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The rare-earth nitrides are the only known series of intrinsic ferromagnetic semiconductors, with a range of magnetic behaviours stemming from the contribution of both spin and orbital 4f moments. The similar chemistry of the rare-earths and the common structure of the nitrides simplifies their combination in superlattices and solid solutions. Recent studies of rare-earth nitride superlattices have shown enhanced superconductivity [1] and magnetic exchange spring behaviour that results from the competition between the Zeeman and Exchange interactions [2]. Yet, little has been published to date exploring the combination of these nitrides in solid-solutions.

We show (with reference to magnetometry, XMCD and anomalous Hall effect measurements) that the same Exchange/Zeeman competition that leads to a complex twisted magnetic phase in superlattices manifests quite differently in solid solutions. Leading, where an orbital-dominant ferromagnet (SmN) is paired with a spin-only ferromagnet (GdN), to a composition exhibiting a net zero magnetic moment (A compensation point).&lt;br&gt;&lt;br&gt;
**References** [1] E.-M. Anton, S. Granville, A. Engel et. al. , Phys. Rev. B, Vol. 94, 024106 (2016)
[2] E.-M. Anton, W. Holmes-Hewett, J. McNulty et. al. , AIP Advances, Vol. 1, 015348 (2021)

MMM 2022

Exchange/Zeeman Competition in the Rare Earth Nitrides and the Resulting Magnetic Compensation

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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MMM 2020

The rare-earth nitrides are the only known series of intrinsic ferromagnetic semiconductors, with a range of magnetic behaviours stemming from the contribution of both spin and orbital 4f moments. The similar chemistry of the rare-earths and the common structure of the nitrides simplifies their combination in superlattices and solid solutions. Recent studies of rare-earth nitride superlattices have shown enhanced superconductivity [1] and magnetic exchange spring behaviour that results from the competition between the Zeeman and Exchange interactions [2]. Yet, little has been published to date exploring the combination of these nitrides in solid-solutions.

We show (with reference to magnetometry, XMCD and anomalous Hall effect measurements) that the same Exchange/Zeeman competition that leads to a complex twisted magnetic phase in superlattices manifests quite differently in solid solutions. Leading, where an orbital-dominant ferromagnet (SmN) is paired with a spin-only ferromagnet (GdN), to a composition exhibiting a net zero magnetic moment (A compensation point). 
**References** [1] E.-M. Anton, S. Granville, A. Engel et. al. , Phys. Rev. B, Vol. 94, 024106 (2016)
[2] E.-M. Anton, W. Holmes-Hewett, J. McNulty et. al. , AIP Advances, Vol. 1, 015348 (2021)

poster

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

VCMA effect describes the fact that in a capacitor, in which one of electrodes is made of a thin ferromagnetic metal, the magnetic properties of the ferromagnetic metal changes, when a voltage is applied to the capacitor[1]. Inside a metal the electrical field is screened by free electrons and cannot penetrate deep inside the metal. As a result, the voltage, which is applied to the capacitor dielectric (gate), may penetrate into and affect only the few uppermost atomic layers of the metal near the gate. However, the change of magnetic properties of the uppermost layer by the gate voltage affects the magnetic properties of the whole film. This can be only the case if the interfacial perpendicular magnetic anisotropy (PMA) is affected by the gate voltage [2]. The strength of PMA is characterized by the anisotropy field Hani and proportional to the strength of spin-orbit interaction, demagnetization field and magnetization of nanomagnet.
Fig.1 shows the measured Hani and coefficient of spin-orbit interaction kso in FeCoB nanomagnet under a different gate voltage. kso defies the strength of the spin-orbit interaction[3]. Hani decreases and kso increases under an increase of gate voltage. It is unexpected because Hani is linearly proportional to kso [3] and should increase when kso increases. It means that even though the strength of the spin-orbit interaction is affected by the gate voltage, but additionally to kso there is another voltage- dependent parameter, which defines the voltage dependence of Hani. The intrinsic field in nanomagnet or demagnetization field might be such a parameter.
Fig.2 shows measured Hani and kso of different nanomagnet of different wafers. The same tendency exists in all measured nanomagnets. 
**References** [1] Y. Shiota, T. Nozaki, F. Bonell, S. Murakami, T. Shinjo, Y. Suzuki, Nat. Mater. 11 (2012) 39–43.
[2] V. Zayets, T. Nozaki, H.Saito, A. Fukushima, S.Yuasa, arXiv:1812.07077 ( 2018).
[3] V.Zayets, IOA-07, MMM 2021. 

