Reading of Magnetically Recorded Bits by Amorphous GdFe Hall Element with High Sensitivity to In-Plane Field

Experiments using a three-electrode amorphous GdFe Hall element to read in-plane magnetically recorded digital data are described. The element was used with a degree of success in decoding signals recorded on mass transit tickets and passes; however, the bit interval was in some cases smaller than the Hall element resolution. Also, some double-cycle noise waveforms, which are in fact planar Hall voltage components, were superimposed on readout waveforms. Hall elements with higher sensitivity and resolution may be obtained by 1) making the sensor film smaller (0.4 × 0.7 mm for this device), 2) decreasing Hc relative to H¿, and 3) eliminating planar Hall voltage components.