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Tohoku-Lorraine Joint Conference 2021
March 3: Scientific session « Spintronic »PROGRAM
8:30 – 11:30 (Nancy) / 16:30 – 19:30 (Sendai)
8:20 – 8:30 / 16:20 – 16:30
8:30 – 9:45 / 16:30 – 17:45
9:45 – 9:55 / 17:45 – 17:55
9:55 – 10:05 / 17:55 – 18:05
10:05 – 11:20 / 18:05 – 19:20
11:20 – 11:30 / 19:20 – 19:30

WelcomeInvited Talks #1 (5)One-Slide Presentation #1 (5)coffee break
Invited Talks #2 (5)One-Slide Presentation #2 (5)INVITED TALKS # 1

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Kaushalya Jhuria: Picosecond spin-orbit torque switching in ferromagets
Takeshi Seki: Origin and Optical Switching of Perpendicular Magnetization for Co-Gd/Pt
Multilayers
Heloise Damas: Self-Spin-Orbit Torque in GdFeCo ferrimagnet
Satoshi Iihama: Optical spin torque in ferromagnet/heavy metal thin films
Maryam Massoura: Artificial spin systems: potential device for random number generation

INVITED TALKS # 2

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Makoto Kohda: Spatiotemporal dynamics of helical spin wave under persistent spin helix state
Claudia De Melo Sanchez : Transport properties of Co2MnSi Heusler compounds
Tufan Roy: A combined study of computational prediction and experimental fabrication ofquaternary Heusler alloy CoIrMnZ (Z = Al, Ga, Si, Ge)
Quentin Remy: Control of Single Pulse All Optical Magnetization Switching of Ferromagnets
Shunsuke Fukami: Spin-orbit torque-induced sub-nanosecond magnetization switching in inplane magnetic tunnel junctions

ONE-SLIDE PRESENTATION

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Hiroto Masuda: Large spin Hall effect in a non-equilibrium Iridium-doped Copper binary alloy
Alberto Anadon: Disentangling the anomalous Nernst and spin Seebeck effect in epitaxial
Graphene/Cobalt heterostructures
Junta Igarashi: Shape-anisotropy magnetic tunnel junctions with multilayered ferromagnets
Xiaofei Fan: Magnetization control and all-optical switching mediated by phase transition of VO2
Takashi Kimura: Valley dynamics of charged exciton in monolayer WS2 treated by organic acid
Wei Zhang: All optical helicity-independent switching in GdTbCo alloys
Kazuaki Ishibashi: All-optical probe of magnetization precession frequency shift due to spin-orbit
torqueKosseila Ait-Oukaci: Stripe domains in thin magnetic films for spin waves channeling
Junpei Sonehara: Anisotropic spin relaxation and precession frequency depending on in-planemagnetic field orientation in GaAs-based wire structures
Jean LoÏs Bello: Zero field current induced switching of GdFeCo

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INVITED TALKS

Picosecond spin-orbit torque switching in ferromagets
Kaushalya Jhuria1, Julius Hohlfeld1, Akshay Pattabi2, Elodie Martin1, Aldo Ygnacio Arriola Córdova1,3,
Xinping Shi4, Roberto Lo Conte3, Sebastien Petit-Watelot1, Juan Carlos Rojas-Sanchez1, Gregory
Malinowski1, Stéphane Mangin1, Aristide Lemaître5, Michel Hehn1, Jeffrey Bokor2,6, Richard B.
Wilson4, Jon Gorchon1,*
1Université de Lorraine, CNRS, IJL, F-54000 Nancy, France

2Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, CA 94720, USA
3Universidad Nacional de Ingeniería, Avenida Túpac Amaru 210, Rímac, Lima, Perú

4Department of Mechanical Engineering and Materials Science and Engineering Program, University of California, Riverside,

CA 92521, USA

5Centre de Nanosciences et de Nanotechnologies (C2N), CNRS, Université Paris Sud, Université Paris-Saclay, 91120

Palaiseau, France

6Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA

Reducing energy dissipation while increasing speed in computation and memory is a long-standing
challenge for spintronics research1. In the last 20 years, femtosecond lasers have emerged as a tool tocontrol the magnetization in specific magnetic materials at the picosecond timescale2–4. However,the use of ultra-fast optics in integrated circuits and memories would require a major paradigm shift.
An ultrafast electrical control of the magnetization is far preferable for integrated systems. Here wedemonstrate reliable and deterministic control of the out-of-plane magnetization of a 1 nm-thick Co
layer with single 6 ps-wide electrical pulses that induce spin orbit torques on the magnetization. We
can monitor the ultrafast magnetization dynamics due to the spin orbit torques on sub-picosecond
timescales, thus far accessible only by numerical simulations. Due to the short duration of our pulses,
we enter a counter-intuitive regime of switching where heat dissipation assists the reversal. Moreover,
we estimate a low energy cost to switch the magnetization, projecting to below 1fJ for a (20 nm)3 cell.
These experiments prove that spintronic phenomena can be exploited on picosecond time-scales forfull magnetic control and should launch a new regime of ultrafast spin torque studies and applications.

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Origin and Optical Switching of Perpendicular Magnetization
for Co-Gd/Pt Multilayers
Takeshi Seki 1,2*
1. Institute for Materials Research, Tohoku University
2. Center for Spintronics Research Network, Tohoku University
2-1-1 Katahira, Aoba-ku, Sendai 980-8577 JAPAN* Mail : go-sai@imr.tohoku.ac.jp

All-optical switching (AOS) of magnetization by femtosecond laser pulses has attracted much attention
as a route for ultrafast magnetization manipulation. The Gd-based alloys such as Gd-Fe-Co are
representative ferrimagnetic materials exhibiting the all-optical helicity independent switching (AOHIS). However, the detailed process of AO-HIS has not been elucidated yet. The perpendicularly
magnetized Gd-based alloys are key materials not only in the AOS experiment, but also in the field of
antiferromagnetic spintronics. Although the combinations of Gd-based alloys and Pt have widely been
exploited for a variety of studies [1,2], the origin of perpendicular magnetic anisotropy (PMA) has beenrarely addressed. These facts make the Gd-based alloys a unique platform to investigate the correlation
between the fundamental magnetic properties and the AOS behavior, which will provide knowledge togain insight into the AOS.
In this study, we paid attention to the combination of Co-Gd and Pt. The origin of PMA and the role ofinterface magnetic moment were first investigated for the Co-Gd/Pt multilayers with various Co-Gd
layer thicknesses (t) and alloy compositions (Co100-xGdx). Then, the AOS experiments were carried out
in order to find the composition dependence of AOS probability. Thin films with the stacking structureof [Pt (2.0)/Co100-xGdx (t)]×3/Pt (2.0) (in nanometer) were prepared on sapphire (11-20) substrates atroom temperature using an ultrahigh vacuum compatible magnetron sputtering system.
We found that the PMA mainly comes from the Co-Gd/Pt interface while the contribution from the bulk
properties of Co-Gd is negligibly small. The proximity-induced magnetic moment in Pt remarkably
appeared for the thin Co-Gd layers, which coupled with the Co moment in parallel. It is noted that theproximity-induced Pt moment largely affected the condition for the magnetization compensation of CoGd. The Co-Gd/Pt multilayers exhibited the single laser pulse AO-HIS in the wide Co-Gd composition
range, and the maximum AOS probability was obtained around the compensation composition of CoGd. The above findings are useful to improve the performance of AOS-based device [3].
This work was done in collaboration with J. Wang, Y.-C. Lau, Y. K. Takahashi, and K. Takanashi, andwas partly supported by JSPS KAKENHI Grant-in-Aid for Scientific Research (S) (JP18H05246),
Grant-in-Aid for Scientific Research (A) (JP20H00299), and Grant-in-Aid for Scientific Research (A)(JP18H03787).
[1] W. Zhou, TS et al., Phys. Rev. Mater. 2, 094404 (2018).
[2] T. Moriyama, TS et al., Phys. Rev. Lett. 121, 167202 (2018).
[3] J. Wang, TS et al. (Submitted).

