on the subtle interplay of light induced magnetization, driven currents and … · 2018. 11. 6. ·...

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On the subtle interplay of light induced

magnetization, driven currents and heat in

ultrafast magnetism… ways towards optical spin manipulation in topological systems

Markus Münzenberg

THz spintronics and ultrafast magnetism

Perspective, J. Appl. Phys. 120, 140901 (2016)

Ke

rr r

ota

tio

n (

a.u

.)

Time (ps)

-5 0 5 10 15

3 ps

Out of planeCurrent bunch I

+M

-M

+M

Ultrafast trigger

Free THz B-field trigger

• Stanford accelerator

Ch. Back et al., Science (1999)

• Photoconductive switch, 1ps

rise time, 0.2 Tesla

Wang et al. JAP (2008)

• Free THz pulse (organic

crystals)

0.5 ps rise time, ~1Tesla

C. Hauri et al. Nature

Photon.(2013)

Perspective, J. Appl. Phys. 120, 140901 (2016)

Skyrmions

Topological matter

Internal spin-orbit field

Large spin-orbit coupling leads

to cyclotron orbit

Topological Insulators

Cyclotron resonance, in 2D

materials quantum Hall effect and

edge states

lsE so

~

h

enH

2

Topological matter

Topological matter

From A. Fert, V. Cros, and J. Sampaio, Nat.

Nano. 8, 152–156 (2013)

Nature Phys. 5 (2009) 438-42

Phys. Rev B 82 (2010) 045122

x

y

Real space x, y Reciprocal space kx, ky

Skyrmions Topological insulators

• The nature of femtosecond spin dynamics

• THz spintronic emitter

• Hard disc: state of the art

• Thermal model of ultrafast demagnetization

• FePt optical writing a storage media

• Summary

Outline

Tim

e (

~1

0 fs)

Ultrafast: spins

~group velocity

Length (~nm)Perspective, J. Appl. Phys. 120, 140901 (2016)

nanoscale spin currents

charge currents je: e-

spin currents js : ms

Tim

e (

~1

0 fs)

Ultrafast: spins

~group velocity

Length (~nm)Perspective, J. Appl. Phys. 120, 140901 (2016)

- +js

s

+ -e-

je

Nanoscale spin currents js: ms

Nanoscale charge currents je: e-






• Summary

Outline

• Fritz-Haber Institut, Berlin, Germany

• Physics and Astronomy, Uppsala

University, Sweden

Tobias Kampfrath

Peter Oppeneer

THz: T. Kampfrath

Spintronic THz emitter

Published in Nature Nanotech. 8, 256 (2013),

Nature Photonics 10, 483–488 (2016).

Theory Spin Currents: Battiato, OppeneerTom Seifert

• Johannes Gutenberg-Universität Mainz

• FZ Jülich


Published in Nature Nanotech. 8, 256 (2013),

Nature Photonics 10, 483–488 (2016).

Mathias Kläui

Emitter: Kläui, Münzenberg

Theory SHE: Mokrousov, Freimuth

Yuri Mokrousov

Frank Freimuth

fs pump

pulse

Pump pulse excites and electrons

: d sp bands become fast

Oppeneer et al., PRL (2010)

Fe (~5 nm)


Ferromagnet

Nature Nanotech. 8, 256 (2013).

Inverse spin Hall effect (ISHE):

Spin-orbit coupling deflects electrons

transverse charge current

Spin hall angle

fs pump

pulse

Metal (NM)

Fe (~5 nm)

g


Kampfrath, Battiato, Oppeneer, Wolf,

Freimuth, Mokrousov, Münzenberg et al.,

Nature Nanotech. 8, 256 (2013)

𝛾 =𝜎SH𝜎𝑥𝑥

𝜎SH - spin Hall

conductivity

𝜎𝑥𝑥 - diagonal

conductivityjc

g

js

Ferromagnet

Nature Nanotech. 8, 256 (2013).

