Quantum computation and cryogenic electronics have gained considerable importance in this last decade. Currently, a bottleneck for advancing it further is the power consumption of conventional electronic components, which is not adapted to the needs of cryogenic circuits. Perpendicular Spin-Transfer-Torque Magnetic Random Access Memory (p-STT-MRAM) has potential to comply with cryo-electronics requirements of low power. Previous works done on cryogenic temperature switching of STT-MRAM have assessed its characteristics and the Write Error Rate for different device diameters [1]. The conditions to write an STT-MRAM are promising (0.7V at 9K with 200ns pulses, corresponding to a writing energy of 11.2 pJ) [2]. However, the full integration of MRAMs into quantum processors demands a much lower operating voltage (below 0.1V).Therefore, we focused our research on engineering MTJs for low anisotropy to reduce the critical switching voltage VC and consequentially the write energy per bit Ebit. Our approach consists in changing the interface of the storage layer by adding an insertion layer as in Mg+Ox/X/FeCoB/W/Y/W, where X can be wedges of Mg, FeCoB and Y is permalloy (Py). This type of device can show high thermal stability at cryogenic temperatures (i.e.4K), while having no retention at 300K. This strategy allows the reduction of the storage layer anisotropy by at least one order of magnitude.
Figure 1 shows a current pulse phase diagram of a junction with Mg insertion. Upon changing the operation temperature the write current density JC for junctions with different insertion layers is varying as reported in Figure 2. Device diameter, composition and thickness play an important role in modulating the anisotropy. Tuning these parameters it is possible to bring the switching currents close to 20µA for a 30nm diameter device at 10K (red curve), corresponding to Ebit=1.2pJ. This can be further improved by modulating the required current density with composition as shown in the figure 2. 
**References** [1] L. Rehm, G. Wolf, B. Kardasz, M. Pinarbasi, and A. D. Kent, "Sub-nanosecond spin-torque switching of perpendicular magnetic tunnel junction nanopillars at cryogenic temperatures", Appl. Phys. Lett. Vol. 115, p.182404 (2019).
[2] Lili Lang, Yujie Jiang, Fei Lu, Cailu Wang, et al, "A low temperature functioning CoFeB/MgO-based perpendicular magnetic tunnel junction for cryogenic nonvolatile random access memory", Appl. Phys. Lett. Vol. 116, p.022409 (2020) 

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Control of Interface Anisotropy for Spin Transfer Torque in Perpendicular Magnetic Tunnel Junctions for Cryogenic Temperature Operation

Magnetic random access memories (MRAM) store information on magnetization direction instead of electric charge. All optical switching (AOS) of a magnetic tunnel junction provides an efficient way to enable writing at speeds orders of magnitude faster than electrical alternatives based on spin torque methods, allowing for write operations at THz frequencies. The [Tb/Co] multilayer is particularly interesting, since its large perpendicular magnetic anisotropy would allow data retention at small sizes and could be integrated into a magnetic tunnel junction [1-2]. This work reports magnetization reversal driven by femtosecond light pulses on a [Tb/Co] based perpendicular magnetic tunnel junction patterned to sub-100nm lateral dimensions. This optical switchable electrode was integrated into an MgO based MTJ having synthetic anti-ferrimagnet reference layer element, where the AOS magnetization direction can be read directly from the resistance state of the junction. The optically switchable electrodes are [Tb/Co]x5 multilayers coupled to a 1.4nm FeCoB layer through a 0.2nm W insertion layer. Patterned AOS-MTJ nanopillars fabricated with diameters down to 80 nm showed TMR ratios up to 74% and a resistance area product of 112 Ω μm2. Figure 1) shows the hysteresis loop for a [Tb 0.6nm/ Co 1.4nm]x5 multilayer. It was possible to observe a toggle switching between low and high resistance states, corresponding to parallel and anti-parallel alignment of the two electrodes, after each 50 fs long laser pulse applied on the device. A systematic study on the switching probability will be compared to existing results of AOS experiments on continuous films. There it was possible to demonstrate that reliable and robust toggle switching can be achieved for specific Tb and Co thickness in the range of 0.6-0.9 nm of Tb and 1.3-1.5 nm of Co. The magnetization reversal is reliable after a 150.000 pulse sequence. Single shot AOS is achievable using laser pulse durations from 50 fs up to 10 ps and fluences 3-6.5 mJ/cm2. These results pave the way towards an AOS ultra-fast and energy-efficient memory. 
**References** 
[1] A. Olivier et al., Nanotechnology 31, 425302 (2020). 
[2] L. Avilés-Félix et al., Scientific Reports 10, 1 (2020). 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/dca0d23bf1cc210d5479056d84ef1c36.png) 
Figure 1 a) AOS-MTJ stack illustration b) R-H loop in perpendicular field c) AOS field-free toggle switching between P and AP states.

