Magnetic Force Microscopy Leon Abelmann and Martin Siekman Systems - - PowerPoint PPT Presentation

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University of Twente Magnetic Force Microscopy Leon Abelmann and Martin Siekman Systems and Materials for Information storage MESA + Research Institute University of Twente Systems and Materials for Information storage Constanta Summerschool,

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SLIDE 1

University of Twente

Systems and Materials for Information storage

Magnetic Force Microscopy

Leon Abelmann and Martin Siekman

Systems and Materials for Information storage MESA+ Research Institute University of Twente

Constanta Summerschool, Sep 2005 (September 14, 2005)

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SLIDE 2

Introduction 2,2(2)

Contents

  • Before break: MFM Operation

– Principle of MFM – MFM tips

  • After break:

– Instrumentation – Artefacts

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 1

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SLIDE 3

Principle of MFM 5,5(3)

Principle of MFM

3 dimensional Scanner Cantilever Specimen Detector Magnetic element

z x y

Computer Control Electronics M

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 2

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SLIDE 4

Principle of MFM 7,7(2)

Magnetic Force Microscopy

500 nm

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 3

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SLIDE 5

Principle of MFM 12,12(5)

Change in resonance

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 4

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SLIDE 6

Principle of MFM 15,15(3)

Amplitude, Phase, Frequency

  • 180
  • 90

Phase difference [deg] Amplitude [nm] Drive frequency [Hz] fresfres

,

phase frequency amplitude

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 5

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SLIDE 7

Principle of MFM 18,18(3)

Image formation

Transform stray field to Fourier space:

  • H(kx, ky, z) =

∞

−∞

∞

−∞

H(x, y, z)e−i(xkx+yky)dxdy

  • H(kx, ky, z) = exp(−|k|z) ·

H(kx, ky, 0)

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 6

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SLIDE 8

Principle of MFM 28,0(10)

MFM Demonstrator

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 7

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SLIDE 9

Principle of MFM 31,3(3)

Tip transfer function

l

non-magnetic bar magnetic coating

s h b z0 x0 t

10 12.5 1.25 0.13 125 1 0.1 10 20 100 200 1000 0.01 0.001

8

10

7

10

6

10

5

10

Force derivative [mN/m] Frequency shift [Hz]

  • 1

Spatial frequency [m ] Wavelength l [nm]

  • Fz(k, z) = −µ0Mt · b sinc(kxb

2 ) · S sinc(kyS 2 ) · H(k, z)

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 8

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SLIDE 10

Principle of MFM 41,0(10)

MFM Demonstrator 2

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 9

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SLIDE 11

Principle of MFM 51,10(10)

Resolution versus distance

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 10

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SLIDE 12

MFM Probes 53,12(2)

Probes

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 11

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SLIDE 13

MFM Probes 55,14(2)

AFM sputtered

  • Sputtered CoCr(X) hard disk materials
  • Low/high moment: layer thickness
  • Fe, NiFe for low coercivity tips

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 12

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SLIDE 14

MFM Probes 57,16(2)

AFM side coated

  • Co, NiFe evaporated
  • Shape anisotropy
  • Stable domain structure

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 13

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SLIDE 15

MFM Probes 59,18(2)

CantiClever Tip plane Cantilever MFM tip

Cross-section determined by layer thicknesses

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 14

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SLIDE 16

MFM Probes 61,20(2)

SEM Images cantilever

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 15

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SLIDE 17

MFM Probes 63,22(2)

SEM Images tip

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 16

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SLIDE 18

Break 0,0(0)

Break

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 17

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SLIDE 19

Instrumentation 2,2(2)

Beam Deflection

  • Laser
  • LED

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 18

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SLIDE 20

Instrumentation 4,4(2)

Interferometer

  • factor 10 better sensitivity
  • difficult to align
  • better reflection coatings

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 19

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SLIDE 21

Instrumentation 7,7(3)

Thermal Noise

  • ∆

∂F ∂z

  • th
  • rms

=

  • 4kTc∆B

ωnQz2

  • sc

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 20

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SLIDE 22

Instrumentation 10,10(3)

Drift

1/Dt 1/(NDt) frequency (Hz) Noise (nm or Hz) DB DB’

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 21

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SLIDE 23

Instrumentation 13,13(3)

Vacuum

  • Reduce damping, improves Q-factor by 105
  • Sound isolation
  • Remove most of water film (meniscus)

Be careful with break-down (Paschen curve)

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 22

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SLIDE 24

Instrumentation 16,16(3)

Magnetic Field

Application of magnetic fields

  • On sample

– Simple – Only in-plane – Low field – Heating

  • On microscope

– Requires very small microscope

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 23

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SLIDE 25

Instrumentation 18,18(2)

Instrumentation

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 24

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SLIDE 26

Instrumentation 20,20(2)

Switching Field Distribution

  • 300
  • 200
  • 100

100 200 300

Field (kA/m)

100 200 300 400

Dots reversed

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 25

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SLIDE 27

MFM Artefacts 22,22(2)

Correct domain image

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 26

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SLIDE 28

MFM Artefacts 24,24(2)

Correct bit pattern

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 27

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SLIDE 29

MFM Artefacts 26,26(2)

Interference stripes

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 28

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SLIDE 30

MFM Artefacts 28,28(2)

Topographic contrast

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 29

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SLIDE 31

MFM Artefacts 30,30(2)

Topographic contrast 2

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 30

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SLIDE 32

MFM Artefacts 31,31(1)

Interaction

  • Sample disturbs tip
  • Tip disturbs sample
  • Reversible/Irreversible

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 31

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SLIDE 33

MFM Artefacts 33,33(2)

Tip reversal on strong sample

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 32

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SLIDE 34

MFM Artefacts 35,35(2)

Tip reversal in external field

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 33

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SLIDE 35

MFM Artefacts 37,37(2)

Domain in tip

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 34

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SLIDE 36

MFM Artefacts 39,39(2)

Sample disturbance

  • Reversible (susceptibility contrast)
  • Irreversible

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 35

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SLIDE 37

MFM Artefacts 41,41(2)

Susceptibility contrast

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 36

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SLIDE 38

MFM Artefacts 43,43(2)

Move domain walls

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 37

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SLIDE 39

MFM Artefacts 45,45(2)

Disturb sample

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 38

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SLIDE 40

MFM Artefacts 47,47(2)

Dot switch

Data Storage

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 39

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SLIDE 41

Conclusions 49,49(2)

Conclusions

  • Imaging principle (deflection, phase, frequency)
  • Fourier transform for image formation
  • Side coated tips
  • Noise, bandwidth
  • Artefacts (interference, topography)
  • Tip/sample interaction

Leon Abelmann Constanta Summerschool, Sep 2005 Slide 40