Spin-valve sensor with an out-of-plane magnetic anisotropy: For small field sensing applications

摘要

This study investigates a spin-valve sensor, which consists of ferromagnetic layers with both an out-of-plane magnetic anisotropy (NiFe/Tb/NiFe layers) and an in-plane magnetic anisotropy (CoFe/IrMn layers). The out-of-plane magnetic anisotropy was able to be tuned by varying the thickness (tTb) of the Tb layer and applying an in-plane magnetic field during film deposition. In addition, the field sensitivity of the spin-valve sensor was also found to be a function of the degree of out-of-plane magnetic anisotropy. As a result, a sensor with tTb=3 nm showed a linear and reversible magnetoresistance (MR) response to an applied in-plane magnetic field with a higher sensitivity of 0.012%/Oe by one order of magnitude than that (∼0.000 75%/Oe) of a sensor with tTb=4 nm. This suggests that the spin-valve sensor can be optimized by changing the Tb thickness so that the magnetic properties of the sensing layer can meet the requirements of a small field sensing application, such as a biosensor.