Thickness dependence of exchange bias and coercivity in a ferromagnetic layer coupled with an antiferromagnetic layer

We present a theoretical investigation on the thickness dependence of exchange bias and coercivity in ferromagnetic/antiferromagnetic bilayer systems, in which the exchange coupling at the interface includes both bilinear (direct exchange) and biquadratic (spin-flop) terms. Two basic formulas for the exchange bias and the coercivity are derived analytically. From these two formulas, many interesting conclusions can be extracted, and a lot of experimental results can be illustrated. The results also show that, although, in general, the biquadratic term lowers the exchange bias, its role in the coercivity is duplex, i.e., it can be tuned to enhance or reduce the coercivity.