High magnetic field sensitivity in anti-ferromagnetically coupled 001-epitaxial [Co₂Fe(Al_0.5Si_0.5)/Ag]_N multilayers

We have investigated the effects of the number of repetition (N) of ferromagnetic/nonmagnetic bilayers on the magnetic property and current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) in [Co₂Fe(Al_0.5Si_0.5) (CFAS)/Ag]_N multilayer for a potential magnetic field sensor application. The antiferromagnetic interlayer exchange coupling (AFM-IEC) between CFAS layers through the Ag(2.1 nm) spacer realized an anti-parallel magnetization configuration between the adjacent CFAS layers with N up to 6, which led to the stable linear response of magnetoresistance (MR) against a magnetic field in the range of 60-70 mT. The resistance change-area product (ΔRA) and the MR ratio were monotonically increased with N from 6.6 mΩ μm² and 16% for N = 1 (CFAS/Ag/CFAS trilayer) to 23 mΩ μm² and 43% for N = 6, respectively, giving an enhancement of field sensitivity with N up to 4.5%/mT. We also found nearly 3 times smaller non-linearity (1.2% Full Scale) in the device with N = 6 compared to that with N = 1. This study suggests a potential of Heusler-alloy based multilayer CPP-GMR device having AFM-IEC for magnetic field sensor applications.