  We report on the noise performance characteristics of magnetic sensors using
both magnetic tunnel junction (MTJ) and giant magnetoresistance (GMR) elements.
Each sensor studied has a notably different noise and detectivity. Of the
sensors we measured, those based on GMR multilayers have the lowest noise and
detectivity. However, the GMR sensor also has a significantly smaller linear
range. To make a direct comparison between sensors we scale the linear
operating ranges of each sensor to be the same. This is the phenomenological
equivalent of modifying the flux concentration. Upon scaling the low frequency
detectivity of the TMR sensors becomes essentially equal to that of the GMR
sensor. Using the scaling approach we are able to place the detectivity in the
context of other key parameters, namely size and power consumption. Lastly, we
use this technique to examine the upper limit for magnetoresistive sensor
performance based on a notional MTJ sensor using present record setting TMR
values.
