The actual mechanisms occurring at interfaces underlying the Dzyaloshinskii-Moriya interaction (i-DMI) remain largely an open question in nanomagnetism. In this study, we investigate the origin of the i-DMI, aiming at estimating how independent the DMI contributions of the two interfaces of a FM layer are and what their relative weight in the effective DMI amplitude is. The effective DMI is measured by the study of the asymmetric domain wall propagation in the presence of an in-plane magnetic field, in Pt|Co|M stacks. These measurements are completed by Brillouin light scattering (BLS) measurements. We then explore the correlation between the effective i-DMI and the properties of metal M, namely, its atomic number, electronegativity, and work function. A clear linear relationship is found between the i-DMI and the work function difference at the Co|M interface (ΔΦ) [1,2]. We define Δφ = φM - φCo. This result is a strong evidence of the independent DMI contributions of the two interfaces for the chosen Co thickness (1 nm). These findings may guide the optimization of the magnetic properties of future spintronic devices.
This work has been supported by DARPA TEE program grant (MIPR HR-0011831554), ANR grant TOPSKY (ANR-17-CE24-0025), FLAG-ERA SographMEM (ANR-15-GRFL-0005), and the Horizon2020 Framework Program of the European Commission, under FET Proactive Grant Agreement No. 824123 (SKYTOP) and under Marie Sklodowska- FQ Curie Grant Agreement No. 754303 for supporting J.P.G together with the LABEX LANEF in Grenoble (ANR-10-LABX-0051). Univ. Paris-Saclay, CNRS INP, Sesame IMAGeSPIN project (nEX039175) and the LABEX NanoSaclay (ANR10 LABX0035, BLS@PSay and SPiCY projects) are acknowledged for the BLS equipment. 
**References** [1] F. Ajejas et al., Phys. Rev. Mat., June 2022
[2] Y.-K. Park et al., NPG Asia Mater. 10, 995 (2018)
 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/7e07896034de7f90918b290a6356d04c.png)

Interfacial potential gradient modulates Dzyaloshinskii Moriya interaction in Pt|Co|Metal multilayers

Spin currents and spin-torques generated by spin-orbit coupling (SOC) are exploited in spintronics to meet the high data demand in information technology. Nowadays, the large SOC of 5d non-magnetic heavy metals (HMs) is required to generate a pure spin current by the spin Hall effect (SHE). In turn, the pure spin current generates a spin-orbit torque (SOT) on an attached magnetic layer [1]. 

It is generally accepted that in magnetic materials, the spin polarization of the generated spin current is aligned with the direction of the magnetization due to the exchange interaction. The generation of such spin current is referred to as the Spin Anomalous Hall Effect (SAHE) [2]. More recent theoretical works [3,4] have shown that the latter description is incomplete for magnetic materials with large spin-orbit coupling. In this case, the spin polarization can be preserved from alignment with the magnetization, as demonstrated in ferrimagnets [5]. The total spin current is therefore the sum of SAHE-like and SHE-like spin currents [2-4] as depicted in Fig 1. The SAHE-like spin current cannot induce a torque on the magnetization because the spin polarization is aligned with the magnetization. However, the SHE-like symmetry can generate a torque if the spin current is absorbed outside the layer. We refer this torque as self-torque because the material is the source of the torque on its magnetization. 

In this talk, we present the study of a ferrimagnet with strong spin-orbit coupling: GdFeCo. The SAHE and SHE spin current contributions are studied by complementary Spin Torque Ferromagnetic Resonance (ST-FMR) techniques and self-torque characterization were performed by means of harmonic Hall voltage measurements. We show in GdFeCo/Cu/NiFe trilayer that the ST-FMR voltage at NiFe resonance that is sensitive to GdFeCo SHE-like symmetry does not change sign across the magnetic compensation temperature [6]. The addition of a dc current to ST-FMR experiments allows to quantify the total contribution [6,7]. Additionally, we show in GdFeCo/Cu that the effective fields associated to the self-torques are amplified in the vicinity of the magnetic compensation temperature of the ferrimagnet and reverse their sign across it [7] (see Fig 2). Finally, we present more experimental results with signatures that highlight the difference between external SOT and self-torque taking advantage of characteristics temperatures in ferrimagnets. This study paves the way for further research into the generation of spin currents in ferrimagnets and the exploitation of self-torque generated in single magnetic layer for spintronic devices. 

