Magneto-ionics (MI) provides a nonvolatile EF modulation of magnetism through the migration of ions toward/away from the magnetic interfaces that allows for low-power spintronics devices. However, the ionic mechanism involved still needs to be explored, as key properties such as reversibility have been shown to strongly depend on the chemical composition and oxidation level of the ferromagnet (FM)/oxide interface, (1–3), and on the degree of crystallinity of the system (4). We have recently shown that the gate-voltage driven degree of oxidation at the FM/oxide interface in Ta/Co20Fe60B20/HfO2 defines two MI regimes: (I) underoxidized to optimally oxidized, and (II) optimally oxidized to overoxidized, accompanied by a change in the magnetization easy axis from in-plane (IP) to out-of-plane (OOP) in regime I and from OOP to IP in regime II (3). Only regime II showed reversibility, which was linked to the different binding strength of the oxygen species in regimes I and II.
In this work, we present the MI behavior in Pt/Co60Fe20B20/HfO2, where also two MI regimes have been identified. In this system, both regime I and II are reversible, but the stability of the nonvolatile magnetic states was found to be significantly different in regime I and II. Magnetic states in regime I was found to be highly stable, with no significant loss of remanence in the hysteresis loops over several weeks after applying the gate voltage. In this regime, a significant variation of the Dzyaloshinskii-Moriya interaction was also observed. In contrast, the magnetic states in regime II (between OOP and IP) were found to evolve with time back to the OOP state within one day after applying the gate voltage. Interestingly, only the final overoxidized IP state is fully stable in regime II.
This disparity in the stability of the MI states in regimes I and II could be attributed to differences in the gate-voltage driven chemical reactions and ionic transport, where also the composition of CoFeB may play an important role. Our results show the importance of studying the link between the ionic mechanisms and the MI state stability, in view of practical applications in spintronics. 

**References:** 
(1) L. Herrera Diez, Y. T. Liu, M. Belmeguenai, et al., Physical Review Applied, 12, 034005 (2019); 
(2) A. Fassatoui, L. Ranno, S. Pizzini, et al., Physical Review Applied, 14, 064041 (2020), 
(3) R. Pachat, D. Ourdani, L. Herrera Diez. et al., Physical Review Applied, 15, 064055 (2021), 
(4) R. Pachat, D. Ourdani, L. Herrera Diez, et al., Adv. Mat. Inter., Accepted (2022) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/ea145b4e40c9304eb75f27a8883b090a.png)

Stability of under/over oxidized magneto ionic states in Pt/Co60Fe20B20/HfO2

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.

![](https://assets.underline.io/uploads/markdown_image/1/image/0d5c24338e22f487f485d4062d620b55.jpg)

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)

![](https://assets.underline.io/uploads/markdown_image/1/image/9276aafb08d714e75ddb64319fe097bf.jpg)

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

Magnetoionics (MI) is a much-in-demand feature for spintronics devices due to its great potential for improving energy efficiency in memory devices. The main feature of MI is to allow for the nonvolatile modulation of magnetic properties [1–5], making MI reversibility a fundamental quality for high device performance. Various studies have addressed issues impacting reversibility such as the presence of different types of ions, oxides and the degree of oxidation at the oxide/ferromagnetic interface [3, 5–8], while the influence of annealing temperature on reversibility has been largely overlooked. Annealing is commonly used to induce crystallization in CoFeB layers leading to the enhancement of perpendicular magnetic anisotropy (PMA), interfacial Dzyaloshinskii-Moriya interaction (iDMI), and tunnel magnetoresistance [9–11], therefore its impact on MI is of great interest. In this study, we show that W/CoFeB/HfO2 thin films annealed at 350°C and 390°C show a significant but irreversible dependence of PMA and DMI on gate voltage. However, an annealing program using a slow ramp that minimizes the exposure to the highest temperatures allows to induce PMA and iDMI while also showing a MI reversibility of 71% in remanence with respect to PMA. This dependence of MI reversibility on annealing profiles and temperatures could be related to the different degrees of crystallinity obtained under different annealing conditions. Such structural differences, such as size and distribution of crystallites, can greatly impact the ion mobility inside the stack and be responsible for observed modulation of the MI reversibility. Our results therefore show that annealing parameters need to be optimized to obtain enhanced magnetic properties without compromising MI performance.

