United States

Hard-magnetic soft materials has a lot of application scenarios in the field of soft robots and flexible sensors. But, due to the coupling of magnetization process and
manufacturing process, the functions of these devices can not be changed. Therefore, the technique of repeatedly program magnetic anisotropy on magnetic elastomer is of great
significance for changing the functions of magnetic soft robot and sensor. This paper presented a reprogrammable mangetic elastomer based on
Liquid-metal/NdFeB/Silicone composites. The NdFeB particles wrapped in gallium can be re-orientated by thermal-ssisted magnetic programming(Figs.1a-1c). Thus, the magnetization
profile can be reconfigurated on the elastomer(Fig.1d).X-ray diffraction (XRD) analysis shows the phase composition of gallium, Silicone and Nd2Fe14B (Fig.2a). The elstomer&#39;s magnetic
properties are tested by the comprehensive physical property measurement system (PPMS). The moment-temperature (M-T) curve shows the material&#39;s moment jumps at 303 K（the melt
point of gallium)(Fig.2b). And the moment-magnetic field (M-H) curves indicate that the elastomer exhibit hard and soft magnetic properties respectively (Fig.2c), when the temperatureis
lower (293 K) or higher (313 K) than the phase-transition temperature of gallium. A hexagon-shape robot was manufactured and then programmed to two modals of grasping and walking
respectively(Figs.2d and 2e).The experimental results verify the reprogrammability of the proposed composite elastomer. The elastomer is expected to be used to manufacture multi-modal
magnetic soft robot.&lt;br&gt;

**References:**&lt;br&gt;

1. H. Chung, A. M. Parsons, L. Zheng.Magnetically Controlled Soft Robotics Utilizing Elastomers and Gels in Actuation: A Review. Advanced Intelligent Systems, 2020,
2000186.&lt;br&gt;
2. Y. Yan, Z. Hu, Z. Yang, etc. Soft magnetic skin for super-resolution tactile sensing with force self-decoupling. Science Robotics, 2021, 6, eabc8801.&lt;br&gt;
3. L. Cao, D. Yu, Z. Xia, etc. Ferromagnetic Liquid Metal Plasticine with Transformed Shape and Reconfigurable Polarity.Advanced Materials, 2020, 2000827.&lt;br&gt;
4. R. Zhao, H. Dai, H. Yao. Liquid-Metal Magnetic Soft Robot with Reprogrammable Magnetization and Stiffness.IEEE Robotics Automation and Letters, 2022, 7(2): 4535-4541.&lt;br&gt;

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/53bc1b0331eab460b69cc42b5f1a161d.png)

MMM 2022

Reprogrammable Liquid metal/NdFeB/Silicone Composite Magnetic Elastomer

Hard-magnetic soft materials has a lot of application scenarios in the field of soft robots and flexible sensors. But, due to the coupling of magnetization process and
manufacturing process, the functions of these devices can not be changed. Therefore, the technique of repeatedly program magnetic anisotropy on magnetic elastomer is of great
significance for changing the functions of magnetic soft robot and sensor. This paper presented a reprogrammable mangetic elastomer based on
Liquid-metal/NdFeB/Silicone composites. The NdFeB particles wrapped in gallium can be re-orientated by thermal-ssisted magnetic programming(Figs.1a-1c). Thus, the magnetization
profile can be reconfigurated on the elastomer(Fig.1d).X-ray diffraction (XRD) analysis shows the phase composition of gallium, Silicone and Nd2Fe14B (Fig.2a). The elstomer's magnetic
properties are tested by the comprehensive physical property measurement system (PPMS). The moment-temperature (M-T) curve shows the material's moment jumps at 303 K（the melt
point of gallium)(Fig.2b). And the moment-magnetic field (M-H) curves indicate that the elastomer exhibit hard and soft magnetic properties respectively (Fig.2c), when the temperatureis
lower (293 K) or higher (313 K) than the phase-transition temperature of gallium. A hexagon-shape robot was manufactured and then programmed to two modals of grasping and walking
respectively(Figs.2d and 2e).The experimental results verify the reprogrammability of the proposed composite elastomer. The elastomer is expected to be used to manufacture multi-modal
magnetic soft robot. 