Field free all optical switching in Tb/Co multilayer magnetic tunnel junction

Since the first all-optical switching experiments carried on GdFeCo ferrimagnet [1-2], the all-optical switching represents an ultrafast and easy method to manipulate magnetization without any applied field. Single pulse helicity independent all-optical switching (HI-AOS) has been demonstrated in ferrimagnetic GdFeCo alloy, Gd/FM bilayers where FM is a ferromagnet, and recently in a ferrimagnetic Heusler alloy and Tb/Co multilayer-based electrode [2-5].
In this work, we demonstrate that robust toggle HI-AOS has been observed in ferrimagnetic Tb based multilayers (Fig.1a). The properties of single pulse HI-AOS in Tb-based multilayers mainly differ in two ways compared to GdFeCo alloys. First, the shape of the state diagram of Tb-based multilayers in which the toggle switching can be observed at a pulse duration of 10 ps is completely different from that of GdFeCo alloy [6] (Fig.1d). The threshold switching fluence (Fswitch) is independent of the laser pulse duration of at least up to 10 ps (Fig. 1b). Moreover, the multidomain fluence (Fmulti), above which a multidomain state is observed in the center of the spot, increases slightly for pulse durations below 3 ps and then remains constant for longer pulse durations. This indicates that the mechanisms responsible for the Tb-based multilayers switching differ from those of Gd-based alloys. Second, the observed equilibrium state after the first laser pulse excitation shows a complex structure with rings of opposite magnetization directions when the fluence increases. This ring structure was observed in all Tb-based multilayer films we have studied so far. The number and the size of the rings depend on the sample composition (thickness of the Tb and transition metal layers) as well as on the annealing condition.
Acknowledgments: UFO, COMRAD 
**References** [1] C. D. Stanciu, F. Hansteen, A. V. Kimel, Phys. Rev. Lett. 99, 047601, 2007.
[2] T. A. Ostler, J. Barker, R. F. L. Evans, Nat. Commun. 3, 666, 2012.
[3] M. Beens, M. L. M. Lalieu , A. J. M. Deenen, Phys. Rev. B 100, 220409(R) , 2019.
[4] L. Avilés-Félix, A. Olivier, G. Li, C. S. Davies, Sci. Rep. 10, 5211, 2020.
[5] C. Banerjee, N. Teichert, K. Siewierska, Nat. Commun., 11, 4444, 2020.
[6] J. Wei, B. Zhang, M. Hehn, Phys. Rev. Applied 15, 054065, 2021. 
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Robust toggle switching in Tb based multilayers by a single

Spiking neural networks have attracted a lot of interest in the past decade as they meet the need of energy efficiency in deep neural network computing (1). Using spikes instead of continuous signals enables low power operation, event-based computations and fast response time, which is better adapted to spatial-temporal data. Combined with unsupervised and local learning rules such as the spike-timing-dependant plasticity rule (2), SNN with magnetic tunnel junction (MTJ) based neurons provide interesting solutions for embedded technologies with better back-end-of-line compatibility (3) compared to other technologies.
For the spike generation, we propose an MTJ-based neuron composed of two magnetized layers (M1 and M2), with low thermal stabilities, separated by an oxide tunnel barrier. Under applied current, the spin-transfer torque (STT) enables an alternating switching of both magnetic layers leading to a so-called “windmill motion” (see Fig1.a-c) previously predicted by simulation for in-plane and out-of-plane magnetized MTJs (4,5). Here we designed, fabricated and characterized such type of structure and were able to achieve steady alternating magnetization reversal of both layers generating a characteristic spike-like resistive response.
MTJ stacks of FeCoB/MgO/FeCoB, with varying FeCoB thicknesses, were deposited by magnetron sputtering and patterned into nano-pillars with diameters ranging from 50 to 200 nm. The electrical characterization of the nano-pillars reveals essential changes of the magnetization dynamics depending on the pillar diameters, layer thicknesses, voltage, applied magnetic field and temperature of the junction. As predicted by the simulation, the frequency of the oscillations and the width of the spikes evolve with the voltage amplitude and the applied field. Important similarities confirm the parameter dependence with temperature and bias voltage. Controlling the spiking rates at low voltages is a critical requirement to build an efficient spiking neural network.
References Acknowledgements:
This work was supported by ANR via grant SpinSpike Projet-ANR-20-CE24-0002. 

