Influence of temperature and annealing on GMR in sputtered permalloy/Cu multilayers

The influence of temperature and annealing on giant magnetoresistance of Si (100)/Cu(20 nm)/Py(2 nm)/(Cu(2 nm)/Py(2 nm))(100) multilayer (Py = Ni-83 Fe -17) sputtered at room temperature in double face-to-face configuration is reported. It was found that giant magnetoresistance value, Delta R-GMR/R-sa t (where R-sat is the resistance in saturation), monotonically decreases wi th increasing temperature (4.5% at 173 K to about 1% at 373 K). This result s from the decrease in magnetic change of resistance, Delta R-GMR, and to t he lesser extent from an increase in R-sat, though both of them are caused by the shortening of electrons mean free path. The observed almost linear d ecrease in giant magnetoresistance saturation field with increasing tempera ture is explained by temperature changes of magnetization profile. Vibratin g sample magnetometer measurements revealed that the increase in temperatur e results in pronounced decrease in remnant to saturation magnetization rat io (M-r/M-s) suggesting that at low temperatures magnetic bridges between P y layers play an important role in magnetization process. It is shown that proper annealing, by an annihilation of bridges and/or lateral decoupling, leads to an increase in giant magnetoresistance ratio from 3.4% in as depos ited state to 4.7%.