New PowerPoint · 2005. 3. 1. · Title: PowerPoint ????? Author?? ?? Created Date: 3/1/2005 3:27:35 PM

Nanomagnetic Studies on Thin Films and Multilayers with Spin Polarized Scanning

Tunneling Microscopy

Herman van Kempen

IMMRadboud University Nijmegen

Madrid, February 1, 2005

A.L. Vazquez de Parga

M.M.J. BischoffT.K.Yamada T. Mizoguchi

Colleagues

We are especially grateful to D.T. Piercefor supplying the Fe whiskers and to G.M.M. Heijnen,

R. Robles, E. Martinez, and A. Vega for computer calculations

Spin electronic devices

10 nm bit size:>5 T bit / inch2

In 2010

We need an instrument to study nm-scale

magnetism

Spin-polarized scanning tunneling spectroscopy (SP-STS)

allows study of magnetism on sub-nanometer scale.

Scientific interest

IMM, Radboud University Nijmegen

STM magnetic imaging

magnetic tip

magnetic sample

Fe-coated W tip


(R. Wiesendanger et al. Solid State Com. 119 (2001) 431)

SampleDOS

DOS

DOS

(dI/dV)/T = Spin-resolved sample DOS

EF

EF

EF

Mechanism of Spin Polarized-STM

Fe-coated W tip


Toyo Yamada

Maarten Bischoff

Sample : Mn/Fe(001)

Fe(001)

Mn(001) Different sample DOS

? The same DOS


SEMPA measurements suggested antiferromagnetic coupling. J.MMM. 222 (2000) 13D.T. Pierce et al.:

Fe(001)-whisker

Mn(001) films

0.14 nm

0.16 nm

Fe(001)

1st Mn

5th Mn

Sample : Mn/Fe(001)

Surf.Sci. 516 (2002) 179T.K. Yamada et al.:

BCT:Body-centered tetragonal

IMM, Radboud University of Nijmegen

Mn grown at 370 K (<4x10-10mbar)

Results with non-magnetic tips (W tips)

7

6

8

8

89

9

97

6

8

8

89

9

9

dI/dV map at +0.2 V

150 nm x 150 nm( -0.5 V, 0.5 nA )

7.2 ML Mn/Fe(001)Topographic image

Sample voltage [V]-1.0 -0.5 0.0 0.5 1.0

dI/d

V[n

A/V

]

0.5

1.5

2.5

3.5 6789

IMM, University of Nijmegen

89

10

9.5 ML Mn/Fe(001)

100 nm x 100 nm( -0.5 V, 0.5 nA )

10

11

11

12

Results with ferromagnetic tips (Fe on W tips)

Sample voltage [V]-1.0 -0.5 0.0 0.5 1.0

dI/d

V[n

A/V

]

0.5

1.5

2.589

1011

dI/dV map at +0.2 V

89

1011

11

10

9

3 nm

Ferromagnetic Mn layers coupled anti-ferromagneticallyT.K. Yamada et al. PRL 90, (2003) 056803

T.K. Yamada et al. APL 82, (2003) 1437


Topographic image

89

10

9.5 ML Mn/Fe(001)

100 nm x 100 nm( -0.5 V, 0.5 nA )

10

11

11

12

Results with ferromagnetic tips (Fe on W tips)

Sample voltage [V]-1.0 -0.5 0.0 0.5 1.0

dI/d

V[n

A/V

]

0.5

1.5

2.589

1011

dI/dV map at +0.2 V

89

1011

11

10

9

3 nm

Ferromagnetic Mn layers coupled anti-ferromagneticallyT.K. Yamada et al. PRL 90, (2003) 056803

T.K. Yamada et al. APL 82, (2003) 1437

Topographic image

10 nmM


Magnetic resolution (Fe-coated W tips)

Hidden Fe step0.02 nm step height

dI/dV map at +0.2 V

70 nm x 70 nm

7

7

5

8

6

7.2 ML Mn/Fe(001)Topographic image

150 nm x 150 nm( -0.6 V, 0.5 nA )

