EPITAXIAL SPIN-VALVE STRUCTURES FOR ULTRA-LOW FIELD DETECTION

A new epitaxial ''spin-valve''-type system for low-field magnetoresist ive detection is described. This system is based on Fe/Pd epitaxial mu ltilayers grown on (100)MgO by MBE. These films show a very abrupt tra nsition from positive to negative magnetization as the reverse field i s applied during hysteresis measurements. We have used these sensitive magnetic properties to fabricate epitaxial spin-valve structures by e pitaxial growth of Fe/Ag, Co/Ag, or Co/Cu bilayers on top of a Fe/Pd b ilayer. Hysteresis loops and magnetoresistance curves clearly indicate a significant field range with antiparallel alignment of the two comp onents. Magnetoresistive sensitivities of up to 0.3% per Oe at low tem peratures have been observed in these structures. The efficiency of th e spin-dependent scattering has subsequently been improved either thro ugh the addition of planar Co impurities, in both the soft and hard ma gnetic layer, or by increasing the number of active Fe/Pd interfaces. This approach leads to a drastic improvement of the sensitivity, up to 1.5% per Oersted at room temperature.