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Self-Spin-Orbit Torque in GdFeCo ferrimagnet
Héloïse Damas1, David Céspedes-Berrocal1,2, Davide Maccariello3, Aldo Arriola-Córdova1,2, Elodie
Martin1, Jean-Loïs Bello1, Ping Tang4, Pierre Vallobra1, Yong Xu1, Sylvie Migot1, Jaafar Ghanbaja1,
Shufeng Zhang4, Stéphane Mangin1, Christos Panagopoulos5, Vincent Cros3, Michel Hehn1, Sébastien
Petit-Watelot1, Albert Fert3 and Juan-Carlos Rojas-Sánchez1
1 Université de Lorraine, CNRS, Institute Jean Lamour, F-54000 Nancy, France
2 Universidad Nacional de Ingeniería, Rímac 15333, Peru

3 Unité Mixte de Physique, CNRS, Thales, Université Paris-Saclay, 91767 Palaiseau, France
4 Department of Physics, University of Arizona, Tucson, Arizona 85721, USA

5 Division of Physics and Applied Physics, Nanyang Technological University, 637371 Singapore

Spin-orbit torque has been widely studied in ferromagnet/heavy metal bilayers due to their high application
potential regarding modern electronic devices [1,2]. The heavy metal is presented as a primordial elementof the structure since it is the source of spin current. However, magnetic materials with large spin-orbit
coupling, like GdFeCo ferrimagnetic alloys, can be a source of spin currents as well. A distinction can be
drawn between the SAHE-like spin current [3,4] with the Spin Anomalous Hall Effect symmetry and the SHElike spin current [5] with the Spin Hall Effect symmetry. In the SAHE symmetry, the spin current Js emitted
from the magnetic material has the spin polarization aligned with the magnetization while in the SHE
symmetry the spin polarization is perpendicular to Js and the injected charge current Jc [3-6]. Only the SHElike symmetry emission could produce damping-like self-torque.
In this talk, we present the study of the self-torque performed by means of harmonic Hall voltage
measurements in bi- or tri- layers where the GdFeCo layer displays out-of-plane magnetization. We first
focus on the temperature dependance of the effective fields associated to the self-torque. We show thatthe effective fields are magnified near the magnetic compensation temperature TM and reverse sign acrossit (see Fig). In a second part, we compare the self-torque in GdFeCo/Cu with torques induced by anadditional heavy metal in GdFeCo/Cu/Pt and GdFeCo/Cu/Ta structures. We show that the addition of a spinsink can improve the damping-like self-torque. Thus, in our work [6], we estimate the global efficiency of
GdFeCo spin emission as 𝜃!"#$%!#$ = 0.78. Moreover, the SHE-like spin emission results 𝜃!#$ = 0.16.
The latter is of the same order of magnitude as heavy metals efficiencies [1]. Our results pave the way to
exploit spin-orbit torque generated in single magnetic layer, which we coined self-torque.

Fig: Temperature dependance of thedamping-like efficiency in

Gd27Fe50.9Co10.2(10nm)/Cu(2nm)/AlOx(2.5nm). The magnetization compensation temperature TM = 330°K is depicted by the
background change of color. The DL effective field changes sign when crossing TM.
[1] Manchon et al. Rev. Mod Phys. 91, 035004 (2019).
[2] Thai-Ha Pham et al. Phys. Rev. Appl. 9, 064032 (2018).
[3] T. Taniguchi et al., Phys. Rev. Appl. 3, 044001 (2015).
[4] S. Iihama et al., Nat. Elecron. 1, 120 (2018).
[5] Amin et al. J. Appl. Phys. 128, 151101 (2020).
[6] David Céspedes-Berrocal, H. Damas et al. Adv. Materials (2021). https://doi.org/10.1002/adma.202007047 ArXiv:
2010.09137
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Optical spin torque in ferromagnet/heavy metal thin films
S. Iihama1,2,3,*, K. Ishibashi4,2, S. Mizukami2,3,5
1. Frontier Research Institute for Interdisciplinary Sciences (FRIS), Tohoku University
2. WPI Advanced Institute for Materials Research (AIMR), Tohoku University
3. Center for Spintronics Research Network (CSRN), Tohoku University
4. Department of Applied Physics, Graduate School of Engineering, Tohoku University
5. Center for Science and Innovation in Spintronics (CSIS), Core Research Cluster (CRC), Tohoku University* Mail : satoshi.iihama.d6@tohoku.ac.jp

An efficient electrical switching of thin film metallic nanomagnets has been demonstrated by using spinorbit torques in ferromagnet/heavy metal heterostructures. The spin-Hall effect in the heavy metal layer
and the Rashba-Edelstein effect at the interface have been widely studied. Light-induced switching of
nanomagnets is expected to be utilized for fast and low-power consumption opto-spintronic memory
device, in which nanomagnets are integrated with photonic circuits [1,2]. A strong coupling between
electron spin and light polarization/helicity is crucial for such applications. Recently, optical-helicity
induced magnetization precession, which we term optical spin torque, in ferromagnet/heavy metal
heterostructures were reported [3,4]. Figure 1 shows magnetization precession induced by the opticalspin torque in a 2-nm-thick FeCo/3-nm-thick Pt heterostructure. The optical spin torque vector in theheterostructure was analyzed in detail. We found that the optical spin torque was induced not only by
non-equilibrium spin generated in the bulk Pt layer via the optical orientation effect but also by the
optical Rashba-Edelstein effect at the interface of the heterostructure. In this talk, details of theexperimental results and the mechanism of the optical spin torque induced by the optical RashbaEdelstein effect will be discussed.

