Epitaxial spin-valve structures for ultra-low-field detection

Abstract

A new epitaxial “spin-valve”-type system for low-field magnetoresistive detection is described. This system is based on FeiPd epitaxial multilayers grown on (100)MgO by MBE. These films show a very abrupt transition from positive to negative magnetization as the reverse field is applied during hysteresis measurements. We have used these sensitive magnetic properties to fabricate epitaxial spin-valve structures by epitaxial growth of Fe/Ag, Co/Ag, or Co/Cu bilayers on top of a Fe/Pd bilayer. Hysteresis loops and magnetoresistance curves clearly indicate a significant field range with antiparallel alignment of the two components. Magnetoresistive sensitivities of up to 0.3% per Oe at low temperatures have been observed in these structures. The efficiency of the spin-dependent scattering has subsequently been improved either through the addition of planar Co impurities, in both the soft and hard magnetic 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.