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

Xuan Li,Jian-Ping Wang,Mahdi Jamali,Hongshi Li

doi:10.1063/1.4994972

Abstract

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.

Highlights

Fe4N has been attracting attentions in spintronics[1,2,3] because it exhibits a highly spin-polarized electrical conductance and a negative spin polarization at the Fermi level.[4]
Inverse giant magnetoresistance is observed in the CPP GMR device, which proves the negative spin polarization of Fe4N and Fe4N/Ag interface
Based on the (001) oriented Fe4N thin films that we have developed, we further prepare a currentperpendicular-to-plane (CPP) giant magnetoresistance (GMR) stack with a multilayer structure of MgO substrate/Fe(5)/Ag(50)/Fe4N(7)/Ag(5)/Fe(7)/Ag(5)/Ru(8)

Summary

Introduction

Fe4N has been attracting attentions in spintronics[1,2,3] because it exhibits a highly spin-polarized electrical conductance and a negative spin polarization at the Fermi level.[4]. Different from the conventional ferromagnetic electrode materials such as CoFeB and CoFe, the spin polarization of Fe4N has been predicted to be negative,[4] namely the conductivity of the minority spin electrons is higher than the majority spin electrons. This characteristic is confirmed by both anisotropic magnetoresistance[8,9,10] and spinresolved photoelectron spectroscopy[11] results. The negative spin polarization of Fe4N provides a pathway for a group of novel spintronic logic devices.[12]

Methods

Results

Conclusion