United States

Magnetic skyrmions is a vortex like nanosized spin swirling texture with particle like property [1]. In the past decade, magnetic skyrmion has triggered great interest as component in futuristic magnetic memory devices due to its topological property, smaller size (few nm) and efficient current driven motion. The chiral cubic β-Mn type (Co0.5Zn0.5)20-xMnx (3 ≤ x ≤ 7) alloys are fascinating as they allow the fine tuning of size and stability of skyrmions in wide temperature range with composition [2]. Among (Co0.5Zn0.5)20-xMnx alloys, magnetic properties of the Co7Zn7Mn6 alloy are of renewed interest due to the detection of two independent skyrmion phases (SkX): (i) a conventional thermodynamically stable SkX below helimagnetic to paramagnetic transition temperature (TC ~ 213 K) and (ii) a disordered skyrmion phase above spin glass transition (Tg ~ 23 K) [3-4]. In spite of much progress made on the investigation of exotic magnetic field-temperature phase diagram of Co7Zn7Mn6 helimagnet, the nature of its underlying magnetic interactions still remains elusive. Thus an elaborate in-field critical behavior study of skyrmion hosting polycrystalline cubic β-Mn type Co7Zn7Mn6 chiral magnet based on magnetic isotherms measured in the vicinity of ordering temperature is presented. The critical exponents β, γ and δ for spontaneous magnetization, initial magnetic susceptibility and critical M-H isotherm, respectively are evaluated through the modified Arrott plot, Kouvel-Fisher method and critical isotherm analysis. The estimated critical exponents β = 0.382(1), γ = 1.386(2) and δ = 4.628(1) follow Widom equality and magnetic scaling equations of state. The values of these exponents corroborate that the critical behaviour of Co7Zn7Mn6 system is akin to that of three-dimensional (3D) isotropic nearest-neighbour Heisenberg ferromagnet in which the attractive extended type short-range interactions between spins decay with distance r as J(r) ~ r-4:94.&lt;br&gt;&lt;br&gt;
**References**&lt;br&gt; 1. S. Mühlbauer, B. Binz, F. Jonietz, Science 323, 915 (2009)
2. Y. Tokunaga, X. Yu, J. White, Nat. Commun. 6 (1) 1–7 (2015)
3. K. Karube, J. S. White, D. Morikawa, Sci. Adv. 4 (9) eaar7043 (2018)
4. V. Ukleev, K. Karube, P. Derlet, npj Quant. Mater. 6 (1) 1–8 (2021)&lt;br&gt;&lt;br&gt;
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/f914361d531608bdd6148afd8e904925.png)

MMM 2022

In field critical behaviour of β

Magnetic skyrmions is a vortex like nanosized spin swirling texture with particle like property [1]. In the past decade, magnetic skyrmion has triggered great interest as component in futuristic magnetic memory devices due to its topological property, smaller size (few nm) and efficient current driven motion. The chiral cubic β-Mn type (Co0.5Zn0.5)20-xMnx (3 ≤ x ≤ 7) alloys are fascinating as they allow the fine tuning of size and stability of skyrmions in wide temperature range with composition [2]. Among (Co0.5Zn0.5)20-xMnx alloys, magnetic properties of the Co7Zn7Mn6 alloy are of renewed interest due to the detection of two independent skyrmion phases (SkX): (i) a conventional thermodynamically stable SkX below helimagnetic to paramagnetic transition temperature (TC ~ 213 K) and (ii) a disordered skyrmion phase above spin glass transition (Tg ~ 23 K) [3-4]. In spite of much progress made on the investigation of exotic magnetic field-temperature phase diagram of Co7Zn7Mn6 helimagnet, the nature of its underlying magnetic interactions still remains elusive. Thus an elaborate in-field critical behavior study of skyrmion hosting polycrystalline cubic β-Mn type Co7Zn7Mn6 chiral magnet based on magnetic isotherms measured in the vicinity of ordering temperature is presented. The critical exponents β, γ and δ for spontaneous magnetization, initial magnetic susceptibility and critical M-H isotherm, respectively are evaluated through the modified Arrott plot, Kouvel-Fisher method and critical isotherm analysis. The estimated critical exponents β = 0.382(1), γ = 1.386(2) and δ = 4.628(1) follow Widom equality and magnetic scaling equations of state. The values of these exponents corroborate that the critical behaviour of Co7Zn7Mn6 system is akin to that of three-dimensional (3D) isotropic nearest-neighbour Heisenberg ferromagnet in which the attractive extended type short-range interactions between spins decay with distance r as J(r) ~ r-4:94. 
**References** 1. S. Mühlbauer, B. Binz, F. Jonietz, Science 323, 915 (2009)
2. Y. Tokunaga, X. Yu, J. White, Nat. Commun. 6 (1) 1–7 (2015)
3. K. Karube, J. S. White, D. Morikawa, Sci. Adv. 4 (9) eaar7043 (2018)
4. V. Ukleev, K. Karube, P. Derlet, npj Quant. Mater. 6 (1) 1–8 (2021) 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/f914361d531608bdd6148afd8e904925.png)