**References:** 

1. H. Chung, A. M. Parsons, L. Zheng.Magnetically Controlled Soft Robotics Utilizing Elastomers and Gels in Actuation: A Review. Advanced Intelligent Systems, 2020,
2000186. 
2. Y. Yan, Z. Hu, Z. Yang, etc. Soft magnetic skin for super-resolution tactile sensing with force self-decoupling. Science Robotics, 2021, 6, eabc8801. 
3. L. Cao, D. Yu, Z. Xia, etc. Ferromagnetic Liquid Metal Plasticine with Transformed Shape and Reconfigurable Polarity.Advanced Materials, 2020, 2000827. 
4. R. Zhao, H. Dai, H. Yao. Liquid-Metal Magnetic Soft Robot with Reprogrammable Magnetization and Stiffness.IEEE Robotics Automation and Letters, 2022, 7(2): 4535-4541. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/53bc1b0331eab460b69cc42b5f1a161d.png)

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.

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

A recent theoretical paper [1] predicted a significant Dzyaloshinskii-Moriya interaction (DMI) and perpendicular magnetic anisotropy induced at the interface of hexagonal boron nitride (h-BN) and ultrathin cobalt (Co) crystals. 

The interfacial DMI of the Au/Co/h-BN heterostructure was investigated through the Brillouin Light Scattering technique (BLS) [2]. The Brillouin spectra consist of two peaks, Stokes (S) and anti-Stokes (AS), associated with counter-propagating spin waves, which are affected by DMI in opposite ways, and so have different frequencies [2]. The high sensitivity of the BLS technique allows detection of the small frequency differences and thus measures the DMI strength.

Fig.1-a shows the BLS data obtained from Si/SiO2/Ta/Au/Co(1 nm)/h-BN/Au at different values of wave vector kSW under an external magnetic field of -962 mT. The sokes and anti-Stokes difference (fAS-fS) varies linearly with kSW (Fig.1-c ) following the expected relation: fAS − fS = vDMI/π .kSW

The magnon non-reciprocal velocity vDMI is proportional to the DMI strength (vDMI = 2/π γ Ds / Ms t ) where DS is the DMI parameter.

The vDMI of the Au/Co/h-BN stack is vDMI ≈ 49 m/s, as large as the one reported for the Graphene/Co/Pt interface (vDMI ≈ 50 m/s) [3]. The vDMI decreases with the Co thickness confirming its interfacial nature.

To check that the large DMI obtained for Au/Co/h-BN emerges from the Co/h-BN interface and not from the Au/Co interface, we have measured a reference sample composed of Au/Co (1nm)/Al and obtained
vDMI ≈ 14 m/s, which is three times smaller than the Au/Co/h-BN proving that hBN induces a large DMI. A similar analysis was performed for the interfacial anisotropy, and we found that a significant anisotropy is induced by the h-BN/Co interface, as predicted [1]. 

**References** [1] A. Hallal et al., Nano Letters 21,17, 7138-7144 (2021)
[2] M. Belmeguenai et al., Physical Review B 91, 180405 (2015)
[3] F. Ajejas et al., Nano Letters 9, 5364-5372 (2018)
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/cfdb85cb0373d5d85b9212a6db706d45.png)

Large Dzyaloshinskii Moriya interaction at the h

Optimization of materials for efficient spin current generation and magnetization switching in ferromagnet(FM)/heavy-metal(HM) bilayers is of interest for SOT-MRAM and other applications. Experimentally, alloys of Pt with other elements have been studied as the HM source of spin current, some of which were found to increase the effective spin-Hall angle ξj DL and/or the dampinglike (DL) torque efficiency ξE DL in FM|Pt1−xXx bilayers. Here we use the tight-binding LMTO implementation of the nonequilibrium Green’s function (NEGF) technique [1] to calculate the DL SOT efficiencies for Fe0.75Co0.25|Pt1−xXx bilayers with different alloying elements X, as a function of concentration. The bcc Fe0.75Co0.25 alloy is chosen for the FM layer due to its good lattice matching with fcc Pt and low Gilbert damping. The atomic potentials are obtained using the coherent potential approximation, and the torquances are then evaluated via supercell averaging over substitutional disorder. We find that the largest SOT efficiency ξE DL is achieved by alloying with 20% Au or 10% Rh. Using the calculated residual resistivities of the Pt1−xXx alloys, we estimate the effective spin-Hall angles ξj DL in the alloyed systems. The results are compared with available experimental data.
This work was supported by NSF grant No. DMR-1916275. 
**References** D.Pashov et al. Comput. Phys. Commun. (2020)