This work was supported partially from Agence Nationale de la Recherche (France) under contract N° ANR-18-CE24-0008 (MISSION), ANR-19-CE24-0016-01 (TOPTRONICS) and ANR-17-CE24-0025 (TOPSKY), from the French PIA project “Lorraine Universite d’Excellence”, reference ANR-15IDEX-04-LUE. This study is partially funded by MSCA-RISE 2020-Project N°101007825 - ULTIMATE-I. D. C.-B., A.Y.A.C and H. D, acknowledge SPIN IJL team for their internship fellow 2018, 2019 and 2020, respectively. DCB also thanks “LUE Graduated” program internship 2019 from “Lorraine Université d’Excellence”. 
**References** [1] A. Manchon et al., Reviews of Modern Physics, vol. 91, no 3, p. 035004, (2019). 
[2] T. Taniguchi et al., Physical Review Applied, vol. 3, no 4, p. 044001, (2015). 
[3] V. P. Amin, et al., Physical Review B, vol. 99, no 22, p. 220405, (2019). 
[4] K-W. Kim, et al., Physical Review Letters, vol. 125, no 20, p. 207205, (2020). 
[5] Y. Lim, et al., Physical Review B, vol. 103, no 2, p. 024443, (2021). 
[6] H. Damas, et al., p. 2200035, PSS RLL (2022). 
[7] D. Céspedes, H. Damas, et al., Advanced Materials, vol. 33, no 12, p. 2007047, (2021). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/eab861e288e40ae2008c11b2ff3ae59c.png)

Spin currents generation and self Spin Orbit torque in GdFeCo ferrimagnet

Spin-orbit interaction in metals and its ability to generate spin-current has been the hallmark of spintronics in the last decade. Beyond its fundamental interest as a source of spin-current, the manipulation of magnetization via transfer of the spin angular momentum has proven to be energy efficient for spin-based memory (e.g. SOT-MRAM) and also neuromorphic devices (e.g. using spin Hall nano-oscillators). Therein, charge to spin conversion is believed to be governed essentially by two main mechanisms, spin Hall effect in the bulk of heavy-metals and Rashba effect at interfaces [1], the latter being often considered negligible in all-metallic interfaces. However, in the case of atomically thin metallic layers, the underlying SOT physical mechanisms at play have not been experimentally fully tackled. 
In this study, we examine the impact of the insertion of a light element interface on the nature of the SOT as well as its efficiency in terms of damping-like (HDL) and field-like (HFL) effective fields in ultrathin ferromagnets. Importantly, we observe unexpectedly large HFL/HDL ratio (∼2.5) upon inserting a 1.4 nm thin Al layer in Pt|Co|Al|Pt as compared to Cu instead of Al as shown in Fig. 1. From our modeling (dotted lines in Fig.1), these experimental results strongly evidence the presence of a large interfacial Rashba effect at Co|Al interface producing giant HFL. The occurrence of such enhanced torques from an interfacial origin is further validated by reducing the contribution from SHE in the bottom Pt layer as well as by demonstrating current-induced magnetization reversal at reduced current. We believe that our results are important from the application point of view as they provide a clear route for reaching ultimate spin-torque efficiency for the associated devices[2]. 
**Acknowledgement:** DARPA TEE (MIPR no. HR0011831554), the Horizon2020 Framework Program of the European Commission under FET-Proactive Grant agreement No. 824123 (SKYTOP) and the the Agence Nationale de la Recherche, France, No. ANR-17-CE24-0025 (TOPSKY). 
**References:** [1] Manchon, A. et al., Rev. Mod. Phys. 91, (2019). 
[2] Krishnia S. et al., arXiv : 2205.08486. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/d8fd135b8e9157bc0dc4a5f819d2811b.png) 
Co thickness (tCo) dependence of (a) DL-SOT field and (b) FL-like SOT fields in Pt8|Co (tCo)|Al1.4|Pt3 (red ) and Pt8|Co (tCo)|Cu1.4|Pt3 (blue ) samples (c) ζ = HFL/HDL as a function of tCo.

