Giant magnetoresistance properties of CoFe/Cu multilayer in the CPP (current perpendicular to the plane) geometry

The MR ratio of multilayer GMR sensors with the CPP (current perpendicular to the plane) structure is expected to be much larger than that of CIP (current in the plane) sensors. We investigated the GMR properties of CTP and CPP elements of a Co0.9Fe0.1/Cu 10-bilayer. For CPP elements, GMR film was connected to the top and bottom terminal layers with a micron-sized contact hole. The measured data was analyzed using a model taking into account of the distribution of sense current. The measured resistance change (Delta R) increased rapidly as the GMR diameter became smaller, and showed close agreement with the calculated results when we assumed the MR ratio of CPP films to be around 30%. This MR ratio was twice as large as that of the CTP film of Co0.9Fe0.1/Cu 10-bilayer. In this study, we used the CPP elements which had wide GMR films and fine contact holes. So, the measured saturation field (H-s) of the CPP elements was almost constant as a function of the contact hole dimension, because the demagnetization held was insensitive to the sensor size. The CPP element in this study will obtain a high output when the GMR diameter becomes small.