Controlling the exchange interaction using the spin-flip transition of antiferromagnetic spins in Ni81 Fe19 α Fe2 O3

We report anisotropy, coercivity, and exchange bias in ferromagnetic Ni81 Fe19 layers coupled to antiferromagnetic (AF) (0001), (11 2̄ 0), and (11 0̄ 2) α Fe2 O3 layers. We show that AF spin configurations which permit spin-flop coupling give rise to a strong uniaxial anisotropy and hence a large coercivity, and that by annealing in magnetic fields parallel to specific directions in the AF we can control either coercivity or exchange bias. In particular, we show that a reversible temperature-induced spin reorientation in the AF can be used to control the exchange interaction.