Damping constant measurement and inverse giant magnetoresistance in spintronic devices with Fe₄N

Fe₄N is one of the attractive materials for spintronic devices due to its large spin asymmetric conductance and negative spin polarization at the Fermi level. We have successfully deposited Fe₄N thin film with (001) out-of-plane orientation using a DC facing-target-sputtering system. A Fe(001)/Ag(001) composite buffer layer is selected to improve the (001) orientation of the Fe₄N thin film. The N₂ partial pressure during sputtering is optimized to promote the formation of Fe₄N phase. Moreover, we have measured the ferromagnetic resonance (FMR) of the (001) oriented Fe₄N thin film using coplanar waveguides and microwave excitation. The resonant fields are tested under different microwave excitation frequencies, and the experimental results match well with the Kittel formula. The Gilbert damping constant of Fe₄N is determined to be α = 0.021±0.02. We have also fabricated and characterized the current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) device with Fe₄N/Ag/Fe sandwich. Inverse giant magnetoresistance is observed in the CPP GMR device, which suggests that the spin polarization of Fe₄N and Fe₄N/Ag interface is negative.