Shear-wave magnetometry

A method of measuring low magnetic fields based on the magnetoelastic effect in amorphous magnetic materials is described. Preliminary results indicate a sensitivity of order 2.5 nT in the frequency range 0-1.6 Hz. The potential sensitivity is estimated to be better than 1 pT. This performance is not particularly impressive, but it has been obtained with as-received material in which the elastic modulus change with applied field is quite small. The phase change for a 1 A/m field change is about 1 degrees , so the field noise observed corresponds to a phase noise of about 2*10^-3 degrees, or 35 mu rad.