Giant magnetoresistance increase in a hard-soft spin valve structure with the growth of a semiconductor layer

Magnetic and transport properties of a hard-soft spin valve structures have been investigated. A first series of sandwiches composed of an artificial antiferromagnetic (AAF) Co/Ru/Co sandwich decoupled from a soft Fe/Co buffe r layer as follows: Fe-50 (Angstrom)/Co-5 Angstrom /Cu-30 (Angstrom)/Co-30 (Angstrom)/Ru-5 Angstrom /Co-30 (Angstrom)/Cu-20 (Angstrom)/Cr-20 (Angstrom ) has been prepared. This sandwich presents a giant magnetoresistance (GMR) of 1.7% and an exchange coupling strength of approximately - 1.73 erg/cm(2 ). Afterwards, we have grown a second series of sandwiches in which the Cu/ Cr capping layer has been replaced by a 15-Angstrom thin semiconductor laye r of ZnS, covered by a soft ferromagnetic layer of Co-5 (Angstrom)/Fe-50 (A ngstrom). Surprisingly, the giant magnetoresistance for the last sandwiches has been increased by a factor of 2, up to 4%. To explain this non-expecte d result, we have performed atomic force microscope imaging at the semicond uctor layer surface. The results show that the semiconductor layer is not h omogeneous and contains a non-negligible density of gin-holes, that are res ponsible of a direct magnetic coupling between the upper 30 Angstrom Co lay er of the AAF and the Co 5 Angstrom /Fe 50 Angstrom bilayer. This coupling induces a strong asymmetry between the magnetic layers of the AAF and conse quently an enhancement of the GMR. (C) 2000 Elsevier Science B.V. All right s reserved.