Microstructure and tunneling magnetoresistance with spin switching in the Co/AlO x/CoFeB cross-strip junctions

Abstract

Characteristics of microstructure and tunneling magnetoresistance of the cross-strip Co/AlO x /CoFeB magnetic tunneling junction (MTJ) deposited on the glass substrates at room temperature are investigated by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) techniques. The deposition sequence was glass/Co(50 Å)/AlO x (22 Å)/CoFeB(60 Å). XRD results confirmed that the Co layer has a face-centered cubic (FCC) structure and (1 1 1)-oriented texturing in this junction. From cross-sectional TEM observations, the two neighboring interfaces of the AlO x tunneling barrier are smooth, i.e. Co/AlO x and AlO x /CoFeB, resulting in a higher TMR ratio. In addition, the switching fields of the MTJ are about ±13 Oe and ±25 Oe, respectively as determined by R– H (magnetoresistance–field) curve and VSM analyses. Moreover, the current–voltage ( I– V) curve of the MTJ indicates that the quantum tunneling mechanism should be effective. The simulated barrier height ( Φ) and thickness ( S) of I– V curve were plotted by Simmons’ equation in the present MTJ system. From the experimental I– V results, the barrier thickness of 22 Å is approximately the simulated one. Based on the results, we can conclude the cross-strip Co/AlO x /CoFeB MTJ system is the simplest and lower power junction, which can achieve the higher TMR ratio further.