Measure THz emission from photoexcited FM/NM bilayers

Kampfrath, Battiato, Oppeneer, Wolf,

Freimuth, Mokrousov, Münzenberg et al.,

Nature Nanotech. 8, 256 (2013)

Note: just used a pulsed

laser oscillator (10 fs, 80 MHz)


fs pump

pulse

MetalFe (~5 nm)

g

300µm GaP,

10fs gate pulse

TH

z s

ign

al

(10

-5)

t (ps)

+M

-M

0 0.5 1-3

-2

-1

0

1

2

3

FePt

Transient changes polarity by reversing M or stacking order

Fe Pt

TH

z s

ign

al

(10

-5)

t (ps)0 0.5 1

-3

-2

-1

0

1

2

3

Really SHE scenario? change NM layer


Calculations:

Freimuth, Blügel,

Mokrousov

e.g. PRL (2010)

Good relative agreement

Simple method to get relative estimates of spin-Hall conductivity

4

3

2

1

0

-1

-2

NM material

1

0.8

0.6

0.4

0.2

0

-0.2

-0.4

Cr Pd Ta W Ir PtPt38Mn62

TH

zam

plit

ude

(norm

aliz

ed

)

Ca

lc. s

pin

Hall c

onductiv

ity(1

05

S m

-1)

Co

Fe

B

NM

Is CoFeB/Pt useful as a THz emitter?


180

160

140

120

100

80

60

40

20

0

-20

Ele

ctr

ic f

ield

(V

/cm

)

3210

t (ps)

STE

ZnTe (1mm)

PCS

3

4

5

6

7

89

0.1

2

3

4

5

6

7

89

1

|Ele

ctr

ic f

ield

| (a

rb. u

nits)

302520151050

/ 2(THz)

Spintronic metalic emitter outperforms standard emitters over large frequency intervals


(5.8 nm)

(interdigitated, SI-GaAs)

Comparison to standard emitters: Spintronic Emitter (STE),

Photoconductive Switch (PCS)

20fs,

0.3mJ300µm GaP,

10fs gate pulse

Bi2Se3

Bi2Se3+

-

• THz emission is

polarization dependent

• Circular photogalvanic

effects?

Helicity

Topological matter

• Spin-momentum locking

J. W. McIver, et al. Nature Nano.(2011).

Ganichev et al. Nature (2002).

T. Seifert and et al. (2016).

-k

TIy

x

F

What is the source?

• Use F dependence

to reduce data

(crystal symmetry)

• THz emission Dependence of pump polarization and sample

orientation:

JS: strongly dependent on both

JP: independent

Topological matter

L. Braun, G. Mussler, et al., Nature Comm. 7, 13259

(2016).

Topological matter

• Circular photogalvanic effect C, thermovoltage D

0 90 180 270 360

0.10

0.12

0.14 data fit

qwp angle (°)

• 3D topological insulator intrinsic doping, 16 nm

(Bi0.57Sb0.43)2Te3)

Topological matter

• 3D topological insulator intrinsic doping, 16 nm

(Bi0.57Sb0.43)2Te3)

0 50 100 150 200 250

0

50

100

150

200

250V

ert

ica

l d

ista

nce

(

m)

Horizontal distance (m)

-1.5 0.0 1.5

D (mV)

photoV

-0.5 0.0 0.5

D (mV)

-0.3

0.0

0.3

D (

mV

)


𝛻T

Topological matter

• Spin accumulation by Spin-Nernst effect


Detail: Hall bar

See also S. Meyer et al. Nature Materials (2017).






• Summary

Outline

• CSIC, Madrid

Oksana Chubykalo-Fesenko

Thermal macrospin modelling

Pablo Nieves, Oksana Chubykalo-Fesenko

• Western Digital Corporation, San Jose

Simone Pisana, Tiffany Santos

Tiffany Santos

FePt storage media

FePt optical writing a storage media

• Kiel UniversityJeffrey

McCordMO-Imaging

Cai Müller, Jeffrey McCord,

• Uppsala University

Marco Berritta, Ritwik Mondal, Peter Oppeneer

• Konstanz University

Denise Hinzke, Ulrich Nowak

Uli Nowak

Inverse Faraday


Peter

Oppeneer

Thermal spin modelling

Spin

Nanostrukturen

Interior of a hard disc

• Hard disc at fs speed

FePt + segregant (12nm)

MgO/heat sink/adhesion layer//glass

Carbon overcoat (6nm)

Western Digital Corporation HAMR media, HC= 4T at room temperature

Hard disc at ultrafast speed

FePt-L10

+ segregant(high temp.)

heat sink

MgO seed

heat sink seed

and adhesion

20 nm


σ-

σ+

12.7 mJ/cm2 (10 mW)

Writing using the helicity of light:

Magneto-optical contrast (Kerr microscopy)

FePt (AgCu) granular recording media

R. John, P. M. Oppeneer, U. Nowak, and M. Münzenberg, Sci. Rep. 7, 4114 (2017)

10 20 30 40

20.0k

40.0k

60.0k

80.0k

Co

ntr

ast

(arb

itra

ry u

nit)

Position X (m)

