1400-1440, Wednesday 8th November 2017, Yukawa Institute for Theoretical Physics (YITP), Kyoto University, Kyoto, JAPAN

Novel Quantum States in Condensed Matter 2017 (NQS2017) 

L(0)

L(H)

Hdc

Dept. of Physics and Electronics, Osaka Prefecture University大阪府立大学 工学研究科 電子物理工学分野

CResCent (Chirality Research Center), Hiroshima UniversitySchool of Physics and Astronomy, University of Glasgow

Yoshihiko TOGAWA （戸川 欣彦）

Functionality of Phase Coherent Chiral Soliton Lattice in Chiral Magnetic Crystals

Collaborators

Hiroshima UniversityA. O. Leonov, K. Inoue

Osaka UniversityM. Hagiwara

Kyushu Tech. UniversityM. Mito

Institute of Molecular ScienceH. Okamoto, S. Hashiyada

Nagoya Tech. UniversityS. Ohara

University of TokyoY. Kato, M. Shinozaki, Y. Masaki

Ural Federal UniversityA. S. Ovchinnikov, I. G. Bostrem, Vl. E. Sinitsyn

University of GlasgowR. L. Stamps, S. McVitie, D. McGrouther, D. MacLaren,M. Kadodwala, G. Paterson, Students

Okayama UniversityY. Kousaka, J. Akimitsu

University of ZaragozaV. Laliena, J. Campo

IFW DresdenA. N. Bogdanov

Open University of JapanJ. Kishine, I. Proskurin

SPing-8H. Ohsumi, K. Tsuruta, T. Nakamura

Osaka Prefecture UniversityF. J. T. Goncalves, Students

International Consortium to exploit Chirality in Advanced Materials

Consortium is now expanding.

This work is supported by JSPS Core-to-Core Program, A. Advanced Research Networks.

Consortium amongJapan(Hiroshima),Russia(Ekaterinburg, Ural),the UK(Glasgow, Scotland),Spain, France, Canada and other countries.

JSPSCore‐to‐Core Program

For details, search by ‘CResCent(Chirality Research Center) and

Hiroshima Univ.’

from 2015. 105 years

Workshop for chiral science (July in 2018)

χ‐mag 2018, July 25 to 28, 2018Nara Kasugano International Forum甍 IRAKA, Nara, Japan

‐ How to make chirality‐ How to measure chirality‐ How to use chirality

Contents

1. Brief introduction of chiral magnetic orderin chiral magnetic crystals

2. Monoaxial chiral magnetic crystalChiral soliton lattice

Structure and functionality

A brief summary of research on‘Chiral Magnetism’

1958: Antisymmetric exchange (Dzyaloshinskii)1960: Microscopic mechanism (Moriya)

1964‐65: Helicoidal (CSL) deformation (Dzyaloshinskii)IC‐C phase transition in chiral spin system

1980: Interfacial DMI (Fert & Levy)1989, 1992, 2002: Chiral vortices (Skyrmion) (Bogdanov)

Chiral helix

1976: Helix (Ishikawa et al.)1982: A‐phase (Date group)

Skyrmions Lattice (SkX)2009: k‐space by neutron 

(Mühlbauer et al.)2010: Real space by LTEM 

(Yu et al.)

Multiaxial system 2D‐3DAtomic layers 2007: Chiral helix 2011: SkX2013: Isolated Skyrmion

(Wiesendanger)Multilayers 2015‐16: Isolated Skyrmion

(EU MagicSky prj., US)

Surface/interfacial system

2DMonoaxial system

1982, 83: Helix (Miyadai & Moriya)

Chiral Soliton Lattice (CSL)1997: k space by neutron 

(Zheludev, Uchinokura et al.)2012: Real and k spaces by electron 

(Togawa et al.)

1D‐2D

Symmetric helix 1959: J1‐J2 frustration (Yoshimori, Kaplan, Villain) Multiferroics

Guiding principal/Symmetry arguments‐‐Moriya rule‐‐ Lifshitz invariant/Particle or wave nature

Chiral magnetic order

Chiral conical phase

Helicoid (Chiral soliton lattice: CSL)

Chiral magnetic vortex (Magnetic skyrmion)

Helicoid (Chiral helimagnetic order: CHM)

Chiral magnetic orderMonoaxial crystals 

with single principal axis (helical axis)Cubic crystals with multiple helical axes

Chiral helimagnetic order (CHM, Helicoid at H = 0)

Chiral conical phase (H // helical axis)

H

Helical axis

Domain formation

Chiral magnetic orderMonoaxial crystals 

with single principal axis (helical axis)Cubic crystals with multiple helical axes

Chiral soliton lattice (CSL, Helicoid at H ⊥ helical axis):   

superlattice of chiral twisted kinks

Magnetic skyrmion

HHelical axis

Domain formation

H

3.4

Co8Zn8Mn4 Tc ~ 300 K, Mn2RhSn Tc ~ 400 K  …

Chiral Magnet：magnet with chiral structure

Crystalline Chirality

Dzyaloshinskii - Moriya（DM）interaction（Twisting Spins）

Spin Chirality

We can control “spin phase” in chiral magnets.

