Bottom giant magnetoresistance spin valves using a radio frequency reactive bias-sputtered α-Fe2O3 antiferromagnetic layer

The giant magnetoresistance (GMR) characteristics were investigated for rf reactive bias-sputtered alpha-Fe2O3(50 nm) based bottom spin-valve structures. The GMR ratio of this structure was found to be affected by Cu interlayer thickness. When the Cu interlayer thickness was changed from 1.6 to 3.1 nm, the GMR ratio varied from 14.2%(t(cu)=1.8 nm) to 8.3%(t(cu)=3.1 nm). The MR sensitivity and MR ratio dependence were studied for Si/alpha-Fe2O3(50 nm)/(NiFe, or Co)/Cu(2.3 nm)/(NiFe, or Co) structures. The MR ratio of NiFe(5.0%) based spin valve was much smaller than that of Co(16.1%), but it (0.6%/Oe) showed much higher MR sensitivity than that of Co(0.3%/Oe). The alpha-Fe2O3 input sputtering power was also changed from 600 to 1000 W for Si/alpha-Fe2O3(50 nm)/Co(or NiFe)/Cu(2.3 nm)/Co(or NiFe) structures. With increasing input power, the MR ratio increased for both Co (up to 15%) and NiFe (up to 3.1%). The main reason for the increase of MR ratio was attributed to the smoother surface. The average surface roughness measured by ex-situ AFM had 1.38 nm (600 W), 0.9 nm (800 W), and 0.87 nm (1000 W), respectively. (C) 2000 American Institute of Physics. [S0021-8979(00)44208-8].