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.

<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.

We investigated the spin-orbit torque (SOT) switching of the single CoTb layer with or without the heavy metals (Pt and W) in different thicknesses to identify the self-torque effects generated in the CoTb layer. The generation of self-torque heavily depends on the thickness of CoTb. The SOT switching was not observed for a single CoTb layer with 3nm in thickness, suggesting self-torque may be quite weak in a very thin film. A deterministic SOT switching can be obtained for a single 9 nm CoTb layer. The amplitude of the self-torque generated in CoTb is comparable to the Pt/Co case with the same switching polarity as the Pt/Co one. When 3 nm CoTb has deposited on Pt or W underlayer, the Jc is smaller in W/CoTb than that of Pt/CoTb, which can be attributable to a high spin hall angle of W and negligible self-torque of CoTb. On the other hand, when the CoTb is increased to 9 nm, the Jc of W/CoTb is significantly increased and becomes higher than that of Pt/CoTb. The enhanced Jc of W/CoTb may result from the opposite sign of spin-orbit torque generated in W and CoTb. Since the self-torque generated in 9 nm CoTb becomes substantial, the competition of spin-orbit torque between W and CoTb occurs, leading to a high Jc. We define the switching efficiency η=(2Hk2-Hx2)1/2*Mst/Jc based on the macrospin model 1, in which Hk and Hx are anisotropy field and applied magnetic field along the x-direction. The variations of η with the layer structure are shown in Table 1. The addition of SOT from Pt and self-torque from CoTb leads to enhanced switching efficiency when the thickness of CoTb is increased. On the other hand, the competition of SOT from W and self-torque in TbCo of W/CoTb devices was revealed by increasing the thickness of CoTb. We further confirm this interplay by reversing the stack order, that is, CoTb/W, in which the efficiency is substantially enhanced. 
**References** 1 T. Taniguchi, S. Mitani, and M. Hayashi, Physical Review B., Vol.92, 024428 (2015).
 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/ec40a41b988acdfdc283eb21e90877ae.png)