![](https://assets.underline.io/uploads/markdown_image/1/image/54d50bab8c546ddbc8fd33ecfea28690.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/bf6e6dbd3a0f9277642eaa6aab5dd034.jpg)

Effect of Annealing on Magnetoionics in W/CoFeB/HfO2

Effect of Annealing on Magnetoionics in W/CoFeB/HfO2

Controlling magnetic properties of materials with electric fields (EFs) is of remarkable importance in spintronics applications due to its potential for much lower power consumption devices. Much like the power efficiency, two other sought-after features to incorporate are non-volatility and reversibility. This has been demonstrated with magneto-ionics, where EFs induce the migration of mobile ionic-species towards/away from the magnetic interface [1–4]. However, several works conducted in a variety of magneto-ionic materials have revealed important issues like irreversibility, the need of elevated temperatures to recover the initial states and chemical and structural degradation [4–6]. Recent studies have also focused on the differences in magneto-ionic reversibility between various oxides [7], pointing out the importance of the mechanisms governing ionic conduction. In this study, we unravel a higher degree of complexity in an HfO2 based device and demonstrate the coexistence of two distinct magneto-ionic regimes. For this purpose, we chose amorphous Ta/CoFeB/HfO2 thin films grown by magnetron sputtering with an ionic-liquid gate. It is shown that a gate voltage drives the anisotropy of the system from an underoxidized state exhibiting in-plane anisotropy (IPA) to an optimum oxidation level resulting in perpendicular anisotropy (PMA) and further into an overoxidized state resulting IPA in a non-volatile manner. The IPA (underoxidized) to PMA regime is found to be highly irreversible and is significantly faster than the PMA to IPA (overoxidized) regime which is fully reversibile under the same gate voltages. In addition, the effective damping parameter also shows a marked dependence with the anisotropy evolution in different regimes; IPA to PMA regime going from 0.029 to 0.012 and only a modest increase to 0.014 in the PMA to IPA regime. The existence of two magneto-ionic regimes has been linked to a difference in the chemical environment of oxygen species added to under/over oxidized layers. Our results show that different magneto-ionic regimes can coexist and that their identification is of great importance for tuning the properties and the design of high performance spintronics devices based on magneto-ionics.

**References:**

[1] U. Bauer, S. Emori, and G. S. D. Beach, Nat. Nanotech. 8, 411 (2013) [2] U. Bauer, L. Yao, A. J. Tan, and G. S. D. Beach, Nat. Mater. 14, 174 (2015) [3] A. J. Tan, M. Huang, C. O. Avci, and G. S. D. Beach, Nat. Mater. 18, 35 (2019) [4] L. Herrera Diez, Y. Liu, D. Gilbert, M. Belmeguenai, J. Vogel, S. Pizzini, E. Martinez, A. Lamperti, J. Mohammedi, A. Laborieux, et al., Phys. Rev. Appl. 12, 034005 (2019) [5] C. Bi, Y. Liu, T. Newhouse-Illige, M. Xu, M. Rosales, J. W. Freeland, O. Mryasov, S. Zhang, S. G. E. te Velthuis, and W. G. Wang, Phys. Rev. Lett. 113, 267202 (2014) [6] D. A. Gilbert, A. J. Grutter, E. Arenholz, K. Liu, B. J. Kirby, J. A. Borchers, and B. B. Maranville, Nat. Commun. 7, 12264 (2016) [7] A. Fassatoui, Phys. Rev. Appl. 14, 064041 (2020)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/739c64ac3b9dc0fe2b2d809ba80bb186.jpg)
Fig. 1: Graphic representation of the Ta/CoFeB/HfO2 magneto-ionic stack covered with an [EMI-TFSI] ionic liquid gate. The gate voltage induces motion of oxygen species in HfO2 that drive anisotropy changes in the CoFeB layer.

![](https://assets.underline.io/uploads/markdown_image/1/image/a9cfb45146f55322b6c3cafa5270f8f3.jpg)
Fig. 2: A progressive oxidation is induced upon exposure to a gate voltage GV=-2V. Different exposure times t drive the system from IPA (a, initial state) through regime I (IPA to PMA) (b) into PMA (c) and back to IPA through regime II (PMA to IPA) (d).