Large interfacial Rashba interaction and giant spin orbit torque in atomically thin metallic multilayers

Magnetic topological textures could serve as powerful tools in the development of next-generation spintronics devices, especially in terms of stability and energy consumption. Two-dimensional (2D) magnetic solitons such as chiral domain walls or skyrmions were mostly under focus for the last decade. Beyond these 2D textures, a new interest has risen for more complex quasi-particles that display variations over the thickness, i.e., three-dimensional (3D) objects. Examples include different skyrmion phases [1], bobbers [2] or even hopfions [3]. In this work, we show how by engineering Pt/Co/Al based multilayers with variable Co thickness, we observe the signature of new textures, called skyrmionic cocoons [4] that are only present in a fraction of the magnetic layers. Interestingly, these cocoons can coexist with more standard ‘tubular’ skyrmions going through all the multilayer as evidenced by the existence of two very different contrasts in the magnetic force microscopy (MFM) images recorded at room temperature (Fig. 1a). Moreover, the field dependence of skyrmionic cocoons has also been studied with Fourier transform holography measurements (FTH) with similar observations (Fig. 1b). FTH additionally puts forward various magnetic phase transitions as well as the existence of an attractive interaction between cocoons. The presence of these novel skyrmionic textures has also been investigated by micromagnetic simulations (Fig. 1c). The relaxed states can easily be identified with the different experimental contrasts: the columnar skyrmion tubes (resp. cocoons) corresponds to the strong contrast (resp. weak contrast). Thus, this coexistence of various magnetic textures in multilayers and the discovery of a novel magnetic texture are particularly interesting as they can open new paths for three-dimensional spintronics. 
**References** [1] A.O. Mandru et al. Nature communications 11,1 (2020)
[2] F. Zheng et al. Nature Nanotechnology 13, 451 (2018)
[3] N. Kent et al. Nature communications 12, 1 (2021)
[4] M. Grelier et al. arXiv: 2205.01172 (2022). 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/b8a97625e75c0927f841711b49e2982a.png)

Skyrmionic 3D cocoons in magnetic multilayers

In the post-Moore era, spintronic is one of the key technologies to break the bottleneck of high energy consumption of electronic devices1. However, as the process node
moves on, conventional ferromagnet-based spintronic devices meet the superparamagnetic size limit. Under such circumstance, perpendicular synthetic antiferromagnets with high
scalability and readability, strong immunity to external field and ultrafast dynamics, become a competitive choice for the next generation spintronics memory and logic devices2. Here, we propose a strategy to energy efficiently operate their magnetic order by spin orbit torque (SOT) under zero external field through the introduction of interlayer Dzyaloshinskii–Moriya interaction (DMI)3,4. By macro-spin simulation, we show that the speed of field-free switching increases with the in-plane mirror asymmetry of injected spins. We experimentally observe the existence of interlayer DMI in our SAF sample by an azimuthal angular dependent anomalous Hall measurement. Field-free switching is accomplished in such a sample and the strength of the effective switching field demonstrates its origin from interlayer DMI. Compared with previous field-free switching solutions, the performance of SOT device is well preserved. Our work pave the way for a wide range of potential high performance SOT devices5. 
**References** 
1 Z. Guo, J. Yin, Y. Bai et al., Proceedings of the IEEE., vol.109, p.8, (2021)
2 R. A. Duine, K. J. Lee, S. S. P. Parkin, M. D. Stiles, Nature Physics., Vol.14, p.217–219 (2018).
3 D. Han, K Lee, J Hanke et.al., Nature Materials., Vol.18, p.703–708 (2019)
4 A. Fernández-Pacheco, et al., Nature Materials., Vol.18, p.679–684 (2019).
5 Z. Wang, P. LI, Y. Yao et al., https://arxiv.org/abs/2205.04740, (2022) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/377f489a894bf078aadba05a26cdde29.png) 
Schematic illustration of SAF field-free SOT switching through interlayer DMI. (A-D) Spin textures' evolution with time during the application of a SOT current pulse along -x. (E) A
sketch of the experimental setup where the switching mechanism under a domain nucleation and propagation regime is indicated. The probe laser is used to detect the MOKE signal in our
experiment. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/7e7d043248771b0807a14e84b77ecab4.png) 
Field-free SOT switching detected by optical Kerr measurement. (A) Normalized p-MOKE signal of the studied film. (B) Kerr image after the application of a current pulse. The switching
area is counted from the composite image below. (C) Summarization of current induced switching behavior as a function of azimuthal direction.