Figure 1 Circularly polarized laser pulse induced magnetization precession observed in a 2-nm-thick
FeCo/3-nm-thick Pt film.
[1] A. V. Kimel and M. Li, Nat. Rev. Mater. 4, 189 (2019)[2] H. Becker et al., IEEE J. Sel. Top. Quant. 26, 8300408 (2020)[3] G. -M. Choi et al., Nat. Commun. 11, 1482 (2020)[4] S. Iihama et al. Nanophotonics, 10, 1169 (2021)

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Artificial spin systems: potential device for random number generation
Maryam Massouras1, Daniel Lacour, Michel Hehn and François Montaigne
1 Université de Lorraine, CNRS, Institute Jean Lamour, F-54000 Nancy, France

A wide range of devices based on domain wall (DW) propagation has been proposed and investigated.
Magnetic storage is obviously the key application either in the form of single bit or multi-level devices
or in “racetrack” devices. But other applications are also targeted like magnetic logic devices, multiturn
position sensors, memresistors... Reproducible and controllable domain wall propagation is therefore
a challenge for most of the evocated devices that require a precise control of the DW propagation. On
the other hand, other devices might benefit from random or pseudo-random propagation for random
number generation[1], cryptography or neuromorphic structures. This aspect will be investigated inthis presentation with the demonstration of the magnetic analog to the Galton board (also called beanmachine or quincunx). We have developed an artificial spin system arranged in honeycomb lattice
optimised to observe one-dimensional propagation of a DW[2] injected by an elliptic pad. We will show
the characteristic features of the DW propagations (reversals, propagation scenario, pinning) alongwith its intrinsic stochasticity. Our artificial spin system can be compared to macroscopic Galton board
in terms of individual weights and output distribution consistent with a binomial distribution. We will
also show that there is only negligible correlation between successive choices at the intersections
emphasising its analogy to the Galton board.

MFM image of our 8-output nanoscale magnetic Galton board with a DW propagation from the pad to output 5 and output
distribution oif the field protocol is performed 197 times (all experiments taken into account are unidimensional DW
propagations).
[1] K. Zeissler et al., Sci Rep 3, (2013). [2] E. Mengotti et al., Nature Phys- ics 7, 68 (2011).
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Helical spin wave under persistent spin helix state
M. Kohda 1,2,3,4,*
1. Department of Materials Science, Tohoku University
2. Center for Spintronics Research Network, Tohoku University
3. Center for Science and Innovation in Spintronics, Tohoku University
4. Division for the Establishment of Frontier Sciences of Organization for Advanced Studies, Tohoku University* Mail : makoto@material.tohoku.ac.jp

In a semiconductor heterostructure, collective exciation of spin texture usually decay rather fast due toD’yakonov-Perel’ spin relaxation. However, when two kinds of spin-orbit (SO) induced magnetic fields
are equal to each other, namely Rashba and Dresselhaus SO interactions, spin relxation is completely
suppressed due to spin SU(2) symmetry. In addition, the persisntent rotation of spatially developed spins
generates a helical spin wave. This electron spin wave holds long spin lifetime as well as spin
precessional motion, being an ideal platform to manipulate and transfer spin information insemiconductors. In this talk, I will show the theoretical prediction of the longest spin lifetime in helicalspin waves among all crytal orientations in III-V semiconductor heterostructures [1,2]. While thepersistent spin helix state has been demonstrated in a [001]-oriented quantum well [3], an ideal crystal
orientation for the heical spin wave is revealed to be a [225] oriention. I will also discuss the origin of
suppressed spin relaxation in a [225] quantm well by considering the cubic Dresselhaus contribution to
the spin orbit effective magnetic field.
The work has been carried out in collaboration with D. Iizasa, M. Kammemeier, J. Nitta, U. Zülicke and
S. Karube. These works have been partly supported by the Grant-in-Aid for Scientific Research (Grants
No. 15H02099, No. 15H05854, No. 25220604, and No. 15H05699) by the Japan Society for the
Promotion of Science and Cooperative Research Projects of RIEC.
[1] D. Iizasa et al., Phys. Rev. B 101, 245417 (2021).
[2] D. Iizasa et al., Phys. Rev. B 98, 165112 (2018).
[3] M. Kohda and G. Salis, Semi. Sci. Tech. 32, 073002 (2017).

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Transport properties of Co2MnSi Heusler compounds
C. de Melo1,2, C. Guillemard1, V. Palin1, J. C. Rojas-Sánchez1, S. Petit-Watelot1, and S. Andrieu1
1 Institut Jean Lamour, UMR CNRS 7198, Université de Lorraine, 54000 Nancy, France

2 Chair in Photonics, LMOPS EA 4423 Laboratory, CentraleSupélec and Université de Lorraine, 57070 Metz

Co-based Heusler compounds are promising candidates for many emerging spintronic applications
regarding the potential full spin polarization, ultra-low magnetic damping, and high Curie
temperatures [1,2]. In this work, we report on the transport properties of Co2MnSi Heusler compounds
grown by molecular beam epitaxy and patterned into Hall bars by standard UV-photolithography. The
formation of the chemically-ordered L21 phase was verified by in-situ reflection high-energy electron
diffraction and transmission electron microscopy (Figure 1, left). Ultralow-magnetic damping
coefficients were measured for all the Co2MnSi thickness series. Negative anisotropy
magnetoresistance ratios confirm the half-metallicity of Co2MnSi. The electron mean free path of
Co2MnSi was determined from the study of electrical resistivity of the films versus thickness. Finally,
the evolution of film resistivity with temperature gives us access to the distance between the Fermi
energy and the minority-spin conduction band minimum (Figure 1, right), and in combination with
spin-resolved photoemission spectroscopy allow us to estimate the Co2MnSi spin gap between 0.55 0.7 eV, in agreement with ab initio calculations [3].

Figure. 1. Reflection high-energy electron diffraction patterns and high-angle annular dark-field scanningtransmission electron microscopy micrograph of the Co2MnSi film (left). Electrical resistivity of Co2MnSi versus
temperature from 300 to 5 K (right). Distance between the Fermi energy and the bottom of the minority spinband versus film thickness (inset).
[1] C. Guillemard, S. Petit-Watelot, S. Andrieu et al., J. Appl. Phys., Vol. 128, p.241102 (2020)[2] C. Guillemard, S. Petit-Watelot, S. Andrieu et al., Phys. Rev. Appl., Vol. 11, p.064009 (2019)[3] S. Picozzi, A. Continenza, and A. J. Freeman, Phys. Rev. B., Vol. 66, p.094421 (2002)TOHOKU – LORRAINE JOINT CONFERENCE 2021

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A combined study of computational prediction and experimental fabrication ofquaternary Heusler alloys CoIrMnZ (Z=Al, Ga, Si, Ge)
T. Roy1*, R. Momma2,3, K. Z. Suzuki3,4, T. Tsuchiya4,5, M. Tsujikawa1,4, S. Mizukami3,4,5, M. Shirai1,4,5
1. Research Institute of Electrical Communication, Tohoku University
2. Department of Applied Physics, Tohoku University
3. WPI-Advanced Institute for Materials Research, Tohoku University
4. Center for Spintronics Research Network, Tohoku University
5. Center for Science and Innovation in Spintronics, Tohoku University
2-1-1 Katahira, Aoba-ku, Sendai 980-8577 JAPAN* Mail: tufan@riec.tohoku.ac.jp

