Interlayer Exchange Coupling in Single Crystal Magnetic Tunnel Junctions Studied by Electron Holography

Ion irradiation has been performed on epitaxial Fe/MgO/Fe magnetic tunnel junctions exhibiting antiferromagnetic exchange coupling. Electron holography and VSM experiments show that the amplitude and the nature of the coupling are modified by the irradiation. We demonstrate that the roughness induced by the irradiation at the Fe/MgO interfaces destroys the AF coupling. The biquadratic coupling experimentally observed in the irradiated samples is the result of the competition between local antiferromagnetic and ferromagnetic coupling. For the largest irradiation doses, the net coupling becomes ferromagnetic.