Chiral Helimagnetic Order

CrNb3S6(P6322)

Nb

S

Cr

From Crystalline Chirality to Magnetic Chirality

Contents

1. Brief introductionWhy chiral magnetic system is interesting?

2. Monoaxial chiral magnetic crystalChiral soliton lattice

“Structure” and “functionality”Emergence of phase coherence

CrNb3S6 (Cr1/3NbS2)Monoaxial chiral magnetic crystal of CrNb3S6

Left-handed

Right-handed

(*deformed image)

a

b

c

Nb (2a, 4f) S (12i)

Cr (2d)

P 6322Chiral space group:

P 6322a0: 0.574 nm c0: 1.207 nm

Chiral space group

Tc ~ 130 KHc⊥c ~ 2 kOe (CSL)

Hc// c ~ 20 kOe (cone)

Monoaxial Chiral Magnet

Helical axis// c -axis

Helical pitch: ~ 40 c0(~ 48 nm)

CrNb3S6 (Cr1/3NbS2)DM interaction in a chiral magnetic crystal

DM

Left-handed

Right-handed

(*deformed image)

a

b

c

Nb S

Cr

Helical axis

c

P 6322Chiral space group: Chiral helimagnetic order(CHM)

CrNb3S6~ 40 c0

(~ 48 nm)

Helical axis

Chiral Helimagnetic order (CHM) (H = 0)

Chiral Soliton Lattice (CSL) (H > 0)

Forced Ferromagnetic State (H >Hc)

Chiral Spin Soliton Lattice（CSL; Helicoid）

Spin Super Lattice

I. E. Dzyaloshinskii (1964-65).

In-focusCrNb3S6 (Cr1/3NbS2)

[11-20]

[0001]

Helical axis

Handedness of CSL

Helical axisCrNb3S6 (Cr1/3NbS2)

1950 Oe

100 nm

110 K

TEM Lorentz Fresnel micrograph

I. E. Dzyaloshinskii (1964-65). YT et al., (2012).

48 nm

100 nm

200 nm

0 OeHelical axis

110 K

2200 Oe

1950 Oe

I. E. Dzyaloshinskii (1964-65). YT et al., (2012).

H⊥c

Theory (Chiral sine-Gordon Model)• effective 1D model→‘soliton’

Topological NonlinearKinetic

Chiral Soliton Lattice

Forced FM

Spatial Period of Chiral Soliton Lattice

48 nm

100 nm

200 nm

0 OeHelical axis

110 K

2200 Oe

1950 Oe

I. E. Dzyaloshinskii (1964-65). YT et al., (2012).

Helical axisCrNb3S6 (Cr1/3NbS2)

1950 Oe

100 nm

110 K

Periodic & Straight & Uniform

Phase Coherence of Chiral Soliton Lattice

J┴

J┴ >> J// >> DEnergy scale

3D Monte Calro simulation by Shinozaki et al., JPSJ (2016).

J┴ ~ 140K, J// ~ 18K, D ~ 2.9K

/ Soliton chains are in phase each other./ Phase coherence exists among soliton chains.

Helical axisCrNb3S6 (Cr1/3NbS2)

1950 Oe

100 nm

110 K

Chiral soliton lattice isa coherent phase object.

Phase Coherence and Material Functionality

Cover Image on a web site, Invited Review,YT et al., J. Phys. Soc. Jpn. 85, 112001 (2016).

“Spin phaseelectronics”

Fröhlich sliding of phase object

H. Fröhlich Proc. R. Soc. London. Scr. A, 233, 290 (1954).

/Phase kinks can locate in arbitrary locations.

/Phase object can slide with no or little energy loss.

/One of the first mechanisms for superconductivity

/Many studies was done in density wave in 1970’s to 80’s. Pinning effect was significant in the density wave system.What about in the chiral spin system?

Contents

1. Brief introduction of chiral magnetic orderin chiral magnetic crystal

2. Monoaxial chiral magnetic crystalChiral soliton lattice

Structure and “functionality”due to phase coherence

Magnetic Superlattice

Potential

SpinTransferTorque

Chiral Spin Soliton Lattice (CSL) = Semi-classical magnetic order

MultipleMR

Moment flowMotive forceCollective modeIsolated soliton

Coupling of CSL to conduction electrons

“Conduction electron spins” Itinerant quantum spins slide on CSL.

“ＣＳＬ dynamics” Very fast＆Giant

Functionality of CSL

“Wave”: Phase coherence, Collective, Stability, Robustness

Chiral soliton lattice : spin phase object

・Soliton Elementary Excitation

・Isolated Soliton Sliding

・Collective excitation as the chiral soliton lattice

Broadband, Tunable Frequency, Fast propagation of phase information, Non-local and Giant response

How does the CSL behave in a finite system?

