Perpendicular coupling at Fe–FeF2 interfaces

We have studied the exchange anisotropy of ferromagnetic Fe films grown on antiferromagnetic ${\mathrm{FeF}}_{\mathrm{2}}$ single crystals. The behavior of the hysteresis loops of the Fe above and below the Néel temperature $T_N$ of ${\mathrm{FeF}}_{\mathrm{2}}$ indicates a 90° rotation of the ferromagnetic easy axis due to the antiferromagnetic ordering. By examining the Fe hysteresis loops together with the ${\mathrm{FeF}}_{\mathrm{2}}$ susceptibility behavior we infer that below $T_N$ the ferromagnetic and antiferromagnetic spins are coupled perpendicular to each other. This behavior can be explained by recent micromagnetic calculations on exchange bias systems, or by magnetoelastic effects.