Linearity of unshielded spin-valve sensors

Linearity of the magnetoresistive (MR) transfer curve for an unshielded spin-valve (SV) sensor was studied. When the NiFe free layer thickness is greater than 5.0 nm, the anisotropic magnetoresistive (AMR) effect in it may overlap the giant magnetoresistive effect of the SV structure and deteriorate the linearity of the sensor response. By using a bilayer of NiFe/NiFeTa as the free layer for suppressing the AMR effect, superior linearity was obtained without a loss of the MR ratio. This new SV structure shows 5.0% as the MR ratio and −32.1 dB as second harmonic distortion, compared to −19.5 dB for a conventional one.