Effect of alloying on spin orbit torque in Fe0.75Co0.25|Pt1−xXx bilayers

The synthesis of topological insulators (TIs) of good crystalline quality provides an attractive material platform for low power-consumption spintronic devices of relevance for non-volatile memory applications. While experimental measurements of strong spin-orbit torque (SOT) have been reported in Bi1-xSbx alloys, one of the earliest discovered TIs, key questions remain about the nature of SOT in this material system. We describe the synthesis of Bi1-xSbx thin films of good crystalline quality by molecular beam epitaxy (MBE) and the characterization of these films using in vacuo angle-resolved photoemission spectroscopy (ARPES) as well as ex situ transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. ARPES measurements of samples with varying compositions allow us to track the band structure across the trivial and topological regimes. After synthesizing Bi1-xSbx/Permalloy heterostructures in vacuo with a clean interface, we use spin-torque ferromagnetic resonance (ST-FMR) measurements at room temperature to study the SOT as a function of alloy composition. The experimentally observed behavior of charge-to-spin conversion in Bi1-xSbx is then compared to theoretical calculations of the spin Hall conductivity in this material system [Phys. Rev. Lett. 114, 107201 (2015)]. Supported by the Penn State 2DCC-MIP under NSF Grant No. DMR-2039351 and by SMART, one of seven centers of nCORE, a Semiconductor Research Corporation program, sponsored by the National Institute of Standards and Technology (NIST).

Spin orbit Torque Study on MBE

Dissipative coupling of resonators arising from their cooperative dampings to a common reservoir induces intriguingly new physics such as energy level attraction. In this
study, we report the nonlinear properties in a dissipatively coupled cavity magnonic system. A magnetic material YIG (yttrium iron garnet) is placed at the magnetic field node of a FabryPerot-like microwave cavity such that the magnons and cavity photons are dissipatively coupled. Under high power excitation, a nonlinear effect is observed in the transmission spectra,
showing bistable behaviors. The observed bistabilities are manifested as clockwise, counterclockwise, and butterfly-like hysteresis loops with different frequency detuning. The
experimental results are well explained as a Duffing oscillator dissipatively coupled with a harmonic one and the required trigger condition for bistability could be determined
quantitatively by the coupled oscillator model. Our results demonstrate that the magnon damping has been suppressed by the dissipative interaction, which thereby reduces the threshold for
conventional magnon Kerr bistability. This work sheds light upon potential applications in developing low power nonlinearity devices, enhanced anharmonicity sensors and for exploring
the non-Hermitian physics of cavity magnonics in the nonlinear regime. 
**References** [1] H. Pan, Y. Yang and Z.H. An, arXiv:2206.01231 (2022)
[2] P. Hyde, B. M. Yao, Y. S. Gui, Phys. Rev. B 98, 174423 (2018)

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/d354dd9cd5e5f679db783aefba0047ef.png) 

FIG. 1. (a) Illustration of the experimental setup, where a YIG sphere is imbedded in an assembly cavity. (b) Transmission coeffcient mapping of the hybridized cavity-magnon system. (c)
Dispersion relation of hybridized cavity and magnon mode, where points A and E indicate off-resonance, and point C indicates on-resonance, and points B and D indicate intermediate
frequencies. (d) The fixed field cut of transmission coeffcient mapping at the coupling condition. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/30da0f70b1cedc9cec9c3ce912929efb.png) 

FIG. 2 The jump position of field foldover hysteresis versus P at cavity frequencies (a) A, (b) B, (c) C, (d) D, (e) E. Purple (blue) circle symbols are experimental results of forward
(backward) H field sweeping. The yellow and cyan solid curves are fitted. (f) The threshold for coherent and dissipative coupling system when off- and on-resonance. The threshold for
coherent coupling is from Ref. [2].