Field free spin

Room-temperature skyrmions have been presented as potential candidates for encoding information bits in several types of new spintronic devices [1]. There have been many recent progresses allowing to stabilize sub-100 nm skyrmions at room temperature in crystalline ferromagnetic thick layers or in (amorphous) thin magnetic multilayers (MML) [2]. In most case, at least in extended films or large structures, the application of relatively large perpendicular field (a few 10 mT) is needed which might be unfavorable for most of the anticipated skyrmion based devices. Hence, the stabilization of zero-field isolated skyrmions or skyrmion lattices is an important step towards application. There are recent works demonstrating isolated zero-field skyrmions stabilized due to interlayer exchange in polycrystalline [3], epitaxial [4] or exchange biased [5] trilayers. Here we demonstrate a new approach showing that room-temperature zero-field skyrmion lattices can be stabilized in MML. We develop a system in which perpendicular magnetic anisotropy, chiral order and bias field strength, through a non-magnetic spacer, can be adjusted simultaneously. Typical stacking sequence is schematically presented in Figure 1 (a). The samples have been characterized first by standard magnetometry (Fig. 1b). Relying on the interlayer electronic coupling to an adjacent bias magnetic layer with strong perpendicular magnetic anisotropy (uniform configuration), we demonstrate by Magnetic Force Microscopy that the remnant wormy-stripe “as-grown” domains (Fig. 1d) can be turned into skyrmion lattice phase (Fig. 1c). The skyrmion density and size can be modified by finely tuning the thicknesses of the layers allowing the control of the parameters related in the stabilization of the lattices. ANR TOPSKY (ANR-17-CE24-0025), DARPA TEE program (MIPR#HR0011831554) and EU SKYTOP (H2020 FET Proactive 824123) are acknowledged for financial support. 
**References** [1] A. Fert, N. Reyren, V. Cros, Nat. Rev. Mat. 2, 17031 (2017)
[2] C. Moreau-Luchaire et al., Nat. Nanotechnol. 11, 444 (2016)
[3] G. Chen et al., Appl. Phys. Lett. 106, 242404 (2015)
[4] R. Loconte et al., doi : 10.1021/acs.nanolett.0c00137
[5] K. G. Rana et al., Phys. Rev. Applied 13, 044079 (2020)
 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/c7358254fecfd168f1a707d1ac7e39b6.png)

Zero field room

In nanomagnetism and spintronics, magnetic multilayers continue to thrive as pivotal structures to engineer complex non-trivial spin textures thanks to the tunability of their composition and their properties. Two-dimensional magnetic textures such as skyrmions or chiral domain walls were mostly under focus for the last decade, but recently interest has surged for more complex objects which display an inhomogeneous behavior over the vertical dimension [1,2]. Interesting examples include bobbers which could become remarkable assets for the development of logic devices [3] or the recently observed hopfions [4] or even different skyrmions phases [5]. Our own efforts to engineer and explore three-dimensional textures in Pt/Co based multilayers allows us to observe the signature of new textures, which we name skyrmionic cocoons. At low magnetic field, they resemble tubular skyrmions but upon an increase of the out-of-plane field, they shrink and disappear in the outer layers (Fig 1.b,c), becoming elongated ellipsoids. To observe such textures, we grew multilayers displaying variable thicknesses of a ferromagnetic material, thereby introducing a non-uniform effective anisotropy. By carefully tuning the thickness of each magnetic layer, it was possible to observe in a single sample two distinct types of objects, as shown by the strong difference in the Magnetic Force Microscopy (MFM) contrasts (Fig 1.a). With the support of micromagnetic simulations (Fig 1.b), we identify them as two vertically coupled cocoons (large contrast) and single cocoons only present in half of the layers (weak contrast). The existence and field-dependent behavior of such textures could represent interesting possibilities for potential applications.

