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))$\text{}_{100}$ multilayer (Py = Ni$\text{}_{83}$Fe$\text{}_{17}$) sputtered at room temperature in double face-to-face configuration is reported. It was found that giant magnetoresistance value, ΔR$\text{}_{GMR}$/R$\text{}_{sat}$ (where R$\text{}_{sat}$ is the resistance in saturation), monotonically decreases with increasing temperature (4.5% at 173 K to about 1% at 373 K). This results from the decrease in magnetic change of resistance, ΔR$\text{}_{GMR}$, and to the lesser extent from an increase in R$\text{}_{sat}$, though both of them are caused by the shortening of electrons mean free path. The observed almost linear decrease in giant magnetoresistance saturation field with increasing temperature is explained by temperature changes of magnetization profile. Vibrating sample magnetometer measurements revealed that the increase in temperature results in pronounced decrease in remnant to saturation magnetization ratio (M$\text{}_{r}$/M$\text{}_{s}$) suggesting that at low temperatures magnetic bridges between Py 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 deposited state to 4.7%.