**References:** 
(1) A. Tavanaei, M. Ghodrati and S.R. Kheradpisheh, Neural networks, 111, 47-63 (2019). 
(2) T. Iakymchuk, A. Rosado-Muñoz and J.F. Guerrero-Martínez, EURASIP Journal on Image and Video Processing 2015, 1-11 (2015). 
(3) D. Shum, D. Houssameddine and S.T. Woo, 2017 Symposium on VLSI Technology. IEEE pp. T208-T209 (2017). 
(4) R. Matsumoto, S. Lequeux, and J. Grollier, Physical Review Applied, 11(4), 044093 (2019) 
(5) G. Gupta, Z. Zhu and G. Liang, arXiv preprint arXiv, 1611.05169 (2016). 

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Spiking dynamics with dual free layer MTJ

In magnetic trilayers composed of heavy-metal/ferromagnet/oxide (HM/FM/MOx), the structural inversion asymmetry gives rise to the so-called interfacial Dzyaloshinskii-Moriya interaction (iDMI) [1]. This antisymmetric exchange interaction is at the origin of non-collinear spin textures, such as spin spirals or magnetic skyrmions [2] with chiral Néel domain-walls (DWs). Their dynamics is directly related to their chirality, imposed by the iDMI sign [3]. Thus, controlling their current-induced motion (CIM) driven by spin-orbit torques can be achieved by controlling the iDMI. In this study, we propose techniques to control the skyrmion motion in a Ta/FeCoB/TaOx trilayer, through the control of the iDMI sign and amplitude. The skyrmion motion can be controlled, or even reversed, either by modulation of deposition parameters or dynamically by applying a gate voltage. We have found that modulation of the oxidation state at the FeCoB/TaOx interface (Fig. 1(a-b)) leads to an inversion of the iDMI sign, as measured by Brillouin light scattering. This iDMI sign crossover is accompanied by an inversion of the skyrmion CIM direction. Skyrmion motion reversal can also be triggered by a gate voltage through the control of iDMI sign (Fig. 1(c-d)). Moreover, our micromagnetic simulations show that a fine control of the iDMI amplitude and sign is feasible on individual nanometer-size magnetic skyrmion without annihilating it (Fig. 2(a-c)). The dipolar energy prevents the spin texture from annihilation when iDMI is close to zero, leading to a stable Bloch skyrmion (Fig 2b). The angle of the moments inside the DWs (Fig. 2d) evolves continuously from 0° to 180° when varying the iDMI value. This allows a fine tuning of the skyrmion CIM direction (Fig. 2e), allowing to suppress the skyrmion Hall angle, otherwise detrimental for device applications.

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Figure 1: Control of iDMI sign : (a-b) Modulation of the FeCoB/TaOx interface oxidation and (c) Gate-controlled skyrmion motion (Magneto-Optical Kerr Effect images)

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Figure 2: (a-c) Micromagnetic simulations : Adiabatic iDMI reversal on a nm-size magnetic skyrmion leading to (d) continuous transformation from CW (D<0) to CCW chirality (D>0). (e) Skyrmion's trajectory controlled by iDMI value

Get skyrmions back on track : Suppressing skyrmion Hall angle by material engineering or gate voltage