 Reversible and Irreversible Magneto-ionic Regimes in Ta/CoFeB/HfO2

Devices based on magnetic domain wall (DW) motion are among the most promising candidates for future spintronic data storage, logic, and neuromorphic devices. One critical issue that hinders DW motion is the presence of structural inhomogeneities such as interface intermixing, interface roughness, or crystalline texture, that cause a distribution of magnetic properties in the material. As a result, domain walls undergo local pinning leading to the so-called creep regime at low driving forces. Even beyond this creep regime, the DW motion remains affected by defects. Thus, to achieve fast and efficient DW motion, good control over the intrinsic defects in the material must be obtained. Ultra-thin CoFeB/MgO-based structures with perpendicular magnetic anisotropy are considered the most promising candidates for the future generation of Magnetic Random Access Memory (MRAM) devices. These films are usually annealed at high temperatures (300-400°C) to crystallize the CoFeB layer and get high Tunnelling Magnetoresistance (TMR). This treatment at high temperatures results in the presence of undesirable intrinsic defects. To address this issue, we have developed a very promising process solution based on post-growth He+ ion irradiation to tailor the structural properties of ultrathin magnetic films at the atomic level and improve their performances [1-4]. The utilization of light ions provides the precise control of inter-atomic displacements through the low energy transfer. The key feature of the technology is the post-growth control of structural properties and the related magnetic properties. To perform these irradiation techniques, we have used a compact ion-irradiation facility (Helium-S® from Spin-Ion Technologies), capable of ultra-fast He+ ion irradiation on 1-inch wafers with energies ranging between 5-30 keV [5]. Here, we have studied the influence of two different processes of crystallization in W-CoFeB-MgO structure on domain wall dynamics. The first process is based on the combination of He+ ion irradiation at low fluences (1014 ions/cm2 to 1015 ions/cm2) with annealing. The second process consists of pure thermal annealing. For both processes, annealing temperatures ranging from RT to 400°C have been used. Our results first demonstrate that ion irradiation can induce full crystallization of the CoFeB-MgO materials at much lower temperatures (&lt;250°C) than the pure annealing process (&gt;350°C). In addition, higher anisotropy values can be obtained, which is consistent with sharper interfaces. Domain wall dynamics measured by Kerr microscopy have been compared for both processes. Strong differences have been evidenced in both the creep (few nm/s) and flow regime (few m/s). In particular, the ion-irradiation-induced crystallization process results in higher domain wall velocities as shown in Figure 1 for the creep regime where structural defects have a strong influence. This is consistent with a much lower density of structural inhomogeneities in the material crystallized by ion irradiation. Finally, we will discuss the crystallization process under ion irradiation and show preliminary results of DW motion in magnetic wires where local ion irradiation can also be used to minimize edge defects. Our results show that He+ ion irradiation is a very versatile tool to enhance magnetic materials and devices.

**References:**

[1] J. Fassbender, D. Ravelosona, and Y. Samson, J. of Phys. D.: Appl. Phys., Vol. 37, no. 16 (2004) [2] T. Devolder, I. Barisic, S. Eimer et al., J. of Appl. Phys., Vol. 113, no. 20, p. 203912 (2013) [3] L. Herrera Diez, F. García-Sanchez, J.-P. Adam et al., Appl. Phys. Lett., vol 107, p. 032401 (2015) [4] X. Zhao, B. Zhang, N. Vernier et al., Appl. Phys. Lett., vol. 115, p.122404 (2019) [5] www.spin-ion.com

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/689f25424d7c3fb6596488bc040d25c7.jpg)
Domain wall velocity as a function of the applied out-of-plane magnetic field in the creep regime for the regular annealing process (400°C, 1h) and the process based on He+ irradiation at lower annealing temperatures.

 Enhancing domain wall motion in W/CoFeB/MgO ultrathin films through He+-irradiation-induced crystallization

