

**References:** 
(1) J.-P. Wang et al, DAC '17: Proceedings of the 54th Annual Design Automation Conference 16, pp. 1-6 (2017). 
(2) Y. C. Liao et al, IEEE J. Explor. Solid-State Computat. 6, pp. 9-17 (2020). 
(3) E. Grimaldi et al, Nat. Nanotechnol. 15, pp. 111-117 (2020). 
(4) D. Zhang et al, Nano Lett., 22, pp. 622-629 (2022). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/cc395ac5760d53440cf052a95d03652a.png)

Ultra low current density switching via voltage

Unidirectional spin Hall magnetoresistance (USMR) is a magnetoresistance effect with potential applications to read two-terminal spin-orbit-torque (SOT) devices directly. In this work, we observed a large USMR value (up to 0.710-11 per A/cm2, 50% larger than reported values from heavy metals) in sputtered amorphous PtSn4/CoFeB bilayers. Ta/CoFeB bilayers with interfacial MgO insertion layers are deposited as control samples. The control experiments show that increasing the interfacial resistance can increase the USMR value, which is the case in PtSn4/CoFeB bilayers. The observation of a large USMR value in an amorphous spin-orbit-torque material has provided an alternative pathway for USMR application in two-terminal SOT devices. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/9b54366f807d7bc80e90d1bd60fd91f2.png)

Observation of unidirectional spin Hall magnetoresistance in amorphous PtSn4/CoFeB bilayers

Application of electric fields (E-fields) on perpendicular magnetic tunnel junctions (p-MTJs) is a promising solution for improving energy efficiency in spintronics based memory and logic systems [1]. Many studies on E-field effects on p-MTJs have focused on voltage-controlled magnetic anisotropy (VCMA) of the p-MTJs free layer to reduce the energy required for p-MTJs to switch magnetization states [2]. In this approach, VCMA temporarily decreases the energy barrier separating the two magnetization states and bidirectional switching is achieved using either an external magnetic field or a spin-polarized current. Another approach is to utilize voltage controlled exchange coupling (VCEC) between two ferromagnetic layers in synthetic antiferromagnetic (SAF) structures. Recently, bidirectional switching through VCEC has been demonstrated on p-MTJs with bottom dual-SAF free layers [3]. Benchmarking on MRAM technologies has shown VCEC-MRAM to have much lower energy dissipation than spin-orbit torque (SOT) MRAM [4]. However, SOT-MRAM has faster write speeds since SOT allows for ultra-fast (≤ 400ps) switching [5]. In this work, we explore the potential for SOT-assisted VCEC switching on p-MTJs with bottom dual-SAF free layers fabricated on bilayer spin hall channels. Fig. 1 shows that the SOT current can tune the coercivity of the p-MTJ, which illustrates that SOT can assist in VCEC switching. Fig. 2 shows that a voltage applied to the MTJ causes either a positive or negative shift in its stray field (center of the field switching curve), which indicates that voltage influences interlayer exchange coupling in the SAF free layer, thus demonstrating VCEC. Since the coercivity of the p-MTJs can be tuned with both VCEC and SOT, dual-biasing of SOT+VCEC can possibly generate stochastic signals for probabilistic-bits. By utilizing the effects of both VCEC and SOT, we introduce a potential solution for low-energy and ultra-fast MRAM technology as well as more novel computing paradigms such as probabilistic spin logic.

![](https://assets.underline.io/uploads/markdown_image/1/image/c46c24b4bba3f3242ec62765e893ac77.jpg)

Fig. 1. Anomalous hall resistance versus field measurements at SOT currents ranging from 1mA to 2.25mA.

![](https://assets.underline.io/uploads/markdown_image/1/image/98c15c49ed5dd8b81e43a340598f2316.jpg)

Fig. 2. Tunneling magneto-resistance (TMR) vs. field measurements at VCEC voltages of +1.1V and -1.1V.

