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Nripen Dhar
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Outlines of PresentationDiscovery
Principles
Importance
Existing measurement system
Applications
New Discoveries
2
Discovery
3
Edwin Herbart Hall
Principles
Due to the transverse (magnetic) force,
→ Mobile charges pressed to one side
→ immobile charges are unaltered
4
Magnetic Force:
PrinciplesAccumulation of mobile charges
→ Creates internal electric potential, known as Hall voltage.
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Figure 1 : Visual presentation of Hall effect
For simple metals, is V =
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Here, n is the no. of charge carriers and t refers to the thickness of the metal along the direction of the B-field
Figure 2 : Visual presentation of Hall effect
VHall
Hall Coefficient
Magnitude parameter:
In metals:
In semiconductors:
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Note: μp refers to the hole mobility and μn refers to the electron mobility.
μ , NA & ρ from Hall Effect Mobility,
Carrier Concentration,
Resistivity,
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Here, n=NA
Features
only electrons moving in same average direction in both hole (p-type) and electron (n-type) conductivity
Opposite sign indicates that electrons in valence bands move in opposite direction than previously thought
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Importance
Measurement of charge carrier mobility, concentration ,
resistivity
Sensitive measurement of an external B-field
No need to use electrochemical materials
Ease to use (no vacuum, ambient temp, etc.)
Less sensitive to switching
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Existing System
Figure 3: HMS-3000 hall effect measurement system
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Important parts of the system
Figure 4: Spring clip board
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Figure 5: Magnet
Figure 6: Low temperature measurement system
HMS-3000 Software
13Figure 7 : Screen-shot showing HMS-3000 Software
I-V & I-R curve
14Figure 8 : I-V & I-R curve from software
Hall Probes
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Figure 9: Pictorial view of hall probe
•Transverse Probe• Axial Probe
In AutomobilesUsed expansively in rotating systemsAnti-lock brakes, motor feedback, ignition
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Figure 10: Using Hall effect in cars
In SpaceHall Effect thrusterTrap electrons in a magnetic field, electrons ionize
propellant, creates thrust
Figure 11 :Hall effect thruster in space17
New Discoveries
Quantum Hall Effect
Spin Hall Effect
Anomalous Hall Effect
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Quantum Hall Effect
Quantization of normal Hall Effect
Seen at low temperature, high magnetic field
Very precise, magnitude determined by Landau levels (single-particle orbital of an electron in a magnetic field) and electron interaction
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Spin Hall Effect
Predicted in 1971 Russian physicists M.I. Dyakonov and V.I. Perel , observed in 2004 via emission of circularly polarized light
Separation of electron spins in current-carrying object, no magnetic field needed
Universal, present in metals and semiconductors at high and low temperature
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Anomalous Hall EffectFerromagnetic materials have internal magnetic field
Much larger than normal Hall Effect.
Figure 12 : Anamolous Hall Effect
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Summary
Physics of the Hall Effect
Existing system
Popular Applications
New discoveries
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Thank you
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