All Tied Up in Knots: Skyrmions in Chemically Substituted Cu2OSeO3

Presenter: Paul Neves

Mentors: Nicholas Butch & Juscelino Leão

NIST Center for Neutron Research

Summer Undergraduate Research Fellowship
2

• What: Can we understand the effects of chemical 

substitution on the stability of magnetic skyrmions?

• Why: Can we control/tune the skyrmion phase?

• Normally small stability window

Our Project Goal
3

Magnetic Structures

Nonmagnetic

Atomic Lattice

Para/diamagnetic

Atomic Lattice
4

Magnetic Structures

Ferromagnetic

Lattice

• What happens when 

we add interactions 

between the spins?

• Ferromagnetism, for 

example

• Can we have other 

structures?

B
5

Magnetic Structures

Helical

Lattice

• More complex interactions can lead to helical 

structures

B
6

An Interesting Material: Cu2OSeO3

Janson, O. et al. The quantum nature of 

skyrmions and half-skyrmions in 

Cu2OSeO3. Nature Communications 5, (2014)

• Insulating

• Magnetically interacting Cu sites

• Helimagnetic
7

An Interesting Material: Cu2OSeO3

Seki, S. et al. Observation of Skyrmions in a 

Multiferroic Material. Science 336, 198-201 (2012)

(10 Oe = 1 mT)
8

• Topologically protected

• <>MNSJKAGHICGSA

• Robust (stable)

• Potential data storage 

applications

Magnetic Skyrmions

(10 – 100 nm size)

B
9

Possible Data Storage Applications

• Protected data storage

• Topological

• Spintronics

• Not just 1’s and 0’s

• High density data storage

• Nanoscale

Zhang, Shilei, et al. "Topological computation based 

on direct magnetic logic communication." Scientific 

reports 5 (2015): 15773.
10

• Control/tune the phase

• Small stability window

• Chemical substitution 

affects the skyrmion 

phase

• Ex) Substitute Zn for Cu

• Splits skyrmion phase?

• Magnetization only

• Structure not directly 

confirmed

(10 Oe = 1 mT)

Wu, H. C. et al. Unexpected Observation of Splitting of Skyrmion 

Phase in Zn Doped Cu2OSeO3. Science Reports 5, (2015)

What is our Goal?

Conical

Helical

Ferrimagnetic

(Cu1.8Zn0.2)OSeO3

CuOSeO3
11

How to Grow Single Crystals

• Chemical vapor deposition

• Manipulates chemical equilibrium with temperature

640 °C 530 °C

CuO + SeO2 (+ substituents)

→

Cu2OSeO3

NH4Cl

Panella, Jessica R., et al. "Seeded chemical vapor transport growth of 

Cu2OSeO3." Crystal Growth & Design 17.9 (2017): 4944-4948.

~20 cm
12

How not to Grow Single Crystals

• Chemical vapor deposition

• Very sensitive to temperatures and pressure

• Limited by chemistry

(Cu1.8Zn0.2)OSeO3 ?

! Cu2OSeO3
13

Making Polycrystals

• Mix/grind CuO and SeO2

• (and any substitutions)

• Seal in evacuated quartz 

tube

• Bake at 600°C

• Press into pellet

• Lather, rinse repeat

CuO SeO2
14

Neutron

detector

Small Angle Neutron Scattering 

(SANS)

SSSSSSSSSSSS

22θθ

Incident neutrons

QQ

B

T
15

SANS in a Single Crystal

Real Space SANS
16

Skyrmions in SANS in a Powder

Wu, H. C. et al.

Real Space SANS

0.000 0.005 0.010 0.015 0.020 0.025

0.1

1

10

100

1000

10000

I(Q) (1/cm)

Q (1/Å)

Nuclear scattering

Magnetic scattering
17

0.000 0.005 0.010 0.015 0.020 0.025

0.1

1

10

100

1000

10000

I(Q) (1/cm)

Q (1/A)

Skyrmions in SANS in a Powders

~65nm

? ?
18

SANS: Cu2OSeO3 Powder

Seki, S. et al. Observation of Skyrmions in a 

Multiferroic Material. Science 336, 198-201 (2012)

parent 0.01 Å -1

 Scattering Peak Area

48 50 52 54 56 58 60 62

Temperature (K)

0

100

200

300

400

500

600

700

Field (G)

0.005

0.01

0.015

0.02

0.025

0.03

0.035

Peak Area (arb. units)
19

SANS: Rotation Technique

No rotation

Rotated Skyrmions

Dustin Gilbert

Precipitating Ordered Skyrmion 

Lattices from Helical Spaghetti

B

n

0 90 180 270 360

0

100

200

300

400

I (a.u.)

Angle (degrees)

χ2=0.91 Rotated Helices
20

B

n Rotation

No rotation

Rotated Skyrmions

0 90 180 270 360

0

100

200

300

400

I (a.u.)