![](https://assets.underline.io/uploads/markdown_image/1/image/e2c9cf21f889d9f4fd7c83a4aa3ac691.jpg)

Fig 1. a) MFM measurement at 265 mT on a multilayer with variable thickness of Co. b) Corresponding micromagnetic simulations at different fields displayed with isosurfaces, mz=0 (white) and mz=-0.8 (red), with plane cuts identified by the coloured lines. The yellow dotted ellipses evidence the two kinds of objects correlated with the MFM image: coupled cocoons (left) and single cocoons (right). c) Simulated vertical cuts showing the evolution of a cocoon at different out-of-plane magnetic fields.

Non-Collinear Three-Dimensional Textures In Magnetic Multilayers: Hatching of Skyrmionic Cocoons

Generation of spin-current and its transport across interfaces, as well as its interaction with magnetic moments, are the central themes of spintronic community to enable fast and efficient magnetization dynamics for data storage devices. There are two main mechanisms to produce the spin-current in non-magnetic materials: (a) spin Hall effect (SHE) in heavy metals such as Pt or Ta and (b) Rashba effect (RE) at the interfaces1. Irrespective of the origin, the spin-current exerts torques on adjacent ferromagnetic layer with two components: damping-like (DL) & field-like (FL)2. However, disentangling properly SHE from RE remains highly challenging. In this experimental study we identify the mechanisms of spin-transport in ultrathin magnetic multilayer whose thicknesses range from less to above the characteristic spin- decoherence length. To this aim, we quantify the different SOT contributions in series of samples Pt8|Cox|Al1.4|Pt3 and P8|Cox|Cu1.4|Pt3 (as a reference ) with x varying from 0.4 to 1.4 nm. We extract, in each case, a spin decoherence length to be around 1.1 nm. Surprisingly, SOT investigation in the Pt8|Cox|Al 1.4|Pt 3 reveals a dominating FL torque (HFL/HDL&gt;1), which is a signature of a strong Rashba interface in Al-based systems. As a comparison, we find that the Rashba interaction is small in Pt8|Cox|Cu1.4|Pt3 samples. Moreover, we determine the SOTs characteristics in Pt(x)/Co(0.9)/Al(5) by varying the Pt thickness (tPt). The bulk spin Hall angle of Pt(θSHE) and ratio of HFL and HDL as a function of tPt are shown in Figure 1(a) and (b). The increase in HFL/HDL in the range of Pt thickness where the bulk SHE of Pt started decreasing, strongly favors our argument of the presence of Rashba interface3, exhibiting thus the specific role of Al insertion layers to enhance spin-orbit effects. Financial support from the Agence Nationale de la Recherche, France, No. ANR-17-CE24-0025 (TOPSKY), the Horizon2020 Framework Programme of the European Commission under FET-Proactive Grant agreement No. 824123 (SKYTOP), FLAGERA SOGRaphMEM and the DARPA TEE programme through grant MIPR no. HR0011831554 are acknowledged

![](https://assets.underline.io/uploads/markdown_image/1/image/ae330d77631623209411e1c48a048ff1.jpg)

Figure 1(a) θSHE vs tPt in Ta(5)/Pt(x)/Co(0.9)/Al(5). (b) Ratio of HFL/HDL as a function of tPt.

Rashba Spin-Orbit Torque in Interface Engineered Ultrathin Metallic Multilayers

EOE: Spin-Orbitronics I

technical paper

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FOB: Spin Hall and Spin-Orbit Torque I

EOD: Skyrmions II

GOE: Magnetization Dynamics V

**Please click on the poster to see the abstract or leave your comment to the author.** 
**Session Chair:** Yue Li, *Argonne National Laboratory*

EPB: Skyrmions and Spin-Orbitronics

poster

**Session chair:** Aisha Aqeel, University of Munich



GOG - Fundamental Interactions in Skyrmions and Novel Phases

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.

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Albert Fert

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Presentations

Interfacial potential gradient modulates Dzyaloshinskii Moriya interaction in Pt|Co|Metal multilayers

Spin currents generation and self Spin Orbit torque in GdFeCo ferrimagnet

Large interfacial Rashba interaction and giant spin orbit torque in atomically thin metallic multilayers

Skyrmionic 3D cocoons in magnetic multilayers

Field free spin

Zero field room

Non-Collinear Three-Dimensional Textures In Magnetic Multilayers: Hatching of Skyrmionic Cocoons

Rashba Spin-Orbit Torque in Interface Engineered Ultrathin Metallic Multilayers

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