Positive and negative exchange bias in CoNi/Gd/CoNi trilayers and CoNi/Gd bilayers

Abstract

Temperature-dependent magnetic properties of CoNi/Gd/CoNi trilayers and CoNi/Gd bilayers were investigated experimentally between room temperature and 90K. The films were deposited by DC magnetron sputtering at room temperature. Strong positive and negative exchange bias were observed due to the diffusion of Co and Ni into the Gd layer. The larger of the Gd or CoNi layer magnetization determines the exchange bias direction due to the antiferromagnetic exchange coupling between Gd and Co, and between Gd and Ni. Cooling magnetic field strength did not change the exchange bias field strength. However, the exchange bias field became zero when hysteresis loop measurements were done in large magnetic field intervals. This may be the sign of the existence of interface domain wall for exchange bias at lower field interval and its annihilation in the larger field interval.