Comparative study of giant magnetoresistance in CoZr/Cu and Co/Cu multilayers

Since amorphous Co"1"0"0"-"xZr"x alloys present ultrasoft properties, higher sensitivity is expected in CoZr/Cu multilayers compared to the Co/Cu system as investigated in the present work from two types (I and II) of hybrid magnetic structures [(F"1/F"2/F"1)Cu]"1"5 where (F"1/F"2/F"1) is a magnetic sandwich corresponding to either [(CoZr/Co/CoZr)]"1"5 (type I) or [(Co/CoZr/Co)Cu]"1"5 (type II) and F"1 is a very thin magnetic layer inserted at the interfaces between the Cu layer and the magnetic F"2-based multilayers. Strong changes in the magnetization hysteresis curve, the indirect exchange coupling J and the magnetoresistive properties are observed with the insertion of a very thin magnetic CoZr (Co) layer at the interfaces between Cu spacer layers and the magnetic Co (CoZr) layer in Co/Cu (CoZr/Cu) multilayers. Insertion of a 2 A thick CoZr layer into interfaces of the Co/Cu type I multilayers induces significant reduction by a factor 5 of J and the magnetoresistance @D R/R. Opposite evolution is observed when a thin Co layer is inserted in CoZr/Cu type II multilayers. The dependences of the magnetic and magnetoresistive characteristics with the insertion are correlated with the interface roughness change as deduced from XRD at low angles.