Exchange biasing observed in the Co/Ir20Mn80 system

Co/IrMn top-configuration systems with variable Co or IrMn layer thickness were investigated in this work. From the high-resolution cross-sectional transmission electron microscopy (HR X-TEM) image and from X-ray diffraction, we conclude that the strongest IrMn (1 1 1) texture was achieved by postannealing at 250 °C for 1 h in a field h = 500 Oe, and then field-cooling to room temperature (RT). The main factor, which may influence magnetic properties, such as the exchange-biasing field (Hex), interfacial energy (Jk), and coercivity (Hc), is the IrMn (1 1 1)-texture effect. If the thickness (x) of the IrMn layer is smaller than 15 Å, Hex = 0. When x is in the range of 15 Å to 60 Å, Hex becomes more effective with increasing x. As x is larger than 60 Å to 90 Å then in systems without postannealing, the (1 1 1) texture near the IrMn/Co interface is less prominent. As a result, we find that a maximum Hex at x ≅60 Å to 90 Å in these systems. However, for the system with postannealing at TA = 150 or 250 °C, when x ≥ 90 Å, Hex tends to saturate, instead of decreasing. This indicates that the strong (1 1 1)-texture effect should stop Hex from decreasing as x continues to increase. Regarding the Jk behaviors, they are also governed by the texture effects. The Hc dependence on x is explained based on the coupling or decoupling effect between the spins of the Co and IrMn layers near the Co/IrMn interface. As to Hc dependence on the Co thickness (y), it is due to the surface-pinning effect. Finally, the optimal values for Hex and Jk from this study are 205 Oe and 0.11 erg/cm2, respectively.