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Unexpected opposite dependencies of anisotropy field and strength of spin orbit interaction on gate voltage measured in FeCoB nanomagnet

This study aims to fabricate a voltage-tuneable magneto resistive sensor with the ability to measure small magnetic field signals in three dimensions. Sensing direction in magneto resistive sensors is linked to the magnetization of reference layer. Materials like CoFe1, CoFeB2 and Heusler alloys3 are good choices as reference layers due to their adjustable magnetic anisotropies. Here, using ionic liquid gating (ILG), we observed that magnetic anisotropy of reference layer CoFeB is switchable in MgO(1.5nm)/CoFeB(1.6nm)/W(0.5nm) stack. We used ionic liquid N, N-diethyl-N-methyl N-(2-methoxyethyl) ammonium bis (trifluoromethylsulfonyl) imide (DEME TFSI) (IoLiTec) for applying the gate voltage (VG) ranging between ±3.5V. Using the magneto-optical Kerr effect, we have investigated the change of anisotropy using different gate voltages. We found that magnetic anisotropy switches from out-of-plane (virgin state) to in-plane upon the application of +3.5V, whereas removal of applied voltage +3.5V or application of -3.5V, switches magnetic anisotropy back to out-of-plane, demonstrating the switching behaviour of the stack is reversible and repeatable. Moreover, we observed that out-of-plane to in-plane anisotropy switching time is higher (~45 sec) compared to in-plane to out-of-plane switching time (~25 sec). Hence, a stack having stronger out-of-plane and switchable anisotropy is ideal to use in voltage tuneable magneto resistive sensors. 
**References** 1. Parkin, S. S. P. et al., Nat. Mater., 2004, 3, 862–867.
2. Yuasa, S. & Djayaprawira, D. D., J. Phys. D. Appl. Phys., 2007, 40, 337-354.
3. Palmstrøm, C. J., Prog. Cryst. Growth Charact. Mater., 2016, 62, 371–397. 

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Switching of Magnetic Anisotropy in MgO/CoFeB/W stack by Ionic Liquid Gating for Voltage Tuneable Magneto Resistive Sensor

Reservoir computing (RC) has been considered as one of the key computational principles beyond von-Neumann computing. Magnetic skyrmions, topological particle-like spin textures in magnetic thin films, are particularly promising for implementing RC [1] since they respond strongly nonlinear to external stimuli and feature inherent multiscale dynamics. We propose and demonstrate experimentally a conceptually new approach to skyrmion RC that exploits the thermally activated diffusive motion of skyrmions [2]. By confining the thermal and low-energy, electrically gated skyrmion motion, together with employing spatially resolved input and readout, we find that already a single skyrmion in a confined, triangular geometry (Fig. 1) suffices to realize non-linearly separable functions, which we demonstrate for the XOR gate along with all other Boolean logic gate operations [3] (Fig. 2). Our proposed concept can be readily extended by linking multiple confined geometries and/or by including more skyrmions in the reservoir, suggesting high potential for scalable and low-energy reservoir computing.

Brownian Reservoir Computing Realized Using Geometrically Confined Skyrmions

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

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). 

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Ultra low current density switching via voltage

Racetrack memory is expected to be a memory device that supports the information society because of its high speed and low power consumption. Although many studies have been conducted to improve the speed of magnetic domain wall movement, few studies have been conducted from the viewpoint of Joule heat. Therefore, we have investigated the relationship between Joule heat and domain wall motion in the 2022 Joint MMM-INTERMAG.(1) 
In elucidating the mechanism of this current-driven domain wall motion, although the domain wall width is an essential parameter for improving the domain wall moving speed and the critical current density, the details of the domain wall width are still unknown. Generally, MFM is used for magnetic domain observation. In MFM, as shown in FIG. 1, it is possible to observe the magnetic domain shape by vibrating a thin magnetic needle up and down, but it is challenging to investigate the accurate magnetic flux density distribution. However, suppose the TMR head can be contacted with the sample and scanned. In that case, the distance between the sample and the TMR head can be kept constant to measure the accurate magnetic flux density distribution created by the magnetic recording domain. FIG. 2 shows a TMR head scan image of a magnetic domain recorded in a racetrack memory having a width of 10 μm and a length of 100 μm. The result of line scanning by enlarging this domain wall is also shown in the figure. The recording material is TbCo ferrimagnetic material, the domain wall movement is fast, and the critical current density is small (2). Despite the small saturation magnetization due to ferrimagnetism and thin film (10 nm), the TMR head could measure a clear change in magnetic flux density within a range of ± 20 mT. 

