A method and an apparatus for detecting a number of variation in resistance within a material stack in response to a scanning and injection of a non-contacting electron stream into a material stack, the material stack having a first conductive contact layer, a variable resistive layer, a fixed resistive layer, and a second conductive contact layer, and the variations in resistance within the material stack being based on one of a plurality of resistive states of the variable resistive layer. The method also includes generating two magnetic fields within a transformer, the transformer being operatively coupled to the first and second conductive contact layers and generating a differential output signal within the transformer based on the two magnetic fields, the differential output signal being associated with one of the plurality of resistive states.