Iron Nitride Based Magnetoresistance Devices For Spintronic Applications

Abstract

The iron nitrides have been attracting a wide interest in spintronics researches due to their unique magnetic properties. In this thesis, I describe the experimental studies of the spintronic devices based on two important iron nitride materials, i.e. Fe16N2 and Fe4N. In the Fe16N2 based magnetoresistance device development, a heavy-metal free, low damping, and non-interface perpendicular current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) device with Fe16N2 magnetic layers has been demonstrated. The crystalline based perpendicular anisotropy of the Fe16N2 in the CPP GMR device is measured to be about 1.9 e7 erg/cm3, which is sufficient to maintain the thermal stability of the sub-10nm devices. The damping constant of the Fe16N2 thin film is determined to be 0.01 by a ferromagnetic resonance measurement, which is much lower than most existing materials with crystalline perpendicular magnetic anisotropy. The non-interface perpendicular anisotropy and low damping properties of make Fe16N2 a promising material for future spintronic applications. In the Fe4N material and device studies, both the (111) oriented and (001) oriented Fe4N thin films are prepared by optimizing the buffer layers, substrate temperatures and N:Fe composition. The most attractive properties of Fe4N in spintronics are the large spin asymmetric conductance and the negative spin polarization. The spin polarization of the (111) oriented Fe4N is investigated. The thickness dependence of the spin polarization of the (111) oriented Fe4N is also explored. Moreover, I have studied the Gilbert damping constant of the Fe4N (001) thin film by ferromagnetic resonance. The αFe4N is determined to be 0.021±0.02. Last but not least, the current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) device with Fe4N/Ag/Fe sandwich have also been fabricated and characterized. Giant inverse magnetoresistance is observed in the Fe4N based CPP GMR device, which confirms that the spin polarization of Fe4N and Fe4N/Ag interface is negative.