Perpendicular Spin Transfer Torque Magnetic Random Access Memory (p-STT-MRAM) needs to combine high speed and low critical switching current at technological nodes below 30 nm. Higher STT write efficiency is therefore required. Double magnetic tunnel junctions (DMTJ) stacks have been proposed to achieve this goal [1-5]. The DMTJ critical switching current is decreased by the combined effect of the STT exerted from two antiparallel polarizers on the storage layer (SL). The retention is increased by doubling the SL/MgO interfaces contributing to the layer’s effective perpendicular anisotropy (PMA). Despite the efficiency advantage, the development of p-DMTJ presents several complexities. First, ensuring enough PMA for the top polarizer [6] and second, controlling the stray field compensation of both polarizers acting on the SL. A p-DMTJ structure having a switchable reference layer was recently proposed [7], showing through magnetic simulation similar performance as conventional p-DMTJ with static polarizers. In this work, we report experimental evidence of the working principle for this type of novel p-DMTJ. We fabricated and optimized an ASL-DMTJ structure having a switchable polarizer acting as a switching assistance layer (ASL). Fig.1.(a) and (b) show the two switching sequences, from AP to P and from P to AP states respectively. Both reversals show a transition through an intermediate resistance state (IRS). Differing from the working principles proposed in [7], the ASL is designed to switch its magnetic orientation during the write operation. This maximizes the STT efficiency independently of the switching direction, while also increasing the SL retention, since the assistance layer always aligns parallel to the SL in standby Fig.2(a)-(b). Validation of the switching sequences was possible by performing time-resolved resistance measurements Fig.2.(c)-(b).

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Figure 1. (a) AP→P and (b) P→AP reversal sequence through an intermediated resistance state.

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Figure 2. (a) RH of ASL-DMTJ (b) RV loops of ASL-DMTJ. (b) Real time AP→P switching sequence and (d) real time P to AP switching sequence both transiting through the IRS with (I) applied field, (II) at zero field.

Real time investigation of Double magnetic tunnel junction with switchable assistance layer for high efficiency STT-MRAM

Perpendicular Double Magnetic tunnel junctions (p-DMTJ) are developed for high-performance STT-MRAM applications. In these devices, the thermal stability factor (Δ) of the storage layer (SL) magnetization is increased by sandwiching the SL between two MgO barriers thus benefiting from the interfacial perpendicular anisotropy from the two SL/MgO interfaces [1][2][3]. The critical current to switch the storage layer magnetization is reduced when using above and below the MgO/SL/MgO sandwich two antiparallel polarizers. This provides two spin-transfer torque contributions acting simultaneously on the SL. In such p-DMTJ, the two polarizers are usually pinned by exchange coupling with a synthetic antiferromagnetic structure, increasing the complexity of the stack and its patterning. Alternatively, a simplified DMTJ structure comprising a switchable assistance layer (ASL) that acts as a second polarizer was proposed [4]. It is expected to present the same enhancement in performance as traditional p-DMTJ. For these devices to work, a balance between the energy barriers of the storage layer and of the switchable assistance layer must be fulfilled. Due to the particular voltage driven dynamics, the magnetization of the switchable assistance layer should switch before that of the Storage layer. Thus, it can be set antiparallel to that of the reference layer, generating cumulative STT contributions from the ASL and reference layer. Figure.1.(a) shows a comparison of the structures of a conventional p-DMTJ versus a simplified DMTJ with ASL, as well as the layers switching sequences. Upon write, when starting from the reference (REF) up/ Storage layer down/ Assistance layer down configuration (Figure1.(b)), in order to switch the magnetization of the SL layer in the up configuration, the electrons have to flow from the REF layer to the ASL layer (positive V pulse). Since in this configuration the REF and ASL layer are in antiparallel configuration, the critical current for switching the SL magnetization is reduced. As a result the SL magnetization switches first followed by the switching of the ASL layer due to their parallel coupling and STT from the SL. When starting from the REF up/ SL up/ASL up configuration (Figure1.c), in order to switch the magnetization of the SL layer in the down configuration, the electrons have to flow from the ASL layer to the REF layer (negative V pulse). Since the ASL energy barrier is lower than the SL one, the critical current to switch the ASL magnetization in this configuration is lower than that to switch the SL magnetization. As a result, the ASL magnetization first switches antiparallel to the REF. This increases the STT efficiency on the SL magnetization, which then switches downwards ending up antiparallel to the REF. In standby conditions, the two free layers will always end up parallel, reinforcing the overall thermal stability of the device by their mutual dipolar coupling. In this work, we report the first experimental observation of the working principal of this type of devices. By comparison with a structure without the Assistance layer, the simplified double magnetic tunnel junction presents an averaged 5-fold increase of the figure of merit (D/Ic) (Figure.2). Secondly, we qualitatively interpreted the experimental observations in these devices by macrospin simulations taking into account heating effect occurring during write cycle. In fact, as a result of the presence of two MgO barriers, Joule heating plays a significant role in the write process [5]. From our model, we have been able to identify that the free layers (SL and ASL)’ blocking temperature can affect dramatically the performance of these devices. If the ASL’s blocking temperature is lower than that of the SL, the temperature rise during the application of the writing pulse can set the ASL in a paramagnetic regime. This suppresses any additional STT or dipolar coupling from this layer and causes an asymmetry on the critical voltage to switch from P to AP and from AP to P. Finally, thanks to an optimization of the structure of our simplified double magnetic tunnel junction, this issue have been solved.

