Tunnelling magnetoresistance effects in FeCoGd(t)/AlO/FeCo multilayers

Abstract

AbstractFeCoGd(t)/AlO/FeCo magnetic tunneling junctions (MTJs) have been fabricated using a shadow mask by magnetron sputtering system on SiO2 wafer, with a simple oxidation in the atmosphere to the bottom electrode FeCoGd layer. From the transmission electron microscopy (TEM) with element content analysis, we found a serious oxidation of the Gd element at the FeCoGd/AlO interface. At room temperature, inverse/normal TMR effects and normal TMR effects were observed simultaneously in the low and high magnetic field region, respectively. The high field curves show superparamagnetic behaviour, which are difficult to be saturated. The saturation field increases with the increase of t. The low field normal or inverse TMR effect is mainly resulted from the existence of the compensation thickness of the FeCoGd layer at room temperature. However, the normal TMR effect in high field region mainly origins from the existence of a granular layer at the FeCoGd/AlO interface consists of FeCo‐rich particles embedded in GdO insulating matrix. With the increase of the external magnetic field, the magnetic moments of the FeCo‐rich particles in the granular layer gradually rotate to the field direction (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)