Effects of self torque in rare earth

Magnetic multilayers are material systems that offer a high degree of tunability with respect to their magnetic and electronic properties. These are essential for today’s spintronics and magnonics-based magnetic applications [1], [2]. The Dzyaloshinskii-Moriya interaction (DMI) [3] is one of the interesting phenomena in such multilayers that give rise to the presence of magnetic skyrmions under certain conditions even at room temperature. Pt/Co is one of the most promising classes of the multilayers that contributes to a significant DMI due to the different characters of Pt/Co and Co/Pt interfaces [4]. The performance of the films may vary depending on the substrates, deposition temperature, layer thickness, and other factors in the Pt/Co multilayers. The thermal stability can be significantly increased and the magnetic anisotropy of Pt/Co multilayers can be controlled by adding spacer layers between two Co layers [5].
In our study, we investigate magnetic bubbles in Pt/Co-based multilayer thin films. The bubbles have been expanded using an external magnetic field both in-plane and out-of-plane. In presence of the in-plane field, bubbles expand asymmetrically as observed in Fig.1(a). The in-plane field-dependent velocities of two opposite chiral domain walls are measured as shown in Fig. 1(b). The asymmetry of bubble expansion is found to be influenced by the thickness of Co which gives us information about the intrinsic chiral properties of the system. Mumax simulations are performed to understand underlying behavior. The study is important for race track memory applications. 
**References** [1]. R. E. Camley, and R. L. Stamps, “Magnetic multilayers: spin configurations, excitations, and giant magnetoresistance,” Journal of Physics: Condensed Matter, vol. 5, no. 23, 1993.
[2]. E. Y. Vedmedenko, R. K. Kawakami, D. D. Sheka, P. Gambardella, A. Kirilyukand, A. Hirohata, C. Binek, O. Chubykalo-Fesenko, S. Sanvito, and B. J. Kirby, “The 2020 magnetism roadmap,” Journal of Physics D: Applied Physics, vol. 53, no. 45, 2020.
[3]. T. Moriya, “Anisotropic Superexchange Interaction and Weak Ferromagnetism,” Phys. Rev, 1960.
[4]. A. W. J. Wells, P. M. Shepley, C. H. Marrows, and T. A. Moore, “Effect of interfacial intermixing on the Dzyaloshinskii-Moriya interaction in Pt/Co/Pt,” Phys. Rev. B, vol. 95, 2017.
[5]. S. Eimer, H. Cheng, J. Li, and X. Zhang, “Perpendicular magnetic anisotropy based spintronics devices in Pt/Co stacks under different hard and flexible substrates,” Science China. Information Sciences, 2021. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/001992406af8d24736a081aa931dd565.png)

Asymmetric Pt/Co magnetic multilayers bubble expansion under in plane and out

Magnetic skyrmion, as one of the topologically protected spin textures stabilized in the materials with perpendicular magnetic anisotropy (PMA) and interfacial Dzyaloshinskii-Moriya interaction (iDMI), are quite small in the nanometer size and can be driven by spin torque with lower current density, which provide a reliable technique for use in next-generation racetrack memory, logical devices, spin transfer nano-oscillator, etc. Magnetic skyrmion in the above applications are mainly based on the controllable motion of skyrmions in the confined geometrics. Furthermore, a controllable, reproducible, and realized skyrmion nucleation is another most important elements in such skyrmion-based devices. Several researchers have proposed and demonstrated skyrmion nucleation schemes, such as, patterning the magnetic structures with notches or defects, domain wall transfer or chopping to skyrmions. However, all these methods include significant structural or even geometrical modifications of the magnetic racetrack which increasing the devices design complexity. Recently works have shown that sputtering process can control magnetic properties, such as PMA and DMI, at the nanoscale. In this work, we adopted a nanoregion without PMA as a skyrmion nucleation core and demonstrate a current driven highly efficient, in-line and on-demand skyrmion nucleation schematic. Fig. 1(a) shows an illustration of skyrmion nucleation devices considered here. One key factor for realizing this is that the vanishing of the PMA and the existing of the DMI induced magnetization tilt and create a chiral perpendicular stripe domain wall at left edges. This stripe domain wall that allows spin torque to efficiently controlled and ejected from the modified region and propelled into the nanowire to form a skyrmion. As shown in Fig. 1(b), this device integrated both skyrmion nucleation and control function is more advantages in simply the devices with two terminals. This working mode could be controlled by the selective current pulse sequence with one for nucleation and another one for shifting which is important to skyrmion-based racetrack memory applications. 
**References** 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/65b7bbe9fea336b04a564b2f3332d1ea.png)

Magnetic skyrmion nucleation via current injection in confined nanowire with modified perpendicular anisotropy region