**References:**

[1] B.Rodmacq et al, patent US8513944B2 (2008) [2] Daniel C. Worledge et al, IEEE MAGNETICS LETTERS, Vol 8, (2017) [3] S.Rao et al, BEOL-compatible double magnetic tunnel junction pSTT-MRAM devices for IoT and edge computing, IEDM 2020 [4] A. V. Khvalkovskiy et al, Journal of Applied Physics 124, 133902 (2018) [5] N. Strelkov et al, Physical Review B: Condensed Matter and Materials Physics, American Physical Society, 2017, 95, pp.184409 (2017)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/053c6589e25028c21ebb9fef1e915cb4.jpg)
Figure 1.(a) Conventional and simplified double magnetic tunnel junctions comparison.(b) Assistance layer – Storage layer switching dynamics for P to AP states. (c) Assistance layer – Storage layer switching dynamics for AP to P states.

![](https://assets.underline.io/uploads/markdown_image/1/image/38e326aa3bd77dd523ecb03bf42ca5cd.jpg)
Figure 2.Figure of merit comparison ( Thermal stability / Critical switching current density) between Sample A with 1.5 nm of assistance layer and sample B without assistance layer as a function of Storage layer thickness.

 Modelling and Optimization of Double Magnetic Tunnel Junctions with Switchable Assistance Layer for High Performance STT-MRAM Applications

Topological non-trivial whirling spin textures such as magnetic skyrmions have recently triggered a lot of interest by virtue of their potential nanosized solitonic nature, stability and tunability. All these attributes, if combined with the efficient current-induced motion via spin orbit (SO) torque, make them attractive to build elementary units of digital information for spintronic logic devices and memories. In ultra-thin ferromagnetic films with Perpendicular Magnetic Anisotropy (PMA) sandwiched between a heavy metal with strong SO and an insulator (i.e. HM/FM/I), the chirality of this spin arrangements is ascribable to an antisymmetric exchange, Interfacial Dzyaloshinskii-Moriya Interaction (iDMI) [1,2]. Among the possible topological magnetic quasi-particles, which can be stabilised in such peculiar trilayer systems, a lower dimension (1D) non-trivial magnetic texture, named Domain Wall Skyrmion (DWSk), has been newly reported and experimentally observed using Lorentz Transmission Electron Microscopy [3]. The DWSk is a 1D topological excitation sharing the same integer topological charge, noted Q, as conventional 2D skyrmions (Q = 1). It is describable as a localized 2π rotation of the In-Plane (IP) component of magnetization within a Néel domain wall which stands between two perpendicular magnetic domains. It can be intuitively viewed as the counterpart of a 2π-vertical Bloch lines coming about in Bloch instead of Néel domain walls. Skyrmions with chiral kinks inside the otherwise homochiral domain wall, hereinafter called Double Skyrmion (DSk), have been numerically predicted as a soliton solution [4,5]. In our work, we investigated the stability and the spin-driven dynamics of the DSk in a sample of the type Pt/Co(0.9nm)/MgO [6] using micromagnetic simulations [7]. Interestingly, as shown in Fig.1a, we are able to stabilise simultaneously various spin-textures including skymion (Sk, Q=1), double skyrmion (DSk, Q=2) and domain wall skyrmion (DWSk, Q=1). It is found that such magnetization pattern is robust against both thermal fluctuations and normally distributed anisotropy, for different grain-like region sizes. We also proved the resilience of double skyrmion to material parameters variation (DMI, anisotropy) and applied field. The static analysis is complemented with the investigation of the dynamic regime of motion under electrical current. Fig.1b shows the trajectory of the double skyrmion induced by spin-orbit torque. In the limit of moderate injected current the skyrmion and the double skyrmion behave similarly (Fig.1c). However, depending on the geometry of the injected current the double skyrmion can be annihilated or splits in two skyrmions, opening the path to conceive logical devices.

