National Physical Laboratory

Low Magnetic Moment Measurements

It is often not possible to provide the quantity of material required for the measurement of magnetic properties using standard methods. In these situations a system is required that has increased sensitivity across a large measurement range. Low magnetic moment measurements systems have been established which allow the determination of the magnetic properties of items ranging from thin films to mass standards.

The magnetic properties of thin films are often measured using commercial magnetometers based on vibrating sample and squid detection techniques. These are typically calibrated using nickel sphere samples. This approach is known to be good to 10 % as a result of variations in the saturation magnetisation of Nickel resulting from chemical purity. Further calibration issues concern the dimensions of the reference and the item being measured. If these are not the same, then different coupling factors apply and unknown corrections to the measured data are required. By having a reference film measured at NPL using these low moment systems this parameter can be accurately realised. Measurements of the same film in the customer system then allows the transfer of this calibration and allows the magnetometer to be used with confidence for further work.

For mass standards the susceptibility is required since this will give rise to additional forces during weighing. These forces represent an error and limits are imposed on the susceptibility in the legal document Organisation Internationale de M├ętrologie L├ęgale (OIML) recommendation R111. The determination of the required susceptibility is possible using a laboratory bench susceptometer. The calibration of this susceptometer involves many issues including geometry corrections, remanence and ambient magnetic field strength. The low magnetic moment systems at NPL are used for the determination of these and information is available. Sets of calibrated susceptibility reference blocks are available for the calibration of commercial mass susceptometers. The sets include the permanent magnet necessary for the measurements and this has been calibrated for magnetic moment.

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Customer Service tel: +44 20 8943 7166
E-mail: current_enquiries@npl.co.uk

Last Updated: 18 Aug 2015
Created: 13 Aug 2007

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