Magnetometer Overview

The MPMS system comprises of two main sections: the dewar, probe and SQUID assembly, and the electronic control system. The probe system is modular allowing the addition of extra component options (such as the RSO option, see Section 4.3.2).

The probe contains a high precision temperature control system, allowing measurements between $ 1.9\ensuremath{\unskip\,\mathrm{K}}$ and $ 400\ensuremath{\unskip\,\mathrm{K}}$ with an accuracy of $ 0.01\ensuremath{\unskip\,\mathrm{K}}$, and superconducting electromagnet, giving a field of up to $ 50\ensuremath{\unskip\,\mathrm{kG}}$ with an accuracy of up to $ 0.1\ensuremath{\unskip\,\mathrm{G}}$.

The dewar consists of an inner liquid helium reservoir and outer liquid nitrogen jacket, to reduce excessive liquid helium boil off. The liquid helium is used both for maintaining the electromagnet in a superconducting state and for cooling the sample space.

Samples are mounted within a plastic straw and connected to one end of a sample rod which is inserted into the dewar/probe. The other end is attached to a stepper motor which is used to position the sample within the center of the SQUID pickup coils.

The pickup coils are configured as highly balanced second-derivative coils, approximately $ 3\ensuremath{\unskip\,\mathrm{cm}}$ long. The coils reject the applied field from the superconducting magnet to a resolution of $ 0.1\%$.

Dr John Bland, 15/03/2003