Abstract: A carrier-domain magnetometer (20) incorporating compensation for changes in its domain rotation frequency/magnetic flux density characteristic due to changes in operating conditions, e.g. electric bias and/or ambient temperature conditions, and/or due to ageing, compensation being obtained by providing means (24 to 28) for monitoring the ratio (F-F.sub.o)/F.sub.o where F is the domain rotation frequency when both a magnetic field biassing the magnetometer onto the linear part of its frequency/flux characteristic and a magnetic field to be sensed are applied, and F.sub.o is the domain rotation frequency when the biassing field only is applied.

Abstract: A semiconductor device incorporates a p-n-p-n structure of circular geometry, within which there may be formed a carrier domain which will rotate around the structure when an appropriate magnetic field is applied. The four regions of this structure are all bounded by a planar surface of the semiconductor, one end region being centrally disposed and the other forming an annular intrusion into the adjacent intermediate region, which is also of annular form and has contact made to it only outwardly of the annular intrusion. The device may be utilized in various ways in magnetic field sensors.