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

Abstract

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 (t(Tb)) 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 t(Tb)=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 (similar to 0.00075%/Oe) of a sensor with t(Tb)=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. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3366708]