Hall effect measurements

Related products: MFLI

The Hall effect appears as the potential difference induced perpendicular to the moving charge carriers and external magnetic field. The effect is widely used for materials characterization and sensing of magnetic fields:

Material Characterization

When the material is characterized, it is exposed to a known magnetic field B. At the same time the Hall Voltage Vxy (see sketch), the voltage across the sample Vxx and the current IR through the material are measured. From these measurements, the following material properties can be inferred:

  • charge carrier density
  • charge carrier polarity
  • charge carrier mobility
  • material conductivity

This technique is also used to measure the novel physical properties of two dimensional electron gas (2DEG) materials by measuring the quantum Hall effect and its many derivatives: integer, fractional, spin, inverse spin and many more.

Magnetic field sensing

When the material properties are well known, the Hall effect can be used to infer the external magnetic field over many orders of magnitude. The measurements can be carried out with DC voltages applied to the sample, however, AC measurements usually lead to faster and more accurate results. Further benefits of AC measurements include higher precision and sensitivity generally leading to a larger signal-to-noise ratio over a wider measurement range.

Documents

Measurement Strategies

As shown in the sketch, the measurement is performed by using two lock-in amplifiers. Lock-in amplifier 1 is providing a constant AC voltage to induce a current into the sample. Often it is sufficient to place a current limiting resistor RL – with a much larger resistance than all other resistances combined in the circuit – and assume the current is constant over the course of the measurement. More accurate measurements can be achieved by also measuring the current through the sample. Lock-in amplifier 1 is measuring the Hall Voltage Vxy and Lock-in amplifier 2 is measuring the voltage Vxy across the sample. In case of the Zurich Instruments MFLI, the current can be measured in addition by utilizing the current input and the MF-MD Multi-demodulator option.

To ensure the data alignment with the magnetic field during the measurement the LIAs need to be frequency, clock and time stamp synchronized. This is achieved using the MDS multi device synchronization feature of MFLIs.

Your benefits measuring with Zurich Instruments

  • High SNR: fast and sensitive AC measurements
  • Increased accuracy: add a second instrument for dedicated current measurement
  • Convenient measurement acquisition and data analysis through precise instrument synchronization, data alignment (MDS) and display within the same user interface

Let us know your measurement challenge!

Principles of Lock-in Detection

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