Spin state of currents and magnets offers a unique ability to store, transport and process information in vector boolean states leading to extreme density of memory and logic [1]. We propose and demonstrate basic vector logic manipulation with six state magnetic and spin currents utilizing spin orbit effect in a reservoir gate. Recently investigated bulk spin orbit coupling (SOC) effects [2,3,4] hold a special solution to this complex logic problem due to the vector phenemenology of spin orbit interaction. We propose three critical gates for GF-n state logic [5, 6], known as inversion gate, and rotation gates (rotation around X axis, Y-axis and Z-axis) using the combination of spin torque switching and spin orbit switching. 6-state memory can increase magnetic memory density of an n-bit word by 3^n, leading to extreme density of memory and logic for future AI and high-performance applications. For example, an 8-bit, 1GB MRAM can be converted into a 6.5TB MRAM with the use of six state signal manipulation. When utilised the complete informaton density of six-state logic can extend the Moore's law for many generations by improving coding [7] and information density [8,9] without needing extreme lithography and materials scaling.
**References** [1] Manipatruni, S.,et al 2018. Beyond CMOS computing with spin and polarization. Nature Physics, 14(4), pp.338-343.
[2] Witczak-Krempa, W., et al 2013. Correlated quantum phenomena in the strong spin-orbit regime. arXiv preprint arXiv:1305.2193.
Vancouver
[3] Everhardt, A.S., et al 2019. Tunable charge to spin conversion in strontium iridate thin films. Physical Review Materials, 3(5), p.051201.
[4] Zhu, L., et al 2021. Unveiling the Mechanism of Bulk Spin Orbit Torques within Chemically Disordered FePt Single Layers. Advanced Functional Materials, 31(36), p.2103898.
[5] Ellison, J.T., 1972. Universal function theory and Galois logic studies. SPERRY RAND CORP ST PAUL MN UNIVAC DEFENSE SYSTEMS DIV. AD0740849.pdf (dtic.mil)
[6] Jain, S.K., Song, L. and Parhi, K.K., 1998. Efficient semisystolic architectures for finite-field arithmetic. IEEE Transactions on Very Large Scale Integration (VLSI) Systems, 6(1), pp.101-113.
[7] Benvenuto, C.J., 2012. Galois field in cryptography. University of Washington, 1(1), pp.1-11.
[8] Lloyd, S., 2000. Ultimate physical limits to computation. Nature, 406(6799), pp.1047-1054.
[9] Krauss, L.M. et al 2004. Universal limits on computation. arXiv preprint astro-ph/0404510.
 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/df57b06616fe9f770bbdd6803bf9bd8a.png)

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/79647f672e61327aa6ae900486db8316.png)

Rotator Gates for Six state Boolean Spin Logic

Chirality is one of important research topics in the diverse field because it leads interesting phenomena.[1] Since the chirality by the inversion symmetry breaking has been observed in magnetic ordered system,[2] researches on asymmetric exchange coupling was actively investigated.[3] Here, the chirality is known as affecting to the dynamic and static phenomena, so it can be one approach that influence on the magnetization state as well. But for understanding the role of chirality deeply, it is necessary to control the chirality as a unique variable while keeping other materials parameters. However, controlling only the chirality is limited because it is determined from the materials and structural origins in general, affecting other parameters simultaneously. Therefore, more consideration is still required for revealing the role of chirality deeply.
For understanding the chirality precisely, we prepared the lateral perpendicular magnetic anisotropy (PMA) symmetry breaking system. In this system, magnetizations of each PMA react differently by the SOT, which results in in-homogeneous spin configuration (i-hSC). Here, notable point is that i-hSC can induce different system energy when it is combined with interfacial Dzyaloshinskii-Moriya interaction (DMI) as seen in Fig. 1.
The effect of i-hSC can be confirmed experimentally by measuring magnetization switching because the chirality reversal also occurs simultaneously (clockwise (CW) ↔ counter-clockwise (CCW)). Here, because more (less) energy should be required for switching the stabilized (destabilized) i-hSC, opposite directional shift of hysteresis loop is shown as seen in Fig. 2. The resultant degree of shift is directly related with the system energy variation, and our experimental analysis suggests the possibility of the chirality as one method determining the magnetization state. 
**References** F. Evers, A. Aharony, N. Bar-Gill, Advanced Materials, Vol.34, p.2106629 (2022)
M. Bode, M. Heide, K. von Bergmann, Nature, Vol.447, p.190-193 (2007)
S.-H. Yang, R. Naaman, Y. Paltiel, Nature Reviews Physics, Vol.3, p.328-343 (2021) 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/028a20add07684733cb11509ae937fe7.png)

