Sample Measurements at Different Magnetic Field Orientation

In physical science and material research, use of electrical resistivity measurements as a function of temperature, pressure doping, and applied field is routine in the characterization of bulk materials. However, with the decrease in dimensionality of the sample, the importance of orienting the magnetic field to the sample increases.

In case of highly anisotropic materials, it is critical to align the magnetic field to the sample for the study of exotic phases of matter. These include electron gases in semiconductors and topological insulators.

Further, as the dimensions go on decreasing, magnetic fields can be used to control electron transport, thereby revealing new physics such as Majorana fermions and quantized transport.

The Challenges

Some of the most common challenges related to magnetic field orientation include:

  • How to adjust the orientation of the field to the sample, with no access to the sample
  • How to maintain electrical contact with the sample
  • How to rotate a large magnetic field relative to the sample
  • How to probe the Fermi surface of my sample
  • How to correct for any misalignment of the sample to the magnetic field

The Solution

The above challenges can be overcome by using the following options:

Mechanical Rotator

For measurements that require high magnetic fields, it is possible to use a mechanical motor to rotate the sample within the magnetic field. Further, flexible electrical connections are made possible with a rotating sample:

  • When the mechanical drive rod is combined with a stepper motor at room temperature, the sample angle can be set accurately
  • Larger magnetic fields can be accessed in this manner, rather than with a vector magnet

Piezoelectric Rotator

In the case where a high magnetic field is required but where it is not possible to install a drive rod for measurements, a piezoelectric rotator can be used. This configuration enables the rotator to be driven electrically, while an encoder can be used to determine the angle of the sample.

Such a configuration means:

  • Greater access to larger magnetic fields than a vector magnet
  • It is electrically driven
  • Installation capability on systems where a mechanical drive rod will not fit
  • Simplified design, with no requirement for a mechanical linkage between sample and room temperature
  • Rotation in multiple axes, when combined with a mechanical rotator

Vector Magnet

A vector magnet, which comprises of 2 or more orthogonal superconducting coils, enables control of the field orientation by varying the current in each coil. This enables the field to be swept through complex paths in multiple axes.

With a fixed sample, measurements that require higher frequency lines or optical access to the sample are made possible.

  • Sample is fixed, allowing for semi-rigid electrical connections to the sample
  • Free space optical access to the sample
  • Negates the need for mechanical drive rods
  • Compatible with fast sample exchange systems
  • Accurate control of field vector through magnet power supply

This information has been sourced, reviewed and adapted from materials provided by Oxford Instruments Nanoscience.

For more information on this source, please visit Oxford Instruments Nanoscience.

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