Improving accuracy of intrinsic coercivity measurement for magnetically soft materials

This paper considers problems associated with an established coercivity measurement procedure, the "pull out" method, used at the Magnet Centre for many years. Such measurements are an important quality control tool for magnetically soft materials. The main emphasis of this paper is on low carbon relay steels, but other materials have been investigated. Relays and actuators play an increasingly important role in automotive and aerospace technology. Here we review the procedure in detail, but our findings are relevant to other "open circuit" methods of intrinsic coercivity measurement. We have found that errors are caused by rapid changes in applied magnetic field strength at a specific part of the hysteresis cycle, between saturation and the open circuit remanent flux density. We have devoted much attention to the geometry of the samples, with particular emphasis on thickness and dimension ratio, as these are major factors in intrinsic coercivity determination. We propose a modification of the relevant international standard for intrinsic coercivity measurement.