Magnetometry

Superconducting Quantum Interference Device – Vibrating Sample Magnetometer (SQUID-VSM)

A VSM is used to measure magnetic moment. The sample is mounted upon a carbon-fibre rod, which is inserted into a helium flow cryostat and sits between two pick-up coils. The sample is then vibrated at a constant frequency, resulting in a change in magnetic flux through the coils. Unlike a traditional VSM, a SQUID VSM detects the flux via a Superconducting Quantum Interference Device, an extremely sensitive detector that can detect small fractions of a flux quantum (one flux quantum in a square metre would correspond to less than a billionth of the Earth’s magnetic field).

Our SQUID-VSM is made by the leading manufacturer in the field, Quantum Design and can measure samples between 1000 K and 1.6 K with magnetic fieleds up to 6T. We also have the ability to supply voltages to our samples during measurement for gate modulated magnetormetry and to rotate the sample whilst it is being measured. Using this system we have been able to measure small nano-magnet ensembles with moments of around 10 nano-emu.


Vibrating Sample Magnetometer (VSM)

We also have a traditional VSM that is used to measure magnetic moment of thin film samples. The sample is mounted upon a carbon-fibre rod, which is inserted into a helium flow cryostat and sits between two pick-up coils. The sample is then vibrated at a constant frequency, resulting in a change in magnetic flux through the coils that, according to Faraday’s Law, induces an EMF. The size of the EMF generated in the pick-up coils is proportional to the magnetic moment of the sample.

The Oxford Instruments VSM used in the CM group allows measurements between 1.2 and 300 K and in magnetic fields up to 8 T with a sensitivity of approximately 10 micro-emu.


Magneto-Optical Kerr Microscope

The Kerr microscope is a facility for visualising magnetic domains and magnetisation processes in materials that show a magneto-optical Kerr effect.  In this effect the polarisation of light reflected from a magnetic material is rotated by an amount that depends on the magnetisation direction. The Kerr microscope thus provides an optical image with magnetic contrast.

Our two microscopes were commissioned from Evico Magnetics in early 2013 and 2016 and are used to study samples in a magnetic field up to 1.3 T in plane or up to 0.9 T out of plane, with simultaneous measurements of electrical transport properties. Our latest microscope has the capability to measure two KERR modes (longitudinal, transverse or polar) simultaneously.


Magneto-Optical Kerr Effect (MOKE) Magnetometer

The MOKE magnetometer also makes use of the Kerr effect to measure the magnetisation of a sample. The MOKE system in Leeds can operate in longitudinal, transverse and polar geometries, in magnetic fields of up to 1.2 T and between room temperature and 625 K.