Magnetic Force Microscopy

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Magnetic Force Microscopy
Fmagntic mtip ?Hsample so one images stray
fields!

Comprehensive review Grutter, Mamin and Rugar,
in Scanning Tunneling Microscopy II Springer,
1991
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Force sensor tip needs to be magnetic
Typical coatings Co, Co80Cr20, Co71Pt12Cr17
(hard) Ni81Fe19, Fe, and Ni50Co50 (soft) by
sputtering or thermal evaporation, Often 5nm Au
protection. Magnetized in 1T field
Different coatings for different MFM
applications!!!
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Domain wall movement as a function of external
field
The magnetic field was applied diagonally along
the scanned area with the magnetic field of
(a)-(h) -2 Oe, 5 Oe, 15 Oe, 45 Oe, 25 Oe, 20 Oe,
12 Oe, -2 Oe respectively. Tip 50 nm
Co71Pt12Cr17, constant frequency shift mode.
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Subtle, reversible tip stray field effects
Bloch walls (black and white lines) in Fe whisker
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Less subtle effect
Displacement of Bloch line in a Bloch wall in a
Fe(001) whisker, Hc lt 1Oe
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Tip Stray Field
Conical shell model calculation of tip stray
field as a function of lateral distance r and
at different z (100 nm, 50 nm, 20 nm) tip 30
nm Co71Pt12Cr17.
Tip stray field close to the tip end is
substantial. Tip stray field decays slowly,
especially for radial component.
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Optimized coating depending on sample
Max field components and their decay lengths for
z20nm
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Tapping/Lift mode
Good separation topography magnetic information
(in most cases)
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Tip influence!
MFM Tip Stray Field Distortion
Three consecutive scans. NiFe 500nm?200nm?10nm
tapping/lift mode Lift height 80 nm
X. Zhu, et al., JAP 91, 7340 (2002).
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Manipulation
elliptical NiFe, 600nm x 150nm x 30nm
MFM can be used to control local magnetic
structure
X. Zhu, et al., PRB 66, 024423 (2002)
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MFM Imaging
Permalloy disk diameter 700 nm thickness 25
nm. Constant height image with 30 nm CoPtCr tip
in vacuum
Vortex core moves closer to the edge
perpendicularly to the field directions with the
presence of external magnetic fields.
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Permalloy Circular Rings
Domain wall propagation
X. Zhu, PhD. Thesis 2002, McGill University
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MFM Imaging
Experiment
Simulation
Stray field
Transverse domain wall
Onion State
NiFe 700 nm
Flux domain wall
Public code OOMMF
NiFe 5 mm
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MFM Imaging
Co (4nm) Cu(3nm) NiFe (6nm)
Mixtures of antiparallel states and parallel
states.
Coexistence of the two different antiparallel
states.
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MFM Imaging of weak stray fields pseudo spin
valve structures
C D are antiparallel, but the two layers are
not completely magnetically equivalent.
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Magnetostatic Couplingcan one build magnetic
cellular automata?
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Coherence length relevant!
H
Coupled 700 nm rings
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Hysteresis Loop of Ensemble
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Switching Field Distribution
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Hysteresis Loop of Ensemble
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Individual Hysteresis Loop, part II
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Individual Hysteresis Loop
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Permalloy Square Rings
H
As-grown flux closure state of Ni square rings
Remanent states after applying magnetic field
diagonally.
Permalloy square rings (t20 nm, w500 nm,
L2mm)
Tip 30 nm Co71Pt12Cr17
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Micromagnetic Simulation
Head-head Domain Wall
Ni square rings (t10 nm, w200 nm, L2mm)
Simulation OOMMF cell size 5nm
With field
Remanence
Stray Field
Tip Closer to the sample
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Magnetic Moment State versus Magnetic Field
H1147 Oe
H2270 Oe
H2256 Oe
H1130 Oe
Remanence after applying -300 Oe
Ni square rings (t10 nm, w200 nm, L2mm)
Four segments of the square rings can be treated
as four single domain state. The magnetic
field parallel to the four segments are Hcos(?)
A and C Hsin(?) B and D.
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Control of Domain Patterns
H500 -500 Oe
H
H180 -180Oe
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110 direction
H300 Oe
H-147 Oe
H-162 Oe
H
H-187 Oe
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Melting of Nb Vortex lattice between 4.5-9 K
M. Roseman, Ph.D. 2001, McGill