Bistability in Dissipatively Coupled Cavity Magnonics

Commercial melt-spun ribbons are typically available in the range of 17–30 µm thickness which limits their high-frequency application due to high eddy current loss. In addition, the ribbons can be annealed for nanocrystallisation to optimise their power loss behaviour 1. However, possible oxidation during annealing and the brittle nature of as-annealed ribbons, makes core fabrication difficult. It is possible, however, to straightforwardly design an alloy composition with moderate Amorphisation Ability (AMA) to in-situ fabricate ultra-thin 2 nano-crystallised ribbons 3, using a high-speed melt spinner. 
By changing the percentages of mainly Si, B and Nb, three alloy compositions with various Amorphisation Ability (AMA) have been designed, based on different liquidus temperatures calculated using CALPHAD, enthalpies of mixing, and atomic mismatch factors. Ultra-thin ribbons of the designed alloys have been synthesised by a high-speed melt spinner, to obtain the advantages of improved material performance and lower costs over commercial ribbons. The melt-spun ultra-thin ribbons (t~5 µm) of Alloys 1 and 2 exhibit nanocrystalline structure owing to their moderate AMA, whereas Alloy 3 with a higher AMA is amorphous (Fig. 1). Interestingly, in-situ nanocrystallised alloys show lower Hc and higher Hk compared to the amorphous alloy (Fig. 2) which makes them perfect candidates for high-frequency applications as they will show lower hysteresis loss (due to low Hc) and lower anomalous loss (less domain wall motion due to high Hk). Additionally, owing to low eddy current loss in ultra-thin ribbons, almost one-fifth of the best available commercially, the total loss is expected to be very low. The lower Hc of nanocrystallised alloys can be attributed to the cancellation of the magnetostriction of the amorphous matrix by the formed nanocrystals. Additionally, the high Hk of such alloys can be owing to the pinned domain walls by the nanocrystals. We have found a cutting-edge methodology to in-situ fabrication of nano-crystallised ultra-thin ribbons which are ideal for minaturised and efficient high-frequency magnetic cores. 
**References:** 1 G. Herzer, J. Magn. Magn. Mater. 133, 248 (1994). 
2 A. Masood, H.A. Baghbaderani, V. Ström, P. Stamenov, P. McCloskey, C. Mathúna, and S. Kulkarni, J. Magn. Magn. Mater. 483, 54 (2019). 
3 K.L. Alvarez, H. Ahmadian Baghbaderani, J.M. Martín, N. Burgos, P. McCloskey, J. González, and A. Masood, J. Non. Cryst. Solids 574, (2021). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/26edc474401a2a615b12e41da81a2288.png) 
Figure 1. XRD patterns of melt-spun alloys. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/aa677410e66f6351ee096321e76ab2cc.png) 
Figure 2. B-H loops of three alloys.

Design and in situ Fabrication of Nano

Soft actuators are required to deform, fold, or unfold in order to interact with their surroundings.[1] One strategy to achieve the movement of mechanically soft systems is
the use of magnetic fields for untethered actuation. Flexible magnetic composites have been demonstrated as functional grippers, rollers, and walkers upon applied external magnetic fields.
[2] Being controlled with electromagnetic coils, magnetic actuators can profit from high-speed actuation to quickly respond to their environment.[3]
The development of an appropriate sensory tracking system for soft actuators is a research topic with open challenges. Light, conformal, and mechanically imperceptible sensing systems
are to be developed to be compatible with soft actuators. In this work, we present flexible magnetosensitive electronic skin which relies on thin-film magnetic field sensors to enable
onboard folding control of origami-like soft actuators. The flexible electronic skin consists of thin film giant magnetoresistive GMR and Hall effect sensors that are used to measure the
magnetization state of the actuator, the applied magnetic fields, and the completeness of the bending process. The resulting intelligent material is mechanically designed to fold even when
the flexible magnetic skin is attached to the soft actuator.[4]
The magnetic origami actuators are made of thin DiAPLEX foils, a shape memory polymer, with embedded NdFeB particles. Such composite can be used to achieve magnetically induced
motion using magnetic fields and a directed light source to increase locally the temperature. We experimentally found the best thickness (60 μm) and concentration (40 NdFeB wt%)
parameters to achieve magnetic folds.[4]
The integration of magnetic soft actuators with e-skins allowed the self-guided assembly of the origami foils. We showed two case studies showing that this approach is useful for
assembling boxes and boat-like origami shapes. This integration process was monitored, followed, and controlled by the output of the laminated sensors. [4] 

**References:** 

[1] A. Miriyev, K. Stack, H. Lipson, et al. Nat. Commun., Vol. 8, p.596 (2017) 
[2] S. Wu, W. Hu, Q. Ze, et al. Multifunct. Mater. Vol. 3, p.042003 (2020) 
[3] X. Wang, G. Mao, G. Jin, et al. Commun. Matter. Vol. 1, p.67 (2020) 
[4] M. Ha, G.S. Cañón Bermúdez, J.A.-C- Liu, et al. Adv. Mater. Vol. 33, p.2008751 (2021)

