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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, …
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