Spin orbit torque driven in

Skyrmion based logic devices are found to be promising for next-generation energy-efficient, high speed information processing technologies owing to the compact size and topologically protected spin texture of the skyrmions [1,2]. Skyrmions are nano-scale swirling spin textures with topological protection that exhibit particle-like behaviour. In this work, we exploit skyrmion for various logic operations using a Gate to locally alter the magnetic properties that control the skyrmion motion in the logic device using micromagnetic simulation. For example, we have shown the OR and AND logic operations in a single device by flowing current through a metallic gate and the resultant Oersted field (HOe) controls the skyrmion trajectory (Fig. 1(a)). The HOe generated near the Gate is one of the efficient ways to realize the logic operations [3]. By simply switching OFF and ON the current at the metallic gate, we can toggle between OR & AND logic operations (Fig. 1(b & c)), respectively. The binary information is denoted by the presence and absence of the skyrmion as “1” and “0”, respectively. Fig. 1(d) shows the realization of the AND logic for a specific combination of skyrmion driving current density (j) and HOe. The logic functions are implemented in the device structure by virtue of several physical effects on skyrmion motion such as spin-orbit torque, skyrmion-edge repulsion, skyrmion-skyrmion topological repulsion and skyrmion Hall effect. To understand the motion of the skyrmions and stability, we estimated the Skyrmion Hall angle. The performance of the logic device is studied by varying the material and geometrical parameters. In this presentation, we would like to explain various logic operations including a majority logic device based on skyrmions with different Gate operation schemes and novel logic device architectures for computation. The results are interesting for next generation energy-efficient and high-density computing technologies. 
**References** [1] A. Fert, V. Cros, and J. Sampaio, Nature Nanotechnology 8, 152 (2013).
[2] Luo S., Y. Long, APL Materials 9, 050901 (2021).
[3] B. Paikaray, M. Kuchibhotla, A. Haldar, and C. Murapaka, ACS Applied Electronic Materials 4, 2290-2297, (2022). 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/bf380a93f99175ed7b74936dbfdd0a55.png)