Magnetically Sensitive Electronic Skins for Supervised Folding of Origami Actuators

For cancer therapy with magnetic hyperthermia by using magnetic nanoparticles (MNPs) [1, 2], alternating magnetic fields (AMF) HAC, typically sinusoidal wave, can deliver the magnetic energy into the deeper location in the body. In this study, we proposed a highly effective heat generation method for the MNPs by the application of an ultra-short pulse. We numerically evaluated the heating power with a variety of parameters, such as pulse width, field amplitude, and frequency [3]. Figure 1 shows effective magnetic hyperthermia with the ultra-short pulse magnetic field (Fig.1 (a)). The hysteresis curve and magnetization dynamics clearly indicate larger energy dissipation (Figs. 1 (b) and (c)). Figure 2 shows the energy dissipation and efficiency [4, 5] on the two-dimensional parameter space of field strength and duty ratio. Hysteresis loss and the input energy increases increasing with field strength and duty ratio (Figs. 2(a) and (b)) and there is a large efficiency power condition (Fig.2 (c)). To evaluate the effective heat generation and practical temperature increment, a larger imaginary part of magnetic susceptibility (Ï‡â€™â€™ &gt; 30) and specific loss power (SLP &gt; 105 W/kg) are required (Figs. 2 (d) and (e)). In addition, larger intrinsic loss power (100 nHm2/kg) is achieved (Fig. 2 (f)). Finally, we found the optimal condition of applied AMF (duty ratio = 1.2% and HAC = 16 kA/m) considering the practical uses. The results indicate that magnetic harmonics signals with a higher frequency range significantly enhance the heat generation of MNPs. We explore further studies of the development of an effective pulse generator for clinical applications and evaluation of the heating effect in animal experiments.

Ultra short pulse magnetic fields on effective magnetic hyperthermia for cancer therapy

Due to their high spin polarization and easy manipulation, ferromagnetic materials dominate as the magnetically active element in spintronic devices but come with drawbacks such as large stray fields, limited scalability, and limited operational frequencies [1-3]. These shortcomings have recently inspired researchers to consider antiferromagnetic spintronics [4], as antiferromagnetic materials have no stray fields and possess ultrafast spin dynamics. However, antiferromagnets have no net magnetic moment, which leads to weak read-out signals and more difficult operation. Compensated ferrimagnets (FiMs) provide an alternative as they combine the properties of ferromagnets and antiferromagnets. In particular, FiMs can have near THz resonances as in antiferromagnets, while still having a net magnetic moment which can be used for strong read-out signals and frequency control, such as efficient tunable microwave signal output from FiM based nano-oscillators. Due to these unique properties, research in FiMs for spintronic applications is intensifying [5-7]. However, to use ferrimagnets in spintronic devices such as in spin Hall nano-oscillators (SHNOs), it is important to ensure that such films retain their advantageous properties in ultrathin films and in nano devices.
In the present study, ferrimagnetic GdFeCo thin films were grown using co-sputtering of Gd and Fe87.5Co12.5 on high resistance Si (100) substrates, and their magnetodynamic properties were studied using broadband ferromagnetic resonance measurements at room temperature. By tuning the stoichiometry of the GdFeCo films, a nearly compensated behavior is for the first time demonstrated in 2 nm thin film, as shown in Fig. 1. Values for the effective magnetization and effective Gilbert damping constant (α) of 0.02 Tesla and 0.0078±0.0002 are obtained for a 2 nm Gd24.4(FeCo)75.6 film [8], where α is comparable to the lowest value obtained in thick films [9]. The vertical dotted lines in Fig. 1 show literature values [6, 9-10] for the spin angular momentum (xa) and magnetic momentum (xm) compensation points in thick films. The composition of the films for the magnetic moment and angular momentum compensation in this work is very close to those reported in the literature.
In search of high-frequency auto-oscillations in spin Hall nano-oscillators (SHNOs), constrictions with 50-300 nm widths were also prepared using GdFeCo(2-10nm)/Pt(5nm) based stacks. Brillouing Light Scattering microscopy measurements on SHNOs show auto-oscillations in the 8 GHz range, as shown in Fig. 2 [11]. Very interestingly, different Gd compositions result in different signs of the threshold current, which indicates different signs of the effective spin-orbit torque as a function of the composition. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/0ec1329d0bf0522e3ffef8763deade00.png) 
Fig. 2. (a,b) Brillouin Light Scattering Spectroscopy (BLS) vs. current of two GdFeCo based SHNOs with different Gd content, believed to operate at opposite sides of the angular momentum conpensation point (SHNO temperature > RT due to Joule heating). While thermal SWs [ferromagnetic resonace (FMR)] are seen at all currents, the Gd rich SHNO only shows auto-oscillations (AO) at negative current, and the Gd poor SHNO only shows AO at positive current. (c,d) Log plots of the BLS counts from (a,b) for the thermal spin waves SWs (green) and the AO SWs (red). While the FMR show a slight current dependence due to heating, the AO intensity shows an initially exponential increase, as expected around threshold. Insets shows the BLS spectrum profile at the highest current.