Co-based Heusler alloys are potential candidates in the field of spintronics applications because of theirhigh Curie temperatures and high spin polarization at the Fermi level. In this family, Co2MnSi/MgO is
the heterojunction studied most extensively. However, the lattice mismatch between Co2MnSi and MgO
is about 5% [1]. Ir being an isoelectronic element with Co, CoIrMnSi could effectively reduce the latticemismatch, maintaining resemblance of electronic structure of Co2MnSi. As the number of valence
electrons plays a crucial role in determining the physical properties, so it is worth investigating CoIrMnZ
systems (Z=Al, Ga, Si, Ge) [2].
Based on first-principles calculations we show that these materials have ferromagnetic ground state with
Curie temperatures moderately higher than the room temperature. CoIrMnSi and CoIrMnGe are foundto have the spin polarized ∆1 band across the Fermi level. Furthermore, we predict CoIrMnAl as a spin
gapless semiconductor (left panel of Fig. 1). In the case CoIrMnZ/MgO (001) heterojunctions, the MnZterminated interface is found to be energetically favourable over the CoIr-terminated interface. We showthat CoIrMnAl/MgO preserves its half-metallicity even at the interface (right panel of Fig. 1).
Recently, CoIrMnAl thin films have been fabricated by using magnetron sputtering on single crystal
MgO (001) substrate. Structural analysis by X-ray diffraction confirms that single-phase B2-orderedepitaxial films were obtained. The saturation magnetization and the Curie temperature are about 70% of
the values theoretically obtained for the XA-ordered CoIrMnAl. The difference between thetheoretically obtained value and experimental result can be explained by taking the Co-Mn antisitedisorder into account [3].
This work is partially supported by CREST (No. JPMJCR17J5).
[1] Y. Miura et al., Phys. Rev. B 78, 064416 (2008).
[2] T. Roy et al., J. Magn. Magn. Mater. 498, 166092 (2020).
[3] R. Monma et al., accepted for publication in J. Alloy. Compd (2021).

Fig. 1. Left and right panels depict the spin polarized density of states (DOS) of bulk CoIrMnAl and CoIrMnAl/MgO (001) heterojunction with the
MnAl termination, respectively. The inset of the left panel shows the DOS in the vicinity of the Fermi level, which is set at 0 eV.

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Control of Single Pulse All Optical Magnetization Switching of Ferromagnets
Q. Remy1, J. Igarashi1,2, S. Iihama3,6, G. Malinowski1, M. Hehn1, J. Gorchon1, J. Hohlfeld1, S.
Fukami2,4,5,6,7, H. Ohno2,4,5,6,7 and S. Mangin1
1 Institut Jean Lamour, UMR CNRS 7198, Université de Lorraine, Nancy, France.

2 Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, 2-1-1

Katahira, Aoba, Sendai 980-8577, Japan.

3 Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, 6-3 Aramaki Aza Aoba, Sendai 980-8578.
4 WPI Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan.

5 Center for Science and Innovation in Spintronics, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan.
6 Center for Spintronics Research Network, Tohoku University, 2-1- 1 Katahira, Aoba, Sendai 980-8577, Japan.

7 Center for Innovative Integrated Electronic Systems, Tohoku University, 468-1 Aramaki Aza Aoba, Sendai 980-0845, Japan.

All Optical Helicity Independent Switching (AO-HIS) of magnetization, using single femtosecond laser
pulses, has been demonstrated in GdFeCo ferrimagnetic alloys for various concentrations [1] as wellas in other structures with antiferromagnetic coupling, Gd/Co, Tb/Co multilayers and Mn2RuxGa[2,3,4]. Up to now, AO-HIS has never been observed for ferromagnetic layers. However, it was shownthat a single pulse magnetization reversal of a ferromagnet could be observed in a spin-valve structure[5]. The switching is then achieved by the ultrashort spin current pulse generated from the ultrafast
demagnetization of GdFeCo [5,6].
In this work, we study Gdx(FeCo)1-x/Cu/FM spin-valve structures, where FM can be different
ferromagnetic layers [7] and the composition x of the GdFeCo alloy is also changed [8]. By increasing
the Gadolinium concentration x, we aim at increasing the spin current injected in the copper layer [6].
We show that this can reduce the laser fluence threshold required to observe the FM magnetization
reversal. In particular, no AO-HIS of the GdFeCo layer is required and the threshold fluence for the FM
layer is around 1.6 mJ/cm² i.e. comparable to GdFeCo and Gd/Co multilayers [1,2] and smaller thanwhat is achieved for Tb/Co [2] and Mn2RuxGa [3]. We also show that by changing the Curie temperatureand the Cu/FM interface, one can control the interaction between the spin current and the FM layerand so the laser fluence threshold. Finally, we change the laser pulse duration and show that this not
only changes the laser fluence threshold but also the entire laser fluence range where the single pulse
FM switching can be observed without having any multidomain state.
[1]
Y. Xu, M. Deb, G. Malinowski, M. Hehn, W. Zhao, S. Mangin, Adv. Mater. 2017, 29, 1703474.
[2]
M. L. M. Lalieu, M. J. G. Peeters, S. R. R. Haenen, R. Lavrijsen, B. Koopmans, Phys. Rev. B 2017, 96, 220411.
[3]
L. Avilés-Félix, A. Olivier, G. Li, C. S. Davies, L. Álvaro-Gómez, M. Rubio-Roy, S. Auffret, A. Kirilyuk, A. V. Kimel, T.
Rasing, L. D. Buda-Prejbeanu, R. C. Sousa, B. Dieny, I. L. Prejbeanu, Sci. Rep. 2020, 10, 5211.
[4]
C. Banerjee, N. Teichert, K. E. Siewierska, Z. Gercsi, G. Y. P. Atcheson, P. Stamenov, K. Rode, J. M. D. Coey, J. Besbas,
Nat. Commun. 2020, 11, 1.
[5]
S. Iihama, Y. Xu, M. Deb, G. Malinowski, M. Hehn, J. Gorchon, E. E. Fullerton, S. Mangin, Adv. Mater. 2018, 30,
1804004.
[6]
G. M. Choi, B. C. Min, Phys. Rev. B 2018, 97, 014410.
[7]
Q. Remy, J. Igarashi, S. Iihama, G. Malinowski, M. Hehn, J. Gorchon, J. Hohlfeld, S. Fukami, H. Ohno, S. Mangin, Adv.
Sci. 2020, 2001996.
[8]
J. Igarashi, Q. Remy, S. Iihama, G. Malinowski, M. Hehn, J. Gorchon, J. Hohlfeld, S. Fukami, H. Ohno, S. Mangin, Nano
Letters 2020 (Accepted).

