International comparison of the properties of NdFeB permanent magnets measured using an electromagnet and a pulsed field magnetometer

Abstract

An IEC TC 68 comparison on the measurement of the magnetic properties of permanent magnets was completed in 2011. Measurements were performed on 6 NdFeB magnets with intrinsic coercivities ranging from 1000 to 2600 kA/m by 8 institutes based in China, Japan, Italy, Belgium, Germany and the UK. Many versions of a Pulsed Field Magnetometer (PFM) that can determine the full BH curve in as little as 100 ms have been developed during the last 2 decades. By comparing measurements made using an internationally accepted electromagnet method and pulsed methods, the influence of the dynamic effects of the latter could be investigated and established. For the quantities remanence, Br, magnetic flux density coercivity, HcB and energy product, BHmax the measurements agree within the combined uncertainties. For the intrinsic coercivity, HcJ, the dependence of the measurement of this quantity on the speed at which the magnetic field is reversed was found to be significant with the largest changes in value occurring as a DC measurement condition is approached.