Effects of Ga⁺ ion implantation on the magnetoresistive properties of spin valves

The effects of Ga⁺ ion implantation in SiO₂/Ta(5 nm)/NiFe(3.5 nm)/CoFe(1.5 nm)/Cu(2.9 nm) /CoFe(2.5 nm)/IrMn(10 nm)/Ta(5 nm) spin valve stacks were investigated. As-deposited films show a giant magnetoresistance (GMR) of 7.3% and an exchange bias field (Hex) of 42 mT. After implantation with 30 keV Ga⁺ ions at doses ranging from 10 ¹² to 10¹⁶ ions/cm², we observe a dramatic decrease in GMR and exchange bias field together with an increase in film resistance. The effects of Ga⁺ ion implantation during FIB milling of small GMR elements was investigated by reducing 10 μm spin valve lines to line widths ranging from 7 to 0.5 μm. The GMR and exchange bias field were found to rapidly decrease with decrease in spin valve width. Magnetic field annealing after Ga⁺ ion implantation does not restore the spin valve properties.