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Spin-orbit torque-induced sub-nanosecond magnetization switching in in-planemagnetic tunnel junctions
S. Fukami 1,2,3,4,5,*
1. Research Institute of Electrical Communication, Tohoku University
2. Center for Spintronics Research Network, Tohoku University
3. Center for Science and Innovation in Spintronics, Tohoku University
4. Center for Innovative Integrated Electronic Systems, Tohoku University
5. WPI-Advanced Institute for Materials Research, Tohoku University
2-1-1 Katahira, Aoba-ku, Sendai 980-8577 JAPAN* Mail : s-fukami@riec.tohoku.ac.jp

High-speed magnetization switching scheme in magnetic tunnel junction (MTJ) is highly demanded forthe progress of magnetoresistive random access memory (MRAM) technology, whose
commercialization has been started from the replacement of NOR-Flash memory. Spin-orbit torque(SOT)-induced magnetization switching is a prime candidate for this purpose. In this talk, I will present
a material and device engineering [1,2] for the demonstration of SOT-MRAM with 55-nm CMOS
circuits fabricated through an industry-compatible 300-mm wafer process [3,4]. Using three-terminal
MTJ with in-plane magnetic easy axis and Ta/W channel, field-free switching is achieved down to thepulse width of 0.35 ns. I will also show our latest studies, in which 0.2-ns magnetization switching in
MTJ with the same material system is achieved at zero magnetic field by a combinatorial effect of spintransfer torque and spin-orbit torque [5].
The work has been carried out in collaboration with H. Ohno, C. Zhang, Y. Takeuchi, T. Endoh, T.
Hanyu, H. Honjo, M. Natsui, H. Sato, and S. Ikeda. These works have been partly supported by the
ImPACT Program of CSTI, JSPS KAKENHI 19H05622, and Cooperative Research Projects of RIEC.
[1] S. Fukami et al., Nat. Nanotechnol. 11, 621 (2016).
[2] S. Fukami et al., VLSI Symp. T06-05 (2016).
[3] H. Honjo et al., IEDM 28-5 (2019).
[4] M. Natsui et al., VLSI Symp. CM2.2 (2020).
[5] C. Zhang, Y. Takeuchi, S. Fukami, and H. Ohno, accepted for publicataion in Appl. Phys. Lett. (2021).

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ONE-SLIDE PRESENTATION

Large spin Hall effect in a non-equilibrium Iridium-doped Copper binary alloy
Hiroto Masuda 1*, Rajkumar Modak 2, Takeshi Seki 1,2,3, Ken-ichi Uchida 1,2,3, Yong-Chang Lau 1,3,
Yuya Sakuraba 2,4, Ryo Iguchi 2, and Koki Takanashi 1,3,5
1. Institute for Materials Research, Tohoku University, Sendai Japan
2. National Institute for Materials Science, Tsukuba, Japan
3. Center for Spintronics Research Network, Tohoku University, Sendai Japan
4. JST PRESTO, Saitama, Japan
5. Center for Spintronics Integrated Systems, Tohoku University, Sendai, Japan* Mail : masuda1610@imr.tohoku.ac.jp

The spin Hall effect (SHE) is one of the phenomena converting a charge current (Jc) into a spin current(Js). In order to improve the performance of spintronic devices, large conversion efficiency of SHE
called spin Hall angle (αSH) is indispensable. Large αSH has been observed in simple nonmagnets withstrong spin-orbit interaction such as Pt, Ta, and W. Element doping and alloying are also effective ways
to enhance αSH. The Iridium-doped Copper (Cu-Ir) [1-4] is an intriguing material because αSH of ~2.1 %was observed in the Ir concentration range from 1 at.% to 12 at.% [1], in spite of the fact that neither Cu
nor Ir exhibits remarkable SHE. Cu-based alloys are also advantageous from the perspective of practicalapplications because of its compatibility to the standard integrated circuit interconnection technology.
However, the comprehensive study on SHE in Cu-based binary alloys in a wide range of concentrationis very limited.
In this study, the SHE in a non-equilibrium Cu-Ir binary alloy was investigated by exploiting a
combinatorial technique based on the thermal imaging for a composition-spread film [5]. The
composition-spread Cu-Ir film was fabricated on the yttrium-iron garnet (YIG) substrate at room
temperature using magnetron sputtering. Repeating the process of deposition of wedge-shaped Cu,
rotation of substrate by 180 degree, and deposition of wedge-shaped Ir led to the Cu-Ir film of which
the composition is varied along the film position. The spin Peltier effect (SPE), which is the phenomenonof heat current generation in a linear response to Js injection, was utilized as a probe of the spin-charge
current conversion. The spatial distribution of the temperature modulation due to the SPE (ΔTSPE) in thecomposition-spread film was visualized using the active infrared emission microscopy called the lockin thermography. From the thermal images, we have found that the optimum Ir concentration forenhancing SHE of Cu-Ir is around 25 at.%, which corresponds to the region beyond the solubility limit
and is not thermodynamically stable in the bulk phase diagram. We also evaluated αSH of the Cu76Ir24
alloy using a Cu76Ir24/CoFeB bilayer. We obtained αSH = 6.29 ± 0.19 % using the harmonic Hall voltage
measurements. This remarkable αSH suggests that the non-equilibrium Cu-Ir alloy is a candidate of spin
Hall material [6]. Furthermore, the temperature dependence of spin Hall conductance revealed that themechanism of SHE in Cu76Ir24 is the side jump or the Berry curvature-induced intrinsic process.
[1] Y. Niimi et al., Phys. Rev. Lett. 106, 126601 (2011). [2] M. Yamanouchi et al., Appl. Phys. Lett. 102, 212408 (2013). [3] J.
Cramer et al., Nano Lett. 18, 1064 (2018). [4] H. Masuda et al., Phys. Rev. B 101, 224413 (2020). [5] K. Uchida et al., Sci.
Rep. 8, 16067 (2018). [6] H. Masuda et al., Commun. Mater. 1, 75 (2020).

TOHOKU – LORRAINE JOINT CONFERENCE 202113

Disentangling the anomalous Nernst and spin Seebeck effect in epitaxial Graphene/Cobalt
heterostructures
Alberto Anadón1,8*, Ruben Guerrero1, P Jiménez-Cavero2,3, Adrian Gudín1, Jose Manuel Díez1, Pablo
Olleros1, Letcia de Melo Costa1, Fernando Ajejas1, I. Lucas2,3,5, L. Morellón 2,3,5, P.A. Algarabel3,7, M. R.
Ibarra2,3,5,6, Rodolfo Miranda1,,4 Julio Camarero1,4, S. Petit-Watelot8, Paolo Perna1 and Juan Carlos
Rojas-Sánchez8
1
IMDEA Nanociencia, 28049 Madrid, Spain
2
Instituto de Nanociencia de Aragón, Universidad de Zaragoza, 50018 Zaragoza, Spain
3Departamento de Física de la Materia Condensada, Universidad de Zaragoza, 50009 Zaragoza, Spain
4
DFMC, Instituto “Nicolás Cabrera” & IFIMAC, UAM, 28049 Madrid, Spain 5Fundación INA, 50018 Zaragoza, Spain
6Laboratorio de Microscopías Avanzadas, Universidad de Zaragoza, 50018 Zaragoza Spain 7Instituto de Ciencia deMateriales de Aragón, Universidad de Zaragoza and Consejo Superior de Investigaciones Científicas, E-50009 Zaragoza,
Spain
8.
Université de Lorraine, CNRS, France Institut Jean Lamour, Nancy, *alberto.anadon@imdea.org