L

-

Starting with remnant magnetization 0% Ms after

growth:


+Ms

-Ms

+

σ-l

σ +

σ -

L

σ-

X

7.5 mW (6.6 mJ/cm2 per pulse)


+Ms

-Ms

+

σ-l

10 20 30 40-4.0k

-3.0k

-2.0k

-1.0k

0.0

1.0k

2.0k

3.0k

4.0k

Co

ntr

ast (a

rbitra

ry u

nit)

Position X (m)

L

-

10 20 30 40-4.0k

-2.0k

0.0

2.0k

4.0k

6.0k

8.0k

10.0k

12.0k

14.0k

Position X (m)

Contr

ast (a

rbitra

ry u

nit)

L

-

Demagnetized

100

Saturated

75

50

No full writing! What is the mechanism? 15 mW (13.2 mJ/cm2 per pulse)

Starting with magnetization 100% Ms, saturated case:

pu

(%)


σ- σ+

Carbon overcoat (3nm)

MgO/NiTa/glass AgC-segregant

• Model to describe the data:

Transition rates

Laser writing region

http://www.codecogs.com/eqnedit.php?latex= $p_u$

http://www.codecogs.com/eqnedit.php?latex= $p_d$

http://www.codecogs.com/eqnedit.php?latex= $w_uu$, $w_ud$, $w_du$, $w_dd$



σ- σ+

0 5 10 15 20 25

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

Only MCD, no IFE

Pro

babili

ty P

u

Number of pulses

Both MCD and IFE

Starting configuration, i=0:

random

all up

all down

• Model to describe the data:

Transition rates

http://www.codecogs.com/eqnedit.php?latex= $p_u$

http://www.codecogs.com/eqnedit.php?latex= $p_d$



• FePt (AgCu) granular recording media:

single/ multiple pulse writing


σ- σ+

5 mW (30 mJ/cm2 per pulse)


l=800 nm

1 2 3 4 5

-0.06

-0.04

-0.02

0.00

0.02

-

KIF

E (

1/T

)

Photon energy (eV)

0 1 2 3 4 5

6

12

18

Imagin

ary

part

n

Photon energy (eV)

-

+M -M

l=800 nm

-I+I

Magnetic circular dichroism (MCD)

• What about the wave lenght dependence?

Inverse Faraday effect (IFE)

1200 nm to 1350 nm, 1.03 to 0.92 eV

1200 nm

1250 nm

1300 nm

1350 nm 39

µm

+ -

0 100 200 300 400 500-3000

-2000

-1000

0

1000

2000

3000

Contr

ast (a

. u.)

A

0 100 200 300 400 500-3000

-2000

-1000

0

1000

2000

3000

Contr

ast (a

. u.)

A

0 100 200 300 400 500-3000

-2000

-1000

0

1000

2000

3000

Contr

ast (a

. u.)

A

0 100 200 300 400 500

-2000

-1000

0

1000

2000

3000

Co

ntr

ast

(a.

u.)

Width (m)

0 50 100 150 200

-0.0006

-0.0004

-0.0002

0.0000

Derivative Y1

0.000000 (2.000000)

1st derivative of "NaN"

Gauss Fit of C"Derivative Y1"

0 100 200

-0.0008

-0.0006

-0.0004

-0.0002

0.0000

Derivative Y1

A

1st derivative of B


0 100 200

-0.0004

-0.0002

0.0000

Derivative Y1

A

1st derivative of B


Gaussian laser

profiles

19 µm

20 µm

19.5 µm

18 µm


• What about the wave lenght dependence?

Writing efficiency can be increased by a factor of two to three.

Glassy vortex networks

• What about topological objects?

• Göttingen University

Claus Ropers

UTEM developement

Tim Eggebrecht, Marcel Möller,

Nara Rubiano da Silva, Claus

Ropers, Sascha Schäfer

Sascha Schäfer


T. Eggebrecht, et al., Phys. Rev. Lett. 118,

097203 (2017).

Ultrafast Transmission Electron

Microscopy

Imaging / Diffraction /

Spectroscopy

UTEM

e-pulse

(probe)

excitation pulse

(pump)

photoemission

laser

sample

Principle

• photoemission from needle shaped

emitter

• Laser-pump/electron-probe experiments

Temporal/spatial/spectral electron pulse properties

3.3nm

2.6nm

-500 0 500

Delay (fs)

300f

s

-2 -1 0 1 2

Energy (eV)

0.6 eV


Lorentz imaging with ultrashort electron pulses

2 µm

Imaging conditions

• 1.5 e-/pulse

• 250 kHz rep.

rate, 60 s

exposure

• Total electron

number: 2x107 e-

Δf < 0

Out-of-focus(add. magnetic

contrast)

• permalloy thin

film on silicon-

nitride membrane

• FIB patterned

magentic nano

islands

Magnetic vortex

structure

Writing of vortex networks

Network

Magneti

-zation

Electron

intensity

Phase


Well defined network that depends on the quench rate

T. Eggebrecht, et al.,

Phys. Rev. Lett., 2017.