Logic devices based on gate controlled skyrmion trajectory

We study the efficiencies of damping-like torque in Nb/Ni and Ta/Ni bilayers by the spin-torque ferromagnetic resonance (ST-FMR) technique1 and compare it with Nb/Ni81Fe19(Py) and Ta/Py as a function of the thickness of ferromagnet. In both these systems, we observe that the sign of the damping-like torque is negative for the Nb/Py and it is positive for the Nb/Ni system suggesting two competing mechanisms responsible for the torque on the magnet: (1) spin-current generated from the bulk of Nb and Ta due to spin Hall effect (SHE) producing the spin-orbit torques that are predicted to have a negative sign1 and (2) orbital current2,3 generated from the bulk of Nb and Ta which convert into the spin-current while entering in the ferromagnet due to the spin-orbit coupling of the ferromagnet which is predicted to produce an orbital-torque with the positive sign4,5. In Ta/Ni and Nb/Ni bilayers, the orbital current is dominant as Ni is predicted to be a good detector of the orbital current as compared to Py resulting in the sign reversal of the damping-like torque efficiency in Ta/Ni and Nb/Ni bilayers as compared to Ta/Py and Nb/Py samples. We further inserted a Cu spacer between the non-magnet and Ni that still shows the positive sign of the damping-like torque suggesting a generation of the orbital current from the bulk of Ta and Nb. Generation of orbital torque will open up new possibilities to manipulate the magnetization more efficiently6.<br >
**References** 1 L. Liu, C.-F. Pai, Y. Li, H.W. Tseng, D.C. Ralph, and R.A. Buhrman, Science (80-. ). 336, 555 (2012).
2 T. Tanaka, H. Kontani, M. Naito, T. Naito, D.S. Hirashima, K. Yamada, and J. Inoue, Phys. Rev. B 77, 165117 (2008).
3 D. Go, D. Jo, C. Kim, and H. Lee, Phys. Rev. Lett. 121, 86602 (2018).
4 D. Go, F. Freimuth, J.-P. Hanke, F. Xue, O. Gomonay, K.-J. Lee, S. Blügel, P.M. Haney, H.-W. Lee, and Y. Mokrousov, Phys. Rev. Res. 2, 033401 (2020).
5 D. Go and H.-W. Lee, Phys. Rev. Res. 2, 013177 (2020).
6 D. Go, D. Jo, H.-W. Lee, M. Kläui, and Y. Mokrousov, EPL (Europhysics Lett. 135, 37001 (2021). 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/8611a9932efb82a8a128742b0ab76442.png)

Observation of non local orbital transport and sign reversal of damping

We investigated orthogonal spin-orbit-induced (SOI) fields generated by a current along the [010] crystallographic direction in a ferromagnetic semiconductor GaMnAs film with 4-fold in-plane magnetic anisotropy. To perforem this study, we fabricated a Hall device aligned with the [010] direction, and carried out magnetoresistance (MR) measurements to monitor the magnetization reversal process in the film. Field scans of MR measured with opposite current polarities (Fig. 1(a)) clearly show shifts in opposite direction, indicating the presence of current-direction-dependent effective magnetic fields. The observed hysteresis shift is caused by the simultaneous presence of Dresselhaus and Rashba SOI fields that are perpendicular to each other when the current is oriented along the [010] direction. In order to quantify the two SOI fields, we performed angle-dependent MR measurements with two opposite current polarities (Fig. 1(b)). The splitting in transition angles between the two polarities increases with decreasing magnetic field. The equation relating this splitting and the applied external field was developed based on magnetic free energy that includes the effect of the two orthogonal SOI fields. Based on this formulation, we were able to obtain the magnitudes of the Rashba and Dresselhaus SOI fields from the magnetization transition angles as 0.568 and 1.632 Oe, respectively, at current density of 4.80×105 A/cm2 (2mA). 
**References** 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/fb024dffe3ee56095c9a34a2a58ffa2f.png)

Measurement of Orthogonal Spin orbit Field Current along the [010] Crystallographic Direction in GaMnAs Film