Conversion between spin and charge currents is essential in spintronics, since it enables a handful of
potentially transformative phenomena such as modifying the magnetization of ultra-thin films bymeans of spin-orbit torque or generating energy by spin-current-driven thermoelectric generation[1,2]. The inclusion of graphene in spintronics has allowed to unravel new arising spin-orbit effects
unique of graphene/metal interfaces [3–5]. However, the thermal magnetotransport properties in Grbased structures with perpendicular magnetic anisotropy have not been investigated at all.
We have studied the thermal magnetotransport in Pt(Ta)/Gr/Co/Ir and Pt(Ta)/ Co/Ir asymmetricepitaxial heterostructures on Al2O3(0001) single crystal substrates produced by means of a
combination of DC sputtering, MBE and CVD techniques (see [3]). By applying a thermal gradient in theout of plane direction a transversal voltage can be observed. This voltage is a combination of several
effects arising from the magnetic (anomalous Nernst effect) and spin-orbit (Spin Seebeck effect)
properties of the materials and interfaces involved. We have disentangled the origin of thesecomponents and observed that the inclusion of a graphene monolayer in the interface between cobalt
and a metal can induce a significant interfacial contribution to the observed voltage, reducing thethermo-spin voltage for two different metals on top with different spin Hall angle: Pt and Ta.
In addition there are ongoing measurements in this system using spin pumping and spin-torqueferromagnetic resonance in order to clarify the origin of the observed reduction in the inverse spin Hall
effect excited by incoherent thermal excitation.
[1]
C. O. Avci et al., “Current-induced switching in a magnetic insulator,” Nat. Mater., vol. 16, no. 3, pp. 309–314, 2017.
[2]
R. Ramos et al., “Unexpected enhancement of the spin Seebeck effect in Fe3O4 multilayer system,” pp. 1–20, 2014.
[3]
F. Ajejas et al., “Unraveling Dzyaloshinskii–Moriya Interaction and Chiral Nature of Graphene/Cobalt Interface,”
Nano Lett., vol. 18, no. 9, pp. 5364–5372, Sep. 2018.
[4]
W. Yan, E. Sagasta, M. Ribeiro, Y. Niimi, L. E. Hueso, and F. Casanova, “Large room temperature spin-to-charge
conversion signals in a few-layer graphene/Pt lateral heterostructure,” Nat. Commun., vol. 8, no. 1, pp. 1–7, 2017.
[5]
B. Raes et al., “Determination of the spin-lifetime anisotropy in graphene using oblique spin precession,” Nat.
Commun., vol. 7, no. May, pp. 1–7, 2016.

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Shape-anisotropy magnetic tunnel junctions with multilayered ferromagnets
J. Igarashi1,*, B. Jinnai2, S. Fukami1,2,3,4,5, and H. Ohno1,2,3,4,5
1. Research Institute of Electrical Communication, Tohoku University
2. WPI-Advanced Institute for Materials Research, Tohoku University
3. Center for Spintronics Research Network, Tohoku University
4. Center for Science and Innovation in Spintronics, Tohoku University
5. Center for Innovative Integrated Electronic Systems, Tohoku University
2-1-1 Katahira, Aoba-ku, Sendai 980-8577 JAPAN* Mail : jigarasi@riec.tohoku.ac.jp

The development of STT-MRAM—non-volatile spintronics memory—helps overcome theincreasing power consumption in semiconductor device scaling. Crucial to integrating STT-MRAM in
advanced integrated circuits is scaling magnetic tunnel junction (MTJ)—a core component of STTMRAM—while improving its performance in data retention and write operation. Shape-anisotropy MTJ
has shown MTJ scaling down to single-digit nanometers while achieving sufficiently high thermalstability factor [1-3]. In the shape-anisotropy MTJ, thermal stability is enhanced by making theferromagnetic layer thick. Once the thickness goes beyond a certain point, however, device reliability
becomes degraded.
To address the issue in the conventional shape-anisotropy MTJ with a single ferromagnetic structure,
we employ a new structure that uses magnetostatically coupled multilayered ferromagnets. The
developed MTJs are successfully scaled down to 2.3 nm in diameter—the world’s smallest MTJ size.
We also achieve high data retention properties up to 200°C and high-speed and low-voltage write
operation down to 10 ns below 1 V at a single-digit-nanometer scale [4].
A portion of this study was carried out under a collaboration with V. Desbuis, S. Mangin, K.
Watanabe, and H. Sato. This work was partly supported by JST-OPERA JPMJOP1611, JSPS
KAKENHI JP19K04486 and JP19J12926, Cooperative Research Projects of RIEC, and DIARE of
Tohoku University. J.I. acknowledges financial support from GP-Spin of Tohoku University and JSTOPERA.
[1] K. Watanabe et al. Nat. Commun. 9, 663 (2018).
[2] B. Jinnai et al. Appl. Phys. Lett. 116, 160501 (2020).
[3] J. Igarashi et al., Appl. Phys. Lett. 118, 012409 (2021).
[4] B. Jinnai et al., IEEE IEDM 2020, pp. 24.6.1-24-6.4 (2020).

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Magnetization control and all-optical switching mediated by phase transition of VO2
Xiaofei Fan1,2, Guodong Wei1, Michel Hehn2, Xiaoyang Lin1, Stéphane Mangin2
1. Fert Beijing Research Institute, School of Microelectronics & Beijing Advanced Innovation Center for Big Data and Brain
Computing (BDBC), Beihang University, Beijing 100191, China
2. Institut Jean Lamour, UMR 7198,CNRS–Universite´ de Lorraine, 54000 Nancy,France

Exploring a new method to regulate the magnetization of a ferromagnet has always been the focus of
spintronics development. Magnetic switching by femtosecond laser pulse is one of the promising
approaches to achieve ultrafast magnetic manipulation. In addition, finding a material, whose
electronic properties can be controlled, will assist the magnetization regulation more efficiently. VO2,a kind of phase transition material, could be a good candidate for this goal. First, with atomically thin
VO2 being the spacer, we realize a reversible switching of interlayer exchange coupling, from
antiferromagnetic coupling to ferromagnetic coupling, induced by the metal-insulator transition(MIT)of VO2. We attribute such an evolution originates from two distinct coupling mechanisms of spindependent tunneling and Rudermann-Kittel-Kasuya- Yosida interaction determined by the electronic
states of VO2. Lately, combining with the all-optical switching, we are making efforts to search a
method for ultrafast magnetic control affected by MIT, for instance, the influence of MIT on thetransport of polarized hot electron. More recently, we have found that the single-pulse switching of aferromagnet can be mediated by MIT of VO2. The effect of VO2-tailored magnetic manipulation
highlights the great potential of controllable spinterface as a magic building block in beyond-CMOS
electronic devices.

Figure. Interlayer exchange coupling regulation of [Pt/Co(1 nm)]2/VO2(t nm)/[Co(0.45 nm)/Pt]2 induced by phasetransition of VO2. With temperature rises, the interlayer exchange coupling switches from antiferromagnetic coupling(AFM) to ferromagnetic coupling (FM).

