The Giant Magneto-Impedance (GMI) effect refers to the strong and sensitive change of impedance of a magnetic conductor with a small variation in the DC magnetic field.
Even though an RVmagnetics MicroWire sensor is a magnetised element, its permeability is ~ 1, like in a vacuum. This enables the sensor to operate in heavily magnetised environments, to provide measurements on the magnetic field, and at the same time to not have biased measurements from the effects of the heavy magnetic environment. Although MicroWire is a magnetic sensor it does not work with GMI effect, it works with audio frequencies.