Spin-orbit torque assisted switching with voltage controlled exchange coupling

The recently proposed probabilistic spin logic (PSL) offers promising solutions to novel computing applications[1], including some that have previously been covered by quantum computing. The PSL’s basic element is probabilistic bit (p-bit). A p-bit outputs random signals continuously while the mean of the output signal is input-dependent. When multiple p-bits are coupled through a network, a PSL is built. So far, several task implementations of PSL, including invertible logic gate, have been simulated numerically. Here, we report an experimental demonstration of a magnetic tunnel junction (MTJ) based hardware implementation of PSL[2]. Differently from the original p-bit proposals, we propose using two biasing methods, magnetic field and voltage, on the MTJ to excite and fine tune the random fluctuation of MTJ[3]. Therefore, our proposed hardware implementation of p-bit carries the benefit of extra tunability of random signal properties, which are eventually used to compensate the variations of mean and rate of random signals due to the intrinsic device-to-device variations of MTJs. As a result, multiple p-bits are tuned to exhibit similar properties even they are built with highly varied MTJs. Another benefit of the proposed p-bit design is that the similar principle could work for not only thermally-unstable MTJs but also thermally-stable MTJs, which are matured for STT-MRAM technologies and are more ready for integration. Then three p-bits are connected by a coupling network so that a PSL of an invertible logic gate is experimentally demonstrated (Fig. 1). As shown in Fig. 2, the invertible AND gate hops between all possible combinations under the AND logic constraint, C=AB. Along with more results from the demonstration, the PSL of an invertible AND logic gate is shown to function as intended. And thanks to the proposed p-bit hardware design that offers high tunability, the entire PSL system does not suffer from the slowest of the system, and shows much greater performance and potential for further scaling.References: [1] K. Y. Camsari, B. M. Sutton, and S. Datta, “P-bits for probabilistic spin logic,” Applied Physics Reviews, vol. 6, no. 1. AIP Publishing LLC, p. 011305, 11-Mar-2019. [2] Y. Lv, R. P. Bloom, and J. P. Wang, “Experimental Demonstration of Probabilistic Spin Logic by Magnetic Tunnel Junctions,” IEEE Magn. Lett., vol. 10, 2019. [3] B. R. Zink, Y. Lv, and J.-P. Wang, “Independent Control of Antiparallel- and Parallel-State Thermal Stability Factors in Magnetic Tunnel Junctions for Telegraphic Signals With Two Degrees of Tunability,” IEEE Trans. Electron Devices, vol. 66, no. 12, pp. 5353–5359, Dec. 2019.

Experimental Demonstration of Probabilistic Spin Logic by Magnetic Tunnel Junctions

***Supported by *** 

![](https://assets.underline.io/uploads/markdown_image/1/image/7647be6e9af5f051a0be439ab0ffd8c0.png)

SB: Recent Developments in Advanced Magnetic Tunnel Junctions

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.

<iframe width="560" height="315" src="https://s3.amazonaws.com/pf-user-files-01/u-59356/uploads/2022-11-02/un13zp7/MMM%20Welcome%20Video%20v5.mp4" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

For tickets to the event, please register at the following link: https://magnetism.org/registration

Please register for the MMM 2022 conference to join the event.

MMM 2022

This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

DOA: Magnetoresistance in Heterostructures (GMR, TMR, TAMR)

**Please click on the poster to see the abstract or leave your comment to the author.** 
**Session Co-Chairs:** Shouzhong Peng, *Beihang University* and Luding Wang, *Eindhoven University of Technology*

DPA: Spintronic Devices for Memory and Computing

poster

**Session chair:** Stephane Mangin, Université de Lorraine



GPE - Magnetoresistance and Voltage-Controlled Magnetic Properties

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.

The 2022 Joint Conference will offer both in-person and prerecorded on-demand content.

For tickets to the event, please register at the following link: https://magnetism.org/register

Please register for the Joint MMM-Intermag conference to join the event.

2022 Joint MMM-INTERMAG

G4: Neuromorphic Computing with Nanomagnets

The 65th Annual Conference on Magnetism and Magnetic Materials (MMM 2020) was held in a virtual form. The COVID-19 pandemic, with its associated uncertainty about international travel and the ability to gather in large groups, meant that the Steering Committee decided to cancel the face-to-face meeting that had been planned in Palm Beach, Florida November 2-6, 2020.

We were reluctant to give up the benefits of meeting face-to-face, and know that shifting to a virtual conference is a significant change for this community. Nevertheless, we are first and foremost concerned about the health and safety of all our Conference participants and their loved ones on returning home after travelling.

The MMM 2020 Steering Committee was working exceptionally hard, along with our sponsors, the IEEE Magnetics Society and AIP Publishing, to make this event serve the needs of our participants, who live in time zones all around the globe, in the best possible way. 

You need a ticket to explore this event.

If you have already registered for MMM 2020, and you have already created an account, then you
just need to login (above).

If you have already registered for MMM 2020, but you have not yet created an account, then you
need to click on &quot;create an account&quot; (above) and then login.

Forgot your password? Go to
https://www.underline.io/log-in

If you have not yet registered for MMM 2020 but would like to do so, go to
https://magnetism.org/register

Still need help? Contact our team!


Yang Lv

6

27

SHORT BIO

Presentations

Perpendicular Magnetic Tunnel Junctions with Crystalline Anisotropy and Energy efficient Switching of Synthetic Antiferromagnet pMTJs by voltage

Large unidirectional spin Hall and Rashba−Edelstein magnetoresistance in topological insulator/magnetic insulator heterostructures

Ultra low current density switching via voltage

Observation of unidirectional spin Hall magnetoresistance in amorphous PtSn4/CoFeB bilayers

Spin-orbit torque assisted switching with voltage controlled exchange coupling

Experimental Demonstration of Probabilistic Spin Logic by Magnetic Tunnel Junctions

Stay up to date with the latest Underline news!

PRESENTATIONS

CONFERENCES

COMPANY

RESOURCES