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Valley dynamics of charged exciton in monolayer WS2 treated by organic acid
T. Kimura1, E. Asakura1, J. Alexander-Webber2, A. O. A Tanoh3, H. Bretscher3, S. Hofmann2, A.
Rao3,4, S. Karube1,5, J. Nitta1,5,6 and M. Kohda1,5,6,7
1. Department of Materials Science, Tohoku University
2. Department of Engineering, Univiversity of Cambridge, England
3. Cavendish Laboratory, Univiversity of Cambridge, England
4. Department of Chemistry, University of Cambridge, England
5. Center for Spintronics Research Network, Tohoku University
6. Center for Science and Innovation in Spintronics, Tohoku University
7. Division for the Establishment of Frontier Sciences of Organization for Advanced Studies, Tohoku University
E-mail: takashi.kimura.t6@dc.tohoku.ac.jp

Two-dimensional atomic layer materials have attracted much attention because of both valley and spin
degrees of freedom for information carriers. Monolayer transition metal dichalcogenide (TMD) exhibits a
direct band gap at K and K’ valleys, showing strong optical absorption and exciton / trion formation. In
addition, because of crystal inversion symmetry breaking, Zeeman-type spin splitting is induced in
conduction and valence band extrema at K and K’ points. Recently, it has been reported that charged exciton(trion) has longer lifetime of valley polarization more than that of exciton in monolayer TMD [1]. However,details of relaxation process of trion have not been identified. In addition to that, recent study reveals thestabilization of trion in addition to the exciton with the surface treatment by organic acid (OA) [2,3]. In thispresentation, we investigated the valley relaxation process of trion in OA-treated monolayer WS2 by thecircularly polarized photoluminescence (PL), time-resolved Kerr rotation measurement (TRKR) andsimulation based on rate equation. TRKR exhibited tri-exponential decay and those time constants could be
identified with PL and simulated decay mechanisms.
[1] G. Wang, et al., Phys. rev., 90.075413 (2014).
[2] M Amani et al., Science 350, 1065 (2015).
[3] A. O. A Tanoh, et al., Nano Lett. 19, 6299 (2019).

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All optical helicity-independent switching in GdTbCo alloys
W. Zhang1, J.X. Lin1, T.X. Huang1, M. Hehn1, G. Malinowski1, S. Mangin1
Université de Lorraine, CNRS, IJL, F-54000 Nancy, France

All optical switching (AOS) of magnetization has been demonstrated experimentally in GdFeCo using afemtosecond laser pulse without the aid of magnetic field[1]. So far, helicity-independent AOS (HIAOS) is mostly observed in Gd based materials. In order to clarify the essential role of Gd, we depositedthe Gd100-R-xTbxCoR alloys with R=78, 80, 84 to study HI-AOS using time-resolved magneto-optical kerreffect (TRMOKE).
Fig.1(a) shows the laser fluence dependent magnetization evolution as a function of time for
Gd14.5Tb5.5Co80 with 𝜏!"#$% = 60 𝑓𝑠. The magnetization shows partial demagnetization、switching andfull demagnetization with the laser fluence increasing from 0.82 to 2.47mJ/cm2. As shown in Fig. 1(b),by changing the pulse duration and laser fluence, we established the state diagram showing HI-AOS orfull demagnetization for various GdTbCo thin films with different compositions of Tb. The laser fluence
window allowing for HI-AOS narrows for longer pulse duration and larger concentration of Tb. In order
to find out the essential parameter determining the HI-AOS in GdTbCo alloys, we present the atomistic
simulations to reproduce the spin dynamics obtained in experiment shown as the solid lines in Fig.
1(a). Within the simulations, element-specific Gilbert damping has to be taken into account toreproduce the state diagram in experiment, suggesting the essential role of Gilbert damping in theunderstanding of HI-AOS in rare-earth transition metal alloys.

Fig1:(a),laser fluence dependance of the laser induced spin dynamics in Gd14.5Tb5.5Co80. (b), the laser fluence window
allowing for HI-AOS in GdTbCo with different composition of Tb as a function of laser pulse duration.

[1] I. Radu, K.Vahaplar, C. Stamm, T.Kachel, N. Pontius, H. A. Durr, T. A. Ostler, J. Barker, R. F. L. Evans, R. W. Chantrell, A.
Tsukamoto, A. Itoh, A. Kirilyuk, Th. Rasing, A. V. Kimel, Transient ferromagnetic-like state mediating ultrafast reversal of
antiferromagnetically coupled spins. Nature 472, 205–208 (2011).

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All-optical probe of magnetization precession frequency shift due to spin-orbit torque
K. Ishibashi1,2*, S. Iihama 3,4, Y. Takeuchi5, K. Furuya5, S. Kanai5,4,6,7, S. Fukami5,4,6,2, S. Mizukami2,4,6
1. Department of Applied Physics, Graduate School of Engineering, Tohoku University
2. WPI-Advanced Institute for Materials Research, Tohoku University
3. Frontier Research Institute for Interdisciplinary Sciences, Tohoku University
4. Center for Spintronics Research Network, Tohoku University
5. Research Institute of Electrical Communication, Tohoku University
6. Center for Science and Innovation in Spintronics, Tohoku University
7. Division for the Establishment of Frontier Sciences, Organization for Advanced Studies, Tohoku University
2-1-1 Katahira, Aoba-ku, Sendai 980-8577 JAPAN* Mail : kazuaki.ishibashi.p1@dc.tohoku.ac.jp

Spin-orbit torque (SOT) is an attractive technique to manipulate magnetization for magnetic
thin films. SOT has been widely studied using the spin-torque-induced ferromagnetic resonanceand the second-harmonic-Hall effect measurements, whereas parasitic voltages induced byspin-charge conversion and thermoelectric effect tend to disturb the precise evaluation of SOT
in these electrical methods [1, 2]. Here we investigate SOT using an all-optical time-resolved
measurement which is free from such parasitic effects. There were a few studies investigating
the SOT effect on the decay time of magnetization precession driven by the laser pulse [3, 4].
In this study, we demonstrated the precession frequency can be modulated by SOT as well.
The films were fabricated by a DC/RF magnetron sputtering and the multilayer stacking was
Si/SiO2/W(5)/CoFeB(2.4)/MgO(1.3)/Ta(1) (thickness in nm) [5]. The film was patterned intoa rectangular stripe. The magnetization dynamics was investigated by the all-optical timeresolved magneto-optical Kerr effect (AO-TRMOKE) microscope, in which an external field
Hext was applied at an out-of-plane angle θH and a direct current I was applied parallel to y-axis[Fig. 1(a)]. Figure 1(b) shows typical normalized MOKE signals measured with I = 0, ±5 mA.
The modulation of the precession frequency was clearly observed. This can be understood by
the change in the equilibrium magnetization angle θ induced by SOT, and the SOT generation
efficiency was evaluated as −0.35 [6]. This work was supported by KAKENHI(19K15430,
19H05622) and the ImPACT Program.

