Improved Signal-to-Noise Ratio in Current-Perpendicular-to-Plane Giant Magnetoresistance Sensors Using Strong Exchange-Biased Reference Layers

We present experimental studies of simple-pinned current-perpendicular-to-the-plane giant magnetoresistance (CPP-GMR) sensors demonstrating large gains in signal-to-noise ratio from improvements in reference layer exchange pinning strength J
_k
and magnetoresistance ratio AR/R. Significant increases in J
_k
from 0.7 to 1.25 erg/cm
²
and AR/R from 7.5% to 13% are achieved by progressive improvements in the sensor structure. The improved sensors show lower spin transfer torque-induced noise due to stronger pinning and higher damping of the reference layer, both the consequence of increases in J
_k
. This enables larger operational bias voltage, which along with higher AR/R, results in signal-to-noise gains of up to 6 dB in the recording heads. Our findings provide important insights for further development of CPP-GMR sensors in hard disk drives and other magnetic sensing applications.