7

6

8

5

6

7

Fe MnMnMnMn

Mn

Fe

(without topological effect)

a*Tanh[(x-xo)/w/2]+b

w = 0.4 nm

Minimum w < 0.5 nmT.K. Yamada et al. APL 82, (2003) 1437


2

1

0dI

/dV

[nA

/V]

3

-0.5-1.0 1.00.50.0

Positive voltagesetpoint

Sample voltage [V]

-0.5-1.0 1.00.50.0

0

-30

dI/d

VA

[%] 30

4

2

0

dI/d

V[n

A/V

]

-0.5-1.0 1.00.50.0

Sample voltage [V]

1

3Negative voltagesetpoint

odd layerseven layers

How to get sample polarization: Asymmetry of dI/dV

(dI/dV) – (dI/dV) (dI/dV) + (dI/dV)

= Ptip PsampleAdI/dV = ??

IMM, Radboud University of Nijmegen


To get ρ one needs T

Origin of the contrastNegative-voltage setpoint

Sample voltage [V]

dI/d

V[n

A/V

]

LDOS = dI/dV / T

T: tunneling probability(Ukraintsev, PRB 53 11176)

0

1

2

3

-2 -1 0 1 2 3Sample voltage [V]

(dI/d

V)/T

= L

DO

S

Peak 2 Peak 1

oddeven

Peak 1 :

two dz2 surface states in the “minority” band

Peak 2 :

dz2 surface state in the “majority” band


-2

-1

0

1

2

Ene

rgy

[eV

]

Peak 1

Peak 2

Γ Χ

Band structure

Band structure: G.M.M. Heijnen

△Negative voltage setpoint Positive voltage setpoint Different tip (setpoint –0.5 V)

Calculation (G.M.M. Heijnen)

-1 0 1 2Sample voltage [V]

A

[

%]

(dI/d

V)/T

-20

20100

-10

-2 3

A(dI/dV)/T: independent of Different set point voltage different tips

[(dI/dV) /T] – [(dI/dV)/T]

[(dI/dV) /T] + [(dI/dV)/T] = Ptip(EF) Psample(eV) for V>0

(= Ptip(eV) Psample(EF) for V<0)

A(dI/dV)/T =



Sub-nanometer resolution in magnetic contrast for technological interesting materials can be obtained.

Conclusions

Quantitative information on the sample polarization.

*

*

* Magnetic multilayers can also be studied with this method.

• Fe/Mn/Fe(100)

• AuMn/Mn/Fe(100)

•Screw dislocation Mn/Fe(100)

Studies of more complex magnetic structures with SP-STM


BCC

BCT

Mn impurities: 5-10 %

Mn

Fe1234567

Fe

Fe/Mn/Fe(001) multilayers


1.5ML Fe on Mn/Fe(100) grown at 300K (100nm X 85nm). (b) and (c) measured with two W/Fe tips with different magnetization Directions.

BCC

BCT

Ferro

Mn impurities: 5-10 %

Non-collinear A-F coupling

Mn

Fe1234567

Fe

Fe/Mn/Fe(001) multilayers: conclusions


Mn

Fe

AuMn/Mn/Fe(001) multilayers


AuMn

AuMn/Mn/Fe(001)

2.2ML Au deposited at RT.An ordered alloy is formed.

6.6nm x 6.6nm

Mn

Fe

AuMn/Mn/Fe(001) multilayers: Magnetic structure


AuMn

0.7 ML Au on Mn measured with Fe/W tip

Calculations:R. Robles, E. Martinez, A. Vega


Screw dislocation in Fe(100) covered by Mn layers

100nm x 100nm

dI/dV of Mn/Fe(100) measured with Fe/W-tip


Complicated magnetic structure around a screw dislocation

400nm x 333nm

Screw dislocation



Conclusions

• Sub-nanometer resolution in magnetic contrast for technological interesting materials and complicatedmultilayer structures can be obtained.

• Quantitative information on the sample polarization.

• Intermixing around interfaces can play an important role.

Documents

New PowerPoint · 2005. 3. 1. · Title: PowerPoint ????? Author?? ?? Created Date: 3/1/2005 3:27:35 PM