Effect of the structural quality of the buffer on the magnetoresistance and the exchange coupling in sputtered Co/Cu sandwiches

The effect of the structural quality of the buffer stack on the structural properties, giant magnetoresistance (GMR) anti the duality of the antiferro magnetic coupling has been investigated for Co/Cu/Co sandwiches: prepared b y DC-magnetron sputtering. Three kinds of buffers were employed: type A: Cr (6 nm)/Co(0.8 nm)/Cu(10 nm), type B: Fe(6 nm)/Co(0.8 nm)/Cu(10 nm) and type C: Cr(4 nm)/Fe(3 nm)/Co(0.8 nm)/Cu(10 nm). For B and C type buffers, the a ntiferromagnetic alignment is very interesting at zero field with a couplin g strength larger than 0.4 erg/cm(2) and a GMR signal reaching 5% at room t emperature. However, for the A type buffer the antiferromagnetic coupling c omplete ly disappears, while the GMR drops to about 0.8%. X-ray diffraction , atomic force microscopy and transmission electron microscopy have been pe rformed in order to understand the origin of the observed difference in the magnetic properties. The results show a strong difference in the average s urface roughness, 1.15 nm and 0.35 nm, respectively for the A and C types b uffers, and demonstrate that the quality of the surface of the buffer is th e key to optimize both the GMR and the indirect exchange coupling.