Tailoring the exchange bias via shape anisotropy in ferromagnetic/antiferromagnetic exchange-coupled systems

Abstract

The magnetic behavior of Fe lines on top of a continous FeF2 antiferromagnetic layer was investigated as a function of the orientation of the lines with respect to the applied magnetic field and a unidirectional anisotropy established by field cooling. The orientational dependence of the asymmetric loop shift, called exhcange bias, shows that the competition between shape and unidirectional anisotropies modifies the exchange bias and the coercivity. Remarkably, in certain cases, exchange bias can be observed even when the applied field is perpendicular to the unidirectional anisotropy. Numerical simulations with a coherent rotation model ilustrate a rich phase diagram, which originates from the noncollinearity of the involved anistotropies. Using this phase diagram, exchange bias and coercivity can be predictably tailored. In particular, different preferred magnetization directions can be designed in separately patterned structures of the same sample with identical preparation and magnetic history.