**References:**

[1] I.E. Dzyaloshinskii Sov. Phys. JETP 5, (1957), J.Phys. Chem Solids, 4, 241 (1958) [2] T. Moriya Phys. Rev Lett., 4, 228, (1960), Phys. Rev. 120, 91, (1960) [3] Li at al., https://arxiv.org/abs/2004.07888 (2020) [4] Kuchkin et al., Phys. Rev. B 102, 144422 (2020) doi.org/10.1103/PhysRevB.102.144422 [5] S.-G. Je Current Applied Physics 21, 175 (2021) doi.org/10.1016/j.cap.2020.10.021 [6] Juge et al., Phys. Rev. Applied 12, 044007 (2019) doi.org/10.1103/PhysRevApplied.12.044007 [7] Vansteenkiste et al. AIP Adv. 4, 107133 (2014). doi/10.1063/1.4899186

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/469f5808fec70a1e12fc572d65ebf2ad.jpg)
Fig. 1: a) Multidomain equilibrium state of 0.5µmx0.5µm ideal Pt/Co(0.9nm)/MgO dot at 0K and no applied magnetic field. The color scale is associated to the perpendicular component of magnetization. b) Sequence of micromagnetic simulation snapshots illustrating the current-induced SOT driven DSk dynamics at 0K with Japp=50x1010 A/m2. The skyrmion Hall angle of DSk is 64°. c) Comparison of DSk and Sk velocities (orange) and effective diameters (black) as a function of injected current density.

 Static and dynamic behaviour of double skyrmions in Pt/Co/MgO trilayer

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

Gate-Controlled Skyrmions in Magnetic Trilayer Tracks

Spin torque nano-oscillators (STNO) generate high frequency output voltage signals upon injection of a spin polarized DC current into a magnetic tunnel junction. For their applications in wireless communications or neuromorphic computing schemes, a central aspect is the control of their phase dynamics via injection locking to an external rf signal [1, 2]. Many interesting, non-linear effects may arise at higher excitation levels that manifest themselves in the Arnold tongue [3, 4]. For the in-plane magnetized STNO (in-plane magnetized polarizer and free layer) [2], we provide here analytical expressions for (i) the asymmetric Arnold tongue boundaries, arising from the dependence of the forcing on the STNO power; (ii) the Takens-Bogdanov bifurcation threshold [4] which leads to a reduced locking range and (iii) the hysteresis boundaries [3,4]. These effects are discussed within a common model for ‘pure’ rf signals arising from either a spin polarized current or a magnetic field. ‘Pure’ refers to a well-defined direction ui (i=x,y,z ; ux the STNO easy axis) of the spin polarization or a magnetic field [2]. In a further study we also investigate synchronization at harmonic order n=1 (rf signal frequency close to the STNO frequency) for mixed spin polarization with x- and y- components. The important and unexpected finding here is that the STNO phase does not follow an arcsine (Adler-type) behavior [5] within the locking range, but shows a discrete jump that can be as large as Pi/2. Our analysis shows that the phase jump results from a competition between locking to the ux- and uy-components of the rf signal, where locking to the ux-component at n=1 is enabled through the fact that the free running oscillation power is non-constant with frequency components at f. This demonstrates that, for mixed rf signals, injection locking can be more complex, and that the results can be of interest for applications such as the phase jump for phase shift keying concepts [6]. MIG was supported by the French Space Agency (CNES) and the CEA NUMERICS program, which has received funding from the European Union's Horizon 2020 program (No 800945). Partial support was provided by the French National Research Agency (ANR-20-CE24-0002).

