Coercivity Enhancement in Exchange Biased Systems Driven by Interfacial Magnetic Frustration

We report the temperature and cooling field dependence of the coercivity of exchange biased ${\mathrm{MnF}}_2/\mathrm{Fe}$ bilayers. When the antiferromagnetic surface is in a state of maximum magnetic frustration and the net exchange bias is zero, we observe a strong enhancement of the coercivity, which is proportional to the exchange coupling between the layers. Hence, the coercivity can be tuned in a reproducible and repeatable fashion in the same sample. We propose that a frustrated interface provides local energy minima which effectively pin the propagating domain walls in the ferromagnet, leading to an enhanced coercivity.