Infinite system

finite system

e.g., CrNb3S6 crystal typical size along helical axis : a few hundreds mCSL period: from 48 nm‐ System size influences or not CSL behavior?‐What is the role of the boundaries?     etc.

10 nm – infinite

10 nm – sample size

Chiral sine Gordon model

L LR

Crystal grains with opposite crystalline chirality

Fresnel

R LL R

Magnetic chirality switch at crystal grain boundary

DPC

H

Spin configuration at chirality grain boundary

Domain boundaryhas in-plane moments,

which are strongly pinned.

Soliton confinement and discretization

chirality grain (1 m width) – 20 solitons

YT et al., PRB 92, 220412(R) (2015), Editor’s suggestion.

H

Micro CrNb3S6 Single CrystalMicro CrNb3S6 Single Crystal

chiral axis

Bulk CrNb3S6 Single Crystal

500 mHelical c axis

V1

I1 I2

Pristine bulk crystal and micron-scale crystal

V25 m

helical axis

Micro CrNb3S6 Single Crystal~ 10 m×10 m (// c)

×500 nm200 solitons

/ Edges can work as a pinning source.

~ 1 mm2 ×200 m (//c)4000 solitons

Helical axis

As a “particle”: Tunability of density

0 0.5 1

0

0.50

1.00

H / Hc

(R -

R c) /

(R0 -

Rc)

5 mA

20 K 40 K 60 K 80 K 100 K 110 K 120 K Order parameter

YT et al., PRL 111, 197204 (2013).

MR Bulk crystal CrNb3S6

Micrometer-sized crystalCrNb3S6

Editor’s suggestion.YT et al., PRB 92, 220412(R) (2015).

As a “wave”: Phase coherence

5 m

Magnetoresistance (MR), scaling to order parameter

1 mm2

×200 m10 m×10 m

×500 nm

0 200 400 600 800701.8

701.9

702.0

702.1

702.2

0 500 1000 1500R

(m

)

H (Oe)

10 K5 mA

Discrete changes of MRMagnitude of MR (~ 25 )：

reproduciblePosition of H ： stochastic

Stepwise (multi-valued) magnetoresistance

0 1000 2000 3000698

699

700

701

702

2800 3000 3200

698.2

698.3

698.4

698.5

R (m

)

H (Oe)

10 K5 mA

10 m×10 m×500 nm

200 solitons

Electric detection of confined solitons

Helical axisYT et al., PRB 92, 220412(R) (2015), Editor’s suggestion.

Hysteresis & discreteness due to confined solitons

c axis

Hdc

Micrometer sized crystal CrNb3S6 t ～200 nm

4 solitons

0 1000 20001.82

1.84

1.86

1.88

1.9

H (Oe)

R(

)

“4”“3”

“2”

“1”

“0”All states can exist in this regime.

Soliton confinement is significant in thin specimen along c axis. Thus, all possible states of CSL （“0”－“4”） can

exist in the same field regime.

Clear step

∆R ~ 15 m

Hbias

Hbias

→Using bias field, all states can exist at around zero field.

Magnetic material with multiple values

S. Nakayama, H. Muramoto, R. Aoki, YT et al., in preparation

Collective resonant dynamics of CSL

Co‐planar waveguide (CPW)

In‐plane field, H rotation

hRF

CrNb3S6

G SG

hrf

c axis

Hdc

CONFIG. I

Collective resonant dynamics of CSL

Co‐planar waveguide (CPW)

In‐plane field, H rotation

hRF

CrNb3S6

G SG

Magne

toresistan

ce

VNA‐

FMR

hrf

c axis

Hdc

CONFIG. I

CONFIG. II

Collective resonant dynamics of CSL hRF

c axisHdc

12×19 m

hRF

Asymmetric

Sensitive to Polarization

CONFIG. I

Discretization

F. J. T. Goncalves, YT et al., PRB 95 104415 (2017).

Laboratory members

Damien in the lab., 11th May 2017.

FY20171 PD researcher6 Master course2 Undergrads. 2 Visiting students1 Tech. staff1 Secretary

Francisco Goncalves

KensakuEndo

HaruhiroMuramoto

Shota Nakayama

RyuyaAoki

YuyaYoshitake

Yusuke Shimamoto

AkitoInui

Damien McGroutherfrom Glasgow

AmyKadodwala

CameronGilroy

Summary

/Rich physics and functionality on structure and dynamics of chiral magnetic order, unique to chiral magnetism

Chiral soliton lattice (CSL, H ⊥ helical axis):   superlattice of chiral twisted kinks

Magnetic skyrmion

H

Helical axis

Monoaxial crystals with single principal axis (helical axis)

Cubic crystals with multiple helical axes

Chiral conical phase

phase coherent, robust, tunable, nonlinear, asymmetric, topological, nonlocal, collective, …