**References:** 
(1) Sota, K. et al. Relationship between pulse width and domain wall velocity in current induced domain wall motion in GdFeCo wire and the effect of joule heat on the racetrack memory, Joint MMM-Intermag Conference, 3628926 (2022) 
(2) Sina, R. et al. Fast Current Induced Domain Wall Motion in Compensated GdFeCo Nanowire, Joint MMM-Intermag Conference, 3786257 (2022) 

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Evaluation of magnetic flux density distribution of magnetic domains recorded in racetrack memory by TMR head

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. 

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

L10-ordered MnAl, a perpendicularly magnetized film material, has attracted much attention due to its high magnetic anisotropy, low saturation magnetization, and low magnetic damping for spin-transfer-torque magnetic random access memory (STT-MRAM) applications. However, in magnetic tunnel junctions (MTJs) with a single MnAl ferromagnetic layer, the TMR ratio has not been confirmed. This is due to the large lattice mismatch between MgO tunneling barrier and MnAl layer, which prevents the coherent tunneling of Δ1 electrons (1). In this work, we utilized Co-doped MnAl and MgAl2O4 tunneling barrier to reduce lattice mismatch and inserted a very thin Fe layer into (MnCo)Al/MgO interface to improve TMR effect.
The structure of the MTJs prepared in this study is shown in Fig.1. The MTJ films were prepared using the ultrahigh vacuum magnetron sputtering method. (MnCo)Al layers with low roughness and high (001) orientation by adding 2% Co. The composition of MgAl2O4 was measured using X-ray photoelectron spectroscopy (XPS). Compositional analysis showed that the composition of MgAl2O4 was Mg : Al : O =9.2 : 18.9 : 41.5 (atom%). MTJ devices were microfabricated and characterized their TMR properties by DC 4-probe method.
We succeeded in observing a TMR ratio of 8% at 300K without an insertion layer by using (MnCo)Al electrode and MgAl2O4 tunneling barrier as shown in Fig. 2(a). In addition, TMR ratio was improved to 9.4% by insertion of ultra-thin Fe layer into the (MnCo)Al/MgO interface as shown in Fig. 2(b). This translates to 18.8% in terms of magnetization parallel state. Since the RA product was decreased from 1.2 MΩμm2 to 223 kΩμm2 by insertion of Fe, coherent tunneling process was thought to be promoted by the interfacial modification.
This work was supported by the Center for Advanced Spintronics Research and Development, the Center for Spintronics Cooperative Research and Education and Development, and the Center for Spintronics Cooperative Research and Education, Tohoku University. 

**References:** 
(1) H.Saruyama, M.Oogane, Y.Ando, 2013, Jpn. J. Appl. Phys., 52, 063003 

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Dependence of TMR and RA on Fe insertion layer thickness in MTJs using L10 (MnCo)Al electrode and MgAl2O4 insulating layer

Magnetoresistive sensors have been enthusiastically selected for applications requiring magnetic field detection with sensors combining small footprint (1), highly linear response curves with low coercivity and low field detectivities. From the viable alternatives (2), MgO-based magnetic tunnel junctions (TMR) offer very competitive performance values, as sensitivity as large as 300 %/mT are reported (3). The optimization of the sensor response includes using soft magnetic free layers, based on CoFeB and NiFe alloys (4).
Here we report the performance of TMR sensors including CoFeBTa and CoFeBSi soft magnetic films as free layers (FL). Magnetic tunnel junction stacks based on (Ta 5/Ru 10)x3/Ta 5/Ru 5/MnIr 8/CoFe 2.2/Ru 0.65/CoFeB 2/MgO/CoFeB/FL2/cap (nm) (fig. 1) were grown on 200 mm wafers using a combination of ion beam and magnetron sputtering deposition from the 14 targets available in the machine. The TMR stacks were magnetically characterized by vibrating sample magnetometry and CIPT, while microfabricated devices (rectangular shaped pillars of varying areas and aspect ratios) were evaluated for transfer curve sensitivity, linear range and noise.
The magneto-crystalline anisotropy, Hk, was assessed for CoFeBTa and CoFeBSi films, with values of 2.1 and 5.3 mT measured for 4 nm films integrated in the TMR stacks. Although these values are larger than for single NiFe FL (1.7 mT)(fig. 2), the global performance of the CoFeBTa/CoFeBSi-based sensors is improved, with magnetoresistance of 210 %, when comparing with 190 % (CoFeB) or 150 % (NiFe). Field sensitivities up to 80 %/mT are obtained, with similar hysteresis (Hc) as for CoFeB or NiFe stacks.
The low frequency noise (1/f dominated) characteristic was evaluated for the microfabricated devices. As an example, sensors with FL2 = CoFeBTa (10 TMR elements connected in series) provided Hooge factor αH = 2.4x10-10 μm2 and detectivity levels of D = 4.5 nT/√Hz at 10 Hz. These values are aligned with previously reported values with similar materials (4).
Acknowledgments: FCT grant UI/BD/151461/2021 

