Young Won Lim11/13/10

● Magnetism● Hall Effect● AMR Effect● GMR Effect

Magnetic Sensor (3B)

Young Won Lim11/13/10

Copyright (c) 2009 Young W. Lim.

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Optical Sensor 3 Young Won Lim11/13/10

Magnetism

Ferro­magnetic material

● Permanent magnet

Ferri­magnetic material

● Below Curie Temp: like ferromagnets

● Above Curie Temp: like paramagnets

Para­magnetic material

● DC Josephson: I > Ic then in the resistiv

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Lorentz Force

B

FLorentz Forceto charges

Lorentz Forceto − charges

v

q0

q0

q=0B

F = q v × B

v

B

v

−F

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Hall Effect (1)

Negative Carrier

B z

B z I x

I x

F 'm

Lorentz Forceto charges

Bz

v x

E x

Fm

Lorentz Forceto − charges

B zI x

v x

E x

Positive Carrier

Optical Sensor 6 Young Won Lim11/13/10

Hall Effect (2)

Transient State

B zI x

Bz

v x

E x

Fm

Lorentz Forceto − charges

Applied external magnetic field

● charges deflect

● charges are accumulated

● electrical potential  (EH) are created

As EH increases, new (+) and (–) charges are 

repelled by those previously accumulated charges.  (balancing effect)

Optical Sensor 7 Young Won Lim11/13/10

Hall Effect (3)

Steady State

E H

Fm : Lorentz ForceFe

The force Fe counteracts Fm.

● Fe : due to E

H

● Fm: due to external magnetic field B

z

Again charges travels straight,but with the Hall angle θ.

B z

v x

Fm

Lorentz Forceto − charges

B zI x

E H

E x

E t

Optical Sensor 8 Young Won Lim11/13/10

Hall Effect (4)

Transient State Steady State

B zI x

Bz

v x

E x

E H

Fm : Lorentz ForceFe

Fm

Lorentz Forceto − charges

B zI x

E H

E x

E t

Optical Sensor 9 Young Won Lim11/13/10

Hall Effect – Geometric Factor (1)

w2 w3w1

l1

l2

l3

l1

w1

l2

w2

l3

w

EH1 EH2 EH3

f H = function lw

,

Optical Sensor 10 Young Won Lim11/13/10

Hall Effect – Geometric Factor (2)

w

lw

Fm : Lorentz ForceFe

The force Fe counteracts Fm.

● Fe : due to E

H

● Fm: due to external magnetic field B

z

More charges are accumulated at the both ends until they repel other new charges.

Optical Sensor 11 Young Won Lim11/13/10

Physical Magneto-resistance Effect

B z B z

Ideal Case Real Case

● Different Lorentz Force to each charge

● Different charges travel different paths

● The total length of paths is increased

● The resistance increases slightly

Semiconductor

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Geometrical Magneto-resistance Effect (1)

Ideal Case Real Cases

Metal Electrode Contact

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Geometrical Magneto-resistance Effect (2)

Min R1

Bz: Max R

1

Min R2

Bz: Max R

2

ratio RRo

=max R1

min R1

ratio RRo

=max R2

min R2

Optical Sensor 14 Young Won Lim11/13/10

Magnetic Anisotropy (1)

Magneto­crystalline Anisotropy

● An intrinsic property of a ferri­magnet

● Magnetization curve along different crystal directions

● Easy direction

● Hard direction

● Intermediate direction

Optical Sensor 15 Young Won Lim11/13/10

Magnetic Anisotropy (2)

Easy directionMagnetization

Permalloy  Resistor

: NiFe (ferri­magnet)

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Permalloy Resistor (1)

Easy direction

Rmax

: small current 

: parallel current direction 

Rmin

: large current 

: perpendicular current direction

Optical Sensor 17 Young Won Lim11/13/10

Permalloy Resistor (2)

Easy direction

Fix the direction of current

45°θ

External Magnetic Field changes 

● the magnetization direction of permalloy

● the resistance

● the current 

H applied

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AMR Sensor (1)

The current direction is fixed 

Rmax

: small current 

: parallel current direction 

Rmin

: large current 

: perpendicular current direction

= 0 ˚

= −90 ˚

= 90 ˚

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AMR Sensor (2)

How the current direction is fixed?  Shortening Bars

Barber Pole Biasing 

: the shortest path 

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Giant Magneto-resistance Effect

Magnetic Layer

Magnetic LayerNon­magnetic Conductor

High Interface Scattering

: Rmax

Low Interface Scattering

: Rmin

Anti­parallel Magnetic Layers

Parallel Magnetic Layers

Current Current

Optical Sensor 21 Young Won Lim11/13/10

GMR Sensor

High Interface Scattering

: Rmax

Low Interface Scattering

: Rmin

Anti­parallel Magnetic Layers

Parallel Magnetic Layers

Current Current

External Magnetic Field Change 

Young Won Lim11/13/10

References

[1] http://en.wikipedia.org/[2] Nam Ki Min, Sensor Electronics, Dong-il Press [3] http://www.sensorsmag.com/ articles