We have studied the magnetic and magnetoresistive properties of $(Cu/Co/Cu/NiFe)_20$ multilayers prepared by sputtering. It was found from the plots of the magnetoresistance versus the thickness of the magnetic layers that the optimum thickness is 20 Å for both Co and NiFe layers. This result demonstrates the importance of interface rather than bulk property for magnetoresistive effect.
We varied the interface roughness and interdiffusion through the interface by the changing sputtering gas pressure and substrate temperature, and investigated how the magnetoresistive effect is affected by them. The largest magnetiresistive effect is observed at the Ar pressure of 10 mtorr and substrate temperature of 373 K, the maximum MR ratio being 7.7% at room temperature at a very weak applied field of 500 Oe or less. When we increased sputtering gas pressure and substrate temperature over 10 mtorr and 373 K, respectively, MR ratio was decreased. We think that was caused by increase of interface roughness and interdiffusion through interface.
In conclusion, The MR effect of $(Cu/Co/Cu/NiFe)_20$ multilayer thin films is sensitively dependent on interface roughness and interdiffusion through the interface.