Arnold tongue of injection locked spin torque nano-oscillators under high and mixed driving signals

In the development of dedicated hardware for neuromorphic applications, the realization of suitable memristive devices as synaptic elements is a key factor. The main drawback of the existing devices is the reliability of the intermediate states and their scalability. In this study we propose a memristive device based on magnetic tunnel junctions (MTJ) and whose functionalities do not depend directly on the size of the device. The state of the memristor relates to the tunnel magnetoresistance (TMR) variation with the relative angle between the two in-plane magnetizations. The specificity of our concept consists in the integration of an isotropically coercive medium as magnetic free layer able to stabilize its magnetization along whatever in-plane direction. Here the current driven rotation of the magnetization is investigated on devices of 100nm of diameter. The spin transfer torque (STT) of the in-plane MTJ is considered together with the contribution of the additional perpendicularly magnetized polarizer. For a proper ratio of the two STT contributions, the magnetization switches from the parallel to the anti-parallel state following a circular out-of-plane trajectory as for the precessional switching [4]. We prove experimentally that by properly designing the voltage pulses we can discretely rotate and stabilize the magnetization along different in-plane directions, reaching an almost continuous range of intermediate resistances. The resistance variation turns out to be monotonous with the voltage polarity confirming the memristive behavior of the device under a train of pulses. A study on the thermal stability of the intermediate states shows a resistance variation below 2% for a 3min timescale. Moreover, the Joule effect, occurring during the application of pulses, adds a random contribution to the resistance jumps. The observed resistance noise is associated to the thermally activated switching of small magnetic areas of the samples, probably due to the granular nature of the sputtered samples. The larger the diameter, the lower the noise due to the increased number of grains.References: 1. Mansueto, M. et al. Phys. Rev. Appl. 12, 044029 (2019). 2. Mansueto, M. et al. 2020 IEEE International Memory Workshop (IMW) 1–4 (2020). 3. Mansueto, M. et al. in preparation 4. Vaysset, A. et al. Appl. Phys. Lett. 98, 242511 (2011)

Spintronic memristor based on the angular variation of TMR

DOB: MRAM, Magnetic Logic and Related Devices

technical paper

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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.

IOA: Magnetic Recording I

GOA: Magnetization Dynamics I

**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

GOD - Skyrmion Stabilization, Voltage Control, and Neuromorphic Applications

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

**Session chair:** Denys Makarov, Helmholtz-Zentrum Dresden-Rossendorf


GOL - MRAM, Magnetic Logic and Related Devices II

*Session Chair: Guohan Hu, IBM*

These on-demand presentations are available to view at your leisure.

CF: Conventional STT-MRAM Materials, Devices and Technology

INTERMAG 2021 Welcome Video



	
<figure class="video_container">
 <iframe src="https://screencast-o-matic.com/player/crflqFVnUpZ?v=6&ff=1&title=0&controls=1" width=640 height=360 frameborder="0" allowfullscreen="true"> </iframe>
</figure>

Want to buy a ticket? 

Register for INTERMAG 2021 here

[![](https://assets.underline.io/uploads/markdown_image/1/image/17ce76e7960db633258024eef8d6da7f.png)](https://intermag.org/register)

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INTERMAG 2021

*Session Chair: Soong-Geun Je, Chonnam National University*

These on-demand presentations are available to view at your leisure.

HP: Skyrmions

**Session chair:** Elton Santos, The University of Edinburgh


GPA - Skyrmions and Spins in Topological Insulator and 2D Materials

**Session chair:** Matthias Benjamin Jungfleisch, University of Delaware



HPB - Magnons, Spin Dynamics and Micromagnetic Modeling

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. 

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If you have already registered for MMM 2020, and you have already created an account, then you
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https://magnetism.org/register

Still need help? Contact our team!


Liliana Buda-Prejbeanu

11

45

SHORT BIO

Presentations

Control of Interface Anisotropy for Spin Transfer Torque in Perpendicular Magnetic Tunnel Junctions for Cryogenic Temperature Operation

Field free all optical switching in Tb/Co multilayer magnetic tunnel junction

Robust toggle switching in Tb based multilayers by a single

Spiking dynamics with dual free layer MTJ

Get skyrmions back on track : Suppressing skyrmion Hall angle by material engineering or gate voltage

Real time investigation of Double magnetic tunnel junction with switchable assistance layer for high efficiency STT-MRAM

Modelling and Optimization of Double Magnetic Tunnel Junctions with Switchable Assistance Layer for High Performance STT-MRAM Applications

Static and dynamic behaviour of double skyrmions in Pt/Co/MgO trilayer

Gate-Controlled Skyrmions in Magnetic Trilayer Tracks

Arnold tongue of injection locked spin torque nano-oscillators under high and mixed driving signals

Spintronic memristor based on the angular variation of TMR

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