At the interface of a heavy metal (HM) with a strong spin-orbit coupling (SOC) and a ferromagnetic material (FM), a break in inversion symmetry arises leading to the appearance of several phenomena. One of them is the antisymmetric exchange interaction called the Dzyaloshinskii-Moriya Interaction (iDMI). It is responsible for the stabilization of chiral magnetic structures such as skyrmions and for the non-reciprocity of spin wave propagation. Another interface phenomenon, subject of extensive research in magnetic heterostructures (e.g. for HM /FM / metal oxide (MOx) type stacks) is interfacial Perpendicular Magnetic Anisotropy (iPMA) [2]. This originates from the level of oxidation, from the interface roughness and from the SOC [3]. These two quantities are of considerable interest because of their crucial importance for applications in spintronic devices, such as non-volatile magnetic memories and hard disk recording [4]. As an example, an MgO layer is often used as a tunnel barrier in magnetic tunnel junctions (MTJs), providing high spin transfer torque (SST), or in tunnel magnetoresistance (TMR), which are key properties for such devices. In order to optimize the magnetic properties at the interfaces of thin films, a thermal treatment is often used because it yields structural changes and atomic rearrangement and thus induces phase transition or alloys formation. However, annealing at high temperatures can also induce oxidation thus reducing the volume magnetic moment or increasing the magnetic anisotropy. In this work, we investigate the effect of the annealing temperature on iPMA and iDMI in Pt/Co/MgO stacks, with variable Co thickness (1≤tCo≤6 nm). These stacks were deposited by magnetron sputtering on a Si substrate and annealed at different temperatures (Ta), up to 400°C. For all the studied films, the saturation magnetic moment per unit area was measured by Vibrating Sample magnetometry (VSM) for each Co thickness. This allowed us to accurately determine the saturation magnetization Ms and the dead layer thickness td which are necessary to evaluate iDMI and iPMA. These quantities have been measured using the Brillouin light scattering (BLS) in the Damon-Eshbach (DE) configuration. Effective magnetizations (Meff) were deduced from measurements with fixed wave vector (ksw = 8.08 µm-1) and variable magnetic fields. The presence of the DMI in the studied structures induces a frequency shift between the two Stokes and anti-Stokes modes, this allowed us to quantify the iDMI effective constant (Deff) which is proportional to this shift. The variation of Meff as a function of the inverse of the Co thickness, shows the presence of two different linear regimes separated by a critical thickness (tc), which depends on Ta. This is generally observed in the case of epitaxial growth with a lattice misfit between the constituents, the strain can contribute to Kv⊥ (regime I: t &lt; tc), or to Ks⊥ (regime II: tc &lt; t). In order to separate the different surface/interface anisotropies (magnetocrystalline, magnetoelastic and Neel type) from the volume anisotropies, we have used an adapted model [1]. In figure (1), we can see the evolution of these different anisotropies as a function of the annealing temperature. For Ta above 200°C, a variation in the different contributions of the surface and volume anisotropies is observed. Similar to the iPMA, the evolution of the iDMI interaction was investigated as a function of the annealing temperature and the thickness of the effective magnetic layer. The measurements show that the effective iDMI constant (Deff) is proportional to the inverse effective magnetic thickness. Therefore, for low thicknesses we find that the values of Deff deviate from the linear regime probably due to the reduction of magnetic thickness (effect of dead layer). The iDMI surface constant Ds is then deduced form Deff wich decreases linearly (with absolute value) with the annealing temperature Ta (see figure(2)). It varies from (-1.9pJ/m) at room temperature to (-0.7pJ/m) at 400°C annealing temperature. We then conclude the possibility to modulate the strength of the iDMI by changing the annealing temperature.

**References:**

[1] M. T. Johnson, P. J. H. Bloemenz, F. J. A. den Broeder, and J. J. de Vries, Rep. Prog. Phys. 59, 1409 (1996). [2] B. Dieny and M. Chshiev, Rev. Mod. Phys. 89, 025008 (2017). [3] N.-H. Kim, et al , AIP Adv. 7, 035213 (2017). [4] Xueying Zhang, et al ACS Applied Materials & Interfaces 2018 10 (19), 16887-16892 [5] J. H. Moon, et al, Phys. Rev. B 88, 184404 (2013)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/dd67d9db22ce764185c90945ff722646.jpg)
Variation of the different anisotropy constants magnetocristalline (Kmc⊥), volume (KIme,v⊥) magnetoelastic , Neel-type interface (KN⊥) and the surface (KIIme,s⊥) magnetoelastic as a function of annealing temperature.

![](https://assets.underline.io/uploads/markdown_image/1/image/a29103b80c55a2aa457283b58a111134.jpg)
iDMI surface constant Ds as a function of annealing temperature.

 Annealing temperature and thickness dependencies of perpendicular magnetic Anisotropy and Dzyaloshinskii-Moriya Interaction of Pt/Co/MgO thin film.

COA: Magneto-ionics

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.

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:** Minori Goto, Osaka University



GOM - Voltage-controlled Magnetic Anisotropy and Switching

*Session Chair: Dennis Meier, Norges teknisk-naturvitenskapelige universitet*

These on-demand presentations are available to view at your leisure. 

FE: Electric Field Effects and Magnetization Switching

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)

Got your ticket, but still can’t access the event?

Contact us and our team will look into it.

INTERMAG 2021

*Session Chair: See-Hun Yang, International Business Machines Corp*

These on-demand presentations are available to view at your leisure. 

GD: Novel Recording and Domain Wall Devices

*Session Co-Chair: Maciej Dabrowski, University of Exeter*

*Session Co-Chair: Yu Shiratsuchi, Osaka University*

These on-demand presentations are available to view at your leisure. 

Mohamed Belmeguenai

6

35

Presentations

Stability of under/over oxidized magneto ionic states in Pt/Co60Fe20B20/HfO2

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

Effect of Annealing on Magnetoionics in W/CoFeB/HfO2

Reversible and Irreversible Magneto-ionic Regimes in Ta/CoFeB/HfO2

Enhancing domain wall motion in W/CoFeB/MgO ultrathin films through He+-irradiation-induced crystallization

Annealing temperature and thickness dependencies of perpendicular magnetic Anisotropy and Dzyaloshinskii-Moriya Interaction of Pt/Co/MgO thin film.

Stay up to date with the latest Underline news!

PRESENTATIONS

CONFERENCES

COMPANY

RESOURCES