**References:** 

[1] M. Romera et al., Nature 2018, 563, 230. 
[2] M. Zahedinejad et al., Nat. Nanotechnol. 15, 47 (2020). 
[3] B. Dieny et al., Nat. Elec. 3, 446 (2020). 
[4] T. Jungwirth et al., Nat. Nanotechnol. 11, 231 (2016). 
[5] S. K. Kim et al., Nat. Mat. 21, 24 (2022). 
[6] C. Stanciu et al., Phys. Rev. B 73, 220402 (2006). 
[7] D. Cespedes-Berrocal et al., Adv. Mat. 33, 2007047 (2021). 
[8] Lakhan Bainsla et al., Adv. Funct. Mater. 32, 2111693 (2022). 
[9] D.H. Kim et al., Phys. Rev. L 122, 127203 (2019). 
[10] Y. Hirata et al., Phys. Rev. B 97, 220403 (R) (2018). 
[11] L. Bainsla, A. A. Awad, J. Åkerman et al., unpublished.

Composition dependent threshold current polarity in ferrimagnetic spin Hall nano oscillators based on GdFeCo

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

Symmetry plays a central role in determining the form of electrically-generated spin torques in magnetic devices. Here, we show that an unconventional out-of-plane damping-like torque can be generated in ruthenium oxide (RuO2)/permalloy devices when the Néel vector of the collinear antiferromagnet RuO2 is canted relative to the sample plane [1]. By measuring characteristic changes in all three components of the electric-field-induced torque vector as a function of the angle of the electric field relative to the crystal axes, we find that the RuO2 generates a spin current with a well-defined tilted spin orientation that is approximately parallel to the Néel vector. This dependence is the signature of an antiferromagnetic spin-Hall effect predicted to arise from momentum-dependent spin splitting within the bandstructure of RuO2, rather than from spin-orbit coupling [2]. The unconventional components are absent in the isostructural but non-magnetic rutile oxide IrO2[3]. The out-of-plane antidamping component of the spin torque from RuO2 is among the strongest measured in any material even with the antiferromagnetic domain structure uncontrolled, suggesting that high efficiencies are useful for switching magnetic devices with perpendicular magnetic anisotropy might be achieved by controlling the domain structure. 

**References:** 

[1] A. Bose, N. J. Schreiber, R. Jain, et. al. Nature Electronics 5, 267 (2022). doi.org/10.1038/s41928-022-00744-8 
[2] R. González-Hernández, L. Šmejkal, K. Výborný et al., Phys. Rev. Lett. 126, 127701 (2021). 
[3] A. Bose, J. Nelson, X. S. Zhang. et al. Effects of anisotropic strain on spin-orbit torque produced by the Dirac nodal line semimetal IrO2. ACS Appl. Mater. Interfaces 12, 55411–55416 (2020). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/6a48eb9c2f8c65dbb2616e8a12630299.png) 

(a) Schematic representation of the tilted spin-current generated from RuO2 from the spin-split bands. Angular dependence of the generated torques in Py/(101)RuO2 bilayers originating from the y-component of the spins (a), z-component spins (b), and x-component spins (c), exhibiting angular dependence of cos2Φ, cosΦ, and sin2Φ respectively.

Premium content

Reprogrammable Liquid metal/NdFeB/Silicone Composite Magnetic Elastomer

Downloads

Next from MMM 2022

Large Dzyaloshinskii Moriya interaction at the h

Stay up to date with the latest Underline news!

PRESENTATIONS

CONFERENCES

COMPANY

RESOURCES