Angle (degrees)

χ2 Dustin Gilbert =0.91 Rotated Helices

Precipitating Ordered Skyrmion 

Lattices from Helical Spaghetti

SANS: Rotation Technique
21

42 44 46 48 50 52

100

200

300

400

500

600

Field (G)

Temperature (K)

(Cu1.8Zn0.2)OSeO3 Powder 0.01 Å-1 Peak Area

42 44 46 48 50 52 54 56

200

250

300

350

400

Field (G)

Temperature (K)

SANS: (Cu1.8Zn0.2)OSeO3 Powder

Wu, H. C. et al.
22

Other Substitutions

40 42 44 46 48 50 52 54 56 58 60

0

100

200

300

400

500

600

700

800

Cu2(O0.9S0.1)SeO3 Powder Skyrmion Phase

Field (Oe)

Temperature (K)

40 42 44 46 48 50 52 54 56 58 60

0

100

200

300

400

500

600

700

800

(Cu0.95Ag0.05)2OSeO3 Powder Skyrmion Phase

Field (Oe)

Temperature (K)

40 42 44 46 48 50 52 54 56 58 60

0

100

200

300

400

500

600

700

800

Field (Oe)

Temperature (K)

Cu2(O0.95S0.05)SeO3 Powder Skyrmion Phase

40 42 44 46 48 50 52 54 56 58 60

0

100

200

300

400

500

600

700

800

Field (Oe)

Temperature (K)

(Cu0.95Ag0.05)2OSeO3 Powder Skyrmion Phase

+Ag +S
23

Summary

• Recent Work

• Synthesized samples

• Performed SANS measurements and analysis on parent 

and substituted powders

• Results

• Possible structural confirmation of second phase in Zn 

substitution

• Can identify and map skyrmion phase in a powder

• Future Work

• Rotation of Zn substitution in SANS

• Perform supplementary measurements

• Investigate other substitutions further
• NG7-SANS

• Dustin Gilbert, Julie Borchers, Markus Bleuel, Jeffrey 

Krzywon, Tanya Dax

• MPMS Magnetometry

• Sheng Ran, I-Lin Liu, Shanta Saha

• Sample Growth

• Kefeng Wang, Sheng Ran

• MANiACS

• Doug Johnson, Patrick Connelly, Scott Slifer, Colin 

Wrenn, Andrew Malone

Acknowledgements
Shameless Plug

25 https://www.nist.gov/blogs/taking-measure/surfing-susceptometers-skyrmions-making-neutron-maniac
26
27

Magnetic Structures

Conical
28

An Interesting Material: 

Cu2OSeO3

Janson, O. et al. The quantum 

nature of skyrmions and halfskyrmions in Cu2OSeO3. Nature 

Communications 5, (2014)

Seki, S. et al. Observation of Skyrmions in a 

Multiferroic Material. Science 336, 198-201 

(2012)
29

X-Ray Powder Diffraction

Meas. data:Cu2OSeO3-Sample1-Bake3

Intensity (cps)

 0e+000

 1e+005

 2e+005

 3e+005

 4e+005

 5e+005

2-theta (deg)

20 40 60 80
30

Magnetization: Parent

Seki, S. et al. Observation of Skyrmions in a Multiferroic Material. Science 336, 198-201 (2012)
31

Magnetization: Zn Doped

Wu, H. C. et al. Unexpected Observation of Splitting of Skyrmion 

Phase in Zn Doped Cu2OSeO3. Science Reports 5, (2015)

Skyrmions

Our data
32

SANS: Zn Doped, H On Axis

Parameter mean median best [ 68% interval] [ 95% interval]

1 A 17.2(39) 15.94 16.21 [ 13.8 21.3] [ 12.5 28.1]

2 G 43(32)e3 38300 30300 [ 11000 73000] [ 4000 113000]

3 background 0.65(22) 0.680 0.619 [ 0.43 0.86] [ 0.14 1.06]

4 peak_pos 0.01014(12) 0.010144 0.010185 [0.01000 0.01025] [0.00991 0.01038]

5 porod_exp 4.54(30) 4.511 4.480 [ 4.26 4.85] [ 3.93 5.13]

6 rg 1.33(17)e3 1401.9 1193.0 [ 1202 1479] [ 850 1495]

7 s 0.102(85) 0.072 0.012 [ 0.02 0.19] [ 0.01 0.29]

8 sigma 0.78(21)e-3 0.000790 0.000779 [0.00054 0.00103] [0.00042 0.00112]
33

SANS: Zn Doped, Transverse H, 12K

B

0 50 100 150 200 250 300 350

10

100

0.01 Å-1 Annular Plot, (Cu0.9Zn0.1)2OSeO3, Transverse Field

I (1/cm)

Phi (Degrees)

70 Oe

200 Oe

310 Oe

410 Oe

500 Oe

580 Oe

690 Oe