Fig. 1(a) Schematic illustration of the experimental setup of AO-TRMOKE. (b) Normalized
MOKE signals Δ𝜃(! as a function of the pump-probe delay time Δt with I = 0, ±5 mA(I // y).
[1] K. Kondou, et al., Appl. Phys. Express 9, 023002 (2016).
[2] C. O. Avci, et al., Phys. Rev. B 90, 224427 (2014).
[3] A. Ganguly, et al., Appl. Phys. Lett. 105, 112409 (2014).
[4] S. Mondal, et al., Phys. Rev. B 96, 054414 (2017).
[5] Y. Takeuchi, et al., Appl. Phys. Lett. 112, 192408 (2018).
[6] K. Ishibashi, et al., Appl. Phys. Lett. 117, 122403 (2020).

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Stripe domains in thin magnetic films for spin waves channeling
K. AIT-OUKACIa,b, D. LACOURa, S. PETIT-WATELOT a, R. BELKHOUb, M. HEHNab.

a.

Institut Jean Lamour, Campus Artem, 2 allée André Guinier, BP50840 - F-54011 Nancy
Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex, France* Mail : kosseila.ait-oukaci@univ-lorraine.fr

The possibility to channel spin waves in domain walls has been first shown by numerical calculations
in materials with perpendicular to film plane magnetization in 2009 [1]. This concept is particularlyinteresting since domain walls can reach lateral sizes of several nanometers (so with ultra-highintegration capabilities) and are reprogrammable (the channel can be erased and rewritten throughan appropriate magnetic field history). The aim this work is the development of new spin-waves guides
and devices based on the use of magnetic domain walls to channel spin waves. To achieve a firstexperimental demonstration in perpendicular to film plane magnetized films materials with low
magnetic damping and control magnetic textures have to be synthetized.
I will present in detail the domain structures in two magnetic systems, high (111) textured [Co/Ni]
Multilayers of thicknesses varying from 10 nm to 200 nm and amorphous CoFeB with thicknesses
varying from 100 nm to 270 nm. The domain sizes and domain shapes have been studied as a functionof thickness, magnetic history and annealing temperature. In [Co/Ni], a quality factor around 1 and adamping parameter of 1.5x10-2 could be measured. We observed by magnetic force microscopy(MFM) that the stabilization of straight stripe patterns is more difficult to obtain in comparison toepitaxial Co layers [2]. In the sample with the optimum thickness of 50nm, straight stripe patterns
could be stabilized. Amorphous CoFeB shows weak stripes domains and a damping parameter of 7x103 could be measured. From the domain pattern and damping point of view, this material appears tobe the most promising for spin wave channeling.
[1] F. Garcia-Sanchez et al., Phys. Rev. Lett. 114, 247206 (2015)S. Author, Journal 100, 101101 (2009)[2] M. Hehn, S. Padovani, K. Ounadjela, and J. P. Bucher, Phys. Rev. B 54,3428 (1996).

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Anisotropic spin relaxation and precession frequency depending on in-plane magnetic
field orientation in GaAs-based wire structures
J. Sonehara 1,*, D. Sato 1,, D. Iizasa 1, M. Kammermeier 2, U. Zülicke 2, S. Karube 1,3, J. Nitta 1,3,4
and M. Kohda 1,3,4,5
1. Department of Materials Science, Tohoku University, Japan
2. School of Chemical and Physical Sciences and MacDiarmid Institute for Advanced Materials and Nanotechnology,
Victoria University of Wellington, New Zealand
3. Center of Spintronics Research Network, Tohoku University, Japan
4. Center for Science and Innovation in Spintronics, Tohoku University, Japan
5. Division for the Establishment of Frontier Sciences, Tohoku University, Japan* Mail : junpei.sonehara.s3@dc.tohoku.ac.jp

In III-V semiconductor heterostructures, there exist Rashba and Dresselhaus spin-orbit (SO)interactions, which yield effective magnetic fields for moving electrons. The induced SO field depends
on the electron momentum that is randomized by scattering, resulting in D’yakonov-Perel spin
relaxation. In order to enhance the spin relaxation time, quantum wire structures are attracted muchattention since the geometrical confinement suppresses momentum randomization [1-3]. Application ofan external magnetic field to the wire induces spin precession and enhances the spin relaxation time,
which depends on the relative angle between the SO field and external magnetic field. Here, weinvestigated the anisotropic spin dephasing depending on the direction of an external magnetic field in
wires based on a 20-nm (001)-oriented GaAs/AlGaAs quantum well (QW). We fabricated 800-nmwidth wires parallel to [1-10] (|| x), [110] (|| y), [100] and [010] crystal orientations by electron beamlithography and reactive ion etching. We employed time-resolved Kerr rotation microscopy formeasuring the spin dephasing time in the wires. In-plane external magnetic field Bex was applied withdifferent angles at 30 K. The evaluated spin relaxation time is twice longer when the external magnetic
field is perpendicular to the SO field in comparison with the parallel external magnetic field. Contrary,Larmor precession frequency is decreased when the external magnetic field was perpendicular to the SO
field. By solving the spin diffusion equation, we obtained the analytical formula to explain such anenhanced spin relaxation time by the lateral confinement of electron momentum.
[1] Th. Schäpers et al., Phys. Rev. B 74, 081301 (2006).
[2] A.W. Holleitner et al., Phys. Rev. Lett. 97, 036805 (2006).
[3] P. Altmann et al., Phys. Rev. B 92, 235304 (2015).

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Zero applied field current induced switching of GdFeCo
Jean-Loïs Bello *,1, Yassine Quessab 2, Jun-Wen Xu 2, Maxime Vergès 1, Sébastien Petit-Watelot 1, JuanCarlos Rojas-Sánchez 1, Andrew D Kent 2, Michel Hehn 1, and Stéphane Mangin 1
1 Institut Jean Lamour, UMR CNRS 7198, Université de Lorraine, Nancy, France.

2 Center for Quantum Phenomena, Department of Physics, New York University, New York, USA.

Amorphous rare-earth transition-metal (RE-TM) GdFeCo ferrimagnetic thin films are wellknown to exhibit many interesting magnetic properties. Indeed its magnetization can be switchedusing a magnetic field, but also because of single femtosecond laser pulse [1] or spin orbit torque [2].
Since this material appears to be promising for future spintronics applications, we focused on the
combine effect of field, light and current on magnetization reversal.
We observed that GdFeCo could show magnetization reversal by Spin Orbit Torque whithout any
applied field (figure 1) . We could then demonstrate that the magnetization switching of Gdx(Fe90Co10)1x ferrimagnetic alloys single layers was caused by the combined effects of the spin-orbit torque andcurrent-induced Oersted field [3] figure 2. We show switching via spin-orbit torque of low coercive
field M(5nm)/Gdx(Fe90Co10)1-x(5nm)/N(5nm) stacks with M or N=Cu, Ir, even at low in-place field.

[1] C. D. Stanciu, et al., Phys. Rev. Lett. 99, 047601 (2007).
[2] N. Roschewsky, et al., Appl. Phys. Lett. 109, 112403 (2016).
[3] O. Boulle et al., J. Appl. Phys. 105, 07C106 (2009).

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