**References:** 
(1) M. Silva, D.C. Leitão, S. Cardoso and P. P. Freitas, IEEE Trans. Magn. 53, 7762720 (2017) 
(2) C. Zheng et al., IEEE Trans. Magn. 55-4, pp. 1-30 (2019) 
(3) TMR9001, MultiDimension Technology, Datasheet available online: http://www.dowaytech.com/en/1866.html (accessed on 24 June 2022) 
(4) M. Rasly et al., J. Phys. D: Appl. Phys. 54, 095002 (2021) 

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CoFeBX layers for MgO based magnetic tunnel junction sensors with improved noise and detectivity

Spintronics-based devices offer certain key advantages like ease of fabrication with Si-substrate, non-volatile memory, low operational voltage, and non-linear device characteristics. Hardware security is a research domain that heavily relies on CMOS-based ICs, and the defense and attack mechanism is developed accordingly.
In this work, we explore shape anisotropy-based PMA Double barrier MTJ based on Verilog-A behavioral model (1) to design a possible Logic locking (2) system for Hardware Security. Logic Locking is a widely used security mechanism to counter multiple threats (3). Due to larger free layer thickness, the s-PMA DMTJ has better thermal stability even in the sub-10nm dimension. The current work focuses on Logic locking applications using this device, analyze its behavior under process variation in certain key parameters using Monte-Carlo simulations, and finally performs Eye-diagram performance analyses to test the design for high-speed digital logic applications. The results indicate that the s-PMA DMTJ has good thermal stability, smaller size (10nm dimension), robustness to device imperfections, and ability to work in high-speed digital circuits compared to other emerging MTJ structures such as STT MTJ, SOT MTJ, VG-SOT MTJ, etc.
Fig. 1(a) represents the block diagram of the logic Locking block, and Fig. 1(b) represents the circuit for implementing the desired operation. We have performed electrical simulations in TSMC 40nm CMOS generic process design kit using the cadence specter simulator with W/L ratio = 3, the temperature at 300K. Fig. 2(a) and 2(c) represent some circuit performance comparisons like the Eye-diagram test for high-speed circuits, and Table 1 presents the simulation data for the same. Fig. 2(b) shows that VG-SOT MTJ (4) fails the eye-diagram test for similar applications for comparison with s-PMA DMTJ. 

**References:** 
(1) H. Wang et al., “Modeling and Evaluation of Sub-10-nm Shape Perpendicular Magnetic Anisotropy Magnetic Tunnel Junctions,” IEEE Transactions on Electron Devices, vol. 65, no. 12, pp. 5537-5544, Dec. 2018. 
(2) H. M. Kamali, K. Z. Azar, F. Farahmandi, and M. Tehranipoor, “Advances in Logic Locking: Past, Present, and Prospects,” Cryptology ePrint Archive, 2022. 
(3) S. Bhunia, and M. Tehranipoor, “Hardware security: a hands-on learning approach,” 1st Edition, 2018. 
(4) K. Zhang, D. Zhang, C. Wang, L. Zeng, Y. Wang and W. Zhao, “Compact Modeling and Analysis of Voltage-Gated Spin-Orbit Torque Magnetic Tunnel Junction,” IEEE Access, vol. 8, pp. 50792-50800, 2020. 
(5) K. Watanabe et al., “Shape anisotropy revisited in single-digit nanometer magnetic tunnel junctions,” Nature Communication, 2018. 

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