A magnetic wire is one of the attractive candidates for high capacity memories and logic devices with low power consumption [1]. We reported that the wire of rare-earth transition metal (RE-TM) amorphous alloy show a current induced domain wall motion (CIDWM) with a faster wall speed of more than 1000 m/sec and a current induced magnetization switching (CIMS) with a lower current density of 5.5 MA/cm2 [2, 3]. However, domain creation method in the wire is one of the key technologies for their applications [4, 5]. In this paper, we demonstrate a laser assisted current induced magnetization switching in TbCo/Pt hetero-structure wire.
Figure 1 shows measuring setup for laser assisted current induced magnetization switching. A wire of 3 µm width is irradiated by laser spot of 1 µm diameter under applying both pulse current and external field. The film was fabricated on a thermally oxidized silicon substrate using a sputtering system. TbCo 12 nm layer was co-sputtered by Tb and Co targets and Pt layer was sputtered by Pt target as 2 nm under layer and 4 nm heavy metal layer. The film was patterned by SEM lithography with a liftoff method. CIMS was observed using a MOKE microscope.
Figure 2 shows 100 nsec pulse current dependencies of magnetizing switched domain diameter with/without laser assist, where external in-plane field of 500 Oe. The inset shows microscope view of the wire. Blue line showed a CIMS threshold for without laser assist. CIMS domain diameter increased with increasing current pulse heights. Laser assisted CIMS could reduce the threshold current more than 40 % that of without a laser assisted.
We demonstrated the laser assisted current induced magnetization switching of the magnetic wire. The method can reduce the current and controlled CIMS by laser. The laser assist CIMS is one of the attractive methods to create the domains in the magnetic wire.
This research was supported by KAKENHI (No. 20H02185, 21K18735, 21K14202), Japan. 
**References** [1] S. S. P. Parkin et al., Science 320, 190 (2008).
[2] D. Ngo et al., APEX Vol. 4, No. 9, 093002(2011).
[3] K. Asari et al., AIP Advances 7, 055930 (2017).
[4] S. Bandira et al., Appl. Phys. Let. Vol 99, No. 20, 202507(2011).
[5] N. Roschewsky et al., Appl. Phys. Let. Vol 109, No. 11, 112403(2016).
 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/10cf51b5e455fcb20c9738f982081384.png)

Laser assisted current induced magnetization switching in a TbCo/Pt hetero structure wire

Interfacial magnetic skyrmions are topological spin textures which have been proposed for use as information carriers in spintronic devices [1]. Hence, it is vital that their creation, annihilation, and motion can be accurately controlled [1]. Still, their thermal stability and interactions with lattice defects are not fully understood. Recently, many groups studied the skyrmion creation/annihilation energy paths by reconstructing associated free energy landscapes (FELs) and calculating the minimum energy paths, by combining micromagnetic simulations with an enhanced sampling technique called the nudged elastic band method (NEBM) [2]. However, micromagnetics and NEBM do not fully account for thermal effects. In addition, most computational models assume defect-free material interfaces with idealized magnetic parameters; while lattice defects alter the skyrmion dynamics and show potential to be used as pinning, destruction/creation points in future devices.

To address these, we use atomic scale magnetic simulations combined with an enhanced sampling technique named metadynamics to reconstruct non-trivial FELs of certain skyrmion degrees of freedom called as collective variables (CVs) in metadynamics. Metadynamics systematically adds a potential bias on the CVs to sample states outside of the thermodynamic equilibrium and explore the whole configurational space [3,4]. Traditionally, this has been used to understand how molecules bind to surfaces. Recently, metadynamics has been used in magnetism to study simple situations such as the temperature dependence of anisotropy CVs [5]. We use it to explore how spin textures interact with defects. Thus, we demonstrate that metadynamics can be extensively used in computational magnetism to study the behaviour of spin textures by selecting appropriate CVs. Mainly, we use metadynamics to study the thermal stability of skyrmions, via studying the annihilation/creation energy barriers as a function of temperature. Additionally, we investigate how various defects modify these FELs and their associated energy barriers. Ultimately, we explore if certain defects alter the skyrmion stability, trap/repel skyrmions, disturb their motion and prevent/help their creation/annihilation. 
**References** [1] A. Fert, N. Reyren, V. Cros, Nat Rev Mater 2, 17031 (2017)
[2] D. Cortés-Ortuño, W. Wang, M. Beg, et al. Sci Rep 7, 4060 (2017)
[3] A. Laio, L. Parrinello, PNAS 99, 20 (2002)
[4] G. Bussi, A. Laio, Nat Rev Phys 2, 200–212 (2020).
[5] B. Nagyfalusi, L. Udvardi, L. Szunyogh, Phys. Rev. B 100, 174429 (2019)

Premium content

In field critical behaviour of β

Next from MMM 2022

Effects of self torque in rare earth

Stay up to date with the latest Underline news!

PRESENTATIONS

CONFERENCES

COMPANY

RESOURCES