• Kiel UniversityJeffrey

McCordMO-Imaging

Enno Lage, Jeffrey McCord,

• Konstanz University

Ulrich Nowak

Uli Nowak

Skyrmion-Bubbles

1 mm

5 m5 m5 m

Field conditioning Single skyrmions Dense skyrmions


• Skyrmions with diameters below 200 nm, DMI

Ta/CoFeB/MgO layer wedge system

• Tilted magnetic field

• In plane static magnetic field with

1° tilt

• Bubbles grow with decreasing field

• Zero field stable bubble phase

dCoFeB = 1.367 nm to 1.375 nm

1.36 1.37 1.380

2

4

stable

ip nucleation

+

oop nucleation

stable

ip nucleation

instable

0H

Z (

mT

)

CoFeB thickness (nm)

instable


100 mT @ 1° 70 mT @ 1° 35 mT @ 1° 12 mT @ 1° 0 mT @ 1°

5 m

Increasing Htilted

40 µm

0 s

6 s

4 s

2 s

Forward

+ -

38V at 545Ohm => I = 2 e12 A/m^2 (2e8 A/cm^2)

B = 0,56 mT

• Forward and

backward motion

• Currents needed

j=2 108 A/cm2

• Already in

regime of current

induced bubble

generation by

heat pulses

Show vid_probe2_8.avi

38V at 545Ohm => I = 2 e12 A/m^2 (2e8 A/cm^2)

B = 0,69 mT

Backwards

198 s

132 s

66 s

0 s

+-


• Current driven motion: 10 µm constriction

• Current driven motion: 10 µm constriction


0 5 10 15-20

-15

-10

-5

0

x (

µm

)

t (s)

0 5 10 15

-2

-1

0

1

2

y (

µm

)

t (s)

0 5 10 15-20

-15

-10

-5

0

x (

µm

)

t (s)

0 5 10 15

-2

-1

0

1

2

y (

µm

)

t (s)

0 5 10 15-20

-15

-10

-5

0

x (

µm

)

t (s)

0 5 10 15

-2

-1

0

1

2

y (

µm

)t (s)

Skyrmion 1 Skyrmion 2 Skyrmion 3


• Motion tracking – testing the local potential

• Motion tracking

SPP Skyrmionics







• Writing of topological objects

• Summary

Outline

Contributions

Priority program

SpinCaT

Priority program

Topologische Isolatoren

Magnonics: Materials and

Devices

Robin JohnJakob Walowski

@spintronicsHGW

Ulrike Martens

Christian Denker

Priority program

Skyrmionics

Collaborations

J. Nötzold, S. Mährlein, Lukas Braun, Tobias

Kampfrath, Fritz Haber Institute

C. Franz, C. Heiliger, Gießen University

Gregor Mussler, Detlev Grützmacher, FZ

Jülich

F. Katmis, J. S. Moodera, MIT Cambridge

Pablo Nieves, Oksana Chubykalo-Fesenko,

CSIC, Madrid

J. McCord, C. Müller, Kiel University

A. Thomas, IFW Dresden

Sascha Schäfer, Oldenburg University

Claus Ropers, Göttingen University

Tiffany Santos,

Western Digital Cooperation San Jose

Uli Nowak, Denise Hinzke, Konstanz University

Mathias Kläui, Mainz University

Ilie Radu, Max-Born-Institute, Berlin

Marco Battiato, Pablo Maldonado, Peter

Oppeneer, Uppsala University

F. Freimuth, Y. Mokrousov, S. Blügel, FZ Jülich

Dagmar Butkovicova, Eva Schmoranzerová,

Charles University Prague

Günter Reiss, Thorsten Hübner Timo Kuschel

Bielefeld University

@spintronicsHGW

SPP Skyrmionics

Greifswald

See NDR feature on our new labs: Nordmagazin or http://www.physik.uni-greifswald.de/

aktuelles.html @spintronicsHGW

Physics

on the subtle interplay of light induced magnetization, driven currents and … · 2018. 11. 6. ·...

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