Increase of precision of surface magnetic field measurements by magnetic shielding

There are different methods to determine the magnetic field in open samples. The common approach is to measure the field near the sample surface. As was shown before, this method is often very inaccurate because of the field gradient above the sample. In our previous work we have tested the extrapolation field method, which greatly reduced the measurement error. It was found that the error strongly depends on the field gradient near the sample and it can still be large for large air gaps between the yoke and the sample. In this work a method of magnetic shielding of the field measurement point to reduce the field gradient is investigated. The field behavior above the sample is experimentally studied for a single C-yoke configuration on high-permeability materials. It was found that the shielding method decreases the field gradient by approximately one order of magnitude thus dramatically decreasing the field measurement error. There are many parameters affecting the shielding efficiency. Some of them are briefly discussed in this work. The extensive study of all of them is planned in the future.